GROWTH AND PHOTOSYNTHESIS OF LYCOPERSICON-ESCULENTUM (L.) PLANTS AS AFFECTED BY NITROGEN DEFICIENCY

Fully expanded leaves of tomato (Lycopersicon esculentum) growing with either complete or nitrogen-deficient nutrient solution were analysed for leaf water status, gas exchange and chlorophyll fluorescence duri ng the vegetative and reproductive phases. N-deficiency did not affect leaf water relations but did decrease light saturated photosynthetic rate as well as stomatal conductance in the vegetative stage. A lower variable to maximum fluorescence ratio (F-v/F-m) was found in N-limite d plants which also showed an increase in leaf starch content and in s tarch to sucrose ratio. The inhibition of photosynthesis and the alter ation of photosynthates partitioning were responsible for the growth r eduction in N-stressed plants. During the reproductive phase the limit ation of photosynthesis may be due to a large accumulation of starch w hich determines both a decrease in the carbon demand from the sinks an d a decrease in CO2 conductance in the mesophyll.