Photosynthetic activities of vegetative and fruiting tissues of tomato

Photosynthetic activities of different chlorophyll-containing parts of tomato plants (Lycopersicon esculentum Mill. cv. Saporo) were assessed using chlorophyll fluorescence techniques. Trusses selected for study contained near mature, green fruit and measurements were carried out on the truss peduncle, pedicels, calyces, and fruit. Activities of these tissues were compared with those of adjacent compound leaves considered to be the primary suppliers of photosynthetic assimilates to fruit. All tissues showed high intrinsic efficiencies of photosystem II, measured as FV/FM, in dark-adapted tissue (range 0.77-0.82). Maximal photosynthetic electron transfer activities varied from 110 to 330 mol m^-2 s^-1. With increasing photon flux density there was a gradation of tissue activity with actual photosynthetic yields, electron transport rates and photochemical quenching coefficients (qP) of tissues decreasing in the order: upper leaf lamina, lower leaf lamina, leaf petiole, truss peduncle, pedicel, calyx, and fruit. The reverse order was found for the rapidity at which absorbed photon energy was diverted to non-photochemical pathways as photon flux density was increased. The onset of FO quenching at high photon flux densities suggested that all tissues contained a regulated mechanism for dissipating excess energy as heat. It was concluded that the non-leaf green tissues of tomato are quite active photosynthetically and therefore potentially contribute significantly to plant growth. At a photon flux density of 185 mol m^-2 S^-1, 29% of photosynthetic electron transport activity on a surface area basis was located in tissues other than leaf laminae, with fruit accounting for 15%.