Ethylene biosynthesis in a chilling-sensitive Arabidopsis mutant chs4-2

Abstract

We investigated chilling-induced changes in ethylene levels in Arabidopsis to find plants with distinct patterns of ethylene production in the cold-related biosynthetic pathway. The sensitive mutants identified here included chs1-2, chs4-2, and chs6-2. Among these, plants of the chs4-2 mutant produced more ethylene than did the wild type after both were transferred from 4°C or 10°C to 22°C. This mutant also showed less freezing tolerance and more electrolyte leakage than the wild-type plants. Our results suggest a relationship between ethylene biosynthesis and chilling sensitivity in the mutant. To determine which of the enzymes involved in ethylene biosynthesis were induced by chilling, we tested the activities of ACC synthase and ACC oxidase in both mutant and wild-type plants, and found greater activity by ACC synthase as well as a higher ACC content in the mutants after all the plants were transferred from 10°C to 22°C. However, ACC oxidase activity did not differ between mutant and wild-type plants in response to chilling treatment. Therefore, we conclude that chs4-2 mutants produce more ethylene than do other mutants or the wild type during their recovery from chilling conditions. Furthermore, we believe that ACC synthase is the key enzyme involved in this response.