REGULATION OF PROLINE BIOSYNTHESIS IN KIWIFRUIT BUDS WITH AND WITHOUTHYDROGEN CYANAMIDE TREATMENT

Proline accumulates in kiwifruit (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) buds in spring du ring budbreak and flower differentiation. However, proline accumulatio n occurred earlier, and to a level approximately 6.5 times greater, in buds treated with the dormancy breaking chemical hydrogen cyanamide ( HC). Peak proline accumulation coincided with peak pyrroline-5-carboxy late reductase (P5CR, EC 1.5.1.2) activities in both HC-treated and co ntrol (untreated) vines. Peak levels of P5CR activity were the same in treated and control vines, suggesting that the activity of P5CR does not regulate proline biosynthesis. Omithine-delta-aminotransferase (OA T, EC 2.6.1.13) activity declined over the sampling period and; conseq uently, was nor correlated with proline accumulation in buds from eith er treated or control vines. This suggests that ornithine does not mak e a significant contribution to the proline pool in this system. Pyrro line-5-carboxylate synthetase (P5CS, EC number nor assigned) and P5CR have been cloned from a kiwifruit bud cDNA library. Northern hybridisa tion analyses indicate that both P5CS and P5CR are transcriptionally r egulated. The P5CS northern hybridisation data, together with the P5CR and OAT enzyme data, suggest that glutamate provides the carbon skele tons for proline synthesis end that P5CS transcription has a significa nt role in the regulation of proline biosynthesis in kiwifruit buds. T his role for P5CS is consistent with those reported in other plants an d demonstrates a conservation of the pathway, and its overall regulati on in quite diverse plants. The only difference in the regulation of p roline biosynthesis between kiwifruit buds from control and HC-treated vines would appear to be temporal.