EFFECT OF SALINITY IN THE EARLY STAGES OF TOMATO FRUIT-GROWTH

In tomato fruits, fruit fresh weight as well as the accumulation of dr y matter as sugars or starch are markedly affected by salinity and dro ught. These changes are already apparent three weeks after fruit set, but the effects of salinity on earlier stages of fruit development had not been characterized. The accumulation of soluble sugars and starch , and the activity of ADPG pyrophosphorylase (enzyme which controls a rate-limiting step of starch synthesis) were studied in the first twen ty days after fruit set, in Fruits of two tomato cultivars which diffe r in salt tolerance. Plants of tomato Lycopersicon esculentum Mill. cv s. Ace, salt sensitive, and Edkawi, salt tolerant, were subject to hig h salinity levels (200 mM NaCl) in sand culture. Flowers were hand-pol linated, and fruits were harvested on day 5,10,15 and 20 after pollina tion (DAP). As expected, salinity decreased fruit fresh weight, in bot h cultivars. Starch and soluble sugar content per lit fresh weight inc reased as a function of fruit age in this period, and were significant ly higher in fruits from salinized plants than in controls. ADPG pyrop hosphorylase activity did not change significantly in fruits from non- salinized plants in the course of this study and it increased under sa linity in cv. Ace. Starch accumulation, however, was not related to th e in vitro activity of ADPG pyrophosphorylase. It is concluded that ca rbohydrate metabolism in the very early stages of fruit development is sensitive to saline stress. However, no correlation between salt tole rance and carbohydrate accumulation could be observed in this period.