TY - JOUR T1 - Comment: Interpretation of Recycling Indices
Response: An Alternative Interpretation of the Appropriateness and Correct Means for the Evaluation of CO2 Recycling Indices. JF - Functional Plant Biology JO - Functional Plant Biol. Y1 - 1997 VL - 24 IS - 3 SP - 395 EP - 405 KW - UR - https://doi.org/10.1071/PP96121 N2 - Pretreatment of maize (Zea mays L.) seeds withCaCl2 solution significantly raised calcium andcalmodulin levels and enhanced intrinsic heat tolerance in maize seedlings.This enhancement is specific to Ca2+ and cannot besubstituted by Mg2+. In contrast, treatments with theCa2+ chelator EGTA or plasma membraneCa2+ channel blockers La3+ orverapamil lowered the intrinsic heat tolerance. Concurrent treatment withCa2+ and Ca2+ -channel blockers(La3+, verapamil) also decreased theCa2+ -enhanced heat tolerance. In addition, calmodulinantagonists chlorpromazine or W7 treatment eliminated theCa2+ -enhanced heat tolerance, whilst W5, a less activeanalogue of W7, had little effect on the Ca2+ -enhancedheat tolerance. Measurement of antioxidant enzyme activities and lipidperoxidation showed that heat stress induced an oxidative stress in maizeseedlings. External Ca2+ treatment enabled the seedlingsto keep relatively higher activities of superoxide dismutase (SOD), catalase(CAT) and ascorbate peroxidase (APX) and lower levels of lipid peroxidationthan Ca2+ -deficient treatments; on the contrary, EGTAtreatment led to more rapid loss of SOD, CAT and APX activities and higherlevels of lipid peroxidation in the seedlings under heat stress. In addition,concurrent Ca2+ and W7 treatment weakened the effects ofCa2+ treatment on SOD, CAT and APX activities and causedmore severe lipid peroxidation. These results suggested that externalCa2+ can enhance the intrinsic heat tolerance of maizeseedlings. This enhancement requires the entry of externalCa2+ into cells across plasma membranes and themediation of intracellular calmodulin, and is associated with the increase ofantioxidant system activity. ER -