Transformation of Japanese persimmon (Diospyros kaki Thunb.) with apple cDNA encoding NADP-dependent sorbitol-6-phosphate dehydrogenase.

Japanese persimmon (Diospyros kaki Thunb. cv Jiro) was transformed with apple (Malus x domestica Borkh.) cDNA encoding NADP-dependent sorbitol-6-phosphate dehydrogenase (S6PDH) by an Agrobacterium-mediated leaf-disc transformation system. Integration and expression of the transgene were confirmed by genomic DNA blot and immunoblot analyses. Sorbitol accumulation in five of six transgenic plants obtained was confirmed by GC-MS. The amount of sorbitol in the leaves of transgenic plants varied from 14.5 to 61.5 µmol g(-1) fr wt(-1). Sorbitol was not found in leaves of non-transformed 'Jiro' or the line PS7 that produced S6PDH protein with no S6PDH activity. Eventually, two transformed lines producing high (PS1) and medium (PS6) amounts of sorbitol, one control transformed line (PS7), and non-transformed 'Jiro' were selected and evaluated for salt-stress tolerance. Under NaCl stress, the activity of photosystem II in leaves was determined in terms of the ratio of the variable (Fv) to the maximum (Fm) fluorescence of chlorophyll. The rate of decline in Fv/Fm under NaCl stress was lower in PS1 than the other three lines, suggesting that PS1 is more tolerant to NaCl stress than the other three lines. The factors that caused enhanced salt stress tolerance in PS1 are discussed in relation to sorbitol biosynthesis and its growth.