CARBOHYDRATE-METABOLISM IN LEAVES AND ASSIMILATE PARTITIONING IN FRUITS OF TOMATO (LYCOPERSICON-ESCULENTUM L.) AS AFFECTED BY SALINITY

Salinity improve tomato fruit quality by enhancing hexose accumulation . To study the involvement of the carbohydrate influx into fruits unde r saline conditions, we have studied carbohydrate metabolism in leaves and the partitioning of photosynthetic C-14 in fruits of tomato pla:l ts exposed to 0, 50, or 100 mM NaCl. Carbohydrate content and the acti vity of ADP-Glc-PPase (EC 2.7.7.27) in the fruits were also determined at different stages of fruit development. Photosynthesis rates per un it leaf area were only slightly affected by moderate salinity (50 mM N aCl) while causing a considerable inhibition of leaf area expansion. S ucrose concentration was higher in leaves of plants exposed to NaCl th an in non-saline controls, correlating with the enhanced activity of s ucrose phosphate synthase (EC 2.3.1.14) and with the low activity of a cid invertase (EC 3.2.1.26). Salinity enhanced the transport of C-14-a ssimilates from the pulse leaf to adjacent fruits and the diversion of C-14 label to the starch fraction of the fruit. It also prolonged the period of starch accumulation in developing fruits. The immature frui t from salinity-treated plants showed significant higher activity of A DP-Glc-PPase with approximately twofold higher starch content than in controls. It is concluded that, under saline conditions, both a higher concentration of sucrose in the leaves and a faster rate of starch sy nthesis in the immature fruit may constitute part of a mechanism respo nsible for a higher sugar content in the mature fruit. (C) 1998 Elsevi er Science Ireland Ltd. All rights reserved.