Changes in Photosynthesis, Carbon Budget and Mineral Content during the Growth of the First Leaf of Cucumber

The relationships between photosynthesis, dry matter accumulationand translocation have been studied during the development ofthe first true leaf of cucumber. The leaf was grown in an irradianceof 50W m^–2 photosynthetically active radiation for 10h^–1 at 20 C and 2 g m^–3 CO₂. The maximum rate of net photosynthesis, on a leaf area basis,occured at full expansion. Photochemical efficiency, based onincident radiation, also increased up to this stage and wasrelated to the concentration of chlorophyll in the leaf. Darkrespiration and the light compensation point fell over the wholeperiod of leaf expansion. A carbon budget analysis showed that the rate of carbon accumulationin the leaf reached a peak at 70 percent expansion. The leafchanged from a net importer to a net exporter of carbon whenit was about 30 percent expanded. The rate of export increasedwith leaf expansion (and with net photosynthesis) and was twiceas high in the day an in the night at full expansion. At fullleaf expansion there was a reduction in the amount of starchlost overnight, and the carbon exported amounted to 80 per centof the daily net carbon fixed. Cucumber, Cumic satinu L., leaf development, photosynthesis, translocation, carbon budget, mineral content