CHILLING OF MAIZE SEEDLINGS - CHANGES IN WATER STATUS AND ABSCISIC-ACID CONTENT IN 10 GENOTYPES DIFFERING IN CHILLING TOLERANCE

The objective of the present paper was to study the relationship betwe en chilling tolerance and chilling-induced abscisic acid (ABA) accumul ation in maize. Ten maize genotypes, five classified as chilling toler ant and five as chilling sensitive, were used. Two of them, Co 125 and F 7, with significant differences in chilling tolerance, were studied in detail. Seedlings at the third leaf stage, without and with previo us acclimation, were chilled at 5 degrees C and at relative humidities (RH) of 65 and 100 %. Immediately before and during chilling the ABA content in the third leaf was measured by RIA. Water content, osmotic potential, and - after recovery - the degree of necrotic injuries were also determined. Chilling of non-acclimated seedlings at 65 % RH caus ed accumulation of ABA in all ten genotypes. The ABA accumulation was significantly higher in the chilling tolerant genotypes than in the ch illing sensitive ones. Chilling of non-acclimated seedlings at 100 % R H, studied in the two inbreds, caused ABA accumulation only in the chi lling tolerant inbred F 7, although there were no significant changes in the water relations. Acclimation (4 days at 14/12 degrees C, 70 % R H) had only marginal influence on the ABA content but increased the ch illing tolerance markedly. The higher chilling tolerance of acclimated seedlings was accompanied by the ability for greater ABA accumulation during chilling, especially in the chilling tolerant inbred F 7. Thre sholds of water content and osmotic potential for the rise of ABA were higher in tolerant than in sensitive genotypes. It is suggested that higher chilling tolerance is related to the ability for greater and fa ster ABA accumulation and better stabilization of water status in resp onse to chilling. Evidence is presented that the rise in ABA is induce d indirectly by chilling-induced water deficit as well as directly by the chilling temperature.