Genetic basis of barley caryopsis dormancy and seedling desiccation tolerance at the germination stage.

The genomic regions controlling caryopsis dormancy and seedling desiccation tolerance were identified using 152 F4 lines derived from a cross between Mona, a Swedish cultivar, and an Israeli xeric wild barley Hordeum spontaneum genotype collected at Wadi Qilt, Israel. Dormancy, the inability of a viable seed to germinate, and desiccation tolerance, the ability of the desiccated seedlings to revive after rehydration, were characterized by fitting the germination and revival data with growth curves, using three parameters: minimum, maximum, and slope of germination or revival rate derived by the least square method. The genetic map was constructed with 85 genetic markers (SSRs, AFLPs, STSs, and Dhn genes) using the MULTIPOINT: -mapping algorithm. Quantitative trait loci (QTLs) mapping was conducted with the MULTIQTL: package. Ten genomic regions were detected that affected the target traits, seven of which affected both dormancy and desiccation tolerance traits. Both the wild barley genotype and the Swedish cultivar contributed the favorite alleles for caryopsis dormancy, whereas seedling desiccation tolerance was attributed to alleles descending from the cultivar. The results indicate that some barley dormancy genes are lost during domestication and that dormancy QTLs are associated with abiotic stress tolerance.

The distribution of the phenolic metabolites barbaloin, aloeresin and aloenin as a peripheral defense strategy in the succulent leaf parts of Aloe arborescens.

Aloe arborescens is a large, multi-stemmed shrub. It is used as hedge plants to protect agricultural fields or stock and as horticultural plants in gardens. In natural habitats it is one of the very common Aloe species along the Indian Ocean coast of southern Africa, from the Cape, in the south, to Zimbabwe and Malawi in the north. Secondary phenolic metabolites such as barbaloin (Rf 0.31-0.35), aloeresin (Rf 0.25-0.3) and aloenin (Rf 0.51-0.55) have been found to be distributed in the succulent leaves of Aloe arborescens in a peripheral defense strategy. The youngest leaves have the highest content. The terminal third of each leaf has the highest content and the basal third, the lowest. Along the leaf margins, on the top third and adaxial side, the content is the highest and in the base third, the lowest along the leaf center on the abaxial side. Similar relative amounts of these three secondary phenolic metabolites were found in the different leaf locations. The leaf orientation may affect the total content of these three phenols but not their relative amounts in the different parts of the leaves. It is possible that the more often the plant parts are damaged by consumption by animals such as elephants, kudu or insects, the greater the increase of their phenolic metabolites. This increase may reduce or prevent further consumption when the content of the metabolites reaches a certain level. The plants then have a chance to renew themselves.

Porcupine diggings as a unique ecological system in a desert environment.

The influence of porcupine diggings upon annual vegetation on a north-facing hillslope in the Negev Desert, Israel, has been observed for some 10 years. It was found that within the porcupine diggins there are changes over time in terms of species richness, plant density and plant biomass, and that such changes take place in three stages. During the initial growing season (stage 1), species richness, plant density and plant biomass are lower than in the surrounding non-disturbed area, followed by progressive plant succession. Subsequently, a maximum level is attained when a dig becomes 50-60% filled in (stage 2). As the extent of filling exceeds 60%, a decrease in species richness, plant density and plant biomass is observed (stage 3). This process concurs with models derived in other ecosystems with animals that create surface disturbances. The role of porcupine diggings as a model of disturbance and recovery is discussed.

Influences of Photoperiodism and light treatments during fruits storage on the phytochrome and on the germination of Cucumis prophetarum L. and Cucumis sativus L. seeds.

Day length, temperature, light quality and hormone treatments given to plants during the ripening of their seeds have been shown to influence the subsequent germination of these seeds. The present work demonstrates that the light conditions, SD, LD or continuous dark, red or far-red light, during storage of ripe fruits of Cucumis prophetarum and Cucumis sativum strongly influence the capacity of seeds, later removed from these fruits, to germinate in darkness.Direct measurement of phytochrome in seeds showed that the various light treatments (continuous dark, red or far-red light but not long or short days) directly affected the quantity of photoreversible phytochrome and more importantly, the percentage of active phytochrome P 730 which is critical for germination. The possible physiological implications of those results are discussed. It seems that the environment affects the dark germination of cucumber seeds through two different pathways: a phytochrome controlled and a daylength dependent mechanism.

The influence of the origin of the mother plant on yield and germination of their caryopses in Aegilops ovata.

Dispersal units of Aegilops ovata contain in their spikelets caryopses differing in morphology, weight and germinability according to their position in the spikelets. Plants originating from caryopses of the diverse orders were grown under various photo- and thermoperiodic conditions, and the caryopses harvested germinated under uniform conditions. Under all conditions tested, the relative difference in weight between the caryopses of the various orders was not affected. But plants grown under long days and/or low temperatures produced heavier caryopses than plants grown under short days and/or high temperatures respectively. There was a positive correlation between weight and germinability in caryopses of the various orders derived from one mother plant, and a reverse correlation in caryopses formed on mother plants grown under low and high temperatures. When mother plants arising from various orders of caryopses were grown under long days and low temperatures, they produced caryopses of different germinability, showing that the origin of the mother plant may affect the germination qualities of its offspring. The implications of these results are discussed.

Delayed seed dispersal and rapid germination as survival mechanisms of the desert plant Blepharis persica (Burm.) kuntze.

Experiments are described which demonstrate that the seeds of the desert species Blepharis persica are capable of germinating within 50 min of being exposed to moisture. Their radicles reach a length of about 49 mm within the first 24 h from wetting. The seeds can germinate in light and dark at temperatures ranging from less than 10° C to more than 40° C. The importance of these facts for survival are discussed.