PHOTOSYNTHESIS IN LEAVES, FRUITS, STEM AND PETIOLES OF GREENHOUSE-GROWN TOMATO PLANTS

Gross photosynthetic capacity (P-G) Of greenhouse-grown tomato plants (Lycopersicon esculentum Mill.) decreased as the leaf aged. The P-G of the 10(th), 15(th) and 18(th) leaves from the top was only 76, 37, an d 18 % of PG of the 5(th) leaf, respectively Quantum yield (Y-Q) and d ark respiration rate (R-D) were also lower in older leaves than in the younger ones. Net photosynthetic rate (P-N) was apparent in young fru its (about 10 g FM) or young petioles but no P-N was found in large fr uits (40 g or more FM) and stems because of high R-D. Both P-G and R-D were lower in older fruits and petioles or in lower parts of the stem compared to the younger ones or upper parts of stem. A sharp decrease in chlorophyll (Chl) content was only measured in the senescing 18(th ) leaf. The Chl content in petioles, stems and fruits was proportional to P-G. Decreases in P-G of older leaves were attributed to decreases in content rather than activity of ribulose-1,5-bisphosphate carboxyl ase/oxygenase (RuBPCO) since soluble protein content was lower in olde r leaves than in the younger ones but the specific activity (activity per unit of protein) of RuBPCO was not so. The estimated values of P-N of the 10(th), 15(th) and 18(th) leaves inside the canopy were only 5 0, 21, and 7 % of that in the 5(th) leaf. Therefore, leaves below the 18(th) can be removed in order to ensure a good air circulation and pr event diseases. The significance of photosynthesis in fruit, stem and petioles is not negligible because photosynthesis re-fixes the respire d CO2.