The effect of temperature of the rate of photosynthetic electron transfer in chloroplasts of chilling-sensitive and chilling-resistant plants

Abstract

1. Photochemical activities as a function of temperature have been compared in chloroplasts isolated from chilling-sensitive (below approximately 12 °C) and chilling-resistant plants. 2. An Arrhenius plot of the photoreduction of NADP + from water by chloroplasts isolated from tomato ( Lycopersicon esculentum var. Gross Lisse), a chilling-sensitive plant, shows a change in slope at about 12 °C. Between 25 and 14 °C the activation energy for this reaction is 8.3 kcal·mole −1. Between 11 and 3 °C the activation energy increases to 22 kcal·mole −1. Photoreduction of NADP + by chloroplasts from another chilling-sensitive plant, bean ( Phaseolus vulgaris var. brown beauty), shows an increase in activation energy from 5.9 to 17.5 kcal·mole −1 below about 12 °C. 3. The photoreduction of NADP + by chloroplasts isolated from two chilling-resistant plants, lettuce ( Lactuca sativa var. winter lake) and pea ( Pisum sativum var. greenfeast), shows constant activation energies of 5.4 and 8.0 kcal·mole −1, respectively, over the temperature range 3–25 °C. 4. The effect of temperature on photosynthetic electron transfer in the chloroplasts of chilling-sensitive plants is localized in Photosystem I region of photosynthesis. Both the photoreduction of NADP + from reduced 2,6-dichlorophenol-indophenol and the ferredoxin-NADP + reductase (EC 1.6.99.4) activity of choroplasts of chilling-sensitive plants show increases in activation energies at approximately 12 °C whereas Photosystem II activity of chloroplasts of chilling-sensitive plants shows a constant activation energy over the temperature range 3–25 °C. The photoreduction of Diquat (1,1′-ethylene-2,2′-dipyridylium dibromide) from water by bean chloroplasts, however, does not show a change in activation energy over the same temperature range. The activation energies of each of these reactions in chilling-resistant plants is constant between 3 and 25 °C. 5. The effect of temperature on the activation energy of these reactions in chloroplasts from chilling-sensitive plants is reversible. 6. In chilling-sensitive plants, the increased activation energies below approximately 12 °C, with consequent decreased rates of reaction for the photoreduction of NADP +, would result in impaired photosynthetic activity at chilling temperatures. This could explain the changes in chloroplast structure and function when chilling-sensitive plants are exposed to chilling temperatures.