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The importance of microenvironment: Opuntia plant growth, form and the response to sunlight
Abstract
Of critical importance to plants is the ability to secure adequate photosynthetically active radiation (PAR) for functioning, growth and reproduction. The Opuntia genus represents plants that produce new cladodes (=pads, the primary photosynthetic surface) annually and whose orientation is a response to PAR. Because of the great variability in orientation, I assess pad orientation and tilt at highly local scales to quantify plant response to variations in PAR receipt, using three datasets collected over two field seasons. Several species and putative hybrids were sampled in the West Coyote Hills in Southern California. Data for orientation, shade direction, surface temperatures on differently oriented cladode faces, and cladode tilt were collected. Following normalization of variables, a variety of parametric and non-parametric tests show that the pattern of pad orientation is not unique to species, but is unique to the microsite, where even shade from another pad 5 cm away strongly affects PAR receipt and orientation response. Orientation is not constrained by position on plant. Pads tilt to increase S and E exposure (at the expense of N and W) in response to local shade. Pad face temperatures are higher on sun-facing sides, but the temperature differences are generally small in winter. I observe that pad orientation is best predicted by shade but at the scale of the areole, pad or plant. Results confirm that the high variability observed in orientation in many populations is due to the lack of consideration of shade at highly local scales (plant- or pad-scale), and that even in environments with seemingly ample PAR (sunny, open environments), plants benefit from orienting photosynthetic surfaces to maximize PAR receipt.
... plants Nobel (1982a) reported that the orientation of Opuntia cactus cladodes occurs to maximize the reception of solar radiation during the growing season, and the direction of orientation is determined by regional factors such as latitude, and topography. Drezner (2020) suggested that plant response to PAR reception is strongly controlled by local-scale factors. Our finding in this study, showed that for all the studied Opuntia spp. ...
... According to Nobel (1982a) and Drezner (2020), orientation is not a mechanism to reduce high surface temperatures, but to maximize the reception of PAR. Photosynthesis is inhibited by low temperatures, as has been documented for Opuntia stricta (Barker et al., 1998). ...
Cactus Opuntia spp. is a perfectly appropriate crop for land rehabilitation in the arid and semi-arid regions of Morocco. Unfortunately, the sustainability of this extremely resilient crop has become seriously threatened by the appearance of Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae), a cochineal specific to Opuntia spp cacti that was introduced in Morocco in 2014. Thus, eight Opuntia spp. varieties were identified by National Institute of Agricultural Research in Morocco as resistant to the cochineal, to provide a solid basis for the national emergency program of rehabilitating the devastated Opuntia spp. ecosystems throughout the country. To produce large quantities of planting material, a rapid Ex-situ propagation method for prickly pears have been developed. For each of the eight varieties, cladodes were harvested in march, 2019 and 2020 in the Experimental Station of the Regional Office of Agricultural Development of Doukkala (ORMVAD). They were cut into 6 pieces of about 140 cm 2 with at least two bud areolas. After 25 days of drying at a temperature range from 17 to 28 °C, the cuttings were soaked for 5 min in 2.5 g/l of a Rhizogen product (containing 0.3% IBA), which represents for us the Auxin, or in talc powder or in talc powder and a rapid soaking in auxin solution (mix 1) or soaking in water then in talc powder (mix 2) or in water. The cuttings were planted in normal polarity in black plastic cylindrical containers (24.6 cm long and 14.1 cm wide), filled with a mixture of fine sand (2/3 w/w) and peat (1/3 w/w) and placed at an average ambient temperature of 28°C/17°C (day/night) in field for growth. In general, auxin (2.5 g/l) and mix 1 treatments were found to be the most effective regarding rooting (20-73 roots number) and growth of cuttings. This research has also allowed us to demonstrate that, in general, for all the varieties studied, basal cuttings planted in orientation (N-S) and normal polarity show very interesting results under optimal conditions concerning rhizogenesis and caulogenesis.
... Among the parameters of photochemical efficiency, chlorophyll-a fluorescence, the maximum quantum yield of photosystem II (Fv/Fm) and electron transport (ETR) are considered particularly robust and extremely reliable tools (Bussotti et al., 2020;Ojeda-Pérez et al., 2017;Oliveira et al., 2020). Cacti show high concentrations of chlorophyll and photoprotective pigments, contributing to their development (Bussotti et al., 2020;Cabrera et al., 2016) and maximising their photosynthetic activity (Drezner, 2020;Ojeda-Pérez et al., 2017). However, despite this marked efficiency, excessive light can cause damage to the photosystem (He et al., 2019;Oliveira et al., 2020). ...
... In this type of plant, because it uses CAM, the PEPC enzyme plays a key role in photosynthetic metabolism, at high concentrations catalysing oxaloacetate and producing metabolic energy (Walker et al., 2011). Above all, this metabolic energy is more efficient when the cladodes are able to intercept photosynthetically active radiation, aiding in the production of a substrate for photosynthesis; an efficiency that can be compromised even in sunny environments due to the overlap between cladodes and to the plant architecture resulting in photoinhibition (Drezner, 2020). ...
Plants with the crassulacean acid metabolism commonly present good adaptation to arid and semi-arid environments, but it highly depends on the type of species. In this study, chlorophyll fluorescence, the concentration of inorganic and organic solutes and the productive performance were evaluated along with their relationships in different clones of the genera Opuntia and Nopalea. The experiment was conducted from 2016 to 2018. Four clones of genus Opuntia were evaluated: ‘Orelha de Elefante Mexicana’ (OEM), ‘Orelha de Elefante Africana’ (OEA), V19 and F8; and two clones of genus Nopalea: ‘IPA Sertânia’ and ‘Miúda’. The experiment was arranged in a randomised block design, with six treatments and three replications. The following parameters were measured when harvesting: initial, maximum and variable fluorescence; the quantum yield of PSII (Fv/Fm); light-induction curves of the photochemical parameters (ΔF/Fm', qP, NPQ and ETR); the chlorophyll and carotenoid content; carbohydrates; the sodium (Na+) and potassium (K+) content; morphometry; and dry matter accumulation. The values for the effective quantum yield of PSII (ΔF/Fm') and the alterations in photochemical quenching were higher in the OEM clone (P < 0.05). There was a difference between clones for non-photochemical quenching, with the F8 clone having the highest values. The Fv/Fm was 0.87 for the OEM. ‘IPA Sertânia’ obtained the greatest Chl a/b, and the highest values for carbohydrate concentration were found in the OEA clone. The OEM clone showed the greatest accumulation of K+, in addition to a higher cladode area index and greater dry matter accumulation. The results of this study show the high physiological tolerance of the forage cactus to a semi-arid environment, which varies according to the clone.
... This is because cloudiness decreases the intensity of PAR and causes a reduction in the photosynthetic efficiency of Opuntia (Geller and Nobel, 1987;Pimienta-Barrios et al., 2000). In addition, several species of Opuntia cacti may undergo changes in morphology due to the anisotropic characteristics of PAR (Drezner, 2020;Geller and Nobel, 1987). High R g and PAR periods coincided with significant rainfall, enhancing cactus photosynthesis and light absorption. ...
Anthropogenic disturbances directly influence environmental processes and increase the concentration of carbon (C) in the atmosphere. Here, we compare the differences in the seasonality of the balance of carbon, energy, and radiation, as well as seek to identify the interrelationships between these environmental variables and their impact on the growth of Opuntia cactus. Data were acquired from an eddy covariance flux tower over a cactus crop agroecosystem (2019–2021) in the Brazilian semi-arid region. In addition, we use plant growth rates, carbon and nutrient stocks, evapotranspiration (ET) and water use efficiency (WUE), and radiation (RUE). We show that the closure of the surface energy balance was 71%, although there are minimal fluxes of available energy lost (29%) by unquantified processes. At all seasons, the highest net ecosystem CO2 exchange (NEE) rate was between 11:00–13:00 (−5.75 μmol m−2 s−1). During the dry and wet-dry season, there was the lowest daily gross primary productivity (GPP) (2.5 μmol m−2 s−1) and net radiation—Rn (217.97 W m−2). Ecosystem respiration was more expressive during the wet season (2.41 μmol m−2 s−1), and maximum diurnal value of 2.65 μmol m−2 s−1. Furthermore, the latent heat flux was higher during the wet season (114.68 W m−2) and lowered in the dry season (9.39 W m−2). The net assimilation rate showed higher values during the dry-wet transition. The dry season presented higher nutrient use efficiency and WUE (14.77 g m−2 mm−1). The highest ET occurred during the wet season (227 mm), and RUE was 81.48% higher than in the dry season. Overall, the cactus was a potential C sink during the three years of assessment (NEE: −377 g C m−2 year−1; GPP: 881 g C m−2 year−1). The results help us to understand that most of the Rn energy is used in the sensible heat flux (58% ratio).
... Particularly, a number of studies have addressed the importance of PAR interception on plant reproductive biology. PAR interception is positively associated with plant photosynthetic activity (Drezner, 2020;Geller & Nobel, 1987;Lee, 1988) and temperature (Herce et al., 2014;Tinoco-Ojanguren & Molina-Freaner, 2000). Therefore, it determines resource availability (i.e., carbohydrates produced through photosynthesis) for the production of flowers, fruits, and gametes (Charlesworth & Charlesworth, 1987;Zhang et al., 2005) and flower size (Ashman & Hitchens, 2000;Herrera, 1991). ...
In columnar cacti, a higher production of reproductive structures on branches oriented towards the Equator has been explained by their higher interception of photosynthetic active radiation (PAR) as well as resource availability. The goal of this study was to evaluate the effect of orientation on diverse aspects of the reproductive biology of Myrtillocactus geometrizans. Phenology was studied in north‐ and south‐facing branches. Floral cycle events, floral visitors, reproductive traits associated with sexual and attraction functions, and reproductive success were estimated from reproductive structures with contrasting orientation. Pollination experiments were conducted to evaluate the effect of orientation on mating system. Our results showed that south‐facing branches had a longer duration of the mature fruit phenophase. Moreover, flower synchrony, production of reproductive structures, and floral traits associated with the male (number of anthers and pollen grains per floral bud), female (number and size of ovules and dimensions of both ovary and ovary cavity), and attraction (petal size) functions had higher values in south‐facing flowers. The beginning and ending of the male function and the end of flower anthesis occurred earlier in south‐facing flowers. Diversity of floral visitors was similar between orientations, except for beetles whose abundance was greater in flowers oriented towards the south. North‐ and south‐facing flowers had a mixed mating system, with similar reproductive success. Our results showed strong differences in the reproductive biology of an intertropical columnar cactus, probably in response to the uneven PAR interception and resource availability in branches and flowers with contrasting orientation.
... Lack of sunlight will make the maximum lack of growth in plants [22]. In addition to the lack of sunlight obtained by plants due to changes in weather, the temperature and humidity of the air will also change following the changes in the weather [23]. Temperature and humidity are also the factors that ensure the quality of hydroponics in meeting the needs of plants. ...
The genus Opuntia has its place in order Caryophyllales of Angiosperms. This group of evergreen, succulent perennial plants belongs to the family Cactaceae. The Opuntia genus is native to Central America, having approximately 181 known species. These species flourish in dry, warmer, and open areas. They are cultivated throughout the world as not only vegetable, crop, and food products like jams, juices, and beverages but used as fodder and forage in Brazil, Mexico, Northern and southern Africa, and in Western Asia. In the early stage, the cladodes are tender and used as a vegetable source known as Nopales, while its fruit is obovoid to spheroidal known as tunas. It is juicy and fleshy used in candies. They are considered alternative natural medicine in diabetes, colon cancer, obesity, gastric ulcers, and coronary heart diseases. The Opuntia species hybridize easily in the wild, leading to continuous morphological variations results in misclassifications. The present study aims to complete the morphological description (qualitative and quantitative) of Opuntia species characterized by flattened cladodes called pads, covered with areoles with tiny detached spines known as glochids. The flowers are mostly yellow, cup-shaped, and lack true petals. The species showed noteworthy differences among color, length, the diameter of cladodes, spines per areole, flower, and fruit shape and color. The Opuntia genus is one of the most ignored plants’ genera, and this morphological characterization overcomes insufficient and inadequate knowledge for its species-level distinction.
Opuntia species express great intraspecific morphological variability. All reproductive structures, cladodes (stem segments), and spines respond to macroenvironmental and microenvironmental variation and all of these form from areoles (axillary buds). However, little is known about areole response to light and temperature differences. In this study, I determined whether Opuntia areole numbers and spacing respond to environmental conditions. Terminal cladodes of Opuntia littoralis (Cactaceae) were sampled in Southern California. Data were collected for pad length, pad width, number of areoles on one pad face, number of areoles on the other pad face, and the distances to the nearest areole from the center one on one pad face and on the other for each pad for each of the four orientation groups (N-S, E-W, NW-SE, or NE-SW) for a total of 24 variables. Two-way analysis of variance, related-samples Wilcoxon signed rank tests, and Pearson product-moment correlation identified relationships across and between variables. Results show that areoles are a rather stable feature with regard to environmental variation; there were only small differences on cladode faces oriented in opposite directions. Areoles do not show the more dramatic responses to environmental variation typically seen on the structures borne from those areoles (such as cladodes and spines).
Background Many barrel or columnar cacti, including some in the Atacama Desert, produce their reproductive tissue at or near the terminal apices of solitary or minimally branched stems that lean toward the equator, reportedly to maximize exposure to photosynthetically active radiation (PAR). Those with lateral reproductive tissue, often produce the tissue on the equatorial side of the stems. An examination of the multi-stemmed, arbuscular cactus, Eulychnia breviflora, was made to determine if it follows the same general strategy. Methods Individuals of the species were evaluated along a 100 km transect in the Atacama Desert. The position of all floral buds and open flowers was documented relative to the center of the plants and relative to the center of the individual stems on which they were located. Results A highly significant majority of the reproductive tissue was located on the equatorial (north) side of the plant and on the equatorial (north) side of the stems on which it was found. Conclusion Our explanation of the phenomenon differs from other researchers. Inasmuch as reproductive tissue contains little or no chlorophyll, we suggest that the flowers emerge from areas of the stems that receive abundant PAR, not because the reproductive tissue itself requires exposure to PAR. Because the translocation of photosynthates in cacti is difficult and energetically expensive, positioning of reproductive tissue in zones of the stems with high photosynthetic capacity is more energetically efficient. In addition, the Atacama Desert is not particularly warm. Exposure of flowers to solar radiation may produce a thermal reward for pollinators, in addition to any nectar rewards received.
The photosynthetic and energy dissipation responses of four differently
oriented photosynthetic surfaces (cladodes) from the cactus
Opuntia stricta (Haw.) Haw. were studied in the field
during the winter in Australia. Even under very low PFD (i.e. <80
µmol m-2 s-1) all surfaces
experienced a dramatic decline in photosystem II (PSII) efficiency during the
morning period when temperatures were below freezing. However, light energy
absorbed during the warmer afternoon period was more efficiently utilised for
photochemistry with less diversion through the thermal energy dissipation
pathway. Low temperature presumably reduced the proportion of excitation
energy that could be utilised photosynthetically, resulting in a high rate of
energy dissipation with a concomitant decline in PSII efficiency. A lag in the
diurnal de-acidification of malic acid, and therefore the availability of
endogenous CO2, may have also contributed to the low
rate of photochemistry during the morning period. We interpret the increase in
energy dissipation and decline in PSII efficiency as a controlled response of
PSII that is dependent upon the de-epoxidised components of the xanthophyll
cycle under conditions when the absorption of light exceeds the capacity of
the photosynthetic apparatus to process the excitation energy through
photochemistry.
Organisms cannot maximize all life functions and therefore must allocate resources to maximize reproductive fitness such that they produce the highest number of surviving offspring. The object of the experiment was to evaluate variation of fruit morphology to determine how Opuntia littoralis optimizes reproductive investment. The experiment focused on fruit volume, sugar concentration, number of seeds and average seed mass on two different aspects (polar-facing and equatorial-facing slopes) in Temescal Canyon Gateway Park, Pacific Palisades, California. The results revealed fruit volume was positively correlated with number of seeds, sugar concentration was positively correlated with number of seeds, and average seed mass was negatively correlated with number of seeds. The study suggests that variation in Opuntia fruit morphology can be explained by the principle of allocation and life history strategies rather than by microhabitat variation alone.
Stem orientation and morphology were investigated for 14 species of cacti in Chile, Ecuador, Mexico, and the United States. The interception of photosynthetically active radiation (PAR) was specifically considered for cladodes (flattened stems) of platyopuntias, for tilted cylindrical stems, and in the presence of surrounding vegetation.
Growth forms of Opuntia compressa (Salisb.) Macbr. were examined in five different habitats of the Lake Wales Ridge region in Florida. Parameters examined included: plant height, width, and length; number of pads; pad temperatures; plant orientation; and spine density. Height growth was found to be greater and pad production less in habitats where tree canopies were relatively dense. Temperatures within a specific pad were observed to vary as much as 3.5⚬C. Plants showed no preferred orientation, and no relationship was seen to exist between cattle grazing and spine density.
Seeds collected from coyote scats in southern California were tested for germination. Eighteen of 38 plant species germinated. Native species that germinated included Arctostaphylos glauca, Arctostaphylos sp., Heteromeles arbutifolia, Opuntia littoralis, Prosopis glandulosa, Prunus ilicifolia, and Washingtonia filifera. Exotic species that germinated included Annona cherimola, Cucumis sp., Ficus sp., Lycopersicon esculentum, Panicum miliaceum, Phoenix sp., Prunus sp., and Pyracantha sp. Additional species thought to be exotic that germinated were Fragaria sp., Vitis sp., and an unidentified species. Compared to seeds directly off the plant, O. littoralis germinated significantly more frequently following passage through coyotes, whereas H. arbutifolia germinated significantly less often. Although coyotes are dispersing exotic plant seeds in viable condition, none of the seeds identified in this study were considered invasive.
The orientations of terminal unshaded cladodes of 23 species of platyopuntias were observed in North America, South America, Australia, and Israel. When the seasonality of rainfall favored cladode development in the winter and the site was located above 27oN, the cladodes tended to face north-south. In all other cases without topographical blockage of incoming radiation, the tendency was to face east-west. For example, terminal cladodes of Opuntia phaeacantha var. discata and O. stricta tended to face north-south in Israel but east-west in the United States. Such dissimilar orientation patterns also occurred for cladodes of O. chlorotica at 2 sites in the Sonoran Desert and for O. basilaris var. basilaris developing at different seasons at a single site. Cladodes of O. ficus-indica and 0. compressa had a significant tendency to orientate. When topographical features affected the direction of prevailing photosynthetically active radiation (PAR), the preferred orientation of terminal cladodes changed to maximize interception of PAR, which is often a limiting factor in the productivity of cacti. -from Author
Literature on distributions, habitat characteristics, and identification of Opuntia species in the southeastern US is scant. Regional treatments of Opuntia are often ambiguous, limited studies based primarily on herbarium specimens. The present work provides a detailed description of the opuntias found in Mississippi along with their distributions and habitat descriptions. Observations, collections, and measurements were made from natural populations within Mississippi and other parts of the southeastern United States. Plants of all taxa were greenhouse grown for approximately two years to monitor morphological characteristics, which sometimes can be quite plastic. Our two-year study encompassed nearly 150 natural populations among several eastern states. Five species are recognized. Of these, Opuntia cespitosa, O. humifusa, and O. pusilla are the most common in Mississippi. O. aff allairei and O. stricta are found infrequently.
There is a paucity of studies examining direct impacts of introduced alien species on biodiversity, a key need for motivating for alien species control in conservation areas. The introduced prickly pear (Opuntia stricta) has invaded some 35 000 ha of Kruger National Park. We investigated the effect of O. stricta on beetle and spider species assemblages in the Skukuza region of Kruger National Park. We used unbaited pitfall traps over a 12-month period in four treatments of varying O. stricta density. Species richness, species density and abundance of beetles and spiders were compared. A total of 72 beetle and 128 spider species were collected. Species richness and species density for beetles and spiders did not differ significantly across the four treatments. Assemblages for spiders did not differ across treatments but beetle assemblages were significantly different from uninvaded control sites. This study suggests that the current density of O. stricta does not significantly affect spider species richness, density or assemblages but that beetle assemblages are significantly affected.
In contrast with other Opuntia species, most of the cladodes of Opuntia puberula have a horizontal position. This study explores whether the horizontal cladodes are an adaptive trait to increase light interception in the understory or are a neutral trait, and if this characteristic may prevent its distribution in full sun habitats. Cladode inclination angle and its effect on light interception, cladode temperature, and carbon gain are characterized, and anatomical and physiological traits of upper and lower cladode surfaces are described. Inclination angle was under 50° for 95% of the cladodes, and the frequency of low inclination angles increases as light availability decreases. Nocturnal acid accumulation increased with total daily PPFD intercepted, but no significant differences were detected between typical horizontal cladodes and the few vertical cladodes. Chlorophyll content differed in the upper and lower surfaces of horizontal cladodes; however, chlorenchyma thickness, stomatal conductance, and nocturnal acid accumulation were similar between surfaces. The horizontal position of O. puberula cladodes, which is anatomically determined, restricts it to shaded habitats, where the plants do not overheat, but seems to have no effect on carbon gain.
Opuntia ficus-indica is a long-domesticated cactus crop that is important in agricultural economies throughout arid and semiarid parts of the world. The biogeographic and evolutionary origins of this species have been obscured through ancient and widespread cultivation and naturalization. The origin of O. ficus-indica is investigated through the use of Bayesian phylogenetic analyses of nrITS DNA sequences. These analyses support the following hypotheses: that O. ficus-indica is a close relative of a group of arborescent, fleshy-fruited prickly pears from central and southern Mexico; that the center of domestication for this species is in central Mexico; and that the taxonomic concept of O. ficus-indica may include clones derived from multiple lineages and therefore be polyphyletic.
Cacti of the genus puntia are an economically important crop. Understanding the mechanisms they possess to protect against UV radiation is important
for assessing their possible response to climatic change. Measurements of the concentrations of UV-screening compounds and
epidermal transmittance for two species of platyopuntia, Opuntia engelmannii Salm-Dyck. and O. phaeacantha Engelm. during 1998 and 1999 were used to investigate the UV-protection afforded by the cactus epidermis. A UV-radiative transfer
model was used to investigate the interception of UV radiation on differently oriented surfaces. We show that vertical morphology
itself confers significant protection against UV radiation compared to a horizontal surface. Concentrations of UV-screening
flavonoids were found to vary depending on the UV exposure of different surfaces. West-facing surfaces had lower concentrations
than east-facing surfaces, although theoretically they should be identical. This might be explained by the higher mean temperatures
on west-facing surfaces. Although UV-absorbing soluble flavonoids in the epidermis block both UV-B and UV-A, the structure
of the epidermis alone may be sufficient to remove up to 94% of the UV-B portion of the spectrum. These data yield insights
into possible mechanisms of recent declines in cacti populations.
The influences of various diurnal stomatal opening patterns, spines, and ribs on the stem surface temperature and water economy of a CAM succulent, the barrel cactus Ferocactus acanthodes, were examined using an energy budget model. To incorporate energy exchanges by shortwave and longwave irradiation, latent heat, conduction, and convection as well as the heat storage in the massive stem, the plant was subdivided into over 100 internal and external regions in the model. This enabled the average surface temperature to be predicted within 1 C of the measured temperature for both winter and summer days.Reducing the stem water vapor conductance from the values observed in the field to zero caused the average daily stem surface temperature to increase only 0.7 C for a winter day and 0.3 C for a summer day. Thus, latent heat loss does not substantially reduce stem temperature. Although the surface temperatures averaged 18 C warmer for the summer day than for the winter day for a plant 41 cm tall, the temperature dependence of stomatal opening caused the simulated nighttime water loss rates to be about the same for the 2 days.Spines moderated the amplitude of the diurnal temperature changes of the stem surface, since the daily variation was 17 C for the winter day and 25 C for the summer day with spines compared with 23 C and 41 C, respectively, in their simulated absence. Ribs reduced the daytime temperature rise by providing 54% more area for convective heat loss than for a smooth circumscribing surface. In a simulation where both spines and ribs were eliminated, the daytime average surface temperature rose by 5 C.
Terminal vertical cladodes (flattened stems) of Opuntia ficus-indica growing in widely separated locations were nonrandomly oriented. On plantations at 33°S latitude in Chile individual cladodes tended to orient in the same direction as the planted cladodes on which they developed. However, after 2 years unshaded new cladodes tended to face east-west. Terminal cladodes also tended to face east-west for irrigated O. ficus-indica in California (at 34°N) and in Israel (32 to 33°N), but cladodes developing in the winter tended to face north-south. Except for the residual effect of initial planting direction, the observed patterns tended to maximize the interception of photosynthetically active radiation (PAR). Specifically, east-west cladode orientation would maximize PAR interception, except for cladodes developing near the winter solstice at latitudes more than 27° from the equator. Nocturnal acidity increases and hence productivity would generally be light-limited, since the nocturnal increase in acidity was 90% saturated for a total daytime PAR of 24 mol m–2 day–1 and the PAR received on vertical surfaces is usually less than this. Topographical features can modify the orientation patterns, since at a site where PAR was considerably blocked by surrounding mountains the maximal nocturnal acidity increases and peak in cladode orientation occurred 20° from facing east–west. Laboratory studies showed that developing cladodes oriented toward a horizontal light and were rotated an average of 16° in a direction that increased PAR interception compared to the cladodes on which they developed. Such phototropic responses, the higher productivity of favorably oriented cladodes, and the tendency to orient similarly to the underlying cladode presumably accounts for the overall orientation patterns observed, where up to four times more cladodes may face in a particular direction than at right angles to it.
Both field measurements and a computer model were used to study the interception of photosynthetically active radiation (PAR) by Agave deserti (Engelm.), a desert CAM plant with a basal rosette of massive opaque leaves. PAR interception was determined in the winter and the summer for upper and lower leaf surfaces on a plant with about 60 leaves. Total daily PAR on the leaf surfaces was approximately 10 mol m⁻² for a winter day and 20 mol m⁻² for a summer day. For a PAR of 15 mol m⁻², the nocturnal increase in acidity was about 0.6 mol m⁻² for both leaf surfaces and various leaf orientations, except for the oldest most horizontal leaves where the increase was less than half as large. The acidity increase measured in the field was 90% saturated at 25 mol m⁻². Thus, daytime PAR in the desert is often limiting for the nocturnal acidity increase, especially for the lower leaf surfaces. Simulated tilting of the plant by 55° so that the vertical axis pointed to the sun at solar noon on a winter day increased the PAR incident on the upper surfaces of the leaves, but did not affect the total nocturnal increase in acidity by the whole plant. Although simulated removal of alternate leaves increased the PAR per unit leaf area for the remaining leaves, it reduced the total increase in nocturnal acidity of the whole plant by 31%. PAR interception by plants on slopes facing steeply north, east, or west was substantially reduced compared to the horizontal. Thus, the model proved to be quite useful for quantifying the relation between leaf orientation, PAR interception, and nocturnal increases in acidity by A. deserti, and it indicated that the lower frequency of plants on north- compared to south-facing slopes was due to PAR limitations.
Because CO2 uptake by cacti can be limited by low levels of photosynthetically active radiation (PAR) and because plant form affects PAR interception, various cactus forms were studied using a computer model, field measurements, and laboratory phototropic studies. Model predictions indicated that CO2 uptake by individual stems at an equinox was greatest when the stems were vertical, but at the summer and the winter solstice CO2 uptake was greatest for stems tilted 30° away from the equator. Stem tilting depended on form and taxonomic group; four barrel cacti in Ferocactus and in Copiapoa and four cylindropuntias in Opuntia tilted toward a horizontal light beam by an average of 18°, 48°, and 52°, respectively, after growth periods of 1 to 4 yr. In contrast, three columnar species showed no significant phototropic response, perhaps because structural stability requires their massive stems to be erect. Field plants of the dense, multiple-stemmed shrub Opuntia echinocarpa had stems which tended to radiate outward from the plant base, and, although this would not influence the total PAR intercepted, it would result in a more uniform PAR distribution and hence higher CO2 uptake. For O. echinocarpa and the even denser, mound-forming Echinocereus engelmannii, PAR and chlorophyll decreased approximately exponentially with depth into the canopy. The canopies of O. echinocarpa and other cylindropuntias did not extend to the ground; in certain species, such truncation apparently resulted from a combination of very low PAR levels just below the lower canopy edge and the light-dependent growth responses of individual stems. In addition, although the canopy surfaces of O. echinocarpa and O. acanthocarpa tilted toward the equator by about 30°, the canopies of other cylindropuntias tilted less or not at all; the computer model predicted that a 30° tilt would decrease interstem shading, increase daily PAR, and increase nocturnal CO2 uptake by as much as 54, 26, and 24%, respectively. Not only can the shape of cacti be affected by PAR, but also shape influences PAR interception and hence CO2 uptake.
Opuntia cespitosa (until recent taxonomic splitting, identified as O. humifusa) is an endangered cactus in Canada, is found in only two populations nationwide after some local extirpations. The larger site is at Point Pelee National Park (PPNP-ON) at the northern edge of its range has little published data. Data were collected for plant size, overlying cover (the species is sensitive to high shade), reproductive variables, and various cladode (pad) characteristics to assess response to local conditions. The PPNP-ON population was considered conspecific to many populations throughout the eastern USA until recently. A southern Humifusa clade population in Florida was sampled to confirm the recent separation of these populations into distinct species. A variety of parametric (e.g., ANOVA) and nonparametric (chi-square, Spearman's correlation) tests were used to determine relationships across variables. This study contributes to our foundational knowledge of an endangered species. Results for this species in its last major Canadian population include that site conditions affect variables such as etiolation, in addition to shade. Plants are taller and have larger pads in Florida, supporting an upcoming taxonomic revision which would split the Floridian populations from the Ontario plants. Past work also suggests that Opuntia pads develop phototropically to maximize PAR (photosynthetically active radiation) receipt. Results show that while pads are statistically more parallel than perpendicular to the pad from which they grow, the offset is random. Thus physiological limitation of orientation is possible, or if there is a phototropic response, it occurs at the pad/areole scale.
Opuntia humifusa (eastern prickly pear cactus) is an endangered species in Canada, found principally in only one remaining location nationally, at Point Pelee National Park (PPNP). This study quantifies fruit and flower production in the population, the pad yellowing phenomenon that has been observed, overlying coverage and shade, and a variety of plant size metrics in order to assess the relationships between these factors. A variety of parametric (ANOVA, Pearson product-moment correlation, t tests) and nonparametric (Spearman's rank correlation, Kruskal-Wallis test) statistical analyses were conducted. Pad yellowing, a presumed sign of ill health, was not significantly related to any aspect of plant size or reproduction, and was statistically related only to shade (less yellowing with greater shade). Shade also affects plant height, with taller plants associated with greater shade. Reproductive effort is lower in shadier sites, and shade also appears to delay reproduction to later in the season. Published research generally suggests that increases in sexual reproduction are a sign of stress, suggesting an overall decrease in stress in the cactus population in the Park. However, I observed that reproduction decreased with shade, and increasing shade is known to cause population decline, making the effects of light stress at PPNP difficult to determine.
The Humifusa clade represents a recent radiation that originated in the late Pliocene or early Pleistocene and consists of about 10 species widely distributed in North America from northern Mexico north to Ontario, Canada, and south to the Florida Keys. This clade likely originated in the edaphically subxeric regions of northern Mexico and the southwestern United States, and from there it later spread to the southeastern United States and ultimately produced a small radiation in the eastern United States. Hybridization among evolutionarily divergent diploid species of the southeastern (SE) and southwestern (SW) United States subclades led to the origin of many polyploid taxa, which today occupy about 75% of the distribution of the clade. Here we present a taxonomic revision of the SE subclade of the Humifusa clade and polyploid derivatives that commonly occur in the eastern United States (i.e., the O. humifusa complex). We recognize eight taxa: Opuntia abjecta, O. austrina, O. cespitosa, O. drummondii, O. humifusa, O. mesacantha subsp. mesacantha, O. mesacantha subsp. lata, and O. nemoralis, as well as the interclade allopolyploid, Opuntia ochrocentra, derived, in part, from a member of the O. humifusa complex. Diagnostic keys, descriptions, original photos, and distribution maps are provided for each taxon. Neotypes are designated for the names O. austrina (NY) and O. youngii (USF), and O. drummondii and O. tracyi are lectotypified from an illustration in Maund & Henslow and a specimen at NY, respectively.
Hundreds of cactus species have evolved the rib and furrow morphology that aids in water storage and provides photosynthetic and thermal benefits. Limited work has been done on understanding rib spacing and furrow size in the context of a wide range of environmental variables. Data were collected in two Carnegiea gigantea Sonoran Desert (Northern Hemisphere) populations, that were analyzed using General Linear Models and MANOVA to assess the relationships between rib and furrow metrics, height and direction on the plants, and several environmental and plant-wide variables (e.g., intraspecific crowding, shade, branching). Furrow sides are smaller lower on the plant, but are not related to orientation suggesting adjustment with growth. Rib spacing is not related to height on the plant, but is related to direction (greater spacing to the north and west), likely due to thermal and photosynthetic differences. Intraspecific crowding and shade affect the size of furrows. This morphology offers both a long-term response to general conditions (furrow size, e.g., shade, regional factors) and short-term response (rib spacing) to seasonal variations in temperature and moisture for direct response to fluctuating conditions. These mechanisms will continue to be important with changing climate, and through range shifts associated with warming.
This publication summarizes 25 years of heretofore unreported efforts to effect the
biological control of prickly pear cacti infesting rangeland on Santa Cruz Island,
situated off the coast of southern California. To date, partial to substantial biological
control of the pest cacti, Opuntia littoralis (Engelmann) Cockerell, O. oricola Philbrick, and their hybrids, has been achieved. The principal biological control
agent is a cochineal insect, Dactylopius sp., which is native to the southern California mainland. It was introduced to the
island free of its principal natural enemies—Hyperaspis taeniata significanis Casey and Laetilia coccidivora (Comstock)—and has multiplied markedly, at the same time destroying numerous clumps
of cacti throughout the island.
Effective range management practices, i.e., eradication of wild sheep and restrained
cattle grazing, have aided the biological control efforts, and both have resulted
in the return and persistence of annual grasses on formerly overgrazed and cacti-infested
grazing lands.
The coreid bugs, Chelinidea tabulata (Burmeister) and C. vittiger Uhler, were also successfully introduced to Santa Cruz Island from Texas and mainland
California, respectively, but neither species is thought significant as a biological
control agent. The cactus-feeding phycitids, Olycella junctolineella (Hulst), Melitara dentata (Grote), and M. prodenialis Walker, were not successfully colonized on Santa Cruz Island.
Morphological analysis led to the conclusion that Florida Semaphore Cactus is a distinct species. That conclusion is congruent with genetic studies reported elsewhere. Our plants are properly called Opuntia corallicola (Small) Werdermann (O. subgenus Consolea). The Florida plants are not O. spinosissima, as recorded in recent literature. Indeed, the Florida plants are probably more closely related to O. rubescens and O. millspaughii than to O. spinosissima. Details of the Florida species, and a key to similar and confusing Caribbean relatives are provided. Because of the limited number of individuals remaining in the wild, the threat from the alien pest moth Cactoblastis cactorum, the low genetic diversity within Florida, and recent damage by Hurricane Georges, the Semaphore Cactus may be the most endangered plant in the United States.
Opuntia parryi, which has cylindroidal stems, and O. littoralis, which has flattened stems, are commonly found in the mixed chaparral-inland coastal sage association of southern California. Both species occur with a similar set of shade-providing shrubs in this association but their position relative to these shrubs differs: O. parryi is found in open sites away from the canopy of the shrubs while O. littoralis occurs both in open sites and under the canopy of the shrubs. Internal stem temperatures for unshaded sites suggest that the platyopuntia, O. littoralis, may be exposed to excessive heat loads. However, the cylindropuntia, O. parryi, remains well below ambient temperatures in unshaded sites. In contrast both species follow ambient temperatures closely when they are found within the canopy of an associated shrub. The flattened stems of O. littoralis may, however, provide greater access to photosynthetically active radiation than the cylindroidal stems of O. parryi. The terminal cladodes of O. littoralis in the open grow so that they face east-west and minimize the heat load buildup that would be experienced by north-south facing cladodes.
Pad temperatures of Opuntia compressa (Salisb.) Macbr. were measured in the field with copper-constantan thermocouples and a null potentiometer. Measurements were made during portions of 5 days in June and July 1971. During periods of intense solar radiation pad temperatures were as much as 10-13⚬C above air temperatures. During periods of low incoming solar radiation pad temperatures were within 2-4⚬C of air temperatures. At any given time throughout the day, there were differences in the temperatures of the east-, west- and top-facing sides of the pad. The daytime differences between air and pad temperatures recorded for O. compressa are compared to those reported for four desert species of Opuntia.
Species of Cylindropuntia and Opuntia cacti, which have segmented stems, have a wide range of morphologies from tall, tree-like forms to prostrate forms. Considerable interest has developed regarding mechanical stresses at joints between stem segments and how these stresses relate to overall morphologies and reproductive capabilities of cactus species. Determinations were made of maximum normal stress at failure for twenty terminal joints per species, the number of joint segments on longest branches for ten plants per species as well as the percentage of detached terminal segments that become established for 25 cactus species. We hypothesized that cactus species with more segments per stem should require more force to remove terminal segments. Regression analyses of mean maximum stress at failure of terminal joints versus mean number of segments for the species tested gave a line equation of y = 380x + 1350 with a regression coefficient of 0.85. We hypothesized that cactus species with few segments per stem for adult plants should have good establishment of detached terminal stem segments while species with many segments on adult plants should have low levels of establishment of detached terminal segments. Regression analyses of mean establishment of terminal segments as a function of mean number of segments gave a line equation of y =-1.73x + 80.6 with a regression coefficient of 0.77. In contrast, plant height was not related to either maximum normal stress at failure or segment establishment. We conclude that number of stem segments on longest stems of plants was a good predictor of force necessary to remove terminal segments. Number of stem segments was also a good predictor of rooting and establishment of terminal segments. Overall, the data of this study show that Cylindropuntia and Opuntia species with large numbers of stem segments along each stem rely mostly on sexual reproduction for procreation while species with fewer stem segments rely mostly on asexual reproduction via rooting of detached stem segments.
The Cactaceae are a diversified group of New World plants with a wide array of evolutionary and ecological strategies that has given them the ability to adapt to many different habitats. The family is both interesting and challenging because of its varied morphology, adaptations to the environment, and reproductive systems. Of the groups within the cactus family, the opuntias are one of the most successful and widespread, but they exhibit many taxonomic difficulties and are, therefore, not well understood. /// Las cactáceas son un grupo de plantas muy diversificado con una impresionante colección de estrategias evolutivas y ecológicas que les ha dado la habilidad de adaptarse a muchos hábitats diferentes en el nuevo mundo. Esta familia es interesante y desafiante debido a su variación morfológica, diversas adaptaciones al medio ambiente, y a sus sistemas de reproducción. Dentro de los grupos de la familia de las cactáceas, las opuntias son de los más exitosos y ampliamente distribuidas, pero presentan muchas dificultades taxonómicas y por lo tanto no son del todo entendidas.
This research describes the morphological variation found in 11 New Jersey populations of Opuntia compressa (Salisb.) Macbr. Anatomical, cytological, and morphological parameters are evaluated. Morphological and anatomical data were analyzed using an analysis of variance for factorial design and the Just Significant Interval test. The quantitative morphological variation could not be correlated with a north-south geographical distribution of the populations; and neither did the qualitative characteristics correlate with geographical trends in color variation. These data indicate that this taxon in New Jersey should be treated as a single species displaying wide morphological variation, without infraspecific taxa.
We evaluated the role that endangered species reintro- duction efforts can play in the larger context of ecosys- tem restoration. To do so, we examined interactions between endangered giant tortoises (Geochelone nigra hoodensis), currently being reintroduced to Isla Espano- la, Galapagos, and an arboreal cactus (Opuntia mega- sperma var. megasperma), which is itself endangered and a keystone resource for many animals on the island. We collected information on spatial patterns of occurrence of cacti, tortoises, and woody vegetation and compared recruitment of juvenile cacti in areas occupied versus unoccupied by tortoises. Reintroduced tortoises ap- peared to suppress cactus recruitment near the few re- maining adult cacti at the study site, but facilitate it at longer distances, with tortoise-cactus interactions medi- ated by the presence of woody vegetation, which likely alters tortoise movements and thereby patterns of cactus seed dispersal. The net effect of tortoises on cacti ap- peared to be positive insofar as tortoise presence was associated with greater recruitment of juveniles into cac- tus populations. Our study provides support for reintro- ducing endangered reptiles and other animals to aid ecosystem restoration in areas where they might once have played an important role in grazing upon and dis- persing plants.
Little empirical data exist on the surface temperatures of the keystone saguaro cactus Carnegiea gigantea despite its well documented adaptations for reducing direct solar radiation and heating. In this study, I document temperatures on the surface of individuals on their ridges and furrows, at two different heights above the ground, in the sun and in the shade and at two sites, in two seasons (winter and summer), based on a total of over 4200 surface temperature readings. ANOVA was used for statistical comparisons. Temperatures are generally warmer lower on the plant, likely due to heating from the ground from the ground below. The spiny ridges have more moderate temperatures than the furrows. Differences in temperature between these two groups were significant, but small. Seasonal differences between the sun-facing and shaded sides of the plants were significant. Temperature differences were much more pronounced during the winter than in the summer. The reasons for this are uncertain, but solar angle may be important, with the sun's rays shining more directly on the surface of this upright plant during the low solar angle months of winter, while in summer, the sun's rays arrive at a near-parallel angle to the plant and the energy is thus spread over a wider area, resulting in smaller temperature differences. Other factors may be important as well, such as photosynthetic changes in the plant, which may sometimes use the C3 pathway (rather than CAM) that would promote evaporative cooling.
The flowers ofOpuntia basilaris andO. littoralis in southern California are visited commonly by beetles(Carpophilus, Trichochrous) and bees (especially anthophorids, megachilids, and halictids), but are pollinated mainly by the bees. This agrees with observations presented in the previous papers in this series for other cactus species in Arizona and Texas. The available evidence indicates that the large, diurnal, cup-shaped flowers in cacti of the American Southwest are primarily bee-pollinated. Our earlier view that theseOpuntia flowers are also pollinated to a significant extent bynitidulid andmelyrid beetles must be modified now in the light of further evidence. Some pollination probably is carried out by small beetles, but it probably represents only a small proportion of the total pollination.
Plant morphology in the field in Virginia, USA, and growth responses to applied NaCl in a glasshouse were determined for two populations of Opuntia humifusa (Rafinesque) Rafinesque, one from an inland site and the other from the marine strand, which differed in potential exposure to salinity. Cladode dimensions, plant height and rooting depth varied significantly between the populations. Application of NaCl in 50 mM increments up to 400 mM every 3 days for 6 weeks caused the cladodes to decrease up to 30% in thickness, the decrease being about 20% more at 50 to 150 mM NaCl for plants from the inland site than from the marine strand. Inhibition by 150 mM NaCl of the maximum rate of net CO2 uptake and of the total CO2 uptake over a 24-h period was greater for the inland population. Growth, especially of roots, was inhibited by applied NaCl, with a decrease in biomass above 200 mM NaCl for plants from the inland site and not until 400 mM for those from the marine strand. Although the root Na+ level was the same for plants from the two populations, reaching a maximum of about 8 mg (g dry weight)−1 at 200 mM NaCl, the cladode Na+ level was two-fold higher for plants from the marine strand than from the inland site. Thus, exclusion of Na+ from the cladodes is not the reason for the greater NaCl tolerance of O. humifusa from the marine strand, which is a habitat that can experience periodic episodes of high salinity.
In the extreme desert environment the potential energy load is high, consequently high temperatures might be a limiting factor for plant survival. Field measurements of plant temperatures in a Sonoran Desert ecosystem were made using fine thermocouples. Temperatures of six desert species were measured: Opuntia engelmannii, Opuntia bigelovii, Opuntia acanthocarpa, Echinocereus engelmannii, Larrea tridentata and Franseria deltoidea. Daily temperature profiles were used to compare the different responses of cacti and shrubs to the desert heat load and also to compare spring and summer responses. Leaf temperature of shrubs was at or near air temperature during both the mild, spring season and the hotter dry season. The cacti, on the other hand, absorbed and stored heat, thus temperatures were often above air temperature. The energy absorbed is determined largely by plant orientation and surface area exposed to the sun. Actual energy absorbed by the plants was estimated from energy diagrams.The flat stem pads of Opuntia engelmannii plants are oriented to receive maximum sunlight without long periods of continuous heating. Opuntia bigelovii spines reflect and absorb much of the environmental energy load, thereby protecting the thick, succulent stems from overheating. The smaller stems of Opuntia acanthocarpa dissipate heat more effectively by their large surface area exposed to convective air currents. Leaves on desert shrubs remain nearer to air temperature than do succulent stems of cacti, because their very large surface to volume ratio allows them to dissipate much heat by convection.
A common cylindropuntia in the northwestern Sonoran Desert, Opuntia acanthocarpa, was investigated for the following hypotheses: its lower elevational limit is set by high temperatures, so its seedlings require nurse plants; its upper elevational limit is set by freezing; spine shading is the least at intermediate elevations; and changes in plant size and frequency with elevation reflect net CO2 uptake ability. For four elevations ranging from 230 m to 1,050 m, the mean height of O. acanthocarpa approximately doubled and its frequency increased 14-fold. Nurse plants were associated with only 4% of O. acanthocarpa less than 20 cm tall at the two lower elevations compared with 57% at 1,050 m, where putative freezing damage was especially noticeable, suggesting that nurse plants protect from low temperature damage. Spine shading of the stem doubled from the lowest to the highest elevation. Net CO2 uptake, which followed a Crassulacean acid metabolism pattern, was maximal at day/night air temperatures of 25/15C and was halved by 4 weeks of drought and by reducing the photosynthetic photon flux from 30 to 12 mol m-2 day-1. The root system of O. acanthocarpa was shallow, with a mean depth of only 9 cm for the largest plants. Root growth was substantial and similar for plants at 25/15C and 35/25C, decreasing over 70-fold at 15/5C and 45/35C. Based on cellular uptake of the vital stain neutral red, neither roots nor stems tolerated tissue temperatures below -5C for 1 h while both showed substantial high temperature acclimation, roots tolerating 1 h at 61C and stems 1 h at 70C for plants grown at 35/25C. The increase in height and frequency of O. acanthocarpa with elevation apparently reflected both a greater ability for net CO2 uptake and greater root growth and hence water uptake. This species achieves its greatest ecological success at elevations where it becomes vulnerable to low temperature damage.
Dactylopius opuntiae reduced an Opuntia stricta var. stricta population in the Central Tablelands of New South Wales, an area where Cactoblastis cactorum has little impact. Cactoblastis cactorum was bivoltine at the experimental site. The proportion of C. cactorum eggs hatching and larvae penetrating segments was much greater for the generation commencing between November and January compared with that commencing between February and June. Failure of first instar C. cactorum to establish during the latter generation appeared to prevent C. cactorum from having a significant impact on the cactus population. Dactylopius opuntiae released at the site decreased new growth of O. stricta var. stricta and caused direct damage to segments. This damage led to a decline in the cactus population in the area. The use of D. opuntiae for biological control of O. stricta var. stricta in similar areas is discussed.
The objective of this work was to construct a model of aerial development of clover that takes into account morphogenetic responses to the light environment, and to use it to analyse and understand these processes in terms of signal perception and integration. The plant model was interfaced with a Monte Carlo model that determines photosynthetically active radiation (PAR) and red/far-red ratio (R/FR) throughout the canopy, taking into account the absorption, reflection and transmission of light by individual leaves. Light intensity and quality were sensed by the plant model at discrete time intervals and at discrete sites of perception: apices, emerging internodes and petiole tips. This input regulated the final size of internodes and leaves, the vertical positioning of leaves, and the branching delay. The empirical relations (regression functions) quantifying this regulation were derived from data reported in the literature and original measurements. Simulations produced realistic visualizations and quantitative characterizations of the modelled plants for different light treatments. These results were in general agreement with observations of real plants growing under similar conditions, suggesting that the dependence of organ size and position on light treatments can be regarded as an integration of the responses of individual plant organs to their local light environment. The model is used to describe the regulation of branch appearance and the impact of self-shading on plant morphogenesis as a function of local light environment. Copyright 2000 Annals of Botany Company
Temperatures of small leaves of many desert plants are within 3 degrees C of air temperature in contrast to the temperature of Opuntia in the same locale; this plant has a temperature 10 degrees to 16 degrees C above air temperature. Theoretical4 justification for the observation is given based on an energy budget analysis.
Light is one of the environmental signals that regulate the development of shoot architecture. Molecular mechanisms regulating shoot branching by light signals have not been investigated in detail. Analyses of light signaling mutants defective in branching provide insight into the molecular events associated with the phenomenon. It is well documented that phytochrome B (phyB) mutant plants display constitutive shade avoidance responses, including increased plant height and enhanced apical dominance. We investigated the phyB-1 mutant sorghum (Sorghum bicolor) and analyzed the expression of the sorghum Teosinte Branched1 gene (SbTB1), which encodes a putative transcription factor that suppresses bud outgrowth, and the sorghum dormancy-associated gene (SbDRM1), a marker of bud dormancy. Buds are formed in the leaf axils of phyB-1; however, they enter into dormancy soon after their formation. The dormant state of phyB-1 buds is confirmed by the high level of expression of the SbDRM1 gene. The level of SbTB1 mRNA is higher in the buds of phyB-1 compared to wild type, suggesting that phyB mediates the growth of axillary shoots in response to light signals in part by regulating the mRNA abundance of SbTB1. These results are confirmed by growing wild-type seedlings with supplemental far-red light that induces shade avoidance responses. We hypothesize that active phyB (Pfr) suppresses the expression of the SbTB1 gene, thereby inducing bud outgrowth, whereas environmental conditions that inactivate phyB allow increased expression of SbTB1, thereby suppressing bud outgrowth.
Mathematical and simulation models for the orientation of the terminal cladodes of platyopuntia
- Chang
submitted for publication. Substrate Variability and the Distribution of Opuntia cespitosa (Cactaceae) in 250,000 Km2 of their Range
- P Adanick
- T D Drezner
The influence of insolation on the distribution and on the developmental sequence of the flowers of the giant cactus of Arizona
- Johnson
Evaluating the potential impact of the proposed land development on coastal sage scrub in northern Orange County, California
- Roach