Optimum temperature and phenological stage for determining cellular membrane thermostability in corn and bean

Abstract

Identification of plant tolerance to heat requires novel strategies for measuring plant responses to this stress. Leaf electrolyte leakage is an indirect method that can be utilized as selection criteria for heat tolerance in plants, but it has to be adapted to each species. The objectives of this study were to measure heat-induced leaf electrolyte leakage in corn and bean to determine heat tolerant genotypes, and also to establish the optimal developmental stage for use of electrolyte leakage as selection criteria. This study included two genotypes of corn (Zea mays L.), and other two of bean (Phaseolus vulgaris L.), measured during the vegetative and floral stages. Heat treatments included 40, 50, and 60 degrees C applied to leaf discs during 60 minutes. Electrolyte leakage, estimated as the relative percentage of damage to the cell membrane, was used as criteria for cellular membrane thermostability. Results showed that the greatest amount of membrane electrolyte leakage occurred during flowering for both corn and bean, and the amount of leakage correlated with the genotype tolerance to heat. The temperature which caused the greatest electrolyte leakage depended on the species, 50 degrees C for corn and 60 degrees C for bean. Our results indicate that use of membrane thermostability, measured as electrolyte leakage, is an effective criteria for identifying genotypes tolerant to heat damage during flowering in genetic improvement programs.