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The breakage of dormancy in Datura ferox seeds as an effect of water absorption
Abstract
Résumé: ZusammenfassungDatura ferox seeds do not germinate when they are incubated intact and in darkness, even after 24 months of dry storage. If allowed to absorb water vapour for 3–4 weeks at 20°C, they lose dormancy, germinating even when incubated in darkness. The breakage of dormancy is directly related to the vapour pressure of the atmosphere where the seeds are stored, and good aeration is necessary for the process to occur.If seeds absorb liquid water, the toss of dormancy is much less than that of seeds stored in a saturated atmosphere. A similar effect is observed when seeds are buried in a soil at field capacity. The results indicate that a certain degree of imbibition, under good gas-exchange conditions, is important for breaking dormancy.As a hypothesis, it is proposed that most of the population remains dormant when not enough O2 is available for (he imbibed seed. The low rate of O2 entry could be due to poor diffusion through the water-saturated seed coat (seeds which absorb liquid water) or to a low O2 level in the surrounding atmosphere (soil at field capacity). One of the possible roles of O2 could be to oxidize the inhibitor(s) present in these seeds.La rupture de la dormance des semences de Datura ferox considérée comme un effet de l'absorplion de l'eau.Les semences de Datura ferox ne germent pas quand elles sont mises au germoir intactes et à l'obscurité, même aprés 24 mois de conservation au sec. Si elles peuvent absorber de la vapeur d'eau pendant 3 à 4 semaines à 20°C, elles perdent leur dormance et germent meme & à l'obscurité. La rupture de la dormance est en relation directe avec la pression de la vapeurd'eau de l'atmosphére dans laquelle les semences sont conservées; une bonne aération est nécessaire pour que le processus se déclanche.Si les semences absorbent de l'eau à l'état liquide, la rupture de dormance est beaucoup moindre que celle de semences conscrvées dans une atmosphére saturée. Un effet analogue est observé lorsque les semences sont ententes dans un sol ayant atteint sa capacity au champ. Les résultats indiquent qu'un certain degriS d'imbibition, sous de bonnes conditions d'changes gazeux. est important pour la rupture de la dormance.Comme hypothtése, il est proposé que la plus grande partie de la population reste dormante lorsqu'il n'y a pas assez d'oxygene disponible pour la semence imbibeée. Le faible taux d'absorption d'oxygéne pourrait étre du à sa fuible diffusion à travers l'enveloppe saturée d'eau de la semence (pour celles qui absorbent l'eau à I état liquide) ou à un bas niveau d'oxygene dans Tatmosphére environnante (cas d'un sol à la capacityé au champ). Un des rôles possibles de l'oxygéne pourrait être d'oxyder les inhibiteurs presents dans les semences.Das Brechen der Keimruhe in Samen von Datura ferox ah ein Effekt der WasseraiifnahmeSamen von Datura ferox keimen nicht, wenn sie bei Dunkelheit gehalten werden; auch nicht, wenn sie zuvor 24 Monate trocken lagerten. Wenn sie bei 20°C, 3 bis 4 Wochen tang Wasserdampf aufnehmen, verlieren sie die Keimhemmung und keimen sogar im Dunketn. Zwischcn dem Brechen der Keimruhe und dem Damptdruck der Luft in der sie gelagert werden, besteht eine direkte Beziehung. Fur diesen Vorgang ist eine gute BelCiflung Vorausselzung.Wenn die Samen flijssiges Wasser aufnehmen, ist der Verlust der Keimhemmung wesentlich geringer als wenn sie in einer gesättigten Atmosphäre gelagert werden. Eine ähnliche Wirkung wird beobachtet. wenn die Samen im Boden bei Feldkapazität gelagert werden. Die Ergebnisse zeigen, dass für das Brechen der Keimruhe ein bestimmtes Mass der Aufnahme bei ausreichendem Gasaustausch wichtig ist.Als cine Hypothese wird vorgeschlagen, dass die meisten der Population dormant bleiben, wenn für die mil Wasser vollgesaugten Samen nicht ausreichend O2 verfügbar ist. Der geringe Zutritt an O2 konnte auf die mässige Diffusion durch die wassergesättigte Samenschale (Samen die fliissiges Wasser aufnehmen), oder auf einen geringen O2-Gehalt in der umgebenden Luft (Boden bei Feldkapazität) zurückzuführen sein. Eine der möglichen Bedeutungen die dem O2 zukommen, könnte in der Oxidation des bzw. der Hemmstoffe der Samen liegen.
... ferox, water vapour for 3-4 weeks at 20 °C caused changing the endogenous inhibitor levels and provoke germination even when incubated in darkness condition [17,18]. Also due to the latest reports the presence of inhibitors of germination in seeds which caused seed dormancy [15]. ...
... Light is the main ecological factor that regulates germination [30]. The condition of darkness can be one of the major reasons for seed dormancy in Datura (in non-scarification seeds) and even the seeds are kept in dry condition in the darkness for 24 months; the seed will be still in dormancy mode [17]. The poor environmental condition for mother plants promotes some changes in dormancy seeds. ...
... In order to obtain different sensitivities to light and dormancy levels, seeds were maintained in a water-saturated atmosphere (WSA) in complete darkness at 258C for 7 –21 d (see supplemen- taryFig. S1, available online; de Miguel and Soriano, 1974). Then, seeds were sown on cotton wool saturated with distilled water (5 ml) in clear plastic boxes and exposed to the different light treatments. ...
... Seeds with different levels of dormancy and sensitivity to light were classified according to their final germination response to a saturating FR pulse, indirectly indicating their dormancy level (de Miguel and Soriano, 1974). The seeds were treated in a WSA for different periods (7 – 21 d) and then irradiated with FR or R pulses, or kept in darkness. ...
Soil tillage operations stimulate germination of buried seeds in cultivated lands, allowing them to perceive light as a germination-promoting factor. The time of burial and the effect of the changing environmental factors affect the physiological state of the seeds, leading to an extremely light-sensitivity and response to the very low fluence response (VLFR) through phytochrome A (phyA). This paper describes the influence of the progressive process of dormancy breakage, that is accompanied by the acquisition of extreme light-sensitivity, over the endosperm weakening (EW) and embryo growth potential (EGP) processes in the VLFR-mediated promotion of Datura ferox seed germination. Our results show that EW is mainly limited by b-mannosidase enzyme activity after far-red light (FR) stimulation, which is highly dependent on the dormancy level of the seeds. In addition, EGP stimulation by FR did not require an extreme light-sensitivity to very low fluence of photons to reach its maximum response, and it was not completely correlated with expansin gene-expression in the embryo. Our work indicates that EW and EGP responses to FR irradiation, dependent on dormancy level, have different requirements to be stimulated by the signalling network initiated by phyA during the course of VLFR in Datura ferox seeds.
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8993828
... The fact that seeds lying on the soil surface showed a higher dark germination compared to artificially stored seeds suggests that the moisture present during the storage conditions favored degradation or leaching of inhibitor substances released by the mother plant, responsible for inducing primary dormancy. For example, De Miguel and Soriano (1978) showed that humidification of Daturaferox seeds for just a few weeks reduced dormancy, which was otherwise maintained for years under dry storage conditions. Smith and Whitelam (1990) hypothesized that etiolated tissue performs an ecological function, and compared it to an "antenna" crucially required to allow the earliest and most effective sensing of the approach of the seedling to the soil surface. ...
... Overall, it appears that deep burial results in an increase of sensitivity to light (724 nm) which establishes low (approximately 0.02, calculated) values of the Pfr:(Pfr+Pr) ratio. This finding is consistent with previous observations (Hartmann and Nezadal, 1990;Scopel et al., 1991Scopel et al., , 1994, and may tentatively be attributed to leaching of inhibitors (De Miguel and Soriano, 1978), and/or involvement of PhyA. ...
A series of experiments investigated the light sensitivity of buried weed seeds both within and outside the soil gas microenvironment. Light sensitivity of Datura stramonium L. seeds was found to be increased markedly by a period of soil burial; seeds showed a pronounced germination response even in far-red light (724 nm). Despite this elevated light sensitivity (even to less than 0.01% of incident light), soil overlying buried seeds was sufficient to neutralize the germination trigger. Furthermore, in situ irradiation of buried seeds was found to be virtually ineffective as a germination trigger, showing that the gaseous environment surrounding buried seeds may represent the main obstacle to germination. It is suggested in this study that the soil environment restricts the removal of the germination-inhibiting products of fermentation metabolism. This suggestion is supported by the finding that gas exchange within the seed:soil complex, achieved by flushing with nitrogen, partially restores seed light sensitivity. In addition, it was found that with increasing sowing depth, the germination response was attenuated and also became less dependent on seed phytochrome photoequilibrium conditions. This demonstrates that the phenomenon of germination photoinduction can be reversed by other environmental factors that reduce or eliminate phytochrome physiological activity. Finally, it was shown that seed very low fluence response (VLFR) is triggered only when gas exchange around buried seeds co-occurs with light exposure.
... The fact that seeds lying on the soil surface showed a higher dark germination compared to artificially stored seeds suggests that the moisture present during the storage conditions favored degradation or leaching of inhibitor substances released by the mother plant, responsible for inducing primary dormancy. For example, De Miguel and Soriano (1978) showed that humidification of Daturaferox seeds for just a few weeks reduced dormancy, which was otherwise maintained for years under dry storage conditions. Smith and Whitelam (1990) hypothesized that etiolated tissue performs an ecological function, and compared it to an "antenna" crucially required to allow the earliest and most effective sensing of S, Benvenuti and M. Macchia / Environmental and Experimental Botany 38 (1997) 61-71 Table 2 Effect of storage conditions and maternal light environment on dark and light irradiated seeds ...
... Overall, it appears that deep burial results in an increase of sensitivity to light (724 nm) which establishes low (approximately 0.02, calculated) values of the Pfr:(Pfr+Pr) ratio. This finding is consistent with previous observations (Hartmann and Nezadal, 1990; Scopel et al., 1991, 1994), and may tentatively be attributed to leaching of inhibitors (De Miguel and Soriano, 1978), and/or involvement of PhyA. ...
The role in germination of the maternal pre-existing far-red absorbing form of phytochrome (Pfr) was studied in seeds harvested at different developmental stages. Datura stramonium seeds acquired marked dormancy in the later ripening stages, independently of phytochrome phototransformation. However, the balance between stimulators, such as Pfr, and inhibitors (probably abscissic acid and/or phenolic substances) in the stage prior to complete dehydration appeared to play a crucial role in the degree of progeny dormancy. Enrichment of the far-red (FR) wavelength (simulated canopy light) induced light-dependent dormancy if stage IV progeny were incubated in darkness in suboptimal conditions. In contrast, natural storage of seeds in soil led to a uniform degree of dormancy. An increase in photosensitivity owing to storage in soil appeared to be linked to simultaneous loss of inhibitors. It should be noted, however, that this extreme sensitivity to very low Pfr levels (724 nm monochromatic light pulse) was acquired only by seeds stored deep in the soil (typical very low fluence response). It is postulated that these reactions are induced by an elevated quantity of phytochrome typical of etiolated tissue, in conditions of near-absence of inhibitors.
... Still, when the seeds were scratched, the germination rate was more than 95% at a concentration of 100 to 500 ppm gibberellin (Schulz et al., 2001). Research has shown that one of the main causes of dormancy in healthy Datura seeds is darkness and lack of light, and another reason is that they are not scratched, and even if these seeds are stored for 24 months in dry conditions, their dormancy will not be removed (Miguel and Soriano, 1974). ...
The seeds of most medicinal plants have a variety of dormancy. Therefore, it is necessary to know the effective methods of breaking the seed dormancy for their production and cultivation. In this study, to determine the best method of breaking dormancy and increasing the germination percentage of tattoo seeds, various factors have been investigated. Different treatments, scratching with sandpaper, embryo culture, GA treatment (100, 150 and 200 PPM) and sulfuric acid treatment (50, 75 and 100%) with filter paper or on MS medium containing BAP (0.5, 1 and 1.5 mg/l) was applied with untreated samples (control). Embryo culture was performed only on MS medium containing BAP hormone. The analysis of variance showed that all interactions with the studied treatments were significantly different in terms of germination percentage, fresh and dry weight of roots and stems (P <0.01). It was observed that the use of benzyl aminopurine (1.5 mg/l) with gibberellic acid (200 ppm) increased the seed germination percentage compared to the control. The use of benzylaminopurine (1.5 mg/l) and sulfuric acid (50%) significantly increased seed germination compared to the control. It was concluded that the effect of GA with BAP on seed germination was greater than sulfuric acid with BAP.
... For example, for a summer annual like Polygonum aviculare presenting dormancy cycling, low winter temperatures alleviate dormancy while high summer temperatures reinforce it (Kruk and Benech-Arnold, 1998). However, there is evidence indicating that the effect of temperature on dormancy release may be modulated by soil moisture (Ada Âmoli et al., 1973; de Miguel and Soriano, 1974; ReismanBerman et al., 1991; Christensen et al., 1996; Christensen Bauer et al., 1998). Also, secondary dormancy can be induced by factors other than temperature as is discussed below. ...
... The role of temperature as a crucial environmental factor in modulating the dormancy states of seeds is widely accepted, although there is evidence that temperature effects in overcoming dormancy can be modulated by soil humidity under some circumstances (Adámoli et al., 1973;de Miguel and Soriano, 1974;Baskin and Baskin, 1992). Seeds buried in superficial soil layers experience seasonal alterations during the year, and fluctuations in the soil water content may influence their state of dormancy and regulate their emergence (Baskin and Baskin, 1976;Batlla and Benech-Arnold, 2010). ...
The involvement of environmental factors in dormancy cycling is well known in temperate annual species, but it is not known how interaction between soil temperatures and humidity can modulate dormancy in perennial tropical species. In this study the effects were evaluated of substrate temperature and humidity on the modulation of the acquisition and overcoming of secondary dormancy in the buried seeds of two endemic Eriocaulaceae species from the rocky fields (
campos rupestres
) vegetation in south-eastern Brazil. Fresh seeds of
Comanthera bisulcata
and
Syngonanthus verticillatus
were buried and subsequently maintained at temperatures of 15, 20, 25 and 30°C, under three substrate humidity levels (boggy, humid and humid/dry). The seeds were exhumed every 3 months and tested for germination (20°C, 12 h photoperiod) and viability (tetrazolium test). The seeds of both species acquired dormancy after burial in all of the treatments. During the experimental period they demonstrated cycles of acquisition and overcoming of dormancy that were most evident in the treatments involving alterations of the substrate humidity (humid/dry regime) that coincided with the environmental conditions found naturally in the region of origin of the species. The seeds gradually lost dormancy during the dry period and re-acquired it when exposed again to humidity; dormancy would once again be overcome during the subsequent dry period. Burial promoted the acquisition of dormancy in
C. bisulcata
and
S. verticillatus
seeds; the lowest temperature tested favoured overcoming dormancy; and varying the humidity regime signalled the acquisition and the overcoming of secondary dormancy.
... After harvest, the seeds were stored in dark glass jars at room temperature. In order to obtain seeds with extreme sensitivity to light, dormancy was reduced by the storage of the seeds in a water-saturated atmosphere (WSA) in complete darkness at 25°C for 10-12 d (de Miguel and Soriano, 1974). The seeds were then sown on cotton wool saturated with distilled water (5 ml) in clear plastic boxes and exposed to the different light treatments. ...
Seed germination can be promoted by the modes of action of two of the phytochromes: the low-fluence response (LFR), which is the classical red (R)-far-red (FR) reversible response and the very-low-fluence response (VLFR) that can be saturated by extremely low levels of Pfr, which can be elicited by a saturating FR pulse. The Datura ferox seed population used in this work had acquired the capacity to germinate through a VLFR after pretreatment in a water-saturated atmosphere (WSA) at constant 25 degrees C. After 12 d in WSA germination after a FR pulse was 82%, while it was less than 10% in darkness. It was found that the VLFR of germination is associated with increments in the embryo growth potential (EGP) and in the activity of two enzymes related to the weakening of the micropylar region of the endosperm (ME); endo-beta-mannanase and beta-mannosidase. The FR pulse also significantly stimulated the expression of DfGA3ox, a GA 3beta-hydroxylase, suggesting that the promotion of germination by the VLFR is associated with an increase in the synthesis of active gibberellins. The promotive action of the VLFR on germination is reduced when the FR pulse is immediately followed by a continuous FR treatment for 24 h (FRc). The effect of FRc cannot be reproduced by hourly FR pulses during the same period, showing that the antagonistic effect of FRc is a high-irradiance response (HIR). The action of the HIR in germination is associated with a decrease of both the mannan-degrading enzyme activity and the expression of DfMan in the ME, whereas no changes in the EGP were observed. The HIR also inhibits the accumulation of DfGA3ox in embryos, indicating that its action on germination is mediated, at least in part, through the modulation of active GA contents in seeds. This is the first report of a gene that participates in the VLFR-HIR antagonism in seeds.
Cultivation, regeneration and conservation of wild plant species are, generally,
challenging, mostly due to their seed dormancy and specific germination requirements.
Jimsonweed (Datura stramonium L.) an important medicinal plant which is also
extensively used in plant virology research has a considerable seed germination
problem. This study was conducted to develop a simple seed germination protocol for
Jimsonweed. A factorial experiment arranged as completely randomized design (CRD)
with three replications, assessing effects of seed scarification, gibberellin and potassium
nitrate (at concentrations of 0, 100, 500, 1000 and 2000 ppm). Five days after treatment,
percentage of seed germination, radicle and plumule length were measured, revealing
the key role of mechanical seed scarification treatment as a prerequisite for germination
of Jimsonweed seeds. The germination rate as well as radicle and plumule length of
scarified seeds were drastically influenced by concentrations of gibberllin and
potassium nitrate. No germination was observed in scarified seeds in the absence of
gibberllin and potassium nitrate in water. Maximum percentage of seed germination
(63%) was obtained when a chemical treatment of 100ppm gibberllin and 500 ppm
Seeds can synchronize their germination and dormancy cycles to regular seasonal environmental changes. The present work sought to evaluate the in-situ longevity of the buried seeds of two species of Syngonanthus and two species of Comanthera (Eriocaulaceae) in the region of natural occurrence (Serra do Cipó Range, south-eastern Brazil), and to relate their germination responses to seasonal climatic changes. Samples were exhumed bimonthly and germination was tested under a 12-h photoperiod (30 μmol m− 2s− 1) at optimal germination temperature. The seeds of Comanthera showed high deterioration after the first year of burial, especially C. elegans, which reflects their incapacity to form viable soil seed banks. The buried seeds of C. bisulcata, S. anthemidiflorus and S. verticillatus acquired secondary dormancy during the rainy season (spring/summer, higher temperatures) which was alleviated during the subsequent dry season (autumn/winter, lower temperatures). It is concluded that C. bisulcata, S. anthemidiflorus, and S. verticillatus form seed banks of the persistent type and demonstrate consecutive cycles of germination/dormancy, accompanying annual seasonal changes for at least 2 years.
Ageing processes during dry storage of Datura ferox seeds resulted in a progressive loss of growth capacity of embryos isolated from non-incubated seeds which ended after 8–10 months with the complete failure to grow of most embryos. Incubation of the seeds for 24 hours or keeping embryos excised from non-incubated seeds during 24 hours in a water saturated atmosphere (WSA) fully restored the growth capacity of the embryos. These repairing effects persisted after drying the embryos back to the water content they had in the non-incubated seeds, and were blocked by inhibition of the metabolism. Removal of the seed coat before incubation did not have any effect, incubating the embryos surrounded by the endosperm alone was sufficient for recovery. The recovery was also complete when the seeds were maintained during four weeks in WSA. The results are in agreement with the hypothesis that maintainance of viability in hydrated seeds is related to metabolism-dependent repair mechanisms and support the suggestion that those mechanisms can operate in less than fully imbibed seeds.
In the course of morphologic-taxonomical and biochemical studies a collection ofDatura has been brought together. The material has been incorporated into the gene bank and is available for breeding programmes in medicinal plants and for the use in basic research. Problems of maintaining of this collection in the gene bank are discussed. In this connection germination behaviour and breeding systems are studied.
For the documentation of the material identification is necessary. Therefore, the genusDatura has been revised, excluding sect.Brugmansia. Keys are given for the determination of the species and also of the infra-specific taxa.
Evolutionary trends within the genus are demonstrated.
The structure of protein bodies in the endosperm and embryo of Datura stramonium was studied with a variety of light-and electron-microscopic techniques. Protein bodies had one to several globoid crystals and one or two protein crystalloids in the proteinaceous matrix. Although the embryo protein bodies rarely had more than two globoid crystals, the endosperm protein bodies had varying sizes and numbers of globoid crystals, even within the same cell. Energy-dispersive X-ray analysis of globoid crystals revealed the presence of P, K, and Mg in all cases. Traces of Fe, Mn, and Zn were also found in globoid crystals of protein bodies from certain cell types. The distribution patterns of these three elements were quite specific; for example, Mn traces were found only in the globoid crystals of the protoderm. Neutron-activation analysis of endosperm and embryo tissues was used to quantitatively measure the concentration of Ca, Cl, Cu, I, K, Mg, Mn, Na, and S. The results from structural studies and the element analysis studies are discussed in the context of solanaceous seeds in particular but also with relation to seeds in general. Key words: protein bodies, Datura stramonium, seed, globoid crystals, energy-dispersive X-ray analysis, Solanaceae.
Freshly harvested Striga asiatica L. seeds will germinate in response to a stimulant only after the passage of time, an after-ripening period, and exposure to moisture at a suitable temperature, a conditioning period. To investigate the role of seed moisture content in the regulation of the after-ripening period, seeds were placed in chambers having specific relative humidity of 6%, 14%, 33%, 75% and 91% for 30, 60, 90 and 150 days. The seeds were then conditioned and germination percentage, response to tetrazolium and seed moisture contents were measured. Seeds at moisture contents less than 10% at the start of conditioning had germination of greater than 93%. Seeds at moisture contents over 10% at the start of conditioning could germinate between 60% and 3%, with germination decreasing as seed moisture content at the start of conditioning increased. The highest moisture content (17%) and lowest germination percentage (3%) occurred in seeds stored at 91% relative humidity for 150 days. There was a linear relationship of a high degree of correlation (0.997) between a positive tetrazolium test and germination capacity. Germination capacity of seeds could be changed from 90% to 3% by prolonged storage in water (dilute benomyl solution), causing `wet dormancy', then returned to 90% germination by returning to dry storage. Seed moisture content at the beginning of conditioning appears to control the responsiveness of the seeds to germination stimulants. The implications of these findings to the control of the parasite are discussed.
Seeds of Datura ferox were collected in soybean fields, grouped into four categories according to the degree of fruit maturity and placed just level with the soil surface or buried to a depth of 7 or 15 cm. Seed survival after 8 months was c. 30% when the seeds were left on the soil surface, but between 40 and 90% when the seeds were buried. The riper seeds were the more persistent. A similar pattern was observed after 20 months. Seedling emergence was negatively related with the degree of seed maturity and depth of burial, but it was never great enough to explain seed losses.
In another experiment seeds from ripe capsules were superficially sown and the soil was: (0) left undisturbed, (1) cultivated in late winter or (2) cultivated in late winter and late spring. In all cases there was a small flush of seedlings at the beginning of the first spring; other flushes occurred only after soil cultivation and were larger during the second spring than during the first. In the plots cultivated twice a year (2) the seedlings that emerged in the first spring represented c. 4% of the initial seed bank. Survival after 20 months was about 25% in all treatments. In an arable field under soybean cropping the seedling flushes during the spring months were related to the pattern of soil cultivation. The seedlings that emerged after crop drilling represented c. 18% of the seed bank (estimated before drilling). Implications for weed management are discussed.
Seed coat structures may play a major role in determining the germination of seeds. The involvement of seed coat characteristics in the inhibition of germination observed when dry seeds of Datura ferox L. and D. stramonium L., were rinsed or soaked in water for 1–5 min (‘soaking effect’) was investigated. Germination was inhibited by soaking D. ferox seeds even at late stages of the germination process up to one day before root protrusion. Simulation of the ‘soaking effect’ was achieved by blocking the hilum with lanolin, enamel lacquer or agar during imbibition. Blocking the hilum did not prevent water uptake by the seeds. Seed coat integrity was necessary for the ‘soaking effect’ since germination inhibition was eliminated by removing or cracking the seed coat. Drying the seeds up to 12 h after soaking reversed the inhibitory effect. SEM observations of both species revealed a loose outer parenchymatous tissue covering the hilum, an inner spongy tissue between the nucellus and the hilum and a space between the seed coat and the nucellus. We concluded that during soaking, water is trapped in the space between the seed coat and the nucellus, and in the intracellular spaces of the spongy tissue within the hilum. This water ‘plug’ may limit the diffusion of gas(es) to and from the embryo through the hilum, thus inhibiting germination.
Reactions regulating seed dormancy can proceed at water contents which are probably too low to permit metabolic activity. The loss of dormancy via afterripening of red rice. (Oryza sativa L.) seeds was examined as a representative case. Equilibration of seeds to various moisture contents showed that afterripening was most rapid at 6–14% moisture content (dry weight basis). Afterripening did not occur at > 18% moisture content and was severely inhibited at < 5% moisture content. Seed viability was greater than 95% for all treatments. Utilization of moisture isotherms to calculate water-binding enthalpy values identified the optimal afterripening range as approximately the boundary between water-binding region 1 and region 2. From these findings, it is suggested that afterripening may involve some oxidative reactions which are inhibited at lower water contents by the rising free-energy and at the higher side by metabolic reactions.
A fiber optic probe inserted into plant tissues was used to investigate the effects of canopy density on the light environment in different organs. The red:far-red ratio inside the stem of Datura ferox L. seedlings and the estimated phytochrome photoequilibrium were strongly reduced by the presence of neighbors forming canopies too sparse to cause any mutual shading at the level of the leaves. In such canopies, changes in plant density had little effects on the light regime inside the leaves of the succulent Aeonium haworthii (S.D.) Webb et Berth., particularly when the lamina was kept nearly normal to the direct rays of the sun. In field experiments using D. ferox and Sinapis alba L. seedlings, the elongation of the internodes responded to various types of localized light-quality treatments that simulated different plant densities in sparse canopies. The responses were quantitatively similar to those elicited by changes in plant density. The evidence supports the hypothesis that, in stands formed by plants of similar size, the red:far-red ratio of the light that impinges laterally on the stems is among the earliest environmental cues that allow plants to detect local canopy density and adjust axis extension accordingly.
Seeds of Avena ludoviciana after-ripened more rapidly with increasing temperatures up to 30°C and with increasing relative humidities between 16 and 100%. In continuous light, these seeds after-ripened more rapidly than in the dark. Seeds of different species and strains of wild oats after-ripened at different rates; primary seeds after-ripened more rapidly than secondary. One week after anthesis 60% of the viable primary seeds of A. ludoviciana were dormant, compared with 100% at maturity. The importance of these findings to studies on the physiology of dormancy and to the control of wild oats in the field is discussed.
Soil Physics Dormancy in seeds of Avcria ludoviciana and Avena fatiia
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KuHNKK H. (1968) Soil Physics. McGraw Hill. New York. QUAIL P.H. & CARTER O.G. (1969) Dormancy in seeds of Avcria ludoviciana and Avena fatiia. Aust. J. agric. Res..
Analisis dc los factores quc deierminan el desbloqueo de la germinaci6n de Datura ferox L. en el suelo Les Obstacles a la Germination The seed coal cfTecl in relalion to the photo-induction of germination in Duliira ferax L
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- A Soriano
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