Response of hormone in rice seedlings to irrigation contaminated with cyanobacterial extract containing microcystins

Microcystins released by cyanobacteria affect crop growth and productivity, and even food safety. Plant hormones play a vital role in regulating growth, development and stress response in plants. Therefore, we studied the response of hormones including abscisic acid (ABA), indole-3-acetic acid (IAA), Zeatin (ZT) and gibberellin (GA(3)) as well as hormone balances (IAA/ABA, ZT/ABA and GA/ABA) to cyanobacterial extract containing microcystins (1, 10, 100 and 1000 mu g/L) during stress and recovery periods. Low concentration microcystins (1 mu g/L) promoted growth of rice seedlings by increasing levels of IAA, ZT and GA(3) and maintaining hormone balances. In addition, the up-regulation of OsYUCCA1 increased IAA level in rice roots by promoting IAA biosynthesis. High concentrations microcystins (10, 100 or 1000 mu g/L) inhibited growth of rice seedlings by reducing levels of IAA, ZT and GA(3) and ratios of IAA/ABA, ZT/ABA and GA/ABA due to increased ABA level. The increase in ABA in rice seedlings induced by high concentrations MCs was resulted from up-regulation of OsNCED1, OsNCED3, OsNCED4 and OsZEP to enhance ABA biosynthesis, and was controlled by up-regulating expression levels of OsABAox1-3 for enhancing ABA catabolism as negative feedback. The highest concentration of MCs (1000 mu g/L) caused irreversible damage to metabolisms of IAA and ABA, partly resulting in unrecoverable inhibition on rice growth. All results demonstrate that low-concentration promotion and high-concentration inhibition of microcystins was associated with changes in hormone levels and balances by affecting their metabolisms, and could be helpful for guiding agricultural irrigation with microcystin contaminated water. (C) 2020 Elsevier Ltd. All rights reserved.