Involvement of abscisic acid in leaf and root of maize ( Zea mays L.) in avoiding chilling-induced water stress

Abstract

In the present study, we investigated the role of abscisic acid (ABA) on chilling tolerance of maize. Two maize genotypes differing in chilling sensitivity (Z7 tolerant and Penjalinan sensitive) were subjected to chilling (5 °C, 12 h photoperiod, 150 μmol m −2 s −1 PPFD) for 3 days under two relative humidity (RH) regimes (60 or 100% RH). Some plants were exogenously treated 24 h before chilling with ABA (100 μM). As expected, high humidity (100% RH) or ABA pre-treatment prevented the leaf water deficit induced by chilling at 60% RH in chilling sensitive Penjalinan plants. ABA pre-treatment improved chilling tolerance of Penjalinan plants, mainly by decreasing leaf conductance and by increasing root water flow. At the leaf level, we found a relationship between ABA content and chilling tolerance in both maize genotypes. No relationship between ABA content and leaf conductance was found. Moreover, during chilling, no differences on leaf conductance between the two genotypes were observed, probably indicating that the different water stress suffered by the two genotypes could be linked to differences in the root water uptake. The rise in leaf ABA content during chilling was independent of the leaf water status, so it must be induced by the low temperature per se, and after a longer cold exposure also by the vapour pressure deficit (VPD) (a higher VPD allows more ABA accumulation). At the root level, we did not observe a relationship between the root hydraulic acclimation to chilling and the root ABA content. Z7 plants chilled at 60% RH had the same root ABA content as those which were chilled at 100% RH and as Penjalinan plants; however, the former showed a higher root hydraulic conductance. The rise in the root ABA content in Z7 plants followed the same pattern as observed in the leaves. In Penjalinan plants, the rise in root ABA content was linked only to low temperatures per se, since it increased in the same way in plants chilled under 60 or 100% RH.