The Use of Maleic Hydrazide for Effective Hybridization of Setaria viridis

An efficient method for crossing green foxtail (Setaria viridis) is currently lacking. S. viridis is considered to be the new model plant for the study of C4 system in monocots and so an effective crossing protocol is urgently needed. S. viridis is a small grass with C4-NADP (ME) type of photosynthesis and has the advantage of having small genome of about 515 Mb, small plant stature, short life cycle, multiple tillers, and profuse seed set, and hence is an ideal model species for research. The objectives of this project were to develop efficient methods of emasculation and pollination, and to speed up generation advancement. We assessed the response of S. viridis flowers to hot water treatment (48°C) and to different concentrations of gibberellic acid, abscisic acid, maleic hydrazide (MH), and kinetin. We found that 500 μM of MH was effective in the emasculation of S. viridis, whilst still retaining the receptivity of the stigma to pollination. We also report effective ways to accelerate the breeding cycle of S. viridis for research through the germination of mature as well as immature seeds in optimized culture media. We believe these findings will be of great interest to researchers using Setaria.     

Methods for Performing Crosses in Setaria viridis,a New Model System for the Grasses

Setaria viridis is an emerging model system for C₄ grasses. It is closely related to the bioenergy feed stock switchgrass and the grain crop foxtail millet. Recently, the 510 Mb genome of foxtail millet, S. italica, has been sequenced ^1,2 and a 25x coverage genome sequence of the weedy relative S. viridis is in progress. S. viridis has a number of characteristics that make it a potentially excellent model genetic system including a rapid generation time, small stature, simple growth requirements, prolific seed production ³ and developed systems for both transient and stable transformation ⁴. However, the genetics of S. viridis is largely unexplored, in part, due to the lack of detailed methods for performing crosses. To date, no standard protocol has been adopted that will permit rapid production of seeds from controlled crosses.The protocol presented here is optimized for performing genetic crosses in S. viridis, accession A10.1. We have employed a simple heat treatment with warm water for emasculation after pruning the panicle to retain 20-30 florets and labeling of flowers to eliminate seeds resulting from newly developed flowers after emasculation. After testing a series of heat treatments at permissive temperatures and varying the duration of dipping, we have established an optimum temperature and time range of 48 °C for 3-6 min. By using this method, a minimum of 15 crosses can be performed by a single worker per day and an average of 3-5 outcross progeny per panicle can be recovered. Therefore, an average of 45-75 outcross progeny can be produced by one person in a single day. Broad implementation of this technique will facilitate the development of recombinant inbred line populations of S. viridis X S. viridis or S. viridis X S. italica, mapping mutations through bulk segregant analysis and creating higher order mutants for genetic analysis.     

31P-NMR study of turnip seed germination and sprout growth inhibition by peroxydisulfate ion

³¹P-NMR was used to study turnip seeds (Brassica rapa L.) incubated in 0.05 M K₂SO₄ solution, where they germinate and grow normally, and in 0.05 M K₂S₂O₈ (potassium peroxydisulfate), where they germinate but do not grow. With ³¹P-NMR it is possible to measure cytoplasmic and vacuolar pH, to identify phosphorus metabolites and to measure their relative concentrations in vivo. Results show a nearly constant vacuolar pH during germination and growth in K₂SO₄ contrasted with a steady decrease in vacuolar pH for seeds exposed to K₂S₂O₈. Cytoplasmic pH decreases during germination and then stabilizes during growth in K₂SO₄; it follows the same course during germination but then drops precipitously in K₂S₂O₈. The quantity of dissolved phosphates increases very rapidly during the first few hours after moistening, then more slowly until germination occurs. Following germination, the amount of vacuolar phosphate continues to increase, while the cytoplasmic phosphate does not. These results are consistent with a mechanism in which K₂S₂O₈ inhibits growth by intercepting indoleacetic acid.     

INBREEDING EFFECTS IN A GYNODIOECIOUS POPULATION OF THE COLONIZING SPECIES TRIFOLIUM HIRTUM ALL.

The demographic consequences of one and two generations of selfing were examined in a gynodioecious population of rose clover (Trifolium hirtum). Seeds collected from a roadside population were used to create an experimental population that consisted of seeds of open-pollinated individuals (S₀), and seeds obtained after one (S₁) and two (S₂) generations of selfing. Seeds from the three groups were equally likely to germinate. However, inbreeding effects were observed in the vigor and survivorship of the seedlings. The proportion of the transplanted seedlings that reached the reproductive stage was 0.42, 0.31, and 0.14 for the S₀, S₁, and S₂ groups, indicating a reduction of 26% and 66% by one and two generations of selfing, respectively. Inbreeding effects on reproductive components of fitness were nonsignificant. Groups were compared by multiplicative fitness functions based on germination, survival to reproduction, and fecundity. The relative fitness of the S₁ and S₂ groups were 0.64 and 0.23 relative to the S₀ group, representing a reduction in lifetime fitness of 36% and 77%, respectively. The differences in relative fitness among the groups were caused mainly by differences in survivorship. Thus, inbreeding depression is apparently an important factor in the maintenance of the gynodioecious breeding system in rose clover.     

The role of fleshy pericarp in seed germination and dispersal under flooded conditions in three wetland forest species

In flooded habitats, inundations affect important forest regeneration processes, such as seed dispersal and germination. The main seed dispersal mechanism used by species in Austral South American temperate swamp and riparian forests is endozoochory, which releases seeds from the fleshy pericarp. Endozoochory could be favorable or unfavorable in wetland habitats, since this mechanism exposes seeds directly to water and can, in some cases, be detrimental to germination. In this study, we studied whether or not the fleshy pericarp favors germination after the flooding period's end. Furthermore, we quantified if the number of days which the fruit was found to be floating related to its germination success. We used the seeds of three common fleshy fruit species of flooded habitats from southern Chile, the trees Luma apiculata and Rhaphithamnus spinosus, and the vine Luzuriaga radicans. We simulated flooding periods of 7, 15, 30 and 45 days submerging seeds, with and without pericarps, in water. We found that the pericarp's presence significantly increased Luma's germination success and significantly decreased that of Luzuriaga. The germination of Rhaphithamnus was low after periods of flooding in both seed treatments, with no significant differences found between them. The fruits could float for an average of one to four weeks, depending on the species, which did not relate to their germination success. These results show that germination was affected by the presence of fleshy pericarps in flooded conditions and furthermore, that flotation allows for hydrochory from one week to one month. We suggest that in swamp forests multiple seed dispersal mechanisms are advantageous, especially for fleshy-fruited species.     

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.     

Effect of priming treatments on seed germination and seedling growth in bamboo [Dendrocalamus strictus (Roxb.) Nees]

Instances of flowering of bamboo species Dendrocalamus strictus are few and far between which are taken as opportunity by nurserymen to collect seeds for propagation. Germination of seeds is reported to be poor. Therefore, different seed priming treatments were applied to D. strictus seeds collected from Ranchi in order to obtain uniform and high germination. Under laboratory conditions, dehusking of seeds before sowing ensured cent percent germination. Seed priming with KNO₃ 1% solution resulted in 80.4% increase in germination followed by hydropriming by 16 h (73.1% increase). In field conditions, dehusked seeds gave 23.0% germination without any priming treatment. Priming treatment with KNO₃ 1% gave the highest rise in germination (39.1%) followed by hydropriming for 16 h (26.1%). Seeds with their seed coats intact could give germination of 9.5% when germinated without any treatment. A rise of 115.8% in germination was obtained by priming with KNO₃ 1% (final germination count 20.5%). The next best treatment was hydropriming for 16 h (final germination 18.5%, a rise of 94.7%). KNO₃ 1% also induced the earliest and the most rapid germination. When seedlings germinated in laboratory were transferred to soil, all seedlings from all treatments established successfully without any mortality whatsoever. Therefore, it is recommended that seeds should be primed for 8 h with 1% KNO₃ and germinated in laboratory or in farm house under normal atmospheric condition before transplanting the seedlings to soil.     

Nuclear replication activities during imbibition of abscisic acid- and gibberellin-deficient tomato (Lycopersicon esculentum Mill.) seeds

The role of cis-abscisic acid (ABA) and gibberellins (GAs) in the induction of cell-cycle activities has been studied during imbibition and subsequent germination of tomato seeds. Using flow cytometry, nuclear replication activity was investigated in embryo root tips isolated from seeds of the ABA-deficient mutant sit ^w , the GA-deficient mutant gib-1, and the wild-type (MM) tomato (Lycopersicon esculentum Mill. cv. Moneymaker) upon imbibition in water, 10 μM GA₄₊₇, 5 μM ABA or 5 μM ABA+10 μM GA₄₊₇. The nuclei of fully matured dry MM, sit ^w and gib-1 seeds predominantly showed 2C DNA signals, indicating that the cell-cycle activity of most root-tip cells had been arrested at the G₁ phase of nuclear division. However, ABA-deficient sit ^w seeds contained a significantly higher amount of G₂ cells (4C DNA) compared with the other genotypes, suggesting that, during maturation, cell-cycle activity in sit ^w seeds is less efficiently arrested in G₁. Upon imbibition in water, an induction of the 4C signal, indicating nuclear replication, was observed in the root tip cells of both MM and sit ^w embroys. The augmentation in the 4C signal occurred before visible germination. Gib-1 seeds did not show cell-cycle activity and did not germinate in water. Upon imbibition in GA₄₊₇, both cell-cycle activity and subsequent germination were enhanced in MM and sit ^w seeds, and were induced in gib-1. In ABA, the germination of MM and sit ^w seeds was inhibited while nuclear replication of these seeds was not affected. It is concluded that GA influences germination by acting upon processes that precede cell-cycle activation, while ABA affects growth by acting upon processes that follow cell-cycle activation.     

Requirement for Ethylene Synthesis and Action during Relief of Thermoinhibition of Lettuce Seed Germination by Combinations of Gibberellic Acid, Kinetin, and Carbon Dioxide

Application of exogenous ethylene in combination with gibberellic acid (GA₃), kinetin (KIN), and/or CO₂ has been reported to induce germination of lettuce seeds at supraoptimal temperatures. However, it is not clear whether endogenous ethylene also plays a mediatory role when germination under these conditions is induced by treatment regimes that do not include ethylene. Therefore, possible involvement of endogenous ethylene during the relief of thermoinhibition of lettuce (Lactuca sativa L. cv Grand Rapids) seed germination at 32°C was investigated. Combinations of GA₃ (0.5 millimolar), KIN (0.05 millimolar), and CO₂ (10%) were used to induce germination. Little germination occurred in controls or upon treatment with ethylene, KIN, or CO₂. Neither KIN nor CO₂ affected the rate of ethylene production by seeds. Both germination and ethylene production were slightly promoted by GA₃. Treatments with GA₃+CO₂, GA₃+KIN, or GA₃+CO₂+KIN resulted in approximately 10-to 40-fold increases in ethylene production and 50 to 100% promotion of germination as compared to controls. Initial ethylene evolution from the treated seeds was greater than from the controls and a major surge in ethylene evolution occurred at the time of visible germination. Application of 1 millimolar 2-aminoethoxyvinyl glycine (AVG), an inhibitor of ethylene synthesis, in combination with any of above three treatments inhibited the ethylene production to below control levels. This was accompanied by a marked decline in germination percentage. Germination was also inhibited by 2,5-norbornadiene (0.25-2 milliliters per liter), a competitive inhibitor of ethylene action. Application of exogenous ethylene (1-100 microliters per liter) overcame the inhibitory effects of AVG and 2,5-norbornadiene on germination. The results demonstrate that endogenous ethylene synthesis and action are essential for the alleviation of thermoinhibition of lettuce seeds by combinations of GA₃, KIN, and CO₂. It also appears that these treatment combinations do not act exclusively via promotion of ethylene evolution as the application of exogenous ethylene alone did not promote germination.     

Assessment of Sublethal and Transgenerational Effects of Pirimicarb on the Wheat Aphids Rhopalosiphum padi and Sitobion avenae

The wheat aphids, Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius), are key pests on wheat crops worldwide. Management practices rely primarily on insecticides. The pirimicarb (carbamate) is used extensively as an effective insecticide to control these two aphids. In addition to the mortality caused by pirimicarb, various sublethal effects may occur in aphids when exposed to low lethal or sublethal doses. Understanding the general effect of pirimicarb on aphids could help increasing rational use of this insecticide. Under laboratory conditions, we assessed the sublethal effects of a low lethal concentration of pirimicarb (LC₂₅) on biological traits and acetylcholinesterase (AChE) activity of R. padi and S. avenae. Both direct and transgenerational effects, i.e. on parent and the F1 generations were assessed, respectively. We found that R. padi and S. avenae responded differentially to the LC₂₅ of pirimicarb. The parent generation of R. padi showed a 39% decrease in fecundity and multiple transgenerational effects were observed in the F1 generation; overall juvenile development, reproductive period, adult longevity and lifespan were longer than those of the control group. By contrast, LC₂₅ of pirimicarb showed almost no effects on S. avenae biological traits in both the parent and F1 generations; only the pre-reproductive duration was reduced in F1 generations. Demographic parameter estimates (e.g. r_m) showed similar trend, i.e. significant negative effect on R. padi population growth and no effect on S. avenae. However, AChE activity decreased in both R. padi and S. avenae treated by the LC₂₅ of pirimicarb. We demonstrated sublethal and transgenerational effects of pirimicarb in the two wheat aphid species; it hinted at the importance of considering sublethal effects (including hormesis) of pirimicarb for optimizing Integrated Pest Management (IPM) of wheat aphids.     

Effect of cold stratification on seed germination in <Emphasis Type="Italic">Solidago</Emphasis> × <Emphasis Type="Italic">niederederi</Emphasis> (<Emphasis Type="Italic">Asteraceae</Emphasis>) and its parental species

In this study, we investigated the influence of cold stratification on seed germination in S. × niederederi, a hybrid between the North American S. canadensis and the European S. virgaurea, using fruit samples collected in 2016 in Poland. We aimed to test the hypothesis that the low temperature exposure decreases the final percentage and speed of seed germination in the hybrid and its parental species. For each species, sets of 100 achenes in three replications were mixed with dry sand and stored in Petri dishes in darkness for 12 weeks, at ?18 °C and?+?4 °C, and?+?25 °C. The seeds were incubated for 21 d at room temperature (+25 °C), under the 12 h photoperiod (630 lx). We showed a lack of significant differences in: (i) the final percentage of germinated seeds of studied species stored at the same conditions, (ii) the final percentage of germinated seeds between the applied stratification conditions in the hybrid and its parental species, and (iii) the mean values of Timson’s index, mean germination time, and coefficient of velocity of germination between the stratification conditions in each species. The statistically significant inter-specific differences in the mean germination time parameter after the +25 °C treatment suggest that the seeds of S. × niederederi are able to germinate faster than the seeds of its parental species. However, to improve our knowledge of naturalization and invasion abilities of S. × niederederi by sexual reproduction, the seed germination and seedling survival of the hybrid should be tested in the field.     

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.     

Seed dormancy and germination in Dodonaea viscosa (Sapindaceae) from south-western Saudi Arabia

Dodonaea viscosa (Sapindaceae) is widespread in the mountainous highlands of the southwestern part of Kingdom of Saudi Arabia, where it is a medicinally important species for the people in Saudi Arabia. Seeds of this species were collected from Mount Atharb in Al-Baha region, at an altitude of 2100 m. The aims of this study were to determine if the seeds of D. viscosa have physical dormancy (i.e. a water-impermeable seed coat) and, if so, what treatments would break dormancy, and what conditions promote germination after dormancy has been broken. The dormancy-breaking treatments included: soaking of seeds in concentrated sulfuric acid (H₂SO₄) for 10 min, immersion in boiling water for 10 min and exposure to 50 °C for 1 min. After seeds had been pre-treated with H₂SO₄, to break dormancy, they were incubated at constant temperatures from 5 to 35 °C, under 12-h photoperiods or in continuous darkness, and germination recorded. Salinity tolerance was investigated by incubating acid-scarified seeds in different concentrations of mM NaCl in the light at 25 °C.Untreated seeds had low final germination 30%. Seeds that had been acid-scarified, immersed in boiling water or exposed to 50 °C all achieved 91% subsequently when incubated at 25 °C. Thus, seeds of this species in Saudi Arabia have physical dormancy, which can be broken by all three treatments designed to increase the permeability of the testa. After pre-treatment, there was a broad optimum constant temperature for germination that ranged between 5 and 25 °C but germination was inhibited by higher temperatures (30 and 35 °C). Light had little effect on this germination response. Scarified seeds were also sensitive to salinity, with the highest germination in distilled water and complete inhibition in 400 mM NaCl. Seeds that failed to germinate in saline treatments were mostly able to germinate on transfer to distilled water, suggesting osmotic inhibition.     

Dormancy of Medicago marina (L.) seed

Medicago marina (L.) is a Mediterranean species whose seeds show strong dormancy that prevents germination. We used an integrated approach of physiological analyses and proteomics to investigate the mechanisms that control M. marina dormancy/germination and that underlie stress tolerance. First, we evaluated the effects on dormancy breaking of the following treatments: mechanical scarification, freezing at −20 °C, storage for 4 months and heating at 100 °C for 1 h. Mechanical scarification and freezing were the most effective treatments in overcoming dormancy. The role of abscisic acid (ABA) in M. marina dormancy was studied by ELISA immuno-enzymatic assay. The ABA content of germinated and non-germinated mature (control) and treated seeds was determined. The level of ABA was higher in treated seeds than in control seeds; the most significant increase occurred in the heated seeds. A comparison of the ABA level in the germinated, control and treated seeds suggests that different mechanisms modulate ABA content in response to different stresses, and that a specific ABA-signalling pathway regulates germination. Proteomic analysis revealed 46 proteins differentially expressed between treated and untreated seeds; 14 of these proteins were subsequently identified by mass spectrometry. Several of the proteins identified are important factors in the stress response, and are involved in such diverse functions as lipid metabolism, protein folding and chromatin protection. Lastly, an analysis of the phosphoproteome maps showed that the function of many proteins in seeds subjected to temperature treatment is modulated through post-translational modifications.     

Structure–activity relationships of <Emphasis Type="Italic">N</Emphasis>- and <Emphasis Type="Italic">S</Emphasis>-analogs of the seed germination inhibitor (3,4,5-trimethylfuran-2(5<Emphasis Type="Italic">H</Emphasis>)-one) for mode of action elucidation

Smoke-derived butenolides are important germination signaling molecules which may be useful in promoting or controlling germination in agriculture and horticulture. The butenolide 3,4,5-trimethylfuran-2(5H)-one (trimethylbutenolide; TMB) was previously isolated from plant-derived smoke and was found to significantly reduce the germination stimulatory activity of the highly active germination promoter, 3-methyl-2H-furo[2,3-c]pyran-2-one (karrikinolide; KAR₁), another smoke-derived butenolide, when applied together. In this study, the germination inhibitory activity of eight N-analogs and one S-analog of TMB, modified in position 1 were evaluated. All synthesized analogs significantly reduced the germination of ‘Grand Rapids’ lettuce (Lactuca sativa) seeds compared to the respective controls, when applied at 1000 µM alone, or in combination with 0.01 µM KAR₁. The S-analog was the most active of the test analogs in this study, with inhibitory activity ranging from 10 to 1000 µM. This was the only compound with activity similar to that of TMB. Thus, these results indicate that N-alkylation of the lactam ring reduces its germination inhibitory activity, while the activity of the S-analog is comparable to TMB. This provides valuable information toward understanding the mode of action of these compounds in regulating germination and for the design of related synthetic compounds with potential use in agriculture or horticulture.     

Adaptation and growth response of Arabidopsis thaliana to deuterium

Summary Arabidopsis seeds were sown aseptically on mineral media containing between 0 and 90% of heavy water (D₂O). Initially, a D₂O level of over 50% was lethal for the plants. However, after culture for six successive generations on 50% D₂O, plants were capable of growing marginally on media containing up to 70% D₂O, but not higher. With increasing concentration, deuterium progressively delays germination, slows growth, reduces survival, results in bleaching of the leaves and delays flowering. Pollen fertility is not affected measurably but seed set is reduced with increasing levels of deuteration so that at 70% D₂O few seeds were obtained. The viability of the seeds harvested from plants grown on deuterated media is low. No chlorophyll or morphological mutants were observed among a large number of plant progenies. Seeds from plants cultured on D₂O media for several generations grow normally on proteated media in the very first generation.     

Reproductive ecology of <Emphasis Type="Italic">Agave colorata</Emphasis>: the importance of nectar-feeding bats and the germination consequences of self-pollination

Agave colorata is a paniculate agave distributed along the migratory route of the nectar-feeding bat Leptonycteris yerbabuenae. In this paper, we evaluate the importance of nectar-feeding bats in the reproduction of A. colorata in a population in Sonora, Mexico, and describe the germination consequences of self-pollination. We estimated abundance using five plots and set pollination treatments to evaluate the importance of bats. We recorded 14.8?±?6.8 plants/400 m², with a bimodal size distribution. Flowers are protandrous and visited mainly (>?20 visits/plant/30 min) by L. yerbabuenae. Pollination exclusion experiments showed that flowers excluded from diurnal visitors had maximum fruit set values (0.49?±?0.42), while the autonomous self-pollination treatment had the lowest value (0.03?±?0.06). Similarly, the greatest number of viable seeds per fruit was recorded in the diurnal exclusion treatment, while the greatest number of empty seeds was observed in the self-pollination treatment. Fruit set values among untreated plants varied from 32 to 54%, with a mean value of 41.8%. Seeds derived from self-pollination had a narrower window of opportunity for germination compared to seeds derived from nocturnal pollination. Self-pollinated seeds had lower germination, rate of germination or lag time in response to light, osmotic potential and heat shock treatments, compared to other pollination treatments, revealing an inbreeding cost. Overall, our results show that L. yerbabuenae is the likely major pollinator of the studied A. colorata population. However, under pollinator limitation A. colorata may produce seeds by autonomous self-pollination, at a cost expressed as lower germination.     

Canopy-Forming Seaweeds in Urchin-Dominated Systems in Eastern Canada: Structuring Forces or Simple Prey for Keystone Grazers?

Models of benthic community dynamics for the extensively studied, shallow rocky ecosystems in eastern Canada emphasize kelp-urchin interactions. These models may bias the perception of factors and processes that structure communities, for they largely overlook the possible contribution of other seaweeds to ecosystem resilience. We examined the persistence of the annual, acidic (H₂SO₄), brown seaweed Desmarestia viridis in urchin barrens at two sites in Newfoundland (Canada) throughout an entire growth season (February to October). We also compared changes in epifaunal assemblages in D. viridis and other conspicuous canopy-forming seaweeds, the non-acidic conspecific Desmarestia aculeata and kelp Agarum clathratum. We show that D. viridis can form large canopies within the 2-to-8 m depth range that represent a transient community state termed “Desmarestia bed”. The annual resurgence of Desmarestia beds and continuous occurrence of D. aculeata and A. clathratum, create biological structure for major recruitment pulses in invertebrate and fish assemblages (e.g. from quasi-absent gastropods to >150 000 recruits kg⁻¹ D. viridis). Many of these pulses phase with temperature-driven mass release of acid to the environment and die-off in D. viridis. We demonstrate experimentally that the chemical makeup of D. viridis and A. clathratum helps retard urchin grazing compared to D. aculeata and the highly consumed kelp Alaria esculenta. In light of our findings and related studies, we propose fundamental changes to the study of community shifts in shallow, rocky ecosystems in eastern Canada. In particular, we advocate the need to regard certain canopy-forming seaweeds as structuring forces interfering with top-down processes, rather than simple prey for keystone grazers. We also propose a novel, empirical model of ecological interactions for D. viridis. Overall, our study underscores the importance of studying organisms together with cross-scale environmental variability to better understand the factors and processes that shape marine communities.     

The novel ethylene antagonist, 3-cyclopropyl-1-enyl-propanoic acid sodium salt (CPAS), increases grain yield in wheat by delaying leaf senescence

Orchid is a major floral crop around the world and Dendrobium hybrids are considered to be one of the most popular orchids. In vitro germination of hybrid seeds is a common practice among orchid growers, however, in many cross pollinations the embryos may not develop to maturity, leading to poor seed germination. The effect of seed maturity and sucrose concentration were investigated via asymbiotic germination of nobile Dendrobium hybrids. Capsules were harvested from two hybrids (Den. Lucky Girl × Den. Second Love ‘Kirameki’ and Den. Lucky Girl × Den. Hamana Lake ‘Kumi’) and one selfing of Den. Second Love ‘Kirameki’ at 2, 3, 4, and 5 months after pollination and immature seeds were taken. Immature seeds from 3- to 5-month old capsules could be successfully germinated on Hyponex based medium. Immature seeds from 4-month old capsules showed greatest germination rate of tested treatments, whereas 3-month old immature seeds showed the least germination. After 6 weeks of in vitro culture, protocorms derived from embryos developed on every concentration of sucrose, but germination was greater at lower concentrations. Greater concentration of sucrose decreased normal-developed protocorms.     

Seed size and capitulum position drive germination and dormancy responses to projected warming for the threatened dune endemic Cirsium pitcheri (Asteraceae)

Among coastal plant species at risk from rapid environmental changes is the North American Great Lakes dune endemic Cirsium pitcheri. Despite being listed as federally threatened, little is known about how C. pitcheri seed attributes influence germination and dormancy‐break patterns in the context of climate change. Following a previous work where we found differences in the number and weight of C. pitcheri seeds among capitulum positions and study sites, here we examine the effects of seed attributes (capitulum position, seed weight, and site of origin) on the proportion and timing of C. pitcheri seed germination under temperature treatments that simulate projected warming in the Great Lakes (20/10, 25/10, and 30/10°C day/night). Our results demonstrate that C. pitcheri produces diverse cohorts of seeds with seed attributes that significantly influence the timing and probability of germination over a 3‐year soil seed bank. Cirsium pitcheri seed germination proportions were highest at 20°C and decreased successively at 25 and 30°C. Seeds from terminal capitula also had higher germination proportions and took longer to germinate than those from secondary capitula. Lastly, the effect of seed weight on germination probability depended on site of origin and capitulum position, with all effects varying in size and significance over time. Ultimately, our results highlight the considerable differences in germination patterns exhibited by seeds from different capitulum positions and sites of origin and provide insight into the dormancy‐break patterns that C. pitcheri might experience under predicted temperature rise in the Great Lakes region of North America.