The effects of gibberellin A(3) (GA(3)) on natural senescence and the relationship between gibberellins (GAs), abscisic acid (ABA), and senescence are not fully understood. For example, it is still unclear whether GA and ABA act antagonistically. There are only few reports on senescence-related changes in physiological parameters of herbaceous perennials. This study was designed to investigate the effects of exogenous GA(3) on the senescence of aerial parts in a herbaceous perennial species, Paris polyphylla, and to test the hypothesis that GA and ABA display antagonistic effects in this process. Physiological changes associated with senescence, in particular of the hormonal and oxidative metabolisms, were also investigated. GA(3) was sprayed on mature leaves at weekly intervals, which significantly impeded senescence of aerial parts and slowed the decline of pigments and total soluble protein. Treated plants suffered less oxidative stress as revealed by reduced lipid peroxidation, a lower hydrogen peroxide level and modified activities of superoxide dismutase, peroxidase, ascorbate peroxidase, and their respective isozyme profiles. In GA(3) treated plants GA(4)+GA(7) (GAs) levels increased progressively and became significantly higher than those of control plants, whereas ABA increased in controls. When plants were treated with GA-synthesis inhibitor paclobutrazol (PCB), GAs decreased, ABA increased, and senescence was promoted. Application of a mixture of GA(3) and PCB restored the accumulation of GAs, reduced ABA, and ultimately senescence was delayed. These results suggest that GA and ABA play antagonistic roles in the senescence of aerial parts in P. polyphylla, and this process is associated with oxidative stress and regulated by endogenous hormones and extrinsic factors. Possible mechanisms that control this GA(3)-mediated inhibition of senescence are discussed.

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Diosgenin accumulation in cell suspension cultures of Dioscorea zingiberensis C. H. Wright was enhanced by treatment with saccharide elicitors from its endophytic fungus Fusarium oxysporum isolate Dzf17. The crude oligosaccharide was prepared by partial acid hydrolysis of the isolated Dzf17 fungal cell wall fragments. Optimal elicitation of diosgenin production by the isolated Dzf17 oligosaccharide in cell suspension culture was achieved when the oligosaccharide was added to the medium at a concentration of 30 mg/L after 16-day's continuous cell suspension culture, and the cells were cultured for another 8 days before harvesting. By using these optimal conditions, the diosgenin yield of the cultured cells reached its maximum of 5.25 mg/L, which was over a threefold increase.

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Paris polyphylla Smith var. yunnanensis (Franch.) Hand.-Mazz. is a rhizomatous, herbaceous, perennial plant that is used as a medicinal plant with a variety of pharmacological activities. However, the functions of the green, leafy sepal of this plant are poorly understood. The main objectives of this study were to: (a) test the hypothesis that sepals make measurable contributions to fruit development and rhizome growth; and (b) investigate the allocation and partitioning of photosynthates produced by sepals and leaves to fruit and rhizome. Net photosynthetic rate, photosynthetic pigment composition and δ13C values were similar for sepals and leaves. Sepal-darkening and sepal-removal treatments resulted in smaller fruit size and decreased rhizome biomass, whereas fruit removal led to a decrease in calyx size and an increase in rhizome yield and saponin content. Fruit and seed mass were positively and linearly related to calyx size. These results indicate that photosynthates produced by sepals are involved in the fruit growth and seed development and that developing fruit and rhizomes compete for the photosynthates exported by leaves. We propose that the sepals of P. polyphylla function partly as leaves to compensate for reproductive costs. Fruit removal increased carbon partitioning to the rhizome and improved rhizome yield and quality, offering a useful strategy for the domestication of this valuable medicinal plant.