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Daily temperature drop prevents inhibition of photosynthesis in tomato plants under continuous light

Ikkonen, E. N., Shibaeva, T. G., Rosenqvist, E., Ottosen, C. -O.
Photosynthetica 2015 v.53 no.3 pp. 389-394
Solanum lycopersicum var. lycopersicum, adverse effects, chlorosis, circadian rhythm, leaf development, leaves, photochemistry, photosystem II, plantlets, temperature, tomatoes
The negative effects of continuous light (CL) seen in tomato plants are often claimed to be linked to effects of offsetting the diurnal rhythm. In this study we tested whether a short-term daily temperature drop prevents the decreased photosynthetic performance seen in tomato plants grown under CL. Tomato (Lycopersicon esculentum Mill.) plantlets were grown at constant temperature of 26°C under 16-h day (16D) or 24-h day (24D) at 150 μmol m⁻² s⁻¹ PPFD. Some 24D plants were treated daily by 2 h temperature drop from 26 to 10°C (24D+DROP). Physiological disorder, such as severe leaf chlorosis, a large decrease in net photosynthetic rate, maximal quantum yield of PSII photochemistry, and the effective quantum yield of PSII photochemistry were observed in 24D, but not in 16D and 24D+DROP plants. The daily 2-h drop in temperature eliminated a negative effect of CL on photosynthesis and prevented the development of leaf chlorosis in tomato plants. This could be due to a change in carbohydrate metabolism as the short drop in temperature might allow maintenance of the diurnal rhythms.