TECHNOLOGIES FOR IMPROVING TOLERANCE TO ENVIRONMENTAL STRESS: GENETIC ENGINEERING OF SALT STRESS TOLERANCE IN JAPANESE PERSIMMON (DIOSPYROS KAKI) WITH THE GENES INVOLVED IN BIOSYNTHESIS OF COMPATIBLE SOLUTE

Many organisms, including certain plants, accumulate water-soluble organic compounds of low molecular weight that have no inhibitory effects on metabolism. These compounds are referred to as compatible solutes and allow them to tolerate certain types of environmental stress not only by adjusting osmotic pressure in cells but also by stabilizing the quaternary structures of complex proteins. Recent studies have shown that enhancement of tolerance to environmental stresses in plants can be achieved by genetic engineering of the biosynthesis of compatible solutes. All these studies, however, deal with herbaceous plant species. We selected Japanese persimmon (Diospyros kaki), which is one of the major fruit crops in Japan and susceptible to damage from salt and drought stresses, as a candidate for the first woody plant species to be genetically engineered for tolerance to environmental stress by transforming the genes involved in compatible solutes. Chimeric genes constructed from the choline oxidase gene of Arthrobacter globiformis and the cDNA for sorbitol-6-phosphate dehydrogenase of apple (Malus x domestica) were integrated into the persimmon genome to confer the ability to produce glycinebetaine and sorbitol, respectively. Tolerance to salt stress of transformed persimmon plants were determined by measuring the ratio of the variable (Fv) to the maximum (Fm) fluorescence of chlorophyll in leaves under NaCl stress. The rate of decline in Fv/Fm under NaCl stress was lower in transgenic persimmon plants producing glycinebetaine or sorbitol than control transformed and non-transformed lines.

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