Photosynthesis in leaves, fruits, stem and petioles of greenhouse-grown tomato plants

Abstract

Gross photosynthetic capacity (P G ) of greenhouse-grown tomato plants (Lycopersicon esculentum Mill.) decreased as the leaf aged. The P G of the 10th, 15th and 18th leaves from the top was only 76, 37, and 18 % of P G of the 5th leaf, respectively. Quantum yield (Y Q ) and dark respiration rate (R D ) were also lower in older leaves than in the younger ones. Net photosynthetic rate (P G ) was apparent in young fruits (about 10 g FM) or young petioles but no P N was found in large fruits (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 18th 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 carboxylase/oxygenase (RuBPCO) since soluble protein content was lower in older 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 10th, 15th and 18th leaves inside the canopy were only 50, 21, and 7 % of that in the 5th leaf. Therefore, leaves below the 18th can be removed in order to ensure a good air circulation and prevent diseases. The significance of photosynthesis in fruit, stem and petioles is not negligible because photosynthesis re-fixes the respired CO2.