Abstract
Abiotic factors inducing osmotic stress can affect plant immunity and resistance against pathogen attack. Although a number of studies have characterized grapevine responses to various forms of biotic and abiotic stresses, the relationships between osmotic stress response and susceptibility of mature berries to Botrytis cinerea still remain unknown. In this study, we investigated the effects of osmotic stress and abscisic acid (ABA) on defense responses of mature grapevine berries before and after B. cinerea infection. We focused on the possible involvement of polyamines in the interaction between osmotic stress response and susceptibility to B. cinerea. We showed that osmotic stress induced by PEG or sucrose, and exogenous ABA induce transient but low defense responses, including weak expression of PR genes and phytoalexin synthesis in mature berries. This was accompanied by an upregulation of NCED2 involved in ABA biosynthesis and a large production of free polyamines. However, osmotic stress followed by B. cinerea infection primed berries for enhanced accumulation of polyamines, but slowed down the defense responses and increased susceptibility to the pathogen. A weak increase of diamine- and polyamine-oxidase activities was also recorded in stressed berries, but declined after pathogen infection. The pretreatment of stressed berries with appropriate inhibitors of diamine- and polyamine-oxidases further increased polyamine level and greatly lowered defense responses, leading to higher susceptibility to B. cinerea. These results suggest that increased polyamine titer through low activation of their oxidative degradation in grape berries may contribute at least in part to the weakening of defense responses and subsequent disease susceptibility.
Highlights
Drought inducing osmotic stress is among the most serious abiotic constraints for global agriculture that may intensify during the few decades (Zhao and Running, 2010)
Using quantitative real-time PCR and specific primers (Supplementary Table S1), we examined the expression levels of some defense-related genes, including STS1, PR2, PR3, and PR5, as well as NCED2 encoding 9-cis-epoxycarotenoid dioxygenase involved in abscisic acid (ABA) biosynthesis
We previously reported that osmotic stress or ABA attenuated defense responses triggered by B. cinerea in grapevine leaves (Hatmi et al, 2014)
Summary
Drought inducing osmotic stress is among the most serious abiotic constraints for global agriculture that may intensify during the few decades (Zhao and Running, 2010). Emerging evidences suggest that abiotic stress can strongly modulate plant–pathogen interactions resulting in plant susceptibility or resistance to diseases (Sinha et al, 2016). Abiotic Stress Affects Grape Immunity plant immunity and microbial pathogenesis in different pathosystems (Bidzinski et al, 2016; Sinha et al, 2016; Gupta et al, 2017). This type of stress can weaken plant immune responses or other metabolic pathways occurring during water stress resulting in a predisposition of plants to pathogen infection. Osmotic stress enhanced barley resistance to powdery mildew caused by Blumeria graminis through the primed formation of papillae (Wiese et al, 2004)
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