This study provides a comparative analysis of the dormancy and germination mechanisms of the indehiscent fruits of hoary cress (Lepidium draba L.) and hairy whitetop (Lepidium appelianum Al-Shehbaz), two invasive weeds of the Brassicaceae. Germination assays comparing isolated seeds (manually removed from the fruits) and intact indehiscent fruits showed that the isolated seeds are nondormant and provided full germination for both species. In contrast to this, the species differed in the germination properties of their indehiscent fruits, in that L. appelianum fruits were nondormant, while the L. draba fruit coat (pericarp) conferred a coat-imposed dormancy. The pericarp of L. draba fresh fruit was water permeable, and neither mechanical scarification nor surface sterilization affected germination, supporting the concept that pericarp-mediated dormancy was not due to water impermeability or mechanical constraint. Washing of L. draba fruits with water, afterripening (dry storage), and treatment with gibberellin (GA) stimulated the germination of this species, all of which are indicative of physiological dormancy. Analyses of endogenous abscisic acid (ABA) and GA levels combined with treatment experiments with wash water from fresh and afterripened L. draba pericarps and with ABA dose–response quantification of germination revealed that ABA is a key component of a pericarp-mediated chemical dormancy in this species. Consistent with this, pericarp ABA levels decreased during afterripening and upon fruit washing, and isolated fresh or afterripened seeds did not differ in their ABA sensitivities. The possible roles of the ABA-mediated pericarp dormancy for the germination ecophysiology and weed management of these species are discussed.

Although pear species (Pyrus spp.) are widely cultivated as an important fruit tree in the world, the regulatory mechanism of their seed dormancy is still unclear. In this research, the role of endocarp, seed coat and embryo in sand pear (Pyrus pyrifolia) seed dormancy was analysed by detecting the endogenous abscisic acid (ABA) and analysing germination experiments with different treatments. The results suggest that a combination of testa and embryo impose sand pear seed dormancy. The high concentration of endogenous ABA in the embryo effectively inhibited seed germination. The high concentration of ABA in the endocarp, as well as in the testa, suggests that dissipation and/or degradation of endogenous ABA in imbibed embryos were suppressed to maintain ABA-inhibited germination. The ABA and gibberellic acid (GA) key signalling genes, including ABI3–5, GAI, RGA and RGL2, were cloned and their expression was analysed in ABA-treated embryos and embryos of imbibed nutlets, imbibed true seeds (endocarp removed) and GA-treated true seeds. The results revealed regulation by ABA of the expression of ABA and GA signalling factors controlling the dormancy release of sand pear imbibed seeds.

Increased leaf phosphorus (P) concentration improved the water-use efficiency (WUE) and drought tolerance of regularly defoliated white clover plants by decreasing the rate of daily transpiration per unit leaf area in dry soil. Night transpiration was around 17% of the total daily transpiration. The improved control of transpiration in the high-P plants was associated with an increased individual leaf area and WUE that apparently resulted from net photosynthetic assimilation rate being reduced less than the reductions in the transpiration (27% vs 58%). On the other hand, greater transpiration from low-P plants was associated with poor stomatal control of transpirational loss of water, less ABA in the leaves when exposed to dry soil, and thicker and smaller leaf size compared with high-P leaves. The leaf P concentration was positively related with leaf ABA, and negatively with transpiration rates, under dry conditions (P < 0.001). However, leaf ABA was not closely related to the transpiration rate, suggesting that leaf P concentration has a greater influence than ABA on the transpiration rates.

The presence and variation of activity of the type 1 ribosome-inactivating protein saporin has been evaluated in cultured roots of the soapwort Saponaria officinalis. Results from western analysis and in vitro protein synthesis inhibition indicate that saporin production is increased in senescing cultures, reaching a maximum value during the late stationary phase. Accordingly, cultures treated with the senescence-related hormone abscisic acid show a significant increase in saporin activity, independently from the culture growth phase. Stress conditions, such as the presence of hydrogen peroxide in the culture medium, had no effect on the modulation of enzymatic activity. The putative regulation of saporin production by abscisic acid and its possible role in accomplishing the ageing programme is discussed.

The use of genetics in plant biology aims at the physiological and molecular genetical characterization of the phenotypic variation for the trait under study. Efficient mutant and gene isolation procedures have been developed for a number of plant models such as Arabidopsis thaliana. For this, the map position of the genes and insertion mutagenesis are used. The latter also allows the characterization of genes that are not easily recognized in mutant approaches, by using enhancer or gene-trapping procedures and reverse genetics. In addition to mutants, natural variation present among wild and cultivated varieties of a species provides an important source of genetic variation. The use of molecular markers, advanced mapping populations and specific cytogenetic stocks in case of polyploids, enables a detailed characterization of such natural variation even when it is of a quantitative and polygenic nature. Examples of the various genetic approaches are given.