Impermeable seed coats, i.e. physical dormancy (PY) influence the germination ecology of plants from 18 angiosperm families. Astragalus adsurgens (Fabaceae; Papilinoidaae) is a perennial plant widespread in temperate regions that is thought to produce both permeable and impermeable seeds. Why seeds vary in the permeability of their coat, in addition to the mechanisms by which impermeable seeds break dormancy, are not completely understood. However, seeds are often consumed by herbivores; a phenomenon that might facilitate the germination of impermeable seeds. Here, we tested whether: (1) moisture content plays a significant role in the onset of seed coat impermeability (and therefore PY) at similar ranges reported for species from tropical ecosystems; and (2) the presence of impermeable coats offer any benefits for seed survival when consumed by animals. We tested these hypotheses using A . adsurgens seeds collected from Inner Mongolia, China. Freshly collected seeds with a moisture content of 9.7% were permeable to water and therefore not physically dormant. However, seeds became impermeable when dried below a threshold of 6.5% moisture content. Treating impermeable seeds with hydrochloric acid effectively broke dormancy. Scanning electron microscope (SEM) revealed that HCl treated seeds had a narrow opening in the hilum and extra-hilar regions, through which water entered. Seeds with impermeable coats survived significantly better than permeable seeds when consumed by cows. Irrespective of coat permeability, most seeds were egested between 12 and 24 h. In seeds that maintained dormancy after gut passage, this was broken by additional acid scarification. Overall results suggest that: (1) seed coat impermeability is induced by reduced moisture content; (2) imbibition primarily occurs at the hilum and extra-hilar region; and (3) impermeable seeds may benefit from endozoochory.

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Different plants have physiological responses under Al stress, but there is no systematic study to examine physiological responses of herbaceous plants under Al stress. The aim of this study is to investigate the effect of Al on physiological characteristics of four herbaceous plants, which distributed in red soil area in South China, and to analyze the differences in physiological responses to Al stress between the four herbaceous plants. Four herbaceous plants (Pharbitis nil, Cassia occidentlis, Echinochloa colonum and Aeschynomene indica) were used, and the seed germination percentage, the contents of chlorophyll, proline, and malondialdehyde (MDA), membrane permeability (MP), soluble sugar, and activities of peroxides (POD) and catalase (CAT) in leaves under five Al 3+ treatments (0, 80, 400, 2 000, and 10 000 mg/L) were assayed with the sand culture method. The results showed remarkable effects of Al 3+ on physiological characteristics of these four herbaceous plants. The seeds of all the four species could not germinate at 10 000 mg/L, and the growth of all plants were retarded under the 2 000 mg/L Al 3+ treatment. Compared with the control, 2 000 mg/L Al 3+ significantly (P < 0.05) reduced the contents of chlorophyll a and chlorophyll a + b, and increased the contents of MDA and MP. The content of proline increased very significantly (P < 0.01) and activities of POD and CAT were depressed. The contents of MDA and MP in leaves of P. nil and A. indica decreased, and the activities of POD and CAT in leaves of the two plants increased under 80 mg/L and 400 mg/L. However, the changes in C. occidentlis leaves were opposite to those of the above two plants. The changes in leaves of E. colonum were similar to those of P. nil and A. indica at 80 mg/L, but were opposite to those at 400 mg/L Al 3+ . It is suggested that plants with higher activities of POD and CAT, more contents of chlorophyll and proline, and lower contents of MDA and MP consequently improve the tolerance to Al stress under low and middle Al treatments.

In order to understand the roles of abscisis acid in soybean exposed to UV-C radiation, soybean seedlings were exposed to UV-C radiation and ABA was applied. The chlorophyll content, active oxygen metabolism and flavonoids content of soybean seedlings were investigated. The present study revealed that UV-C radiation significantly attenuated the chlorophyll content and suppressed PSII activity. It was observed that the contents of H 2 O 2 , malondialdehyde and O 2 were markedly increased, and the activities of antioxidant enzymes such as superoxide dismutase, peroxidase and catalase were enhanced, so were the flavonoids content, whereas the seedling height and biomass were significantly reduced. ABA application improved the activities of superoxide dismutase, peroxidase, catalase and the contents of flavonoids, decreased the contents of H 2 O 2 , MDA and O 2-, and also increased the chlorophyll content and enhanced PSII performance, thus enhancing biomass accumulation. The results suggested that ABA alleviated UV-C damage to soybean seedlings by reducing ROS generation and enhancing antioxidase activity. The isoflavones daidzin and genistein were significantly responsive to UV-C.

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