S. V. Klimov, N. V. Astakhova, M. A. Bocharova, and T. I. Trunova
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, ul. Botanicheskaya 35, Moscow, 127276 Russia
Received April 26, 1995
Abstract—Tomato (Lycopersicon esculentum L., cv. Sibirskii skorospelyi) and cucumber (Cucumis sativus L.,
cv. Konkurent) plants were grown in soil culture at 18°C, 5 klx, and a 16-h photoperiod to the stage of 3 to
5leaves. The plants were exposed to 6°C for 5 days at the same illuminance and photoperiod. Cold tolerance,
CO2 assimilation rate, water and sugar contents in leaves, and ultrastructure of leaf parenchyma cells and chlo-
roplasts were studied. Most of the cucumber plants did not survive chilling, while the tomato plants remained
undamaged. In cucumber plants, photosynthesis was irreversibly inhibited by the end of the chilling period,
while in tomato plants, photosynthetic activity persisted and subsequently recovered at 18°C. In both species,
chilling decreased leaf water content and the number of thylakoids per granum, whereas sugar content
increased. The cucumber contained five times more starch grains per chloroplast section than the tomato. The
area occupied by starch grains on the chloroplast section increased by five times in cucumber leaves after expo-
sure to cold, while in tomato leaves, this area remained almost unchanged. The cells of both species had no lipid
globules in cytoplasm or plastoglobules in the chloroplasts. It was suggested that the differences in cold toler-
ance of tomato and cucumber plants were caused by contrasting sensitivities of photosynthesis and carbohy-
drate metabolism to low temperatures.
Key words: Lycopersicon esculentum - Cucumis sativus - cold tolerance - photosynthesis - ultrastructure
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