Endogenous auxin and jasmonic acid levels are differentially modulated by abiotic stresses in rice

Abstract

Abiotic stresses such as drought, salinity, and adverse temperatures are major limiting factors for plant growth and reproduction. Plant responses to these stresses are coordinated by arrays of regulatory networks including the induction of endogenous abscisic acid (ABA), a well documented phytohormone for stress responses. However, whether or how these abiotic stresses affect the endogenous biosynthesis or metabolism of other phytohormones remains largely unknown. Here, we report the changes of endogenous indole-3-acetic acid (IAA) and jasmonic acid (JA) levels and expression of genes related to the biosynthesis or signaling of these hormones in rice under various abiotic stress conditions. The IAA content was decreased after drought stress, but it was significantly increased under cold and heat stresses. And the auxin-regulated gravitropism of root tip was inhibited by cold stress. Many genes involved in the IAA biosynthesis and signaling were changed in transcript level under these stresses, and the changes were essentially in agreement with the change of endogenous IAA level. Interestingly, the endogenous JA content was increased markedly under drought and cold stresses, but it was reduced by heat stress. Accordingly, many genes involved in JA biosynthesis and signaling were induced by drought and cold treatment but these genes were significantly suppressed by heat stress. We concluded that endogenous levels of IAA and JA were differentially regulated by abiotic stresses in rice, implying diverse roles of these hormones in stress responses.

Micronutrients (Zn/Mn), seaweed extracts, and plant growth-promoting bacteria as cold-stress protectants in maize

“…4), similarly reported also by Imran et al [14]. Apart from lipid peroxidation, an increased oxidative degradation of auxins as a consequence of CuZnSOD limitation has been discussed as a mechanism for reduction of plant growth in response to Zn deficiency [6,30]. Accordingly, external Zn/Mn supply to cold-stressed plants inducing an increased SOD activity (Fig.…”

Alterations of Endogenous Hormonal Levels in Plants under Drought and Salinity

“…Despite of these fluctuations, in the literature there are numerous studies showing a JAs endogenous increase under abiotic stresses. For example, JA increased in spear tips of Asparagus officinalis [32], Carica papaya seedlings [33], Pinus pinaster plants [34], Oryza sativa leaves and roots [35] and citrumelo CPB 4475 (a commercial citrus rootstock) [36] exposed to drought. Similarly, under salinity, JA increased in salt-tolerant cv HF tomato from the beginning of salinization, while in salt-sensitive cv Pera it decreased after 24 h of treatment [37].…”

“…Likewise, in Arabidopsis, the activation of YUCCA7 and YUCCA6 [69] gene, encoding a flavin monooxygenase belonging to the tryptophan-dependent auxin biosynthetic pathway, resulted in elevated endogenous Aux levels and enhanced drought tolerance. Recently, [70] reported alterations of IAA levels according to drought severity in rice leaves. Thus, under slight drought IAA level had no significant change, after moderate drought stress IAA level was reduced to about 81%, and after severe drought stress the level of this Aux was reduced to 72% of the control.…”

Emerging Roles of Auxin in Abiotic Stress Responses

“…The overexpression of OsGRX8 in Arabidopsis enhanced tolerance to multiple abiotic stresses and several auxin-responsive genes were found to be upregulated in the transgenics (Sharma et al 2013 ). Based on the microarray and quantitative PCR analysis, differential expression of IAA biosynthesis and metabolism-related genes in different rice varieties have also been reported (Du et al 2013a ). IAA biosynthesis-related genes were found to be upregulated by cold and heat stress, but suppressed by drought stress.…”

“…On the contrary, after 3 days of cold stress, IAA level was estimated to be 1.6-fold higher and after 6 h of heat stress, IAA level was 1.3-fold higher as compared to control. Overall, these observations suggest that abiotic stresses modulate endogenous levels of IAA (Du et al 2013a ). The expression of a GH3 family gene, OsGH3-2 (catalyzing IAA conjugation .1 Schematic diagram depicting crosstalk between auxin, salt and drought stress signalling pathways.…”