ISHS Acta Horticulturae 554: World Congress on Soilless Culture: Agriculture in the Coming Millennium
DOES CARBOHYDRATE ACCUMULATION AFFECT THE PHOTOSYNTHETIC EFFICIENCY OF TOMATO LEAVES? |
| Authors: | M. Dorais, O. Ayari, G. Samson, A. Gosselin |
| Keywords: | Lycopersicon esculentum, greenhouse, photosynthesis, sugar, photochemical efficiency, photosynthetic electron transport, quantum efficiency, sink activity |
| Abstract:
Under northern latitudes, where light is often the major limiting factor for greenhouse cultures, supplemental light and CO2 enrichment techniques are used to increase productivity of tomato (Lycopersicon esculentum Mill.) plants. Over the long-term, however, loss of photosynthetic efficiency is observed under high light and CO2 levels. In previous experiments (Ayari et al. 2000a, b), we have shown that the photosynthetic rate in the fifth and tenth tomato leaves were maximal early in the morning in May, and then markedly declined during the day even though the incident PPF was still rising. These changes in photosynthetic activity were accompanied by large accumulations of carbohydrate in leaves, especially hexoses and starch. In order to better understand the role of leaf carbohydrate accumulation on the photosynthetic efficiency of greenhouse tomato plant, we investigated the effect of carbohydrate accumulation in source leaves induced by exogenous glucose feeding on the maximum photosynthetic rate (Pmax), on the soluble sugar and starch accumulation, on leaf pigment content, and on the PSII and PSI photochemical efficiencies. In glucose fed leaves, there were marked increases of soluble sugar and starch concentrations accompanied by a decline of Pmax and leaf pigment content. Leaves fed with glucose consistently showed lower maximum and operational  PSII, qP and higher qN than water-control leaves.
Carbohydrate accumulation in tomato leaves induced a preferential loss of the maximum photochemical efficiency of PSII relative to PSI in dark-adapted leaves and a light-induced restriction transport between PSII and PSI.
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