Reduced nitric oxide levels during drought stress promote drought tolerance in barley and is associated with elevated polyamine biosynthesis

Gracia Montilla-Bascón,Frans J M Harren,Julien Mandon,Elena Prats,Simona M Cristescu,Diego Rubiales,Luis A J Mur,Kim H Hebelstrup

doi:10.1038/s41598-017-13458-1

Abstract

Nitric oxide (NO) is a key messenger in plant stress responses but its exact role in drought response remains unclear. To investigate the role of NO in drought response we employed transgenic barley plants (UHb) overexpressing the barley non-symbiotic hemoglobin gene HvHb1 that oxidizes NO to NO3−. Reduced NO production under drought conditions in UHb plants was associated with increased drought tolerance. Since NO biosynthesis has been related to polyamine metabolism, we investigated whether the observed drought-related NO changes could involve polyamine pathway. UHb plants showed increases in total polyamines and in particular polyamines such as spermidine. These increases correlated with the accumulation of the amino acid precursors of polyamines and with the expression of specific polyamine biosynthesis genes. This suggests a potential interplay between NO and polyamine biosynthesis during drought response. Since ethylene has been linked to NO signaling and it is also related to polyamine metabolism, we explored this connection. In vivo ethylene measurement showed that UHb plants significantly decrease ethylene production and expression of aminocyclopropane-1-carboxylic acid synthase gene, the first committed step in ethylene biosynthesis compared with wild type. These data suggest a NO-ethylene influenced regulatory node in polyamine biosynthesis linked to drought tolerance/susceptibility in barley.

Highlights

Drought is considered the most important stress contributing to yield and economical losses in many regions worldwide[1]
nitric oxide (NO) production has been observed in response to exogenously applied polyamines[14].This is of particular relevance to drought, as a protective role for specific polyamines against drought stress has been reported in Arabidopsis
wild type (WT) plants NO production increased more than two fold compared to controls whereas used these transgenic barley lines (UHb) plants showed no significant differences in NO levels (Fig. 2A)

Summary

Introduction

Drought is considered the most important stress contributing to yield and economical losses in many regions worldwide[1]. As with other environmental stresses, elicits profound changes in the plants at gene, protein and metabolite levels as they either succumb to its effects and/or deploy tolerance mechanisms. The coordination of such changes via signaling events is of immense interest and over the years a number of key molecules have been defined; most abscisic acid (ABA)[2]. Polyamines are low molecular weight nitrogenous metabolites considered to be ubiquitous in all living cells These molecules are positively charged at physiological pH and initially, their biological function was associated with their capability of binding to negatively charged molecules, such as nucleic acids, phospholipids, and proteins. The effect was equivalent to previous observations in Arabidopsis[27] demonstrating that barley class 1 Hb is as efficient as Arabidopsis class 1 Hb in scavenging NO

Methods

Results

Conclusion