CHILLING TOLERANCE OF 10 MAIZE GENOTYPES AS RELATED TO CHILLING-INDUCED CHANGES IN ACC AND MACC CONTENTS

We studied chilling-induced changes of 1-aminocyclopropane-1-carboxyli c acid (ACC) and of 1-(malonylamino)cyclopropane-l-carboxylic acid (MA CC) contents in seedlings of ten maize genotypes with different chilli ng tolerance. Seedlings at the third leaf stage were chilled at 5 degr ees C and at 6% RH. Immediately before and after two and five days of chilling the contents of ACC and of MACC in the third leaf were measur ed. Water content and after recovery - the degree of necrotic injuries and the percentage of seedling survival were also determined. After 2 days of chilling, the ACC content increased in all genotypes investig ated. The increase was significantly higher in the sensitive genotypes than in the tolerant ones. There was a significant correlation betwee n ACC content and necrotic injuries of seedlings. Chilling for 5 days increased the ACC content further and the difference between the two g roups of genotypes still existed.The MACC content increased after 5 da ys of chilling in all genotypes investigated. The increase was greater in the tolerant genotypes than in the sensitive ones. However, the di fference in MACC accumulation between the two groups of genotypes inve stigated was not significant, and thus no correlation between MACC acc umulation and chilling susceptibility was found. The possible causes f or the increase of ACC and MACC contents under chilling conditions and the possibility of using the ACC content as an indicator of chilling tolerance in maize breeding are discussed.