Abstract
Tomato plants were grown using a nutrient film technique to evaluate the effects of salinity on the distribution of photosynthates and sucrose-degrading enzymes in fruit in relation to sink strength. From first flower anthesis until harvest of the 2nd truss, saline treatment of sodium chloride added to the standard nutrient solution to an EC of 8.0 dS/m was applied. The average fruit weight in the salinity treatment was 59% of the control at the mature red stage. Total soluble solids (Brix%) were 6.5% in the control and 9.2% in the salinity treatment. The photosynthetic rate per unit leaf area was decreased by salinity treatment. Salinity decreased 13C assimilation in the whole tomato plant, while it increased the transport and distribution of 13C assimilates to the fruit significantly. The activities of soluble and cell wall-bound acid invertase were not affected by salinity; however, the activity of sucrose synthase in fruit exposed to the salinity was higher than that in the control during fruit development. We concluded that the increase in total soluble solids in fruit subjected to salinity was not only a result of condensation caused by reduced water uptake, but active transport of photosynthates to the fruit due to increase in sucrose-degrading enzyme activities, especially sucrose synthase.
