The expression of photosynthetic traits during and following severe chilling stress of European and tropical maize genotypes

Four genotypes of maize (Zea mays L.), one from North‐West Europe, two from tropical highlands and one from tropical lowlands were grown at 24°C until full expansion of the second leaf. Seedlings were then subjected to 2 days at 5°C, with or without a previous conditioning phase at 10°C for 4 days. After stress plants were allowed to recover at 24°C for 5 days. Previous conditioning protected the tropical lowland variety to some extent against losses in chlorophyll content and ribulose I,5‐bisphosphate carboxylase (EC 4.1.1.39) activity by severe chilling stress. Without conditioning heavy losses occurred during the recovery phase. In all other genotypes the values of these traits decreased more with than without conditioning. Phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity was little affected during stress, but declined considerably during the recovery phase, with the exception of the North‐West European genotype. Previous conditioning prevented or retarded losses of NADP+ malate dehydrogenase (EC 1.1.1.82) activity during the stress phase. However, at the end of the recovery phase losses were as high with as without conditioning, and activity was very low in one tropical highland genotype and in the tropical lowland genotype. In summary, the chilling stability of photosynthetic traits was better in the North‐West European genotype than in the tropical ones.