Showing papers on "Germination published in 2001"

A postgermination developmental arrest checkpoint is mediated by abscisic acid and requires the ABI5 transcription factor in Arabidopsis

Abstract: Seed dormancy is a trait of considerable adaptive significance because it maximizes seedling survival by preventing premature germination under unfavorable conditions. Understanding how seeds break dormancy and initiate growth is also of great agricultural and biotechnological interest. Abscisic acid (ABA) plays primary regulatory roles in the initiation and maintenance of seed dormancy. Here we report that the basic leucine zipper transcription factor ABI5 confers an enhanced response to exogenous ABA during germination, and seedling establishment, as well as subsequent vegetative growth. These responses correlate with total ABI5 levels. We show that ABI5 expression defines a narrow developmental window following germination, during which plants monitor the environmental osmotic status before initiating vegetative growth. ABI5 is necessary to maintain germinated embryos in a quiescent state thereby protecting plants from drought. As expected for a key player in ABA-triggered processes, ABI5 protein accumulation, phosphorylation, stability, and activity are highly regulated by ABA during germination and early seedling growth.

Effect of salt and osmotic stresses on germination in durum wheat (Triticum durum Desf.)

Abstract: In order to determine the relative importance of ionic toxicity versus the osmotic component of salt stress on germination in durum wheat (Triticum durum Desf.), seeds of three cultivars differing in their salt and drought resistance (Omrabi-5, drought-resistant; Belikh, salt-resistant and Cando, salt-sensitive) were incubated in various iso-osmotic solutions of NaCl, mannitol and polyethylene-glycol (PEG) (osmotic potential of −0.15 (control solution) −0.58, −1.05 or −1.57 MPa). Moderate stress intensities only delayed germination, whereas the highest concentration of NaCl and PEG reduced final germination percentages. PEG was the most detrimental solute, while mannitol had no effect on final germination percentages. All osmotica reduced endosperm starch and soluble sugars content as well as α-amylase activities recorded after 48 h of treatment while β-amylase activities were, in contrast, slightly stimulated in all cultivars. Deleterious effects of NaCl and PEG were higher on isolated embryos germinated onto an in vitro Linsmaier and Skoog (LS) medium comparatively to whole seeds. All PEG-treated embryos, however, recovered after the stress relief while NaCl-treated embryos exhibited a lower rate of recovery and some extent of abnormal germination after rinsing. It was concluded that stress inhibition of germination could not be attributed to an inhibition of mobilisation of reserves and that the main effect of PEG occurred via an inhibition of water uptake while detrimental effects of NaCl may be linked to long-term effects of accumulated toxic ions. The behaviour of the three cultivars during germination did not fully reflect their mean level of putative stress resistance in field conditions and germination is, therefore, not recommended as a reliable selection criterion for breeding purposes.

Proteomic Analysis of Arabidopsis Seed Germination and Priming

Abstract: To better understand seed germination, a complex developmental process, we developed a proteome analysis of the model plant Arabidopsis for which complete genome sequence is now available. Among about 1,300 total seed proteins resolved in two-dimensional gels, changes in the abundance (up- and down-regulation) of 74 proteins were observed during germination sensu stricto (i.e. prior to radicle emergence) and the radicle protrusion step. This approach was also used to analyze protein changes occurring during industrial seed pretreatments such as priming that accelerate seed germination and improve seedling uniformity. Several proteins were identified by matrix-assisted laser-desorption ionization time of flight mass spectrometry. Some of them had previously been shown to play a role during germination and/or priming in several plant species, a finding that underlines the usefulness of using Arabidopsis as a model system for molecular analysis of seed quality. Furthermore, the present study, carried out at the protein level, validates previous results obtained at the level of gene expression (e.g. from quantitation of differentially expressed mRNAs or analyses of promoter/reporter constructs). Finally, this approach revealed new proteins associated with the different phases of seed germination and priming. Some of them are involved either in the imbibition process of the seeds (such as an actin isoform or a WD-40 repeat protein) or in the seed dehydration process (e.g. cytosolic glyceraldehyde-3-phosphate dehydrogenase). These facts highlight the power of proteomics to unravel specific features of complex developmental processes such as germination and to detect protein markers that can be used to characterize seed vigor of commercial seed lots and to develop and monitor priming treatments.

Release of Reactive Oxygen Intermediates (Superoxide Radicals, Hydrogen Peroxide, and Hydroxyl Radicals) and Peroxidase in Germinating Radish Seeds Controlled by Light, Gibberellin, and Abscisic Acid

Abstract: Germination of radish (Raphanus sativus cv Eterna) seeds can be inhibited by far-red light (high-irradiance reaction of phytochrome) or abscisic acid (ABA). Gibberellic acid (GA3) restores full germination under far-red light. This experimental system was used to investigate the release of reactive oxygen intermediates (ROI) by seed coats and embryos during germination, utilizing the apoplastic oxidation of 2′,7′-dichlorofluorescin to fluorescent 2′,7′-dichlorofluorescein as an in vivo assay. Germination in darkness is accompanied by a steep rise in ROI release originating from the seed coat (living aleurone layer) as well as the embryo. At the same time as the inhibition of germination, far-red light and ABA inhibit ROI release in both seed parts and GA3 reverses this inhibition when initiating germination under far-red light. During the later stage of germination the seed coat also releases peroxidase with a time course affected by far-red light, ABA, and GA3. The participation of superoxide radicals, hydrogen peroxide, and hydroxyl radicals in ROI metabolism was demonstrated with specific in vivo assays. ROI production by germinating seeds represents an active, developmentally controlled physiological function, presumably for protecting the emerging seedling against attack by pathogens.

Proteomic Analysis of Arabidopsis Seed Germination and Priming 1

Abstract: To better understand seed germination, a complex developmental process, we developed a proteome analysis of the model plant Arabidopsis for which complete genome sequence is now available. Among about 1,300 total seed proteins resolved in two-dimensional gels, changes in the abundance (up- and down-regulation) of 74 proteins were observed during germination sensu stricto (i.e. prior to radicle emergence) and the radicle protrusion step. This approach was also used to analyze protein changes occurring during industrial seed pretreatments such as priming that accelerate seed germination and improve seedling uniformity. Several proteins were identified by matrix-assisted laser-desorption ionization time of flight mass spectrometry. Some of them had previously been shown to play a role during germination and/or priming in several plant species, a finding that underlines the usefulness of using Arabidopsis as a model system for molecular analysis of seed quality. Furthermore, the present study, carried out at the protein level, validates previous results obtained at the level of gene expression (e.g. from quantitation of differentially expressed mRNAs or analyses of promoter/reporter constructs). Finally, this approach revealed new proteins associated with the different phases of seed germination and priming. Some of them are involved either in the imbibition process of the seeds (such as an actin isoform or a WD-40 repeat protein) or in the seed dehydration process (e.g. cytosolic glyceraldehyde-3-phosphate dehydrogenase). These facts highlight the power of proteomics to unravel specific features of complex developmental processes such as germination and to detect protein markers that can be used to characterize seed vigor of commercial seed lots and to develop and monitor priming treatments.

Handbook of plant and crop physiology

Abstract: Plants, Crops, and Growth Environment: Nutrient Uptake by Plants Plant Water Relationships Current Perspectives in Water Loss from Plants and Stomatal Action Physiology of Plant/Crop Growth and Developmental Stages: Germination and Emergence Cell Cycle Control in Plants Vegetative and Elongation Growth Stages Ecophysiological Aspects of the Vegetative Propagation of Salt-bush (Atriplex spp) and Mulberry (Morus spp). Plant Growth Regulators - The Natural Hormones (Growth Promoters and Inhibitors) Physiological Responses of Plants and Crops Under Stressful (Salt, Drought, and Other Environmental Stress) Conditions: Physiological Adaptation of Plants to Environmental Stresses Adaptive Components of Salt Tolerance Photosynthesis In Plant/Crops Under Water and Salt Stress Physiological Mechanisms of Nitrogen Absorption and Assimilation in Plants Under Stressful Conditions. Physiology of Lower-Plant Genetics and Development: Developmental Genetics In Lower Plants. Physiology of Higher-Plant/Crop Genetics and Development: Transpiration Efficiency - Avenues for Genetic lmprovement, Physiological Mechanisms Relevant to Genetic Improvement of Salinity Tolerance in Crop Plants. Whole Plant vs Reductive Research on Physiological Genetics of Crop Physiology: Whole-System Research Complements Reductive Research, AMMI Statistical Model and Interaction Analysis, Photoperiod x Temperature Interaction Effects on the Days to Flowering of Bean (Phaseolus vulgaris L.) Genotype, Temperature and Genotype x Temperature Interaction Effects on Yield of Bean (Phaseolus vulgaris L) Control of Days to Flowering of Bean (Phaseolus vulgaris L) by Interaction of a Photoperiod Gene and a Non-photoperiod Gene. Physiological Aspects of Sustainable Plant/Crop Production: Sustainable Primary Production - Green Crop Fractionation: Effects of Species, Growth Conditions, and Physiological Development of Fractionation Products. (Part Contents).

A Role for Brassinosteroids in Germination in Arabidopsis

Abstract: This paper presents evidence that plant brassinosteroid (BR) hormones play a role in promoting germination. It has long been recognized that seed dormancy and germination are regulated by the plant hormones abscisic acid (ABA) and gibberellin (GA). These two hormones act antagonistically with each other. ABA induces seed dormancy in maturing embryos and inhibits germination of seeds. GA breaks seed dormancy and promotes germination. Severe mutations in GA biosynthetic genes in Arabidopsis, such as ga1-3, result in a requirement for GA application to germinate. Whereas previous work has shown that BRs play a critical role in controlling cell elongation, cell division, and skotomorphogenesis, no germination phenotypes have been reported in BR mutants. We show that BR rescues the germination phenotype of severe GA biosynthetic mutants and of the GA-insensitive mutant sleepy1. This result shows that BR stimulates germination and raises the possibility that BR is needed for normal germination. If true, we would expect to detect a germination phenotype in BR mutants. We found that BR mutants exhibit a germination phenotype in the presence of ABA. Germination of both the BR biosynthetic mutant det2-1 and the BR-insensitive mutant bri1-1 is more strongly inhibited by ABA than is germination of wild type. Thus, the BR signal is needed to overcome inhibition of germination by ABA. Taken together, these results point to a role for BRs in stimulating germination.

Ecology of seed and seedling growth for conservation and restoration of tropical dry forest : a review

Abstract: Dry forests are among the most threatened ecosystems and have been extensively converted into grasslands, secondary forest, savanna or agricultural land. Knowledge of seed germination and seedling establishment is required for the success of efforts on restoration of these forests. This review focuses on the ecological requirements at seed and seedling stages, and collates the current knowledge of seed viability, dormancy, germination pattern and seedling behaviour of dry tropical tree species. The spatio-temporal variations within the tropical dry forest biome in soil moisture, light, temperature, nutrients and intensity of predation, significantly affect the seed and seedling traits of component species. The majority of dry tropical species possess orthodox seeds which are characterized by dormancy, while a few have recalcitrant seeds which possess little or no dormancy. Seed coat dormancy, which can be overcome by mechanical or acid scarification or sometimes by transit through animal guts, is most prevalent in the dry tropical forest species. Persistent species dominating the undisturbed portions of the forest have bigger seeds compared to those that mostly occur in disturbed regions and require shade for the survival of their seedlings. Shade demand is associated with drought endurance, and may be absolute in species such as Guettarda parviflora and Coccoloba microstachya, or facultative as in Plumeria alba and Bursera simaruba. The fluctuation in temperature significantly affects seed germination in several species of dry Afromontane forest trees of Ethiopia. Seedling mortality is primarily a function of moisture stress during the dry period. Adaptive responses of seedlings to drought stress include increased chlorophyll content, for example in Acacia catechu, and root biomass, as in several dry forest species (for example Drypetes parvifolia, Teclia verdoornia) of Ghana. Mulching, application of fertilizers, interplanting of leguminous species and mycorrhizal inoculation are useful tools for promoting seedling establishment in nutrient-poor dry tropical soils. Periodic forest fires, and predation affect recruitment and seedling development according to their intensity. Many species experiencing frequent fires have evolved thick seed coats, produce fire-hardy seedlings, or escape the effect by temporal separation of seed dispersal and fire events. Predation may result in abortion of fruits or may enhance germination and recruitment by scarification and dispersal, as in most species of the Guanacaste dry forest. Exposure to elevated CO2 has increased relative growth rate, total leaf area and water use efficiency in most of the dry tropical seedlings tested, but the magnitude of the effect has varied markedly among species. Due to the availability of a large source of energy, large seeds show higher germination percentage, greater seedling survival and increased growth. Seeds originating from different provenances exhibit differences in germination and seedling growth (for example Prosopis cineraria, Albizia lebbeck, Eucalyptus camaldulensis and Acacia mangium), efficiency of nodulation (for example Acacia nilotica, A. auriculiformis), and stress resistance (for example Populus deltoides, Dalbergia sissoo). The review points out the need for coordinated, long-term, field-based studies for identification of multiple cues and niches for germination, on seed and seedling dynamics in response to fire, and on within-species genetic variability for selection of suitable provenances. Field-based studies at species and community levels are also needed to permit manipulations of biotic components to augment the recruitment of desired species and to suppress that of undesirable species.

Effect of Garlic Mustard [Alliaria petiolata (Beib. Cavara & Grande)] Extracts on Plants and Arbuscular Mycorrhizal (AM) Fungi

Abstract: We examined the effects of garlic mustard (Alliaria petiolata) leachates on germination of arbuscular mycorrhizal (AM) fungal spores, colonization of plant roots by AM fungi and germination and root growth of monocot and dicot plants under laboratory conditions. In the field we examined the effect of garlic mustard on AM inoculum potential (MIP). Water leachates of garlic mustard prevented germination of spores of the AM fungus Gigaspora rosea, inhibited the formation of AM associations with tomato (Lycopesicum esculentum) and significantly reduced germination of tomato seeds. Garlic mustard leachates also reduced root length of tomato and sorghum (Sorghum bicolor) seedlings. Under field conditions we found a significant negative correlation between the density of garlic mustard and the mycorrhizal inoculum potential of the soil in which the plants grew. These results suggest that garlic mustard may reduce the competitive abilities of native plants by interfering with the formation of mycorrhizal associations and root growth.

Stored proteinases and the initiation of storage protein mobilization in seeds during germination and seedling growth

Abstract: Though endopeptidases and carboxypeptidases are present in protein bodies of dry quiescent seeds the function of these proteases during germination is still a matter of debate. In some plants it was demonstrated that endopeptidases of dry protein bodies degrade storage proteins of these organelles. Other studies describe cases where this did not happen. The role that stored proteinases play in the initiation of storage protein breakdown in germinating seeds thus remains unclear. Numerous reviews state that the initiation of reserve protein mobilization is attributed to de novo formed endopeptidases which together with stored carboxypeptidases degrade the bulk of proteins in storage organs and tissues after seeds have germinated. The evidence that the small amounts of endopeptidases in protein bodies of embryonic axes and cotyledons of dry seeds from dicotyledonous plants play an important role in the initiation of storage protein mobilization during early germination is summarized here.

Studies on germination conditions and antioxidant contents of wheat grain.

Abstract: Germination time and conditions for wheat grain were studied to determine optimum conditions that would maximize the production of antioxidants. Wheat grains were first steeped in water for 24 or 48 h, followed by incubation in the dark for 9 d at 98% RH and 16.5 degrees C. The changes in the concentration of vitamins C and E, beta-carotene, ferulic acid and vanillic acid were monitored over the germination period. Vitamins C and E and beta-carotene were barely detectable in the dry grains. However, upon germination the concentrations of these antioxidant vitamins steadily increased with increasing germination time, reaching their peaks after 7 d at 550 mu/g for vitamin C, 10.92 micrograms/g for alpha-tocopherol, and 3.1 micrograms/g for beta-carotene. Concentrations of ferulic and vanillic acids were also increased, reaching their maxima after 7 d at 932.4 micrograms/g and 12.9 micrograms/g, respectively. The grains steeped for 48 h before germination became wet, sticky, yellow-brown color with acidic smell after 7 d. These results suggested that wheat grains steeped for 24 h and germinated for 7 d would produce the most desirable sprouts with respect to antioxidant concentrations and sensory properties.

A mechanism for promoting the germination of Zinnia elegans seeds by hydrogen peroxide.

Abstract: H(2)O(2) promotes seed germination of cereal plants such as barley, wheat and rice, and several mechanisms have been proposed for its action [Naredo et al. (1998) Seed Sci. Technol. 26: 675-689]. We investigated the role of H(2)O(2) in the germination of Zinnia elegans seeds. H(2)O(2) promoted seed germination in a dose-dependent manner as did respiratory inhibitors, indicating that H(2)O(2) itself possibly promotes seed germination rather than O(2). Seed germination was promoted by removal of pericarp from seeds or by removal of ethanol-soluble compounds from the seeds with pericarp. The ethanol-soluble compounds suppressed the germination of seeds having no pericarp, and this effect was reversed by H(2)O(2). These findings indicate that oxidation of the germination inhibitor(s) present in the pericarp by H(2)O(2) promotes seed germination. Antioxidants which are derivatives of well-known germination inhibitors suppressed seed germination in a dose-dependent manner, suggesting that, to initiate seed germination, a germination inhibitor(s) should be decomposed by an oxidant such as H(2)O(2).

Constraints to symbiotic germination of terrestrial orchid seed in a mediterranean bushland.

Abstract: Summary • The dependence of seeds of terrestrial orchids on specific fungi for germination provides a means of locating these fungi in the wild and to investigate the role of appropriate fungi in the germination of orchid seed and development of seedlings under natural field conditions. • Seed baits, comprising orchid (Caladenia arenicola) seed enclosed in fine nylon mesh, were placed at sample points along four transects through two orchid populations in bushland in Western Australia. Seed germination was scored and compared with adult orchid plant distribution and soil factors. • A small fraction of available seed (< 1%) germinated to a stage of tuber formation where survival over the subsequent dry season would have been possible. Germination increased in the vicinity of adult C. arenicola plants, but other factors, such as soil potassium levels and presence of leaf litter, were also correlated with seed germination. • The measurement of the spatial variability in germination events within an orchid habitat demonstrated the availability of new recruitment sites. This information is required to assess the natural recruitment capacity and the potential for orchid reintroduction in natural habitats.

In vitro Arabidopsis pollen germination and characterization of the inward potassium currents in Arabidopsis pollen grain protoplasts

Abstract: The focus of this study is to investigate the regulatory role of K(+) influx in Arabidopsis pollen germination and pollen tube growth. Using agar-containing media, in vitro methods for Arabidopsis pollen germination have been successfully established for the first time. The pollen germination percentage was nearly 75% and the average pollen tube length reached 135 microm after a 6 h incubation. A decrease in external K(+) concentration from 1 mM to 35 microM resulted in 30% inhibition of pollen germination and 40% inhibition of pollen tube growth. An increase in external K(+) concentration from 1 mM to 30 mM stimulated pollen tube growth but inhibited pollen germination. To study how K(+) influx is associated with pollen germination and tube growth, regulation of the inward K(+) channels in the pollen plasma membrane was investigated by conducting patch-clamp whole-cell recording with pollen protoplasts. K(+) currents were first identified in Arabidopsis pollen protoplasts. The inward K(+) currents were insensitive to changes in cytoplasmic Ca(2+) but were inhibited by a high concentration of external Ca(2+). A decrease of external Ca(2+) concentration from 10 mM (control) to 1 mM had no significant effect on the inward K(+) currents, while an increase of external Ca(2+) concentration from 10 mM to 50 mM inhibited the inward K(+) currents by 46%. Changes in external pH significantly affected the magnitude, conductance, voltage-independent maximal conductance, and activation kinetics of the inward K(+) currents. The physiological importance of potassium influx mediated by the inward K(+)-channels during Arabidopsis pollen germination and tube growth is discussed.

Effect of brassinosteroids on salinity stress induced inhibition of seed germination and seedling growth of rice (Oryza sativa L.)

Abstract: The effect of 24-epibrassinolide and 28-homobrassinolide on the inhibitionof germination and seedling growth of rice (Oryza sativa) induced bysalinity stress was studied. Brassinosteroids were found to reverse theinhibitory effect on germination and seedling growth. The activation ofseedling growth by brassinosteroids under salinity stress was associatedwith enhanced levels of nucleic acids and soluble proteins.

Changes in oligosaccharide content and antioxidant enzyme activities in developing bean seeds as related to acquisition of drying tolerance and seed quality

Abstract: Seeds of bean (Phaseolus vulgaris cv. Vernel) were collected throughout their development on the plant and dried at 15 degrees C and 75% relative humidity to a final moisture content of about 16% (fresh weight basis) to determine whether the onset of tolerance to this drying condition was related to changes in soluble sugars or the activities of the main antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR). Measurements of soluble sugars and enzyme activities were made after drying the seeds, and drying tolerance was evaluated by the ability of dried seeds to germinate and to produce normal seedlings. Seeds became tolerant to drying at 45 d after anthesis, a time marking physiological maturity. At physiological maturity, the moisture content of seeds was about 50-55% (fresh weight basis) and seed dry matter reached about 190 mg per seed. Seed vigour, evaluated by controlled deterioration and conductivity measurements, continued to increase after seed mass maturity, but decreased when seeds remained thereafter for more than 7 d on the plant. Acquisition of drying tolerance was coincident with an accumulation of raffinose and stachyose. Dried-tolerant seeds were also characterized by a high amount of sucrose, the most abundant sugar, and by a low content of monosaccharides. The (raffinose+stachyose)/sucrose ratio increased during seed filling, reaching a value close to 1 when all the seeds became tolerant to drying, and maintaining this proportion during the final stages of maturation. Acquisition of drying tolerance was also related to a reorientation of the enzymatic antioxidant defence system. Drying-tolerant dried seeds displayed high CAT and GR activities and low SOD and APX activities, while the opposite condition was observed in immature dried seeds. The shift in antioxidant enzymes corresponded to the beginning of the maturation-drying phase. These results suggest that oligosaccharide metabolism and enzymatic antioxidant defences may be involved in acquisition of drying tolerance during bean seed development, but are not related to seed vigour.

Responses of Phaseolus Vulgaris Chromium and Cobalt Treatments

Abstract: The effects of Cr and Co supplied either individually or mixed together in the nutrient solution on seed germination, enzyme activities, photosynthesis, metabolic products, and yield were investigated. Cr and Co reduced germination percentage only at the highest concentration used but markedly decreased radicle growth which might be attributed to depressive effect of Cr and Co on the activity of amylases and subsequent transport of sugars to the embryo axes. Protease activity, on the other hand, increased with the metal treatment. The highest concentration (10−2 M) tested of both metals was harmful on plant growth, while the low and moderate concentrations (10−6 and 10−4 M) enhanced the contents of chlorophylls and sugars, and activity of Hill reaction. Fresh mass of the produced pods increased at low and moderate concentrations of Cr and at Cr+Co treatment, but decreased in plants treated with Co.

Inducing salt tolerance in maize (Zea mays L.) through seed priming with chloride salts: Growth and ion transport at early growth stages

Abstract: The study was conducted to determine whether salt tolerance could be induced in maize at germination stage by soaking of seeds for 8 h in distilled water or in 200 meq·L−1 of NaCl, KCl, CaCl2·2H2O. Both primed and un-primed seeds were subjected for 14 days to 0, 100 or 200 mol·m−3 NaCl under controlled conditions. Although all priming agents were effective in alleviating adverse effects of salt stress on maize at germination stage, CaCl2·2H2O proved to be more effective since the seeds primed with this salt had significantly higher final germination, rate of germination and fresh and dry weights of plumules and radicles than those treated with other salts or distilled water. Concentration of Na+, K+ and Ca2+ increased significantly in all parts of germinating seeds of maize seeds primed with NaCl, KCl, or CaCl2·2H2O, respectively. In addition, seeds primed with CaCl2·2H2O were the highest in Cl− accumulation in all parts of the germinating seeds, followed by seeds treated with NaCl and KCl. Most of the Ca2+ was retained in seeds and mesocotyl, because of which, transport of this ion to plumules and radicles was low.

The seed coat as a modulator of seed-environment relationships in Fabaceae

Abstract: The seed coat is one of the main determinants of seed germination, vigor and longevity potentials. It is also intimately associated with temporal and spatial dispersion of seed germination in a large number of plant species. The understanding of its properties and characteristics may explain, anticipate or even allow the modification of seed performance under certain environmental conditions. There is a growing volume of evidence associating seed coat characteristics to specific seed problems. For example, susceptibility to mechanical damage is related to lignin content of the seed coat, while seed longevity and tolerance to field weathering depends on seed coat integrity. Seed performance in many legumes has been associated with certain seed coat structures, such as the hilum, strophiole and micropyle. In soybean, permeability is also related with porosity, color, and cerosity, that affect seed vigor, storage potential, resistance to shrinking and fungi infection, and to susceptibility to imbibition damage. The understanding of these associations is necessary before genetic alterations through breeding for desirable characteristics and is fundamental for the development and improvement of seed pre-sowing treatments, production, handling and quality evaluation procedures, which may ultimately result in reduction of seed quality losses and increase the efficiency of agricultural production systems.

Passage through bird guts causes interspecific differences in seed germination characteristics

Abstract: Summary 1 Seed germination characteristics are often modified after seeds are ingested by frugivores. Factors that are intrinsic either to the plant or to the frugivore’s digestive tract are responsible for the great variation observed in germination response. 2 Our objectives were to determine whether and how the seed germination patterns of five common western Mediterranean plant species are affected by seed passage through the guts of their major dispersers, and to elucidate the mechanism by which such patterns are changed. 3 We used captive birds (Turdus merula and Sylvia melanocephala) to obtain ingested seeds and compared their germination rate (speed) and germinability (final percent germination) with those of controls (uningested, pulp-removed seeds), controlling for seed age, size and source. Germination was monitored for 2 years in an experimental garden. We evaluated the possible changes in seed traits after ingestion by measuring weight and coat thickness, and by observing seed coat sculpture. 4 Rate of seed germination, but not germinability, changed in all species after gut treatment. The greatest effect was in Osyris, in which germination was much enhanced. A great acceleration of germination, which is likely to translate into a seedling size advantage, was also found in Asparagus. In the other three species tested, germination was slower for ingested than for control seeds. 5 For Rubus and Rubia seeds, we found a different germination response depending upon the frugivore species tested. A different degree of seed coat scarification caused by differences in gut retention time, chemical and/or mechanical abrasion probably account for such responses. 6 In three of the species (Osyris, Rubia and Phillyrea), seed weight decreased after gut treatment. Such weight loss was not caused by any change in coat thickness, but may have been because of the scarification and consequent alteration of the seed coat structure. 7 The five Mediterranean species studied germinate when rains are most likely to fall (mostly autumn and spring). The different speed of germination promoted by gut treatment within frugivores may increase the probability that seeds can recruit successfully at a given time and in a given place. 8 This study suggests that frugivores contribute to the heterogeneity in germination characteristics not only within plant populations but also within plant communities, each frugivore species having a particular effect on the seeds of each plant consumed.

Effect of salinity on seed germination and early seedling growth of sugar beet (Beta vulgaris L.)

Abstract: Five varieties of sugar beet (Beta vulgaris L.) were studied in order to assess the effect of NaCl on seed germination and growth of young seedlings. Five salt treatments, 0, 50, 100, 150, and 200 mM NaCl were applied and germination was carried out at 21°C for 14 days. The results showed that germination percentage, rate of germination, and the relative germination percentage, were all inhibited by NaCl treatments. The strongest inhibition of germination occurred at the higher salt concentrations. Growth of young seedlings was also reduced, especially at the higher salt concentrations. The use of isotonic mannitol solutions indicated that the inhibitory influence of NaCl on sugar beet seed germination was principally a specific ionic effect and only a small portion of the inhibition could be attributed to an osmotic effect.

Sunflower (Helianthus annuus L.) response to broomrape (Orobanche cernua Loefl.) parasitism: induced synthesis and excretion of 7‐hydroxylated simple coumarins

Abstract: The interaction of the parasitic plant Orobanche cernua with resistant and susceptible cultivars of Helianthus annuus L. was investigated. Using different bioassays to evaluate the early stages of the parasite life cycle (germination, attachment, penetration, and establishment), differences were observed between O. cernua-resistant and O. cernua-susceptible sunflower varieties. Germination of O. cernua seeds in the presence of resistant sunflower roots was approximately half that of germination in the presence of susceptible roots, and germinated seeds displayed enhanced browning symptoms. Parasite radicles or host-tissue around the contact point turned brown after O. cernua attachment to sunflower roots, especially in the resistant varieties. These observations suggested the possible accumulation of toxic compounds as a defence strategy in the resistant sunflower varieties. Sunflower 7-hydroxylated simple coumarins may play a defensive role against O. cernua parasitism by preventing successful germination, penetration and/or connection to the host vascular system. This hypothesis is supported by the following data: (i) coumarins inhibited the in vitro germination of O. cernua seeds induced by the strigol analogue GR(24) and caused a browning reaction in germinated seeds and (ii) resistant sunflowers accumulated higher levels of coumarins in roots and excreted greater amounts than susceptible varieties in response to O. cernua infection.

Light, temperature and burial depth effects on Rumex obtusifolius seed germination and emergence

Abstract: Trials were carried out to investigate the effects of light and temperature on germination of Rumex obtusifolius L. After several months of storage, seeds gradually lost dormancy and became photosensitive. Thermal optima for germination were between 20 °C and 25 °C in light or in darkness. At lower temperatures there was a greater demand for light, so that the greatest differences in germination percentage (between low and high temperatures) were found within the 10-15 °C temperature range. The calculated thermal minimal (x-intercept method) in light and darkness were 8.3 °C and 6.1 °C respectively. Daily temperature fluctuation increased germination even after seed irradiation with far-red light, suggesting a lower demand for the far-red-absorbing form of phytochrome. Seed burial inhibited germination in proportion to depth; however, germination inhibition was independent of seed phytochrome photo-equilibrium, which had been diversified by seed pretreatment with light Seedlings did not emerge when seeds were buried > 8 cm deep. Recovery of ungerminated seeds showed that excessive burial did not impede seedling emergence but rather prevented seed germination. However, this induction of dormancy was lost once germination processes were activated (24-48 h at 20 °C) that made germination irreversible. Temperature was also involved in inhibition, and low temperature ( < 15 °C) induced the least inhibition. This is discussed in terms of processes of respiration and fermentation in buried seeds.

Influence of fly ash on soil physical properties and turfgrass establishment.

Abstract: A field study (1993-96) assessed the benefits of applying unusually high rates of coal fly ash as a soil amendment to enhance water retention of soils without adversely affecting growth and marketability of the turf species, centipedegrass [Eremochloa ophiuroides (Munro) Hack] A Latin Square plot design was employed that included 0 (control, no ash applied), 280, 560, and 1120 Mg ha-1 application rates of unweathered precipitator fly ash The fly ash was spread evenly over each plot area, rototilled, and allowed to weather under natural conditions for 8 mo before seeding High levels of soluble salts, indicated by the electrical conductivity (EC) of soil extracts, in tandem with an apparent phytotoxic effect from boron (B), apparently inhibited initial plant establishment as shown by substantially lower germination counts in treated soil However, plant height and rooting depth were not adversely affected, as were the dry matter (DM) yields throughout the study period Ash treatment did not significantly influence water infiltration rate, bulk density, or temperature of the soil, but substantially improved water-holding capacity (WHC) and plant-available water (PAW) Enhanced water retention capacity improved the cohesion and handling property of harvested sod

The effect of high temperature and high atmospheric CO2 on carbohydrate changes in bell pepper (Capsicum annuum) pollen in relation to its germination.

Abstract: Pollen viability and germination are known to be sensitive to high temperature (HT). However, the mode by which high temperature impairs pollen functioning is not yet clear. In the present study, we investigated the effect of high temperature on changes occurring in carbohydrate of bell pepper (Capsicum annuum L. cv. Mazurka) pollen in order to find possible relations between these changes and pollen germination under heat stress. When pepper plants were maintained under a moderate HT regime (32/26 degrees C, day/night) for 8 days before flowers have reached anthesis, pollen count at anthesis was similar to that found in plants grown under normal temperatures (NT 28/22 degrees C). However, the in vitro germination, carried out at 25 degrees C, of pollen from HT plants was greatly reduced. This effect matched the marked reduction in the number of seeds per fruit in the HT plants. Maintaining the plants at high air CO2 concentration (800 mmol mol-1 air) in both temperature treatments did not affect the in vitro germination of pollen from NT plants, but restored germination to near the normal level in pollen from HT plants. Under NT conditions, starch, which was negligible in pollen at meiosis (8 days before anthesis, A-8) started to accumulate at A-4 and continued to accumulate until A-2. From that stage until anthesis, starch was rapidly degraded. On the other hand, sucrose concentration rose from stage A-4 until anthesis. Acid invertase (EC 3.2.1.26) activity rose parallel with the increase of sucrose. In pollen from HT plants, sucrose and starch concentrations were significantly higher at A-1 pollen than in that of NT plants. Under high CO2 conditions, the sucrose concentration in the pollen of HT plants was reduced to levels similar to those in NT pollen. In accordance with the higher sucrose concentration in HT pollen, the acid invertase activity in these pollen grains was lower than in NT pollen. The results suggest that the higher concentrations of sucrose and starch in the pollen grains of HT plants may result from reduction in their metabolism under heat stress. Elevated CO2 concentration, presumably by increasing assimilate availability to the pollen grain, may alleviate the inhibition of sucrose and starch metabolism, thereby increasing their utilization for pollen germination under the HT stress. Acid invertase may have a regulatory role in this system.