A Comparison of the Effects of Chilling on Leaf Gas Exchange in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.)

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Abstract
The effects of chilling on the photosynthesis of a chilling-resistant species, pea (Pisum sativum L. cv Alaska) and a chilling-sensitive species, cucumber (Cucumis sativus L. cv Ashley) were compared in order to determine the differences in the photosynthetic chilling sensitivity of these two species. For these experiments, plants were chilled (5.degree. C) for different lengths of time in the dark or light. Following a 1 hour recovery period at 25.degree. C, photosynthetic activity was measured by gas exchange (CO2 uptake and H2O release), quantum yield, and induced chlorophyll fluorescence. The results show that pea photosynthesis was largely unaffected by two consecutive nights of chilling in the dark, or by chilling during a complete light and dark cycle (15 hours/9 hours). Cucumber gas exchange was reduced by one night of chilling, but its quantum yield and variable fluorescence were unaffected by dark chilling. However, chilling cucumber in the light led to reduced CO2 fixation, increased internal leaf CO2 concentration, decreased quantum yield, and loss of variable fluorescence. These results indicate that chilling temperatures in conjunction with light damaged the light reactions of photosynthesis, while chilling in the dark did not.