DROUGHT AND SALINITY STRESS: CHANGES IN HYDRATASE AND DEHYDRATASE ACTIVITIES OF THYLAKOID-ASSOCIATED CARBONIC ANHYDRASE IN PEA SEEDLINGS

摘要

Changes in hydratase and dehydratase activity of thylakoid-associated carbonic anhydrase (tCA) was examined and compared with the changes in photosynthetic electron transport in pea seedlings exposed to drought and salinity stresses (for 24 h and for 48 h) in combination with additional nonstressed (recovery) time (48 h). It was established that drought and salinity stresses provoked different effects on tCA activity. The hydratase reaction increased by ～2.5 times in plants exposed to 24 h of dehydration, while the salt treatment caused a sharp increase in hydratase reaction only after 48 h of exposure. There was a decrease in dehydratase activity in drought-stressed plants, while in salt-stressed plants it increased after 48 h of exposure. As for recovery, all CA activities returned to control levels after 48 h except hydratase activity after the salinity treatment, where 25% higher values were observed. Electron-transfer rates through the whole electron-transport chain displayed constant behavior under both stress treatments, while photosystem II (PSII) activity decreased by 35%. During the recovery period, whole electron-transport chain rate did not change, while PSII recovered to some extent. We observed that, after subjecting pea plants to drought or salt stress (for 24 h and for 48 h), inhibition of carbon fixation on illumination showed no correlation between changes in measured tCA (hydratase and dehydratase activity) and PSII activity. We nevertheless argue that under our low-CO2 conditions, luminal thylakoid CA obtained as a 27-kDa polypeptide has an important adaptive role in the thylakoid membrane-mediated CO_2-concentrating mechanism.