Nuove Prospettive Nello Studio dei Fattori che Controllano la Germinazione Dei Semi

Abstract

New perspectives in the study of factors which control seed germination. — Seedlings of Triticum durum, cv. « Cappelli », coming from unirradiated embryos grafted on to irradiated endosperms (EM(u)/EN(i) of presoaked seeds (in distilled water for 24 h. at 20[ddot]C.) (treatment: X-rays, doses, 2,4,6,8,10 and 20 Kr), grow more than seedlings of control EM(u)/EN(u) (dose 0) (fig. 1). To have this reaction, it is necessary that the used seeds be after-ripe; at the various stages of seed ripening, be ginning from the milk stage, the phenomenon is not present.

On this basis, the author has thought that a natural inhibitor occurs in the after-ripe endosperm of « Cappelli », which is neutralized or destroyed by X-rays.

As an experimental demonstration, some trials have been made of growing wheat seedlings in Petri dish, on moistened (distilled water) filter paper, together with excised embryos or isolated endosperms (fig. 2): the after-ripe endosperm is able to depress the seedling growth (fig. 3). In the same experimental conditions, X-rays, dose 6 Kr, neutralize the inhibition effect given by the endosperm. (fig. 4).

A completely different situation occurs in wheat seed, during its ripening: endosperm is inactive, embryo produces inhibition effects on the seedling growth, which, also in this case, are reduced by X-rays.

These phenomena, put in relation with dormancy in Triticum durum, cv. « Cappelli », which is a relative dormancy, having its maximum at the milk stage, have led the author to the general conclusion that, during dormancy, a germination inhibitor occurs in the embryo of wheat seed; when dormancy is finished, the inhibitor appears in the endosperm, in a situation which becomes stable and definitive.     

Comportamento Alla Germinazione e Mutabilità Cromosomica Spontanea in Triticum Durum Desf. Durante I Primi Due Anni di Vita del Seme

Abstract

Germination and spontaneous chromosome mutations in Triticum durum Desf. during the first two years of storage of the seed. — Spontaneous chromosome aberrations were recently observed in the meristem of radicles of seedlings raised from seeds (caryopses) of Triticum durum cv. Cappelli erop 1966. Germination and frequency of chromosomal aberrations, starting from the ripening of the caryopses to the end of the second year of their storage at room temperature were investigated. Cytological analysis and germination tests were accomplished at monthly intervals. It was shown that: 1) soon after ripening, the germination process was very slow, but chromosomal damage was high; 2) at the end of the dormancy period the percentage of aberrant anaphases and of chromatid breaks fell to a «minimum». This low chromosomal damage lasted for almost the whole of the two years of storage; 3) the nuclear damage was esclusively of chromatide type. This result and fact that the cytological damage is decreasing with time, are interpreted as evidence that the mutagenic agent(s) responsible is (are) more active during the germination period than during the quiescence of the embryo.     

Azione della luce sulla crescita allo stadio di plantula di un mutante clorofilliano di Triticum durum Desf

Abstract

ACTION OF LIGHT ON SEEDLING GROWTH IN A YELLOW-GREEN MUTANT OF TRITICUM DURUM DESF. — Dry grains of Triticum durum cv. « Cappelli » and its radiation-induced yellow-green mutant were sown in sand in four environment, different for light conditions (daylight, artificial light, ultraviolet rays, darkness), having all the same temperature (23°C.). Seven days after sowing, the following data were registered: a) growth (in cm.) of the shoot and of the longest root; b) fresh weight (in gr.) of shoots and roots; c) water content of shoots and roots.

The following main results were obtained:

1. the yellow-green mutant always shows less growth and less weight increase than normal « Cappelli », with the exception of the seedlings grown at daylight, which have shorter shoots and longer roots than the normal « Cappelli » but the same weight:

2. artificial light, besides depressing the growth of the roots of the yellow-green mutant, which becomes green under these conditions, induces a remarkable decrease in the water content of the roots of the two wheats.

     

Studio Comparato di Alcuni Effetti Fisiologici Prodotti Dai Neutroni Veloci su Triticum Durum Normale e Bianconato

Abstract

A comparative study of physiological effects induced by fast neutrons on normal and mealy-endosperm seeds of TRITICUM DURUM. — Normal and mealy-endosperm seeds of Triticum durum « Cappelli » were irradiated in the dry state with different doses (700, 1000, 1300 and 1600 rep) of fast neutrons for a study of their radio-sensitivity.

Analysis of growth in sand and field survival shown that the normal seeds are more sensitive than those with mealy-endosperm: this is shown by a greater growth reduction at 14 and 21 days after sowing and a lower survival, especially with the dose 700 rep.     

Marked differences in seed dormancy in two populations of the Mediterranean shrub,Cistus albidus L.

Background: Population structure and dynamics in natural ecosystems can be affected by seed viability and dormancy. However, how the endogenous contents of phytohormones and vitamin E in seeds relative to the environment affect viability and dormancy is not yet fully understood.

Aims: We studied seed viability and germination capacity in two populations of the Mediterranean shrub, Cistus albidus, exposed to contrasting environmental conditions.

Methods: We measured seed viability and germination capacity and endogenous contents of abscisic acid (ABA), gibberellins and vitamin E in seeds collected from two populations, in two environmentally contrasting environments in north-eastern Spain.

Results: Plants growing in the natural site produced seeds with lower germination percentage but similar viability, indicating higher seed dormancy. Enhanced seed dormancy was paralleled with higher contents of ABA and lower contents of gibberellins (GAs). Contents of tocopherols and tocotrienols were higher in seeds of the natural population. Tocopherol contents in seeds correlated positively with the ratio living:total aerial biomass.

Conclusions: Two Mediterranean populations of C. albidus growing in two sites with contrasting environmental conditions showed marked differences in seed dormancy and germination, which may be explained, at least in part, by differences in seed hormonal contents.     

Promoting Effect of Fusicoccin on Seed Germination

The effects of fusicoccin on the germination of dormant, light-requiring or abscisic acid-inhibited seeds has been investigated. (1) Fusicoccin (10^?6M) induces germination in dormant wheat seeds (Triticum durum cv. Cappelli; 1972 crop) and stimulates it in seeds already relieved from dormancy (1971 crop), with an effect similar to that of gibberellic acid. (2) Fusicoccin (1.5 × 10^?6M) is more active than the two phytohormones gibberellic acid and benzyladenine and than white light in stimulating light-requiring lettuce seeds (Lactuca sativa cv. Grand Rapids) to germinate. Germination of radish seeds (Raphanus sativus) is also accelerated by fusicoccin, while benzyladenine and gibberellic acid are less active in this material. (3) Fusicoccin (1.5 × 10^?5M) removes almost completely the inhibitory effect of abscisic acid on germination of radish and lettuce seeds, whereas benzyladenine (10^?4M) and gibberellic acid (3 × 10^?4M) remove the inhibition only partially. The possible relationship between these results and previous information on growth by cell enlargement is discussed in terms of the mechanism of action of fusicoccin as compared with natural hormones.     

Seasonal variation in the bryophyte diaspore bank of open grasslands on dolomite rock

Abstract

Seasonal changes in the diaspore bank of bryophytes and background processes were investigated in two open grasslands on dolomite rock in Hungary by means of soil samples. To test the longevity of propagules and to collect information about their potential dormancy, a part of each sample was stored air-dried in the laboratory for periods of half a year and 1 year. In contrast to results of earlier studies, temporal variation was detected in the number of propagules stored in the soil of three species (Bryum argenteum, Bryum erythrocarpum agg. and Weissia controversa). There is evidence of dormancy in vegetative gemmae of species of the Bryum erythrocarpum complex and Weissia controversa. Dormancy is also hypothesized in spores of Phascum cuspidatum. We suggest that dormancy in bryophyte propagules is less rare than had hitherto been assumed. Probably this is due mainly to the relatively small number of investigations of species living in habitats with periodically unfavourable moisture and temperature conditions.     

Polyamine metabolism during early germination of Triticum durum Desf. cv. Cappelli

Abstract

Changes in polyamine metabolism have been studied during early germination of Triticum durum Desf. cv. Cappelli. In the embryos of dry seeds, the adequate polyamine content decreases with a minimum at 36 h of water imbibition. A great need for polyamines during germination is expressed by reactivation of their biosynthetic enzymes. Putrescine biosynthesis mostly occurs via the ornithine–decar–boxylase pathway until 42 hours of hydration. Arginine–decarboxylase activity, almost absent in the first stages of imbibition, reaches its maximal level around 36–42 hours, when ornithine–decarboxylase falls. These changes suggest that the polyamine metabolism could be differently activated depending on the growth process related to the germination phases.     

Sugli Effetti Provocati Dallo Scambio Degli Embrioni Fra Cariossidi Normali E Bianconate Del Grano “Cappelli”

Abstract

Effects induced by the exchange of embryos between normal grains and yellow-berries of « Cappelli » (Triticum durum Desf.). — Normal grains of « Cappelli » give seedlings, the shoots of which are longer than those coming from yellow-berries (Meletti e Onnis, 1961, a). The exchange of embryos between the two grain types shows the influence of endosperm on the seedling growth: the normal endosperm stimulates, while the yellow-berries endosperm depresses. The causes of this phenomenon are to research probably within the limits of the relationship, at biochemical level, between embryo end endosperm, with special regard to a likely different hormonic situation in normal grains and yellow-berries.     

Althenia filiformis Petit: contributo alla conoscenza della ecologia della germinazione

Abstract

New data on the ecology of germination of Althenia filiformis Petit. – The author investigated the natural environment where this species, halophyte and hydrophyte, germinates. The relationships between temperature, salt concentration of pools in which Althenia filiformis lives, and the dormancy of seeds were examined. In particular the author studied the behaviour of this species considering the natural conditions of pools of Orbetello (Tuscany) and Simbirizzi (Sardinia).     

Distribution of seed dormancy classes across a fire-prone continent: effects of rainfall seasonality and temperature

Background and AimsDifferent seed dormancy classes control the timing of germination via different cues. The ecological dissimilarities between classes therefore suggest that they are likely to be subject to different selective pressures, and that species within each class will have diverse functional responses. We aimed to investigate this by assessing how variation in the distribution of dormancy classes is correlated with regional environmental factors, in particular rainfall seasonality and temperature. Additionally, we compare the relative proportions of species with physiological (PD) or physical (PY) dormancy to assess whether dormancy class influences their ability to persist under different rainfall seasonality regimes.MethodsDormancy class was assigned for 3990 species from 281 genera occurring across two climate regions, with either winter or aseasonal rainfall, across temperate fire-prone Australia. All regions have similar vegetation and fire regimes. Using a Bayesian framework, we compared the distribution of dormancy classes across temperature and rainfall climate gradients, for threatened and common species.Key ResultsA high dormant:non-dormant species ratio highlighted the critical role of dormancy across our study regions. Critically, species showing PD were more likely to be threatened in aseasonal rainfall climate regions.ConclusionsOur results support the assumption that dormancy is favoured in environments with stochastic disturbance     

Temperature effects on dormancy levels and germination in temperate forest sedges (Carex)

The effects of stratification temperatures and burial in soil on dormancy levels of Carex pendula L. and C. remota L., two spring-germinating perennials occurring in moist forests, were investigated. Seeds buried for 34 months outdoors, and seeds stratified in the laboratory at temperatures between 3 and 18 °C for periods between 2 and 28 weeks, were tested over a range of temperatures. Seeds of the two species responded similarly to stratification treatments, except for an absolute light requirement in C. pendula. Primary dormancy was alleviated at all stratification temperatures, but low temperatures were more effective than higher ones . (≥ 12 °C). Dormancy induction in non-dormant seeds kept at 5 °C occurred when seeds were subsequently exposed to 18 °C. Dormancy was not induced by a transfer to lower temperatures. Buried seeds of both species exhibited seasonal dormancy cycles with high germination from autumn to spring and low germination during summer. Temperatures at which the processes of dormancy relief and of dormancy induction occurred, overlapped to a high degree. Whether, and when, dormancy changes occurred depended on test conditions. The lower temperature limit for germination (> 10%) was 9 °C in C. remota and 15 °C in C. pendula. Germination ceased abruptly above 36 °C. Germination requirements and dormancy patterns suggest regeneration from seed in late spring and summer at disturbed, open sites (forest gaps) and the capability to form long, persistent seed banks in both species.     

Effects of primary seed dormancy on lifetime fitness of Arabidopsis thaliana in the field

Background and AimsSeed dormancy determines the environmental niche of plants in seasonal environments, and has consequences for plant performance that potentially go far beyond the seed and seedling stages. In this study, we examined the cascading effects of seed dormancy on the expression of subsequent life-history traits and fitness in the annual herb Arabidopsis thaliana.MethodsWe planted seeds of >200 recombinant inbred lines (RILs) derived from a cross between two locally adapted populations (Italy and Sweden), and both parental genotypes at the native site of the Swedish population in three consecutive years. We quantified the relationship between primary seed dormancy and the expression of subsequent life-history traits and fitness in the RIL population with path analysis. To examine the effects of differences in dormancy on the relative fitness of the two parental genotypes, we planted dormant seeds during the seed dispersal period and non-dormant seeds during the germination period of the local population.Key ResultsIn the RIL population, strong primary dormancy was associated with high seedling survival, but with low adult survival and fecundity, and path analysis indicated that this could be explained by effects on germination timing, rosette size and flowering start. The relationship between primary seed dormancy and germination proportion varied among years, and this was associated with differences in seasonal changes in soil moisture. The planting of dormant and non-dormant seeds indicated that the lower primary dormancy of the local Swedish genotype contributed to its higher germination proportion in two years and to its higher fecundity in one year.ConclusionsOur results show that seed dormancy affects trait expression and fitness components across the life cycle, and suggest that among-year variation in the incidence of drought during the germination period should be considered when predicting the consequences of climatic change for population growth and evolution.     

Functional analysis in Arabidopsis of FsPTP1, a tyrosine phosphatase from beechnuts,reveals its role as a negative regulator of ABA signaling and seed dormancy and suggests its involvement in ethylene signaling modulation

By means of an RT-PCR approach we isolated a specific tyrosine phosphatase (FsPTP1) induced by abscisic acid (ABA) and correlated with seed dormancy in Fagus sylvatica seeds. To provide genetic evidence of FsPTP1 function in seed dormancy and ABA signal transduction pathway, we overexpressed this gene in Cape Verde Island ecotype of Arabidopsis thaliana, which shows the deepest degree of seed dormancy among Arabidopsis accessions. As a result, 35S:FsPTP1 transgenic seeds showed a reduced dormancy and insensitivity to ABA and osmotic stress conditions accompanied by a reduction in the level of expression of RAB18 and RD29, well-known ABA-responsive genes. Taken together, all these data are consistent with a role of this tyrosine phosphatase as a negative regulator of ABA signaling. In addition, phenotypes of FsPTP1 transgenic plants resemble those observed in ethylene constitutive mutants, accompanied by an increase in the level of expression of a key gene involved in ethylene signaling such as EIN2. All the data presented along the paper suggest that the effect of tyrosine phosphatases in ABA action during the transition from seed dormancy to germination may be through modulation of ethylene signaling.     

A major QTL for resistance to soil-borne cereal mosaic virus derived from an old Italian durum wheat cultivar

Abstract

The genetic basis of resistance to soil-borne cereal mosaic virus (SBCMV) in the Triticum turgidum L. var. durum cv. Neodur was analyzed in this study, using a linkage mapping approach. We performed phenotypic and molecular analyses of 146 recombinant inbred lines derived from the cross Cirillo (highly susceptible)×Neodur (highly resistant). A major quantitative trait locus (QTL) that explained up to 87% of the observed variability for symptom severity was identified on the short arm of chromosome 2B, within the 40-cM interval between the markers Xwmc764 and Xgwm1128, with wPt-2106 as the peak marker. Three minor QTLs were found on chromosomes 3B and 7B. Two markers coding for resistance proteins co-segregate with the major QTL on chromosome 2B and the minor QTL on chromosome 3B, representing potential candidate genes for the two resistance loci. Microsatellite markers flanking the major QTL were evaluated on a set of 25 durum wheat genotypes that were previously characterized for SBCMV resistance. The allelic composition of the genotypes at these loci, together with pedigree data, suggests that the old Italian cultivar Cappelli provided the SBCMV-resistance determinants to durum cultivars that have been independently bred in different countries over the last century.     

Effect of light and gibberellic acid on chromosome endoreduplication in leaf epidermis ofTriticum durum Desf.

Summary The first foliage leaf ofTriticum durum Desf., cvs. Capelli and Creso, was studied for the action of light and gibberellic acid on different aspects of plant growth. Creso is a short-strawed cultivar carrying theRht 1 gene, that influences both plant height and sensitivity to applied gibberellins. In this study, a cytophotometric analysis of chromosome endoreduplication in bulliform cells of the leaf epidermis was undertaken. The bulliform cells are arranged in long rows and comprise 4C, 8C, and 16C cells. The relative percentage of these cells was recorded under different light regimes and in the presence or absence of gibberellic acid (GA₃). Our data indicate that light strongly affects the occurrence of chromosome endoreduplication. Although cvs. Cappelli and Creso show the same frequency of endo-reduplicated cells in the dark, all light treatments induce lower endo-polyploidy in cv. Creso whereas, in cv. Cappelli, a reduction in endo-polyploidy is observed when plants are irradiated with blue-lacking lights. This indicates that the action of a blue-light responsive photo-receptor determines high endopolyploidy. With respect to GA₃ treatment, cv. Creso is again shown to be insensitive to hormone application, whereas in cv. Cappelli, gibberellic acid influences endopolyploidy level in the dark, causing very high frequencies of 8C cells and relatively high frequencies of 16C cells.This paper is dedicated to the memory of Sergio Baroncelli, Professor of Plant Breeding at the University of Pisa.