Vegetative and reproductive growth responses of pea (Pisum sativum L. cv. Alaska) to periodic seismic (shaking) stress were investigated during fall, winter, and spring seasons in a greenhouse. Growth changes caused by equivalent shaking treatment varied quantitatively among seasons, with the least response occurring during winter, but they were qualitatively similar during all three seasons. Shaking caused significant reduction in all growth parameters measured except root dry weight and leaf number after 16 days of treatment. Reproductive growth responses to shaking (occurring from 16 to 35 days of treatment) included delay of anthesis but no difference in number of fruits set after as much as 35 days of treatment. Seismic stress significantly reduced the number but not the weight of individual seeds per pod. Mean relative shoot growth rate was reduced by shaking during reproductive as well as vegetative growth. During both periods of development this response was caused almost entirely by inhibition of net carbon assimilation rate.
During tropic bending in the stem of the mushroom fruit body of Coprinus cinereus the majority of extension occurred in the upper 20-30% of the stem. By attaching inert markers to the stem, it was shown that the outer flank of the bend initially has a faster rate of extension, although the inner flank matches this growth rate later in the response. Thus bending results from differential enhancement of growth rate rather than sustained differences. Large voids, up to 85 micrometers in diameter, observed in tropically bent stems showed no significant difference in number between inner and outer flanks but are implicated in bending because of their absence from unbent stems. Such voids may prevent the propagation of cracks through the stem tissue during bending. Creases at the external and lumen surfaces were also peculiar to bent stems and could represent constrictions caused by localized accumulation of stresses. Cell morphometric analysis of transverse sections of both flanks of the bend revealed no significant differences in hyphal diameter, distribution, or populations of cell types, but cells of the outer flank were four to five times longer than those of the inner. Thus, tropic bending requires only an increase in length of pre-existing inflated hyphae in the outer flank tissue.
Alterations in internal partitioning of carbon were evaluated in plants exposed to limited nitrogen supply. Vegetative, nonnodulated soybean plants (Glycine max (L.) Merrill, 'Ransom') were grown for 21 days with 1.0 mM NO3- and then exposed to solutions containing 1.0, 0.1, or 0.0 mM NO3- for a 25-day treatment period. In nitrogen-limited plants, there were decreases in emergence of new leaves and in the expansion rate and final area at full expansion of individual leaves. As indicated by alterations in accumulation of dry weight, a larger proportion of available carbon in the plant was partitioned to the roots with decreased availability of nitrogen. Partitioning of reduced nitrogen to the root also was increased and, in plants devoid of an external supply, considerable redistribution of reduced nitrogen from leaves to the root occurred. The general decrease in growth potential and sink strength for nutrients in leaves of nitrogen-limited plants suggested that factors other than simply availability of nitrogen likely were involved in the restriction of growth in the leaf canopy and the associated increase in carbon allocation to the roots.
Caulonemata of the moss Funaria were examined to determine whether they are gravitropic. Funaria and Physcomitrella were also evaluated to compare amyloplast sedimentation with that of Ceratodon. Protonemata were either chemically fixed in place or examined alive using infrared timelapse videomicroscopy. Funaria caulonemata were found to be negatively gravitropic, i.e., they grew upwards in the dark. Upward curvature reversed temporarily before cytokinesis in Funaria, a phenomenon already known for Ceratodon and Physcomitrella. Most horizontal and upward-curving Funaria tip cells contained a broad subapical zone where plastid sedimentation occurred. In dark-grown Physcomitrella caulonemata, sedimentation was detected by the presence of a thin, amyloplast-free strip of cytoplasm at the top of the cell. These results suggest that gravitropism and subapical amyloplast sedimentation may be relatively common in moss caulonemata.
Mung beans (Phaseolus aureus Roxb.) were grown for 2 weeks in gravel-vermiculite soilless mix in a growth chamber and subjected to a 1-week waterlogging period followed by a 1-week recovery period. Sequential harvests were made to determine the time course of effects of waterlogging and subsequent recovery on growth parameters by techniques of growth analysis. Root dry matter was the first to be affected, along with an increase in leaf dry matter and specific leaf weight. After a 1-week waterlogging period, specific leaf weight had more than doubled in the stressed plants. Leaf area declined in relation to the control plants as did the ratio of root dry matter to shoot dry matter. During the recovery period there was an increase in the dry matter allocation to the roots relative to the shoot. Specific leaf weight fell to control levels although the rate of leaf area elaboration did not increase during this time, suggesting a redistribution of stored assimilates from the leaves. Net assimilation rate increased during the waterlogging period, probably due to a restriction in root metabolism and reduced translocation out of the leaf rather than to an increase in photosynthesis. Net assimilation rate of waterlogged plants was severely reduced compared with control plants during the recovery period. Both relative growth rate and leaf area duration declined during the waterlogging period and declined further subsequent to the waterlogging treatment. The results illustrate the interrelationships between root and shoot carbon budgets in mung bean during response to the stress of waterlogging.
Apical cells of 5-day-old dark-grown protonemata of the moss Ceratodon purpureus (Hedw.) Brid. are negatively gravitropic and appear to utilize amyloplasts as statoliths. These cells exhibit a characteristic plastid zonation (five zones) with one zone (No. 3) specialized for the lateral sedimentation of amyloplasts. Basipetal centrifugation displaces all amyloplasts in the apical cell to the end wall. In basipetally centrifuged protonemata observed using infrared videomicroscopy, tip extension occurred with or without amyloplasts present in the apical dome. The initial return of upward curvature was always correlated with the return and sedimentation of amyloplasts in zone 3. Subsequent vigorous upward curvature was correlated with distinct amyloplast zonation and further sedimentation in zone 3. Initial downward ("wrong way") curvature, which often preceded upward curvature, correlated with the presence of amyloplasts in the apical dome (zone 1). These data support the hypotheses that nonsedimenting amyloplasts in zone 1 are necessary for initial downward curvature and that amyloplast sedimentation in zone 3 is necessary for upward curvature.
Shrubs in the forest understory may be bent by their own weight or by overstory debris. To maintain height growth they must respond to bending by vertical growth of new shoots, reorientation of older axes, or by releasing preventitious buds to form epicormic shoots. I tested for these responses in Ilex verticillata L., Cornus amomum Mill., Gaylussacia baccata (Wang.) K. Koch, Viburnum cassinoides L., Hamamelis virginiana L., and Kalmia latifolia L. For each species, I removed potentially supporting vegetation adjacent to 20 stems, left 10 stems untreated to test for bending by self weight, and bent the remaining 10 stems to 45 degrees to simulate effects of fallen debris. Stem angles and curvatures were measured from before leaf out until just before leaf fall to detect either sagging from self weight or upward bending from tension wood action. Control stems initially leaned out of vertical and five of six species sagged further into a cantilever form. Several control stems failed and bent to the ground. Stems of H. virginiana, I. verticillata, and C. amomum formed tension wood, but only the first two species bent upward. Viburnum cassinoides, G. baccata, and K. latifolia formed no tension wood and sagged further down after being bent. Epicormic shoots formed with varying frequencies in all species except K. latifolia. Epicormic shoots were the major response in C. amomum, V. cassinoides, and G. baccata. New terminal shoots on bent stems recovered toward vertical in I. verticillata and K. latifolia. Negative gravitropic response of shoots was the only recovery mechanism for K. latifolia.
To describe the different types of geotropic reactions of hevea (Hevea brasiliensis), young seedlings were cultivated in root observation boxes and submitted to a double gravistimulation (90 degrees rotation of the minirhizotrons in the vertical plane). It was demonstrated that the taproot is a strongly orthogeotropic organ since it resumed rapidly its prestimulation vertical position. Morphological and morphogenetic modifications were associated with the geotropic response: reduced speed of growth coupled with a reduction of the apical diameter as well as an alteration of ramification density in the curving zone and the following one. Early secondary roots showed a somewhat reduced orthogeotropism that was weaker as the growth direction before gravistimulation was more distant from the vertical. Secondary roots of the acropetal sequence were semiplagiotropic, that is only those roots oriented upward after the gravistimulation resumed, more or less, the original direction. Tertiary roots didn't respond to the gravistimulation and therefore were ageotropic. Complementary observations conducted in large laboratory rhizotrons showed that late forming secondary roots were plagiotropic in their younger stages, thereafter loosing most of their sensitivity to gravity. Quaternary roots were ageotropic. On the basis of these data, a geotropic gradient was defined within the hevea root system, where the strongly responding taproot and late secondary roots are opposed to the weakly or nonresponding tertiary and quaternary roots. Functional significations of the differential geotropic reactions in different hevea root types are discussed.
Growth of Arabidopsis thaliana (L.) Heynh. in decreasing oxygen partial pressures revealed a linear decrease in seed production below 15 kPa, with a complete absence of seed production at 2.5 kPa oxygen. This control of plant reproduction by oxygen had previously been attributed to an oxygen effect on the partitioning between vegetative and reproductive growth. However, plants grown in a series of decreasing oxygen concentrations produced progressively smaller embryos that had stopped developing at progressively younger stages, suggesting instead that their growth is limited by oxygen. Internal oxygen concentrations of buds, pistils, and developing siliques of Brassica rapa L. and siliques of Arabidopsis were measured using a small-diameter glass electrode that was moved into the structures using a micromanipulator. Oxygen partial pressures were found to be lowest in the developing perianth (11.1 kPa) and pistils (15.2 kPa) of the unopened buds. Pollination reduced oxygen concentration inside the pistils by 3 kPa after just 24 h. Inside Brassica silique locules, partial pressures of oxygen averaged 12.2 kPa in darkness, and increased linearly with increasing light levels to 16.2 kPa. Measurements inside Arabidopsis siliques averaged 6.1 kPa in the dark and rose to 12.2 kPa with light. Hypoxia in these microenvironments is postulated to be the point of control of plant reproduction by oxygen.
After branching from the primary root, secondary roots of castor bean (Ricinus communis) grow laterally for 15-20 mm, after which they bend downward (i.e., become positively gravitropic). During the first 10 mm of growth, the lengths of caps of secondary roots increase from 120 +/- 26 to 220 +/- 28 micrometers. Although this increase is statistically significant (P < 0.1%), the resulting secondary roots are only minimally graviresponsive. A subsequent doubling of the lengths and widths of the root caps (i.e., to 420 +/- 34 and 450 +/- 41 micrometers, respectively) is positively correlated with the onset of gravicurvature. The graviresponsiveness and dimensions of caps of positively gravitropic secondary roots are not significantly different from those of positively gravitropic primary roots. These results indicate that (i) a statistically significant increase in the length and length : width ratio of a root cap does not necessarily result in the root becoming positively gravitropic, (ii) there may be a minimum cap length and (or) width necessary for graviresponsiveness, and (iii) the degree of graviresponsiveness exhibited by a particular root may be related to the size of its root cap.
When dark-grown tip cells of protonemata of the moss Ceratodon purpureus are turned to the horizontal, plastids first sediment towards gravity in a specific zone and then the tip curves upward. To determine whether gravitropism and plastid sedimentation occur in other orientations, protonemata were reoriented to angles other than 90 degrees. Qualitative and quantitative light microscopic observations show that plastid sedimentation along the cell axis occurs in both upright and inverted cells. However, only some plastids fall and sedimentation is incomplete; plastids remain distributed throughout the length of the cell, and those plastids that sediment do not fall all the way to the bottom of the cell. Tip cells are gravitropic regardless of stimulation angle, and as in higher plants, the maximal rate of initial curvature is in response to a 120 degrees reorientation. Infrared videomicroscopy, time-lapse studies of living, inverted protonemata indicate that amyloplast sedimentation precedes upward curvature. Together, these data further support (i) the hypothesis that amyloplast sedimentation functions in gravitropic sensing in these cells, and (ii) the idea that gravity affected the evolution of cell organization.
A morphometric analysis of the ultrastructures of columella cells in primary and lateral roots of Phaseolus vulgaris was performed to determine the precise location of cellular components in these cells. Roots were fixed in situ to preserve the in vivo ultrastructure of the cells. All cellular components in columella cells of both types of roots were distributed asymmetrically. The nucleus and vacuome were located primarily in the middle third of both types of columella cells. Dictyosomes, mitochondria, and amyloplasts were most abundant in the lower third of the columella cells in both types of roots. The distribution of amyloplasts was the most asymmetrical of all cellular components examined, with the lower third of the columella cells containing approximately 90% of the relative volume of amyloplasts in both types of roots. The distribution of cellular components in columella cells of primary roots was not significantly different from that of columella cells of lateral roots. These results indicate that differences in georesponsiveness of primary and lateral roots of P. vulgaris are probably due to factors other than the ultrastructures of their individual columella cells.
Temperature and photoperiod each have direct effects on growth rate of excised embryos of soybean (Glycine max (L.) Merrill). To determine if the effects of photoperiod are altered by temperature, embryos of 'Ransom II' were cultured in vitro at 18, 24, and 30 degrees C under photoperiod durations of 12 and 18 h at an irradiance of 9 W m-2 (700 to 850 nm) and a photosynthetic photon flux density of 58 micromoles m-2 s-1 (400 to 700 nm). Accumulation rates of fresh and dry weight were greater under 18-h than 12-h photoperiods over the entire range of temperature. Water content of the culture embryos was not affected by photoperiod but was greater at 18 and 30 than 24 degrees C. The accumulation rate of dry weight increased from 18 to 26 but declined at 30 degrees C.
Half-tipped primary and lateral roots of Phaseolus vulgaris bend toward the side of the root on which the intact half tip remains. Therefore, tips of lateral and primary roots produce growth effectors capable of inducing gravicurvature. The asymmetrical placement of a tip of a lateral root onto a detipped primary root results in the root bending toward the side of the root onto which the tip was placed. That is, the lesser graviresponsiveness of lateral roots as compared with primary roots is not due to the inability of their caps to produce growth inhibitors. The more pronounced graviresponsiveness of primary roots is positively correlated with the presence of columella tissues that are 3.8 times longer, 1.7 times wider, and 10.5 times more voluminous than the columellas of lateral roots. We propose that the lack of graviresponsiveness exhibited by lateral roots is due to the fact that they (i) produce smaller amounts of the inhibitor than primary (i.e., strongly graviresponsive) roots and (ii) are unable to redistribute the inhibitor so as to be able to create a concentration gradient sufficient to induce a pronounced gravitropic response.
Differentiation of the endodermis was examined in third internodes of etiolated Pisum sativum L. cv. Alaska seedlings. The endodermis in young internodes contains large, sedimented amyloplasts; in older internodes, a casparian strip differentiates and the endodermis becomes depleted of starch except for the proximal region of the stem, which retains sedimented amyloplasts and remains graviresponsive. Sedimentation occurs in the hook but does not occur consistently until cells reach the base of the hook, where the axis becomes vertical, rapid cell elongation starts, and amyloplast diameter increases substantially. Contact between endoplasmic reticulum and amyloplasts was observed. Endoplasmic reticulum is not distributed polarly with respect to gravity. No symplastic or apoplastic blockages exist in the endodermis at the level of the stem where lateral gradients may be established during tropic curvature.
The control of primary root growth in Zea mays cv. Merit by ethylene was examined. At applied concentrations of ethylene equal to or greater than 0.1 microliter L-1, root elongation during 24 h was inhibited. The half-maximal response occurred at 0.6 microliter L-1 and the response saturated at 6 microliters L-1. Inhibition of elongation took place within 20 min. However, after ethylene was removed, elongation recovered to control values within 15 min. Root elongation was also inhibited by green light. The inhibition caused by a 24-h exposure to ethylene was restricted to the elongating region just behind the apex, with inhibition of cortical cell elongation being the primary contributor to the effect. Based on use of 2,5-norbornadiene, a gaseous competitive inhibitor of ethylene, it was concluded that endogenous ethylene normally inhibits root elongation.
Tissue cultures of tobacco grown for 12 weeks in contact with lunar material returned by Apollo 12 contained 21 to 35% more total pigment than control tissues. This difference is due primarily to increased chlorophyll a concentrations per gram fresh weight of tissue in experimental cultures. No differences were noted in the fresh or dry weight of the experimental and control cultures.
Source leaves of Panicum and Flaveria C3, C3C4 intermediate, and C4 species were fed 14CO2 in the mid-afternoon. Immediate export, calculated when isotopic equilibrium existed between 14CO2 and the 14C translocates, was compared with 14C export during the feed period, and both were compared with subsequent 14C export of primary reserves during daytimenighttime chase periods. Sugars and starch supported export in all species. In addition, regardless of differences in partitioning into starch and sugars during labelling, similar photosynthesis, immediate export, and daily export occurred in some Panicum C4 species. Within both genera, C4 types fixed and exported the most carbon. The Panicum "type I" C3C4 intermediates behaved in an "intermediate" manner with respect to both export during photosynthesis and daily. In contrast, compared with C3 and C4 species within the Flaveria, "type II" C3C4 intermediates had the lowest initial export during the feed period and total 14C export by the next morning. In spite of the plasticity in carbohydrate storage, export in all species was greater in the light than in the dark. Interestingly, daily 14C export correlated better with immediate export rates than with photosynthesis or other parameters of leaf function.Key words: C export, C partitioning, C3C4 intermediates, Flaveria, Panicum, photosynthesis.Les auteurs ont alimenté des feuilles sources chez des Panicum et des Flaveria, soient des espèces en C3, C3C4 intermédiaires et C4, avec du 14CO2, au milieu de l'après-midi. Ils ont comparé l'exportation immédiate, calculée lorsqu'il existe un équilibre isotopique entre le CO2 et les translocats 14C, avec le 14C exporté au cours du marquage, et ils ont également comparé les deux avec le 14C subséquemment exporté à partir des réserves primaires, au cours de périodes diurnesnocturnes de déplacement. Les sucres et l'amidon supportent l'exportation chez toutes les espèces. De plus, indépendamment des différences dans la répartition entre l'amidon et les sucres au cours du marquage, on retrouve une photosynthèse comparable et un transport diurne immédiat chez certaines espèces de Panicum en C4. Dans les deux genres, les espèces en C4 fixent et exportent les plus grandes quantités de carbone. Les Panicum du « type I » intermédiaire en C3C4 se comportent de façon intermédiaire en ce qui a trait au transport au cours de la photosynthèse et en phase diurne. Au contraire, comparativement aux espèces en C3 et en C4 du genre Flaveria, les espèces du « type I » intermédiaires en C3C4 montrent l'exportation initiale la plus faible au cours du marquage et du 14C total exporté le matin suivant. En dépit de la plasticité dans l'accumulation des glucides, l'exportation chez toutes les espèces est plus élevée à la lumière qu'à l'obscurité. Il est intéressant de noter que l'exportation diurne du 14C montre une meilleure corrélation avec les taux d'exportation immédiate qu'avec la photosynthèse ou d'autres paramètres de la fonction foliaire.Mots clés : exportation du C, partition du C, espèces intermédiaires en C3C4, Flaveria, Panicum, photosynthèse.[Traduit par la Rédaction]
To determine the variation in flowering among species and the contribution of flowering to the recovery of forest herbs, we counted the flowering shoots, vegetative shoots, and first-year seedlings in old-growth forests affected by tephra from the 1980 eruption of Mount St. Helens. Using permanent 1 m 2 plots with either undisturbed tephra or with the tephra removed, we obtained 2-9 years of flowering data during 1980-2000 for six sites that received 2-15 cm of tephra. Flowering was infrequent for most species. Most of the 12 commonest species had 2%-4% of their shoots flowering (range 0%-15%). Among growth forms, deciduous nonclonal species flowered most. Flowering percentage increased with plant density; thus microsites favorable for growth were also favorable for flowering. Flowering varied considerably among sampling years. Incidence of flowering was higher on shallow than on deep tephra, and higher on natural tephra than in cleared plots. Seedlings were more common on shallow than on deep tephra. The 20-year increase in shoot density on tephra (ratio of 2000 to 1981 values) was positively related among species to the number of seedlings produced per previous-year flowering shoot. Our results indicate how species vary in the quantity and timing of flowering and also in their reliance on seedling establishment versus clonal growth for population increase following disturbance.
The increase in thallus diameter and apothecium production, and the population size structure of the saxicolous lichens Umbilicaria cylindrica (L.) Del., Umbilicaria hyperborea (Ach.) Hoffm., Umbilicaria proboscidea (L.) Schrad, and Umbilicaria torrefacta (Lightf.) Schrad, were measured in a chronosequence of 240 years in a glacier foreland in the alpine Jotunheimen National Park in Norway. All four species exhibited a pattern of fast growth in the early decades of their life history, followed by a rapid decrease in growth, slowly approaching a maximum body size. There were clear interspecific differences in initial estimated growth rate, growth period, and maximum size. In all species, apothecium production is strongly correlated with thallus size, but in U. hyperborea the relationship approximates an exponential function, while in the other species the trend is more linear. In U. proboscidea, the slowest to mature, a fairly high proportion of sterile individuals also occur in the higher size classes. There was no observed trade off between growth and reproduction. Quite the contrary: the species that grow faster also start to reproduce abundantly and early. The relatively slow growth and reproductive maturation of the species implies that a population of 40- to 50-year-old individual thalli is still a population consisting mainly of immigrants. The population size structure of all four species remains strongly skewed during the entire chronosequence, with a predominance of small thalli.
We examined long-term rates of dry peat accumulation in 32 14C-dated cores from poor fens in Alaska, to bogs and fens in midcontinental North Dakota and Minnesota, to oceanic bogs in Maine and the Atlantic Provinces of Canada. Sites along this belt transect exhibit mostly linear relationships between cumulative mass and age. Long-term rates of peat accumulation range from 16 to 80 g·m-2·year-1, with a median rate of 47 g·m-2·year-1 and a mean rate of 50 g·m-2·year-1. Rate of accumulation is inversely correlated with mean annual precipitation, but is not correlated with the area of the peat basin, basal age, or mean annual temperature. Four of the five highest rates are from relatively dry midcontinental locations in North Dakota and Minnesota; the other is for a coastal site in Newfoundland. The two lowest rates are from extremely rainy sites on Pleasant Island in the Alaskan panhandle. Individual accumulation rates between adjacent dates are quite variable within the peat cores, and across the transect, they do not correlate significantly with immediately previous rates. The same is true of the four sites with the greatest numbers of dates. There is a small but significant negative correlation within the Red Lake Peatland.
Diatom ecology and species compositional patterns across current arctic treeline can provide important paleoecological information associated with climatic and environmental change. In this paper we examine the relationships between measured environmental variables and modern diatom assemblage composition from 77 lakes across the treeline ecozones of the Central Canadian Arctic. The weighted-average optima for selected environmental variables were calculated for 74 of the most common diatoms, and photographic plates of these taxa are included. Our results indicated that both forest-tundra and arctic tundra lakes differed significantly in diatom assemblage composition from boreal forest lakes. In general, planktonic diatom taxa (e.g., Cyclotella species) were more common in forested lakes, which may be due to ecological conditions related to climate. Small, benthic, alkaliphilic Fragilaria taxa reached their highest abundances in forested lakes, likely because of the more alkaline nature of these lakes. Arctic tundra lakes were characterized by higher abundances of circumneutral to acidophilic taxa. Heavily silicified Aulacoseira taxa (e.g., Aulacoseira lirata, Aulacoseira perglabra) were more common in deeper tundra lakes, likely because of the less alkaline nature of these lakes and greater wind-induced turbulence in this zone. These trends provide important information on the variability of aquatic ecosystems across this climatically sensitive vegetational gradient.
The inheritance of aspartate aminotransferase (AAT) isozymes was investigated in Cucumis sativus L. (CC; 2n = 2x = 14), Cucumis hystrix Chakr. (HH; 2n = 2x = 24), the synthetic amphidiploid species C. hytivus Chen & Kirkbride (HHCC; 2n = 4x = 38), and the allotriploid (HCC; 2n = 3x = 26) from backcrossing C. hytivus to C. sativus. Two polymorphic loci, Aat-1 and Aat-2, and one monomorphic locus, Aat-3, were detected among these parents and their progenies by using polyacrylamide gel electrophoresis. Cucumis sativus displayed the fast-migrating anodic band for Aat-1 (2), while C. hystrix contained a slow-migrating cathodic band (1). For Aat-2, the slow-migrating cathodic band was observed with C. sativus (1), whereas C. hystrix contained the fast-migrating anodic band (2). Cucumis hytivus, a synthetic species derived from doubling the chromosome number of a F1 from a C. sativus x C. hystrix mating, exhibited the typical hybrid dimeric banding pattern resulting from the combination of two parental homomeric products with equal staining intensity and a heteromeric product with intermediate mobility and greater staining intensity than either homomeric product. The difference in band intensity between C. hytivus and its backcross progenies, when C. sativus was the recurrent parent, were due to the dosage effects of alleles at Aat-1 and Aat-2. These banding morphotypes can be used for typing of C. hytivus and BC1 progenies that are similar in morphology. Aat-3 was monomorphic in this mating, encoding a single allele Aat-3 (1).
Characterization of the North American ginseng (Panax quinquefolius L.) inflorescence, the floret abscission zone, and its stimulation by ethylene were undertaken to gain insights into the potential for floret abscission induction as a replacement for the industry practice of expensive manual removal of the inflorescence. In each of 3 years, peduncle length of 3-year-old cultivated ginseng inflorescences increased rapidly in June, reaching maximal values of 140-180 mm. During this period, seed head diameter also increased to about 35 mm, while seed head fresh mass increased in July and August to 6.5-8.0 g. Flowering in 1996 and 1997 began in the last 2 weeks of June and lasted through July, with open flowers never exceeding 35%. Anatomical studies and manual dissection of 1- and 3-year-old perennating buds revealed development of the floral primordia first at their periphery and progressing centripetally. Stamen initials were seen as a pentamerous whorl just under the petal primordia, and the characteristic inferior ovary initiated as a slight depression at the centre of the floral meristem. Sections through 3-year-old inflorescences harvested on May 23, 1996, showed that distal floral apices had already formed constriction zones between the flower and the pedicel, indicating the position of the abscission zone. Length of time to ethylene-induced abscission zone formation was less than 24 h in 3-year-old ginseng harvested on July 23, 1997. The abscission threshold for ginseng berry drop was in the range of 10-100 μL·L-1 ethylene.
Previous studies on frugivory in temperate bird-dispersed plants have concluded that fleshy fruits are removed more rapidly in cold than in warm winters. However, these studies do not distinguish between fruit abscission and frugivory. The implicit assumption that fruit loss reflects frugivory may not be valid; fruit abscission may be important and respond differently to weather. During two winters, we measured fruit loss from an invasive shrub (Lonicera maackii (Rupr.) Herder) using fruit traps. We examined the effects of temperature and precipitation on fruit retention on shrubs and fruit abscission. In the first year of our study, there was no effect of temperature or precipitation on fruit retention. In the second year, both warmer temperatures and lower precipitation resulted in more fruit retention. In both years, fruit abscission was greater during periods of cold temperatures and high precipitation. These findings suggest that weather-dependent "frugivory" reported for other bird-dispersed plants may actually reflect patterns of abscission.
To address concern for loss of bryophyte biodiversity within managed forests, we compared community composition and environmental characteristics among three disturbance regimes: (i) naturally regenerated clear-cut forests, (ii) cutover spruce plantations (established on clear-cut forest land), and (iii) afforested field spruce plantations (established on agricultural fields) across a range of ages (19-102 years) in the Acadian Forest region of New Brunswick, Canada. Abundances of all forest floor bryophyte species, available substrates, microtopographical features, and tree canopy were measured as percent cover (1 m2) in 26 stands: 12 naturally regenerated clear-cut forests, eight cutover plantations, and six afforested field plantations. Multivariate analyses indicated that both bryophyte community composition and associated environment differed significantly across disturbance regimes, with no strong trends related to time since clearing (i.e., stand age). Spruce plantations were characterized by low substrate diversity and microtopographic and canopy homogeneity. Both plantation types had lower bryophyte species richness, evenness, and diversity (H′) relative to naturally regenerated clear-cut forests; cutover plantations had the highest total bryophyte cover. The bryophyte community of plantations was composed of a subset of species found within naturally regenerated clear-cut forests: many liverworts and epixylic mosses were absent, with fewer pioneer species and more perennial stayers (equivalent to K-strategists) than expected.
Few studies have considered ethylene involvement in plant responses to ultraviolet-B (UVB) radiation. We studied the responses to UVB radiation of one wild-type (WT, 'Westar') canola (Brassica napus L.) with normal ethylene evolution and two transgenic (C1, C2) lines with lower ethylene evolution. Canola plants were grown under biologically effective levels of UVB (UVB(BE)) radiation: 0.03 (low), 4.88 (medium), and 9.78 (high) kJ center dot m(-2)center dot d(-1) in controlled-environment growth chambers. The growth and physiological parameters of the plants were measured. Of the two transgenic lines, C1 demonstrated higher ethylene evolution than C2 but lower than WT. The lowest aboveground and belowground biomass was found with exposure to high UVB radiation. WT produced more biomass than C2. Net Co(2) assimilation and transpiration did not vary among plant lines or UVB treatments. Water-use efficiency was lower under high UVB radiation than under low UVB. The quantum yield of photosystem 11 was higher for C2 than for either WT or Cl. WT did not differ from transgenic plants in respect to photosynthetic pigments and UV-screening compounds. Photosynthetic pigment concentration decreased, but concentration of UV-screening compounds, thickness of epicuticular wax, and the rate of root hydraulic conductance were increased by exposure to UVB radiation. While there appears to be-a lack of ethylene involvement in some of the measured physiological parameters, the transgenic plants exhibited differential sensitivity to UVB in a few key measured parameters.
Correlative data from monocots suggest that cytokinin (CK) regulates seed development. The involvement of CKs in seed growth was investigated using pea, a eudicot with an unknown CK profile, as a model system. CK profiles were measured by liquid chromatography - tandem mass spectrometry against major stages of embryogenesis, which were documented histologically. Like other grain legumes, CK levels of developing pea seeds fluctuated through development and had mainly nucleotide and riboside forms. Among the 11 CKs detected, cis-isomers (cis-[9R]Z (zeatin riboside), and cis-[9RMP]Z (zeatin riboside 5' monophosphate)), along with their isopentenyl precursors, were the major forms during pea embryogenesis, whereas corresponding trans-isomers appeared as minor constituents. Highest CK concentrations occurred at the heart-shape stage, when there are high rates of cell division and sugar metabolism. To assess the significance of high CK concentrations observed at the heart-shape stage, a bioassay was developed wherein heart-shaped embryos were excised and cultured on medium containing either cis-[9R]Z, trans-[9R]Z, or kinetin. Growth of cultured heart-shaped embryo explants was significantly augmented by all exogenous CKs relative to controls that were not supplemented with CK. Moreover, at concentrations equivalent to those experienced by an embryo in vivo, cis-[9R]Z was active in enhancing the growth of cultured pea embryos to an extent equal to that of trans-[9R]Z. Overall, the results endorse a growth-promoting role for cis-CKs during seed development.
Growth, photosynthesis, and induction of two low CO2-inducible genes of Chlamydomonas reinhardtii Dangeard strain CC125 were quantified in a range of physiologically relevant CO2 and O2 concentrations (5%0.005% CO2 and 20% or 2% O2) using airlift bioreactors to facilitate the simultaneous measurement of both growth and in situ photosynthetic rates. Within these CO2 concentration ranges, O2 concentrations (20% vs. 2%) had no discernable effect on growth, photosynthetic rate, or induction of the periplasmic carbonic anhydrase (Cah1) and glycolate dehydrogenase (Gdh) genes in wild-type C. reinhardtii. These results failed to support the hypothesis that the CO2/O2 ratio plays any role in signaling for the up-regulation of limiting CO2-induced genes and (or) of the CO2-concentrating mechanism (CCM). The mRNA abundance of the Cah1 and Gdh genes appeared to be regulated in concert, suggesting co-regulation by the same signaling pathway, which, because of a lack of an O2 effect, seems unlikely to involve photorespiration or a photorespiratory metabolite. Instead, it appeared that the CO2 concentration alone was responsible for regulation of limiting CO2 acclimation responses. Based on growth, photosynthesis, and gene expression characteristics, three distinct CO2-regulated physiological states were recognized within the studied parameters, a high CO2 (5%0.5%) state, a low CO2 (0.4%0.03%) state, and a very low CO2 (0.01%0.005%) state. Induction of Cah1 expression and Gdh up-regulation occurred at a CO2 concentration between 0.5% and 0.4% CO2, delineating the high from the low CO2 states. Photosynthetic characteristics also were distinct in the three CO2-regulated physiological states, e.g., the estimated K0.5(CO2) of the high CO2, low CO2, and very low CO2 states were 72, 10, and 0.9 µmol·L1 CO2, respectively. In addition to a greater photosynthetic CO2 affinity, the very low CO2 state could be distinguished from the low CO2 state by an increased cell-doubling time and a smaller cell size.Key words: algae, Chlamydomonas, CO2, gene expression, induction, photorespiration, photosynthesis.Les auteurs ont quantifié la croissance, la photosynthèse et l'induction de deux gènes induits par une faible concentration en CO2, chez le Chlamydomonsa reinhardtii, sous un ensemble de concentrations en CO2 et en O2 physiologiquement pertinentes (5 % à 0,005 % en CO2, et 20 % à 2 % en O2); à cette fin ils ont utilisé des bioréacteurs à agitation par bullage d'air pour faciliter la mesure simultanée des taux de croissance et de photosynthèse, in situ. Sous cette gamme de concentrations en CO2, les concentrations en O2 (20 % vs 2 %) ne montrent pas d'effet discernable sur la croissance, le taux de photosynthèse, ou l'induction des gènes de l'anhydrase carbonique (Cah1) périplasmique et de la déshydrogénase du glycolate (Gdh), chez le type sauvage du C. reinhardtii. Ces résultats ne supportent pas l'hypothèse proposant que le ratio CO2/O2 joue un certain rôle dans la signalisation conduisant à une régulation à la hausse des gènes induits par une limitation du CO2 et/ou de la CCM. L'abondance en mARN, des gènes Cah1 et Gah, semble régulée de façon concertée. Ceci suggère une co-régulation par le même sentier de signalisation lequel, dû à l'absence d'effet du O2, ne semble pas vraisemblablement impliquer la photorespiration ou un métabolite photorespiratoire. Au contraire, il semble que la concentration en CO2 à elle seule est responsable de la régulation des réactions d'acclimatation au CO2 limitant. Sur la base de la croissance, des caractéristiques de la photosynthèse et de l'expression des gènes, on peut reconnaître trois états physiologiques distincts régulés par le CO2 ; un état de CO2 élevé (5 % à 0,5 %), un état de CO2 faible (0,4 % à 0,03 %), et un état de CO2
To gain further insight into the metabolic role of gamma-aminobutyrate (GABA), we determined the pool sizes of GABA and its catabolic products, alanine and gamma-hydroxybutyrate (GHB), as well as key amino acids (Glu, Gln, Asp, Asn, Pro, Gly, Ser), in Arabidopsis leaves as a function of the light-dark cycle, leaf age (old versus young), and N stress (continuous versus interrupted N supply). Regardless of time of day and leaf age, there was a close relationship among Glu, GABA, and GHB when N was supplied continuously, indicating that GABA and GHB were probably derived exclusively from Glu and GABA, respectively. Ala was also closely linked to GABA in young leaves, but not in old leaves, a result consistent with the existence of multiple sources of Ala. The nature of the responses of GABA and GHB to an interrupted N supply depended on leaf age, and differed from responses exhibited by Glu, Gln, and Asn. Overall fluctuations in primary amino acids under both continuous and interrupted N supply, as well as those associated with photorespiration, aging, and stress, suggest that the old and young leaves chosen for study here function in Arabidopsis as source and sink leaves, respectively.
This paper describes the leaf epidermal characteristics of the New World species of Lotus L. subgenus Acmispon Raf. (Fabaceae: Loteae), computes their phenetic relationships based on morphological and anatomical characters, and compares these results with previous classifications and a recent phylogenetic hypothesis for the group based on morphological data. Leaves of 16 species of Acmispon were cleared and examined using light microscopy. Data on epidermal cells, stomata, stomatal index, and trichomes were described and summarized. To test the taxonomic value of epidermal characters and to ascertain phenetic relationships, we performed two numerical analyses using unweighted pair-group arithmetic average clustering. Results of the numerical analysis (16 operational taxonomic units (OTUs) x 13 epidermal characters) suggested that epidermal characteristics are insufficient to resolve sections Simpeteria and Microlotus. An additional analysis (16 OTUs x 23 characters) demonstrated that epidermal micromorphological features, together with other characters, are useful and informative for distinguishing these two sections. Results generated by the latter analysis accord well with earlier classifications and a previous phylogenetic hypothesis by showing that the sections Simpeteria and Microlotus are coincident with the two monophyletic subgroups Grandiflorus and Salsuginosus, respectively, inferred using cladistic analysis.
Predispersal seed predation by a moth larva, Eupithecia immundata Leinig & Zeller (Geometridae), and its impact on population dynamics of the perennial herb Actaea spicata L. were studied during 7 years in deciduous and mixed coniferous forest populations in southeastern Sweden. Twelve population matrix models were constructed based on transition probabilities among six stage classes in the populations. The fraction of seeds consumed varied between 21% and 80% but was not significantly correlated with seed production. Experimental seed addition compensating for seed losses caused by the seed predator resulted in increased seedling emergence in one of the populations. Population growth rate was positive (λ > 1) in 1 of 6 years in the deciduous forest population and in 2 of 6 years in the mixed coniferous forest population. Survival among reproductive individuals contributed most strongly to λ in both populations. In some years, the projected λ changed from positive to negative values because of seed loss caused by E. immundata. However, results suggest that seed predation did not affect λ to any large extent, despite a considerable seed predation. This study is one of the rare efforts to estimate the impact of seed predation on population dynamics of perennial plants.
Fifty-eight streptomycete and 35 non-streptomycete actinomycetes were isolated from cucumber rhizosphere soil. These isolates were screened for the production of cell-wall-degrading enzymes using mycelial (Pythium aphanidermatum (Edson) Fitzp.) fragment agar. Eighteen promising isolates were screened for their competence as root colonizers. Eight isolates showing exceptional rhizosphere competence significantly inhibited, in vitro, P. aphanidermatum, the causal agent of postemergence damping-off of cucumber (Cucumis sativus L.) seedlings. The four most inhibitory isolates (Actinoplanes philippinensis Couch, Microbispora rosea Nonomura and Ohara, Micromonospora chalcea (Foulerton) Orskov, and Streptomyces griseoloalbus (Kudrina) Pridham et al.) produced in vitro beta-1,3-, beta-1,4-, and beta-1,6-glucanases and caused lysis of P. aphanidermatum hyphae. None of these produced volatile inhibitors or siderophores. Only S. griseoloalbus produced diffusible inhibitory metabolites, whilst A. philippinensis and Micromonospora chalcea parasitized the oospores of P. aphanidermatum. These four isolates were subsequently tested in the greenhouse, individually or as a mixture, for their ability to suppress damping-off of cucumber seedlings in soil with or without cellulose amendment. The treatment, which included all four isolates in soil amended with cellulose, was significantly superior to all other treatments in suppressing damping-off and was nearly as good as the metalaxyl treatment. Results show that there is a potential to use a mixture of antagonistic rhizosphere-competent actinomycetes along with cellulose amendment rather than fungicides for the field management of this disease. This is the first study that has involved the screening of rhizosphere-competent non-streptomycete actinomycetes capable of producing cell-wall-degrading enzymes, for the management of Pythium diseases.
We have produced the largest population of activation-tagged poplar trees to date, approximately 1800 independent lines, and report on phenotypes of interest that have been identified in tissue culture and greenhouse conditions. Activation tagging is an insertional mutagenesis technique that results in the dominant upregulation of an endogenous gene. A large-scale Agrobacterium-mediated transformation protocol was used to transform the pSKI074 activation-tagging vector into Populus tremula x Populus alba hybrid poplar. We have screened the first 1000 lines for developmental abnormalities and have a visible mutant frequency of 2.4%, with alterations in leaf and stem structure as well as overall stature. Most of the phenotypes represent new phenotypes that have not previously been identified in poplar and, in some cases, not in any other plant either. Molecular analysis of the T-DNA inserts of a subpopulation of mutant lines reveal both single and double T-DNA inserts with double inserts snore common in lines with visible phenotypes. The broad range of developmental mutants identified in this pilot screen of the population reveals that it will be a valuable resource for gene discovery in poplar. The full value of this population will only be realized as we screen these lines for a wide range of phenotypes.
The white-pine blister rust fungus, Cronartium ribicola Fisch. in Rabenh., continues to spread in North America, utilizing various aecial (primary) and telial (alternate) hosts, some of which have only recently been discovered. This introduced pathogen has been characterized as having low genetic diversity in North America, yet it has demonstrated a capacity to invade diverse environments. The recent discovery of this rust fungus on the telial host Pedicularis racemosa Dougl. ex Benth., raises questions of whether this host association represents a recent acquisition by C. ribicola or a long-standing host association that was overlooked. Here we explore two questions: (i) is host specialization detectable at a local scale and (ii) is the capacity to infect Pedicularis racemosa local or widespread? Genetic analysis of C. ribicola isolates from different aecial and telial hosts provided no evidence for genetic differentiation and showed similar levels of expected heterozygosity within a geographic population. An inoculation test showed that diverse C. ribicola sources from across North America had the capacity to infect Pedicularis racemosa. These results support a hypothesis that ability to infect Pedicularis racemosa is common in C. ribicola from North America. Utilization of Pedicularis racemosa by C. ribicola may be dependent on the co-occurrence of this host, inoculum, and favorable environments.
Nitrate exsorption in relation to light was studied in four wheat (Triticum aestivum L.) cultivars, Sais, Jouda, Marchouch, and Khair, using four experimental treatments: intact plants, excised roots, defoliated plants, and decapitated plants. Data show that nitrate exsorption was dramatically reduced from excised roots compared to controls. This efflux reduction was also observed from the roots of decapitated plants. On the contrary, defoliation triggered a significant increase in the quantity of exsorbed NO3, as compared to intact plants. This increased efflux was much more dramatic when defoliated plants were exposed to darkness; nitrate exsorption from roots was then 8 to 10 times larger than from excised roots. In 21-day-old wheat plantlets, the aboveground parts are the main site for efflux regulation at the root level. Both leaves and apex are the aboveground organs responsible for this regulation. Indeed, the efflux was reduced by the leaves and, on the contrary, stimulated by the apex. Light was involved in controlling this efflux. This control involves a flow, between the aboveground parts and the roots, of two types of factors, one of which (or both) being sensitive to light. The first factor is of apical origin, whereas the second is of foliar origin. However, the chemical nature of these two types of photosensitive factors involved in NO3 ions efflux regulation remains to be determined.Key words: nitrate, efflux, light, darkness, common wheat.[Journal translation]L'exsorption des nitrates en relation avec la lumière a été étudiée chez quatre cultivars de blé tendre (Triticum aestivum L.), Sais, Jouda, Marchouch et Khair, dans quatre conditions expérimentales : plantes intactes, racines excisées, plantes défoliées et plantes décapitées. Les résultats obtenus montrent que l'exsorption des nitrates est fortement diminuée chez les racines excisées comparativement aux plantes témoins. Cette diminution est aussi observée chez les plantes décapitées. La défoliation provoque, au contraire, une augmentation significative de la quantité de NO3 exsorbé par rapport aux plantes intactes. Cette augmentation de l'efflux est beaucoup plus spectaculaire lorsque les plantes défoliées sont exposées à l'obscurité; les racines exsorbent alors 8 à 10 fois plus de nitrates que les racines excisées. Chez les plantules de blé âgées de 21 jours, la partie aérienne est le site principal de régulation de l'efflux au niveau des racines. Les feuilles et l'apex constituent conjointement les organes de la partie aérienne responsables de cette régulation. En effet, l'efflux est freiné par les feuilles et stimulé, au contraire, par l'apex. La lumière est impliquée dans le contrôle de cet efflux. Ce contrôle met en jeu un trafic, entre la partie aérienne et les racines, de deux types de facteurs dont l'un et (ou) l'autre sont sensibles à la lumière. Le premier facteur est d'origine apicale, alors que le second est d'origine foliaire. Il reste toutefois à déterminer la nature chimique de ces deux types de facteurs photosensibles impliqués dans le processus de contrôle de l'efflux des ions NO3 dans le milieu.Mots clés : nitrate, efflux, lumière, obscurité, blé tendre.
We examined whether the responses of dry tropical tree seedlings to elevated nitrogen (N) inputs were associated with functional types, and whether the growth traits of seedlings emerging from seeds of different size within a species were differentially affected by increased N inputs. The study comprised five dry tropical tree species: Albizia procera (Roxb.) Benth, Acacia nilotica (L.) Delile, Phyllanthus emblica L., Terminalia arjuna (Roxb.) Beddome, and Terminalia chebula Retz. Of these, Albizia procera, Acacia nilotica, and P. emblica are pioneer species. The former two are N-fixing legumes. Terminalia arjuna and T. chebula are nonpioneer, nonleguminous species. Albizia procera, P. emblica, and T. arjuna are fast growing, while the remaining two are slow-growing species. Seedlings of these species from large and small seeds were grown at four N input levels (0, 30, 60, and 120 kg N·ha-1). Height and leaf area were measured periodically. At the end of the experiment (after 4 months) biomass and other growth traits, namely relative growth rate, net assimilation rate, specific leaf area, and root/shoot ratio, were determined. Foliar N and net CO2 assimilation rates were also determined. The species responded differentially (66%-282% increase in biomass) to elevated N supply, but the response was not associated with between-species seed size variation. However, within species, small-seed seedlings exhibited a greater response. The elevated N input resulted in a greater enhancement in relative growth rate of the slow-growing species. The species response did not follow functional types such as pioneer versus nonpioneer, legumes versus nonlegumes, and deciduous versus evergreen, but rather was individualistic.
Fifteen strains representing each Penicillium ser. Corymbifera taxa were compared using phenotypic and chemotaxonomic characters by cluster analysis and discriminant partial least squares regression. Variability in phenotypic expression of species strains resulted in a more fragmented classification compared with secondary metabolite expression. Although the observed phenotypic expression varied for strains cultured upon the same media, it was possible to classify strains into species groupings based only upon a few distinctive phenotypic traits. Data analysis of secondary metabolite profiles generated from HPLC-diode array dectection analysis gave reliable strain classification when more than one media type was employed. Depending on the species, Czapek yeast autolysate agar typically yielded the greatest chemical diversity; however, several metabolites (terrestric acid, corymbiferone, the corymbiferan lactones, and daldinin D) were only produced when strains were grown on either yeast extract sucrose or oatmeal agar. For the classification of strains based on a binary data matrix, application of the Yule coefficient gave the best clustering. Several secondary metabolites, of importance for the classification of ser. Corymbifera strains, were identified by discriminant-partial least squares regression analysis. A diagnostic key based on phenotypic, chemotaxonomic, and pathogenic traits is provided as an aid for species identification.
Forty-one remnants of the aspen-dominated upland forest in three subregions of the dry boreal mixed-wood in Alberta were studied to determine effects of fragment size and shape on native and alien plant species richness and abundance in agro-environments. The percent cover of all vascular plant species was visually estimated in 5 m diameter circular plots along transects that covered the length and the width of each fragment. A subset of 12 of the largest fragments (>900 m 2) that had distinct interiors (portions of the fragment >15 m from any edge) was used to measure edge effects on the vegetation. Regression analyses revealed significant positive relationships between species richness and area regardless of the subregion. Species richness stabilized in fragments that were larger than I I ha. Edges did not affect shrub species richness and only affected herbaceous species richness on west- and south-facing aspects. Shrub abundance decreased and herb abundance increased up to 20 m from the edges regardless of orientation. Edges did not support a different suite of species than interiors, although several species occurred more frequently in the interior than along the edges. Alien species richness and abundance reached their highest values between 5 and 15 m from the edge, and some of those species could be found up to 40 m from the edge. Although larger fragments generally supported more alien species than smaller fragments, the smallest fragments had the greatest number of species per metre squared. Results from this study indicated that it would be preferable to conserve larger woodlots rather then several smaller woodlots on the landscape.
Cryptosporiopsis Bubák & Kabát isolates were obtained for the first time from roots of apparently healthy aspen seedlings in Alberta. These isolates were similar in all the major morphological features previously used to separate Cryptosporiopsis species, but sequencing data of the ITS1-5.8S-ITS2 region indicated that they were separated into two groups, one belonging to Cryptosporiopsis ericae Sigler and the other to Cryptosporiopsis radicicola Kowalski & Bartnik. Scanning electron microscopy of ex-type cultures and selected isolates from aspen roots revealed that C. ericae and C. radicicola differed in morphogenesis and structure of conidiomata: those of C. ericae were either synnematous or sporodochial, whereas those of C. radicicola possessed a peridium-like mycelial envelope bearing amorphous adhesive material. Phialides in the hymenium of C. radicicola were also embedded in amorphous matrix material but such material was absent in C. ericae. Microscopic examination of artificially inoculated aspen roots indicated that both species are endophytes of the host. Hyphal penetration by C. ericae was only occasional and confined to the host epidermis, whereas C. radicicola was more aggressive and its hyphal ingress extended to the cortical region.
Mountain pine beetles (Dendroctonus ponderosae Hopkins; (MPB)) have spread into lodgepole x jack pine hybrid (Pinus contorta Douglas x Pinus banksiana Lambert) forests in Alberta and are predicted to spread into jack pine forests. Their success in these forests is uncertain but will be influenced by multiple factors, including the ability of their associated blue-stain fungi to colonize the trees and the health of the encountered trees. Healthy and dwarf mistletoe infected pines at three sites across Alberta (one site per pine species) were inoculated with three isolates each of Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer and Wingfield and Ophiostoma montium (Rumbold) von Arx. Both fungi grew and caused lesions on all hosts, suggesting that MPB will not be limited by a lack of fungal growth. Both fungi caused longer lesions in jack and hybrid pines than in lodgepole pines, indicating that susceptibility varies among hosts and is greater in the novel systems than in the co-evolved one. G. clavigera caused longer lesions than O. montium in hybrids and lodgepole pines, while the two species caused similar-sized lesions on jack pine. Intraspecific variation was high in G. clavigera, with one isolate producing much shorter lesions than the other two. Dwarf mistletoe infestation had little effect on infection lesion length.
Allergenic activity in the atmospheric aerosol of small particles in the size range of a few micrometres or less may play an important role in causing allergic reactions in the lower regions of the lungs, often seen in pollinosis. Orbicules (= Ubisch bodies) are small, mostly spherical granules of sporopollenin, which can occur on the radial and innermost tangential wall of secretory tapetum cells. In instances where orbicules of allergenic species are dispersed into the atmosphere, they may act as effective vectors of allergens. We investigated the presence and morphology of orbicules in 15 allergenic species using scanning electron microscopy. Orbicules were present in all species investigated of the families Betulaceae, Chenopodiaceae, Fagaceae, Poaceae, Polygonaceae, and Urticaceae. In the species of the Asteraceae and Oleaceae studied, orbicules were lacking. Almost all orbicules observed were spiny. Their mean diameters range from 0.342 to 1.130 μm. Orbicules can be part of the fraction of small particles in the size range of a few micrometres or less, emitted from the anthers. Our results clearly indicate that a thorough investigation of the sites of allergens across the whole anther is required to reveal whether or not these orbicules possess allergens.
The cytological events of wall modification in the endodermis and exodermis of Allium cepa L. roots were examined with fluorescence and transmission electron microscopy. In the endodermis, Casparian bands, suberin lamellae, and tertiary walls developed in succession. At the site of the future Casparian band, the plasma membrane was bound to the wall before deposition of detectable hydrophobic components in the radial wall. Suberin lamellae were deposited on the inner faces of the primary walls, first along the outer tangential walls and then the inner tangential walls. On both walls, segments of the lamellae were formed earlier in primary pit fields than at nonprimary pit field regions. Suberin lamellae then extended to the radial walls. When they reached the Casparian bands, the lamellae intruded between the bound plasma membranes and the walls, so that the cells' plasma membranes remained intact. In this way, suberin lamellae that were continuous around the cells were laid down. Later, tertiary walls were deposited internal to the suberin lamellae. None of the wall modifications interrupted the symplastic connections of the endodermis. During suberin lamella and tertiary wall formation, more dictyosomes and ER profiles appeared than during Casparian band development. In the exodermis, although Casparian bands were readily detected with fluorescence microscopy, they were rarely detected with electron microscopy. Suberin lamellae were formed in long cells severing their plasmodesmata. As in the endodermis, dictyosomes and ER were prominent during suberin lamella formation. Tertiary walls were not formed in the exodermis.
Biomass allocation patterns in plants are known to be affected by soil nitrogen availability. Since nitrogen availability can depress symbiotic nitrogen fixation, and nitrogen fixation can make plant growth independent of soil nitrogen availability but is energetically costly, it is unclear how allocation patterns in nitrogen-fixing species should respond to variation in soil nitrogen availability. We examined the effect of nitrogen source and concentration on the growth and allocation patterns in the nitrogen-fixing shrub Alnus viridis subsp. crispa (Aiton) Turrill. Plants were grown with either NH4+-N or NO3--N at a range of low N concentrations, from 0 to 2 mmol.L-1, and either inoculated with Frankia or not. Plants without nodules had 25.1% lower biomass and had double the allocation to roots at all but the 2 mmol.L-1 nitrogen concentration. Even though nodulated plants increased growth with nitrogen concentration, allocation to roots as a fraction of total biomass did not vary in these plants, suggesting increased growth resulted from more efficient nitrogen acquisition. Allocation to roots was a significant predictor of plant growth in non-nodulated plants (r(2) = 0.318, for linear least squares fit with log mass) but not for nodulated plants (r(2) = 0.108). As nitrogen concentrations increased, allocation to nodules, specific nodule numbers, and the proportion of nitrogen fixed by the plants decreased, demonstrating a shift to soil nitrogen use.
High light requirements limit the distribution of several rare plant species endemic to the southern Appalachian region. We studied the influence of light and nitrogen availability on carbon allocation and morphology in one of these species, Houstonia montana Small. Insights into growth and nutrition of H. montana are needed for predicting how it will respond to ongoing changes in its environment associated with atmospheric nitrogen deposition and resulting from succession and (or) management of grassy-bald habitats in which it occurs. We hypothesized that low light constrains belowground allocation, and that elevated N availability reduces limitations to aboveground growth at low light. We tested growth and mycorrhizal colonization of H. montana in response to interactions of light and N availability in a greenhouse experiment. Shade reduced plant biomass, root:shoot ratios, and mycorrhizal colonization, and increased specific leaf area (area/mass). Elevated N reduced root:shoot ratios and mycorrhizal colonization. Under low light, N addition increased specific root length (length/mass) and foliar chlorophyll. We found support for the hypotheses that low light and high N reduce belowground allocation in H. montana. However, we did not find that high N significantly alleviates limitation to plant growth in the shade, despite changes in allocation, morphology, and chemistry that were consistent with more efficient use of C for aboveground growth. Thus, variation in the soil N availability is unlikely to have a marked effect on the ability of H. montana to tolerate shade in its native habitat.
A successional sand dune system along the Lake Michigan shoreline was chosen to study the impact of edaphic factors, vegetation cover, and topographic position on Frankia strain distribution and infectivity. On this site, three actinorhizal species, Myrica gale L., Alnus incana (L.) Moench subsp. rugosa (Du Roi) Clausen, and Shepherdia canadensis (L.) Nutt., grew in different communities. Soil samples were collected on plots devoid of actinorhizal plants and serially diluted to inoculate the three native host plants in a greenhouse study. Strains present in the nodules formed were then genetically characterized using PCR-RFLP of the 16S-23S intergenic spacer (IGS). An additional study site was included to estimate the impact of the sympatric presence of the three host species on soil infectivity and strain diversity. On this second site, soils used as inocula were collected in the rhizosphere of M. gale and S. canadensis. The M. gale and A. incana nodular strains belonged to an homogeneous cluster, whereas the S. cana densis nodular strains were separated into two distinct genetic clusters, irrespective of edaphic conditions and proximity to the host's root systems. A chi(2) analysis conducted on Shepherdia-infective strains showed the dominance of two distinct genotypes, with one of them being specific to newly formed dunes lacking plant cover and the other specific to older, stable dunes with dense vegetative cover.
Plants growing in vegetative shade are subjected to reductions in both red to far-red (R/FR) light ratio and in irradiance levels of photosynthetically active radiation (PAR). In this report we have attempted to uncouple the reduced R/FR ratio-and low PAR-mediated effects of shade on flowering in the ramets of Stellaria longipes Goldie s. 1. (Caryophyllaceae) ecotypes collected from alpine "sun" and lower elevation prairie "shade'' habitats. Both ecotypes were also tested for their flowering response (defined as the number of open flowers per ramet) to daylength. The alpine ecotype plants can best be classified as day-neutral, whereas prairie ecotype plants require long-days (LD). Under a low PAR of 115 mu mol m(-2).s(-1) given under LD conditions at a reduced (0.7) R/FR ratio, alpine ecotype plants flowered significantly later relative to plants grown under the low PAR at a normal (1.22) R/FR ratio. In contrast, plants of the prairie ecotype flowered earlier under the reduced R/FR ratio combined with the same low PAR. Flower number per ramet differed significantly between the two ecotypes, with alpine ecotype plants developing fewer flowers under a low PAR (109 mu mol m(-2).s(-1) irradiance) relative to a high PAR of 611 mu mol m(-2).s(-1) (both given at a normal R/FR ratio). The prairie ecotype plants responded differently and had similar flower numbers under both low and high PARs at the normal (1.22) R/FR ratio. However, growing the prairie ecotype plants under a reduced R/FR ratio at a low PAR showed a significant increase in number of flowers. In contrast, plants grown under high (2.7) and normal (1.9) R/FR ratios combined with low PAR produced many more flowers than the alpine ecotype. Thus, the two components of shade, reduced R/FR ratio and low PAR can cause distinctly different flowering responses in sun and shade plants of S. longipes.
Exposed cliffs in the northern Swiss Jura Mountains harbour a highly diverse flora with numerous endangered and relic plant species. On these cliffs, sport climbing is enjoying increasing popularity. We examined the ecological effects of sport climbing on vascular plants at the cliff base and on the cliff face by assessing plant cover and species density at various distances from frequently used climbing routes. Plant cover was significantly reduced at the base of climbing routes. Furthermore, species density (number of species per square metre) at the cliff base, as well as plant cover and species density at the cliff face, tended to increase with distance from the route. We also compared the vegetation of five frequently climbed cliffs with that of seven unclimbed cliffs. Climbing significantly altered the plant composition. Specialized rock species occurred less frequently on climbed cliffs than on unclimbed cliffs. Management plans and conservation actions are needed to preserve the threatened plant species on frequently climbed cliffs. Such plans should include the establishment of climbing-free protection areas on cliffs with a high number of specialized, relic plants and the protection of entire cliffs that are not yet climbed.
Low, static concentrations of ammonium have less negative effects on nodulation of pea (Pisum sativum L.) than nitrate and in some cases may actually stimulate nodulation. Two experiments were carried out to assess the effects of supplying both forms of mineral N, separately and in combination, on nodule initiation, nodule development, nodule distribution between primary and lateral (secondary) roots, tertiary root development, and N2 fixation in pea. Pea plants were grown for up to 24d after inoculation in hydroponic culture with no mineral N (zero N), NO3- (0.5mmol·L-1), NH4+ (0.5mmol·L-1), or NO3- (0.25mmol·L-1) plus NH4+ (0.25mmol·L-1). Concentrations of nitrate and ammonium were monitored on a daily basis and held relatively constant by continuous, automatic additions of stock solutions. Pea plants accumulated the most total dry mass (DM) and total N when supplied with the combination of nitrate plus ammonium but had the lowest nodule DM and percentage of nitrogen derived from the atmosphere. Whole-plant nodulation (nodules per plant) and DM-specific nodulation (nodules·g-1 root DM) were 2.3- and 2.4-fold greater, respectively, in pea plants receiving NH4+ at 0.5mmol·L-1 than in those supplied with NO3- at 0.5mmol·L-1. The nodulation responses of plants receiving NO3- at 0.25mmol·L-1 plus NH4+ at 0.25mmol·L-1 were more similar to those of plants receiving only nitrate than only ammonium, indicating that when both forms of mineral N are available to plants, nitrate has a predominant effect on the nodulation response. Assessment of the stage of development of nodule primordia and nodules during the time course of the experiments indicated that nitrate not only decreased the degree of nodule initiation but also the rate at which those nodules developed. Microscopic observations indicated that the more negative effects of the nitrate treatment on DM-specific nodulation as compared with the ammonium treatment were consistent on both the primary and lateral roots. Quantification of nodulation and tertiary root development on lateral roots indicated that the stimulating effects of ammonium were specific to nodulation; the effects on tertiary root development were different. The study demonstrates for the first time that when both forms of mineral N are available at equal concentrations, the nodulation response in pea is influenced more by nitrate than by ammonium and that the effects of nitrate and ammonium on tertiary root initiation and development are unlike those on nodulation.Des concentrations statiques faibles d'ammonium ont moins d'effets négatifs sur la nodulation du pois (Pisum sativum L.) que le nitrate, et dans certains cas peuvent même stimuler la nodulation. Les auteurs ont mené deux expériences pour évaluer les effets d'un apport en N minéral sous les deux formes, séparément et en combinaison, sur l'initiation des nodules, le développement des nodules, la distribution des nodules entre les racines primaires et latérales (secondaires), le développement des racines tertiaires, et la fixation de N, chez le pois. Ils ont cultivé des plants de pois jusqu'à 24 jours après l'inoculation, en culture hydroponique, sans azote minéral (N = zéro), 0,5 mmol·L-1 NO3-, 0,5 mmol·L-1 NH4+, ou 0,25 mmol·L-1 NO3- plus 0,25mmol·L-1 NH4+. Ils ont suivi les concentrations en nitrate et ammonium sur une base quotidienne, qu'ils ont maintenues relativement constantes par addition continue automatisée de solutions de base. Les plants de pois ont accumulé la plus grande masse total sec (DM) et le plus fort contenu en N lorsqu'ils ont reçu la combinaison nitrate-plus-ammonium, mais le plus faible DM de nodules et le plus faible pourcentage d'azote d'origine atmosphérique.
Hawthorns and medlars are closely related genera in Rosaceae subfamily Maloideae, whose taxonomy remains poorly understood. Gametophytic apomixis occurs in polyploids, and diploids are sexual out-crossers, so ploidy level is of great interest, but suitable material for chromosome counts is of limited availability each year. The promise of flow cytometry is that it permits rapid measurement of nuclear DNA amounts from most tissues, and ploidy level can be inferred if climatic and taxonomic differences do not interfere. Our DNA measurements cover most of the taxonomic series in Crataegus, adding cultivated and naturalized Eurasian plants to the many wild plants collected mainly from south-central Canada and the southeastern and northwestern United States. We found that some variation in DNA amount per genome copy distinguishes certain taxa, but ploidy-level estimates are at least as clear as the published chromosome counts, especially in the most common diploid-triploid-tetraploid range, and to the single published higher (hexaploid) chromosome count, we add evidence of pentaploids. By comparing ploidy evaluations to morphology, we hypothesize that both autopolyploidy and allopolyploidy contribute to the taxonomic complexity. We compared DNA amounts in Maloideae with those in Gillenia, a likely sister genus to the subfamily, which has a smaller chromosome number.