Action of Phytochrome During Prechilling of Amaranthus retroflexus L. Seeds

Dark germination of Amaranthus retroflexus L. seeds at 35° increased after several days of prechilling at 20° or lower. Irradiation with far-red light for short periods during the early hours of a prechilling period at 10° inhibited subsequent dark germination at 35°. The inhibition was completely reversible with red light. Far-red irradiation in the latter part of the prechilling period was less effective. Increased dark germination of A. retroflexus seeds following a prechilling period at 20° or less is attributed to action of preexistent P_FR, the far-red absorbing form of phytochrome, within the seeds. Inactivation of P_FR was found to proceed ca. 4 times more rapidly at 25° than at 20°. Failure of imbibition temperatures above 20° to increase dark germination of A. retroflexus seeds is attributed to the rapid thermal reversion of pre-existent P_FR. We suggest that the action of prechilling (layering) on many other seed kinds arises in a similar way.     

Phytochrome Action during Prechilling Induced Germination of Betula papyrifera Marsh

Seeds of paper birch (Betula papyrifera Marsh.) were induced to germinate by prechilling at 3 C or by red light. The light requirement was mediated by phytochrome and the action of phytochrome during prechilling was investigated. Red irradiation (R) prior to prechilling markedly enhanced the effectiveness of the prechilling treatment in inducing subsequent germination at 18 C. Reversal of this enhancement by far-red irradiation (FR) was more effective when FR was supplied after a 1-week prechill treatment than after a 2-week treatment. The R enhancement effect exhibited a sharp drop as prechilling temperature was increased from 5 to 7 C. This decline is consistent with a membrane phase transition at about 7 C where Pfr action is diminished by a loss in sensitivity of its receptor sites. Although phytochrome action was observed during prechilling treatments, the seeds failed to germinate at prechilling temperatures. Therefore, it was concluded that while potentiation of germination by Pfr occurred during prechilling, some other reaction(s) leading to radicle protrusion requires higher temperatures. In one seed source loss of germination potential was observed with protracted storage at 3 C. This was prevented by R supplied during the prechilling treatment. Taken collectively the data suggest that action of phytochrome during prechilling is accentuated in these seeds by two factors: (a) an increase in the sensitivity (or number) of Pfr receptor sites; and (b) preservation of Pfr by deferment of thermal reversion.     

Inhibition of Prechill-induced Dark Germination in Sorghum halepense (L.) Pers. Seeds by Phytochrome Transformations

A 10 C dark prechilling of johnsongrass [Sorghum halepense (L.) Pers.] seeds, when terminated by a 2-hr, 40 C temperature shift, potentiates about 40% germination at 20 C in darkness. Irradiation of the seeds before, during, and at the end of prechilling with far red light reduces the subsequent germination, although red irradiation after the far red can overcome some of the inhibition. However, either brief red or far red irradiation given immediately after the temperature shift inhibits subsequent germination by one-third to one-half. The results suggest that the far red-absorbing form of phytochrome is a factor in the prechill-induced dark germination and that phytochrome participates in the inhibition of germination by irradiations immediately after the temperature shift.     

Hoary cress (Cardaria draba (L.) Desv.) seed germination ecology,longevity and seedling emergence

The effects of gibberellic acid (GA₃), potassium nitrate (KNO₃), prechilling, temperature, salt stress and osmotic potential on seed germination and sowing depth on seedling emergence and burial depth on seed viability of hoary cress (Cardaria draba (L.) Desv.), were studied in a series of laboratory, glasshouse and outdoor experiments. The optimal temperature for hoary cress seed germination was 20°C, both in light/dark and darkness regimes. Seed germination of hoary cress at 400 ppm concentration of GA₃ in a light/dark regime was maximal. Potassium nitrate concentrations increased the percentage of germination in comparison with the control treatment. Increasing the duration of dry prechilling to 30 and 45 days promoted the seed germination of hoary cress. Germination of hoary cress markedly decreased as salt and drought stress increased. Seed germination of hoary cress occurred at a range of pH from 3 to 11. Seedling emergence significantly decreased as planting depth increased. Total seed viability decreased with increasing burial depth. The maximum increase in mortality occurred in seeds that were buried at 5‐cm depth.     

Studies of the Mechanism of Enhancement of Phytochrome-dependent Lettuce Seed Germination by Prechilling

Temperature and kinetic studies were performed to examine the mechanism by which prechilling stimulates phytochrome-dependent seed germination in lettuce, Lactuca sativa, L. cv. Grand Rapids. Imbibed seeds were given a short far red irradiation and one day of dark incubation at 20 C to establish very low levels of the far red-absorbing form of phytochrome—(Pfr). Germination was greatly stimulated by subsequent prechilling treatments when they were followed by a second short far red irradiation. Prechilling therefore increased germination sensitivity to the low, normally inhibitory Pfr levels established by far red irradiation. This sensitivity increased with lowered prechilling temperature to a maximum near 4 C. It was linearly dependent upon duration of prechilling at 4 C up to a near maximal response at 10 hours, and it decayed in a converse manner when seeds were returned to 20 C after 10 hours at 4 C. Prechilling also increased germination responses to subsequent periods of high levels of Pfr which were initiated by red and terminated by far red irradiations. High Pfr periods adequate to promote the germination of unchilled seeds produced sharp inflections at 18 C in the dependence of germination on prechilling temperature. Rates of phytochrome potentiation of germination were not affected by prechilling. The response to prechilling fit a mechanism involving homeoviscous adaptation of membrane lipids to temperature.     

Germination responses of four native terrestrial orchids from south-west Western Australia to temperature and light treatments

We report an investigation into the impact of temperature and illumination on in vitro symbiotic and asymbiotic germination of the threatened taxon Caladenia huegelii, and three other orchid spp. namely—Caladenia latifolia, Microtis media and Pterostylis sanguinea, all species from south-west Western Australia, a recognized biodiversity hotspot. High symbiotic germination on oatmeal agar (OMA + fungal symbionts specific to each species) was recorded in three species in continuous dark incubation i.e. C. huegelii seeds (98 % germination at 25 °C), and M. media and P. sanguinea (93 and 98 % respectively at 20 °C). Highest symbiotic germination for C. latifolia (100 %) was observed at 15 and 20 °C under light treatment (12/12 h light/dark). Low temperature incubation (10 °C) significantly suppressed symbiotic germination/development of seedlings across all species. Asymbiotic media treatments assessed (OMA minus fungal symbionts, Pa₅ and ½ MS), failed to stimulate any germination with C. latifolia seeds at 20 °C in either light or dark treatments after an 8 week incubation period. Seeds of M. media sown onto ½ MS medium resulted in higher germination in all developmental stages (3–5) in dark treatment than OMA and Pa₅. Seeds of P. sanguinea sown onto ½ MS medium resulted in higher overall germination in all developmental stages (3–5) in light and dark incubation compared to OMA and Pa₅. OMA supported the highest asymbiotic germination (100 %) in both light and dark incubation with M. media (only to stage 3) but did not support germination and development with other spp. tested. Caladenia huegelii seeds reached developmental Stage 3 (i.e. germinated), but only on Pa₅ medium and only at a relatively low rate in either light (2.6 %) or dark (2.1 %). Germination was higher and development of seedlings faster overall in all test species in symbiotic compared with asymbiotic media treatments. P. sanguinea seeds demonstrated the best response (among species tested) to asymbiotic germination on ½ MS with 40–53 % of germinated seeds spread over developmental stages 3–5 in light or dark incubation (at 20 °C) respectively. Illumination had no effect on fungal symbiont growth across all species, however incubation temperature treatments (10, 15, 20 and 25 °C) affected fungal growth rate. Growth of the fungal symbionts of C. huegelii, M. media and C. latifolia demonstrated significantly lower activity at 10 °C, but the cumulative radial growth rate of the P. sanguinea fungal symbiont reached 64 cm² after only 2 weeks at all temperatures tested, including 10 °C. The study highlights differences in symbiotic and aysmbiotic germination and early protocorm development in vitro between co-occurring herbaceous terrestrial Australian orchid taxa in response to variations in basal media, temperature and light.     

Factors Influencing Spore Germination and Early Gametophyte Development in Anemia mexicana and Anemia phyllitidis

Spores of Anemia mexicana Klotzsch and Anemia phyllitidis (L.) Swartz were tested comparatively to investigate the effects of various treatments on spore germination and early gametophyte development in light and darkness. The optimum pH for induction of spore germination is approximately 6. Both species have a minimum 8 hour light insensitive preinduction phase for spore germination. An additional 8 to 12 hours of light are needed to induce 50% germination in A. phyllitidis while at least 24 hours of light are needed for A. mexicana spores. A. phyllitidis has greater sensitivity to the four gibberellic acids tested (GA₃, GA₄, GA₇, and GA₁₃) than A. mexicana for induction of spore germination in darkness. In both species the greatest response was observed with GA₄ and GA₇. GA₁₃ was clearly the least effective. Gametophytes of each species are 100 times more sensitive to their own antheridiogen than to the antheridiogen of the other species. AMO-1618 (1 millimolar), fenarimol (1 mm), and ancymidol (0.1 mm) had essentially no effect on light-induced germination. The latter two did, however, inhibit gametophyte development.     

Expansion of trait of gibberellin-induced dormancy in the Tertiary relict species of the genus Dioscorea (Dioscoreaceae)

Effects of the application of gibberellin A₃ (GA₃) on sprouting of rhizomes and germination of seeds were tested in five species of the genus Dioscorea which are considered to be Tertiary relicts growing disjunctively in the Appalachians, the Balkans, and the Caucasus. Applied GA₃ at higher than 1 micro;M markedly inhibited sprouting of rhizomes of all species. However, inhibition of seed germination of these species by GA₃ application was not observed. It is hypothesized that before disjunction in the Tertiary period GA-induced dormancy probably prevailed in rhizomes of all members of the genus Dioscorea.     

GEOGRAPHIC DIFFERENCES IN THE SEED GERMINATION OF PAPER BIRCH (BETULA PAPYRIFERA)

The effects of light and temperature on germination of paper birch (Betula papyrifera Marsh.) were examined in seeds from different geographic locations. Under continuous light at 14–18 C northern seed sources germinated more rapidly and achieved higher germination percentages than southern ones. Seed source influenced the range of temperatures over which germination occurred. Northern seeds had a wider temperature range than southern ones due to depression of the low temperature limit in northern seeds. At 15 C, seeds exhibited a photoperiodic-like response with progressive increases in germination as daily photoperiod was increased. This was not a true photoperiodic effect because seeds responded to the total amount of light rather than to the relative length of light and dark periods. It is suggested that at temperatures near 15 C, this response may be important in preventing fall germination. Prechilling at 3 C promoted subsequent dark germination in most seed sources tested, and northern seeds were much more sensitive to the treatments than southern seeds. In some seeds the prechilling stimulus was lost with protracted storage at 3 C; this was observed in both northern and southern seeds. Prechilling enhanced the seeds’ sensitivity to subsequent light. Although acquisition of the prechilling stimulus does not serve to measure the length of winter in these seeds, the high light sensitivity induced by prechilling probably accelerates spring germination. Northern seeds typically had thinner, more translucent pericarps than their southern counterparts.     

Factors affecting the induction of secondary dormancy in lettuce

The relationship between the temperature at which germination of 50% of the seeds is inhibited in the light (GT₅₀ Light) and secondary dormancy was investigated in three cultivars of Lactuca sativa L. Seeds were incubated for varying periods under non-germinating conditions and subsequent germination in response to red light (R) was determined over a wide range of temperatures. Dark incubation at 32 C reduced the GT₅₀ Light of cv. New York but did not affect germination at temperatures below 24 C. Dark, 32 C incubation had no effect on the GT₅₀ Light of cv. Great Lakes. In cv. Grand Rapids, dark incubation at 15, 24, 32, or 35 C initially reduced the GT₅₀ Light. However, longer incubations induced a secondary dormancy, i.e., the seeds became unable to germinate at all temperatures in response to R given after the high temperature incubation. A single exposure to R at the beginning of a 32 C incubation slowed the induction of secondary dormancy. Repeated exposures to R prevented the induction of secondary dormancy, but did not prevent a decline in the GT₅₀ Light. GA₃ mimicked the effect of repeated R.     

Influence of temperature on the in vitro pollen germination and pollen tube growth of various native Iranian almonds (Prunus L. spp.) species

Pollen germination and pollen tube growth was quantified among various native Iranian wild almonds (P. dulcis (Mill.) D. A. Webb, P. eleaegnifolia Mill., P. orientalis Mill., P. lycioides Spach, P. reuteri Bioss. et Bushe, P. arabica Olivier, P. glauca Browick and P. scoparia Spach in order to identify differences in the tolerance of pollen to temperature variations. Pollen germination and pollen tube growth were observed after incubation in darkness in a germination medium for 24?h at 10?C50°C at 5°C intervals. Maximum pollen germination of the wild almond species and specify that 60% was obtained for P. orientalis pollen and 98% for P. scoparia. Pollen tube length ranged from 860???m was obtained in P. lycioides and 1490???m in P. scoparia. A modified bilinear model best described the response to temperature of pollen germination and pollen tube length. Almond species variation was found for cardinal temperatures (T _min, T _opt and T _max) of pollen germination percentage and pollen tube growth. Mean cardinal temperatures averaged over eight almond species were 14.7, 24.2, and 43.7°C for maximum percentage pollen germination and 14.48, 25.3, and 44.4 °C for maximum pollen tube length. The principal component analysis (PCA) identified maximum percentage pollen germination and pollen tube length of the species, and T _max for the two processes as the most important pollen parameters in describing a species tolerance to high temperature. PCA also classified Prunus L. spp. into four groups according to the tolerance of pollen to temperature variations. The T _min and T _opt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating species for high temperature tolerance.     

Seed germination behavior of five Resedaceae species from arid Arabian desert: gibberellic acid and light effects

Abstract

Light and growth-promoting compounds, such as gibberellic acids (GA₃), are among the most important factors that can break physiological seed dormancy. Here, we investigate the effects of GA₃ and light on germination of five species of Resedaceae that are known to have different levels of physiological dormancy. Seeds were incubated at 20/30?°C in both 12-hr photoperiod and complete darkness. To study the effect of growth hormone on germination, seeds were soaked for 24?h in different concentrations of GA₃ before sowing. The annuals (Reseda aucheri and Oligomeris linifolia) and the perennial Ochradenus arabicus had deep physiological dormancy, and exogenous application of GA₃ enhanced their germination in the light, but not in darkness; few or no seeds germinated in the dark in these species. Ochradenus aucheri and O. baccatus had intermediate and non-deep dormancy, respectively, and application of GA₃ enhanced their germination in both light and darkness. Germination of the annual species was much slower than that of the shrubby perennials. Overall, these results indicate that conditions under which seed developed, matured and stored on maternal plants as well as incubation conditions should be taken into consideration when assessing germination behavior of the perennial species of Resedaceae.     

Intermediate complex morphophysiological dormancy in seeds of the cold desert sand dune geophyte Eremurus anisopterus (Xanthorrhoeaceae; Liliaceae s.l.)

Background and Aims

Little is known about morphological (MD) or morphophysiological (MPD) dormancy in cold desert species and in particular those in Liliaceae sensu lato, an important floristic element in the cold deserts of Central Asia with underdeveloped embyos. The primary aim of this study was to determine if seeds of the cold desert liliaceous perennial ephemeral Eremurus anisopterus has MD or MPD, and, if it is MPD, then at what level.

Methods

Embryo growth and germination was monitored in seeds subjected to natural and simulated natural temperature regimes and the effects of after-ripening and GA₃ on dormancy break were tested. In addition, the temperature requirements for embryo growth and dormancy break were investigated.

Key Results

At the time of seed dispersal in summer, the embryo length:seed length (E:S) ratio was 0·73, but it increased to 0·87 before germination. Fresh seeds did not germinate during 1 month of incubation in either light or darkness over a range of temperatures. Thus, seeds have MPD, and, after >12 weeks incubation at 5/2 °C, both embryo growth and germination occurred, showing that they have a complex level of MPD. Since both after-ripening and GA₃ increase the germination percentage, seeds have intermediate complex MPD.

Conclusions

Embryos in after-ripened seeds of E. anisopterus can grow at low temperatures in late autumn, but if the soil is dry in autumn then growth is delayed until snowmelt wets the soil in early spring. The ecological advantage of embryo growth phenology is that seeds can germinate at a time (spring) when sand moisture conditions in the desert are suitable for seedling establishment.     

Effect of Light and Moisture Conditions and Seed Age on Germination of Three Closely Related Myosotis Species

Germination of three closely related species from the Myosotis palustris group (M. nemorosa, M. palustris subsp. laxiflora, M. caespitosa) differing in their habitats and capacity for clonal growth, was compared in two greenhouse experiments. To evaluate both inter- and intraspecific variation, each species was represented by seeds from several populations. Final germination percentage and germination rates T₅₀ were compared both between species and populations within species. In the first experiment, we studied the influence of two external factors, moisture and light. Four moisture levels (dry, wet, periodically flooded and permanently flooded soil) and three types of shading (without shading, shaded with green foil, shaded with solid paper sheet) were combined in a complete factorial design. In all three species, total germination percentage was the same in the three wettest treatments, and decreased in the dry treatment. Germination in the treatments shaded with green foil (simulating vegetation cover, which changed light quality) was significantly slower than in treatments without shading and treatments shaded with a solid paper sheet. There were significant differences among species, but we also found very pronounced differences among populations within a species. M. caespitosa had the uniformly highest germination percentage (reaching in some cases 100%) and also fastest germination. Germination of M. palustris subsp. laxiflora populations was slower and reached lower final proportions, and medium variability among populations. Inter-population variability in the final germination percentage was highest, and the final germination the lowest in M. nemorosa. In addition, M. nemorosa, a species typical for permanent meadow communities was delayed by permanent flooding. In the second experiment, we studied the effects of seed age and storage conditions. Three combinations of seed age and storage were used: younger seeds (half year old) with no-chilling, younger seeds with chilling and old seeds (three years old) with chilling. M. caespitosa had again the highest final germination percentage and fastest germination rates T₅₀. In addition, final germination percentage of this species slightly increased with seed age, whereas it decreased in the other two species. The germination behaviour corresponded well to expectation based on species life histories and habitat preferences. Remarkably stable and high germination percentages and fastest germination rates T₅₀ were ascertained in M. caespitosa, a species of disturbed habitats, with lowest capacity for clonal spread. M. palustris subsp. laxiflora (species with highest clonal capacity) and M. nemorosa (species with medium clonal potential) achieved lower, but still very high final germination percentage. In addition, M. nemorosa showed the highest inter-populations variability in our experiments.     

Nondeep simple morphophysiological dormancy in seeds of Ilex maximowicziana from northern (subtropical) and southern (tropical) Taiwan

In this study, we show that seeds of Ilex maximowicziana collected from northern and southern Taiwan differ in germination responses to temperature. Seeds produced by plants growing in the tropical environment of southern Taiwan were more responsive (in a positive way) to higher incubation temperatures than those produced by plants growing in the subtropical environment of northern Taiwan. On the other hand, seeds produced in northern Taiwan were more responsive (in a positive way) to low incubation temperatures and to cold stratification than those from southern Taiwan. Germination percentages and rates of seeds from northern Taiwan were higher at 20/10°C than at 30/20°C, reaching a plateau of >80% germination after 12 weeks incubation, whereas germination of seeds from southern Taiwan reached >80% at 30/20 and 25°C but not at 20/10°C. Gibberellic acid (GA₃) increased germination rate but not germination percentage of seeds from both southern and northern Taiwan. Freshly matured seeds of I. maximowicziana have rudimentary embryos. During dormancy break, embryo length increased 11.5- and 8.0-fold in northern and southern seeds, respectively, before radicle emergence. Thus, seeds of Ilex maximowicziana have nondeep simple morphophysiological dormancy. This is the first detailed study of the germination requirements of a subtropical/tropical species of the large cosmopolitan genus Ilex.     

Strong light inhibits germination of Artemisia sphaerocephala and A. ordosica at low temperature and its relevance to revegetation in sandy lands of Inner Mongolia, China

Artemisia sphaerocephala and A. ordosica are two dominant shrub species in Mu Us sandy land (Inner Mongolia, China) and are widely used for vegetation restoration. However, there are two different conclusions about the effect of light on their germination: light promotes germination versus light inhibits germination. The aim of this study was to evaluate these two conclusions and relate the results to instances of failure of these two species to germinate well when air-dispersed in revegetation projects. The effects of fluctuating temperature, light/dark, source (population), position on mother plant, storage condition, and storage time were tested on germination of achenes of these two species. At low temperature, final percent germination (FPG) of achenes in dark and nearly dark conditions was significantly higher than those in light. At 10:20°C, achenes of both A. sphaerocephala and A. ordosica had higher FPG in dark than in light regardless of source, position on mother plants or storage condition. At suboptimum (5:15°C) and supraoptimal (25:35°C) temperatures, germination of A. sphaerocephala and A. ordosica achenes was inhibited in both light and darkness. It was concluded that light inhibits germination of A. sphaerocephala and A. ordosica achenes at low (10:20°C) temperature but not at high (15:25°C) temperature. Since the temperature in Mu Us sandy land is around 10:20°C in early June, when air sowing is done, achenes should germinate best when they are covered by a thin layer of sand.     

The effect of deuterium oxide on light-sensitive Paulownia tomentosa seed germination

The effect of deuterium oxide on the germination of light-sensitive Empress tree (Paulownia tomentosa) seeds was studied. Kinetics of germination in both light- and gibberellic acid (GA₃)-induced seeds was decelerated by increasing concentrations of deuterium oxide (D₂O) in the medium. Deuterium oxide in increasing concentrations also changed the duration of the light necessary for germination, from 5 min in H₂O to more than 3 days in 60% D₂O. A far-red (FR) pulse reversed the effect of inductive, prolonged red (R) irradiation; maximum germination could subsequently be restored by only 5 min of red light. The escape from FR reversibility was delayed from 1 day in water to 2 or 3.5 days in D₂O. The light reactions of D₂O-treated seeds resemble those of skotodormant seeds of the same species.     

Seed germination responses to varying environmental conditions and provenances in Crucianella maritima L., a threatened coastal species

Seed germination (effects of light, temperature, NaCl and KNO₃) of the coastal endangered species Crucianella maritima was investigated by testing seeds from three different populations. Data were analyzed by means of Generalized Linear Mixed Model (GLMM). The principal results showed that germination of C. maritima seeds was characterized by photoinhibition, absence of primary dormancy and salt-induced secondary dormancy, with no need for high nutrient availability (KNO₃). Intraspecific differences in germination pattern emerged, apparently due to a different seed mass. These results show important germination traits of C. maritima which should be taken into account in possible reintroduction attempts aimed at restoring threatened populations of this species.     

Dual Effect of Light on the Gibberellin- and Nitrate-Stimulated Seed Germination of Sisymbrium officinale and Arabidopsis thaliana

Red light (R) has a dual effect on the seed germination of the two related species Arabidopsis thaliana and Sisymbrium officinale. The two species provide different means to separate the light-effects. In S. officinale, stimulation of germination by R depends on the stimultaneous presence of nitrate (light-effect I). The effect of both factors is completely blocked by tetcyclacis, an inhibitor of gibberellin (GA)-biosynthesis. Addition of a mixture of gibberellins A₄ and A₇ (GA₄₊₇) antagonizes the inhibition. In the absence of nitrate, R shifts germination to lower GA-requirement (light-effect II). In A. thaliana a similar second light-effect is seen on the GA-requirement of GA-deficient ga-1 mutant seeds. R stimulates germination of wild type seeds in water (light-effect I). For both species, light-effect I shows a fluence threshold value of approximately 10⁻⁵ moles per square meter, which is independent of the nitrate concentration. Increasing nitrate concentrations narrow the fluence-range required for maximal germination whereby the product of nitrate concentration and fluence value determines the germination level, indicating a multiplicative interaction between R and nitrate. Fluence-response curves for light-effect II are similar for both species. Germination occurs in the range of 10⁻⁶ to 10⁻² moles per square meter fluence. The maximal level of germination is determined by the level of dark-germination and light-effect II. Increasing GA₄₊₇ concentrations induce a shift to lower fluence values. It is shown that in the second effect the co-action of R and exogenous GA₄₊₇ is clearly additive. It is concluded that light-effect I induces a chain of events leading to GA biosynthesis. Light-effect II seems to enhance the sensitivity of the seeds to GAs.     

The Origin, Development and Germination of Bulbils in Two Dioscorea Species

The origin, development and germination of aerial bulbils ofDioscorea alata and D. bulbifera are described and the significanceof the primary nodal complex (PNC) in bulbil ontogeny discussed.Further evidence is provided for the view that the PNC, or itsinitial, is the site of renewed growth in Dioscorea species. Dioscorea species, yams, bulbil germination, primary nodal complex