Plant growth and cultivation under environmental stresses

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We have studied the mechanisms useful for the adaptation of plants to the conditions of environmental stresses.(1) We found a new gravimorphism of plants using agravitropic mutants of rice and barley.Furthermore, we discovered that gravimorphogenesis of cucurbitaceous seedlings was negatively controlled by gravity, which was accounted by the threshold theory of auxin concentration. By cloning and expression analysis of auxin-inducible genes and its transcriptional factor, we established a working hypothesis for the auxin regulation of the gravity's negative control.(2) A variety of wheat, Hong Mang Mai, was found to be tolerant to deep-seeding conditions in semi-arid area because it was super-sensitive to gibberellins in inducing strong elongation of the first internode. Surprisingly, the presence of potassium in culture media was absolutely required for the GA-induced elongation.(3) We established the experimental system for the study of hydrotropism in the roots of cucumber and Arabidopsis. It was found that auxin transport and distribution, calcium ion, abscisic acid and endo-xyloglucan transferase played important roles in root hydrotropism.(4) We established a model system for the study of the high-temperature-induced injury of the reproductive growth in barley. It was suggested that the expression of a calcium-dependent protein kinase was involved in the male sterility caused by high-temperature stress. We also discovered some genes that could be induced or suppressed in response to high temperature by adopting the serial analysis of gene expression.We have cloned several genes responsible for above responses of plants, which accounted, at least in part, for the mechanisms of plant adaptation to particular environment such as gravitational field and arid area. The accomplishments of the present study may lead to the development of new plants and regulatory methods of plant growth for improving crop yield.