Driesenaar, A.R.J. and Malkin, S.  - Weizmann Institute

The susceptibility of citrus leaves to artificially induced photoinhibition was studied. Detached leaves were subjected to illumination by white light at 5 C. The resulting change in the photochemical quantum yield (probed by chlorophyll fluorescence parameters) was measured as the indication of photoinhibition. The main results were: (i) within the range of 500–5400 uEinstein/s per sq.m of photosynthetically active radiation the photoinhibition increased linearily, depending on the total light fluence rather than on fluence rate; (ii) eight different citrus cultivars were equally susceptible to photoinhibition; (iii) "shade" leaves were more sensitive to photoinhibition than "sun" leaves; (iv) young developing leaves were extremely vulnerable. The possible implications to orchards are discussed.