Salicylic acid induced cysteine protease activity during programmed cell death in tomato plants

Abstract

The hypersensitive response (HR), a type of programmed cell death (PCD) during biotic stress is mediated by salicylic acid (SA). The aim of this work was to reveal the role of proteolysis and cysteine proteases in the execution of PCD in response of SA. Tomato plants were treated with sublethal (0.1 mM) and lethal (1 mM) SA concentrations through the root system. Treatment with 1 mM SA increased the electrolyte leakage and proteolytic activity and reduced the total protein content of roots after 6 h, while the proteolytic activity did not change in the leaves and in plants exposed to 0.1 mM SA. The expression of the papain-type cysteine protease SlCYP1, the vacuolar processing enzyme SlVPE1 and the tomato metacaspase SlMCA1 was induced within the first three hours in the leaves and after 0.5 h in the roots in the presence of 1 mM SA but the transcript levels did not increase significantly at sublethal SA. The Bax inhibitor-1 (SlBI-1), an antiapoptotic gene was over-expressed in the roots after SA treatments and it proved to be transient in the presence of sublethal SA. Protease inhibitors, SlPI2 and SlLTC were upregulated in the roots by sublethal SA but their expression remained low at 1 mM SA concentration. It is concluded that in contrast to leaves the SA-induced PCD is associated with increased proteolytic activity in the root tissues resulting from a fast up-regulation of specific cysteine proteases and down-regulation of protease inhibitors.

Salicylic acid-induced ROS production by mitochondrial electron transport chain depends on the activity of mitochondrial hexokinases in tomato (Solanum lycopersicum L.)

“…In this article, comparative biochemical and molecular analyses of HXKs were carried out in time course experiments after sublethal (0.1 mM) and cell death-inducing (1 mM) SA treatments in order to reveal their putative role in the initiation of cell death in tomato leaves. The appearance of cell death symptoms in tissues of tomato plants exposed to these SA concentrations have already been studied in our group (Kovács et al 2016;Poór et al 2013). It was found that the first markers of PCD appeared 24 h after SA treatment, so this point seemed to be suitable to compare the differences between the effects of the two SA concentrations.…”

Role of Nitric Oxide in Salt Stress-induced Programmed Cell Death and Defense Mechanisms

“…In both cases, the execution of cell death is mediated by the induction of cysteine proteases, some of them showing caspase-like activities. Caspase-like activity seems to be activated by K + deficiency in plant cells (Demidchik et al 2010), which is in good correlation with the induction of cysteine protease activity in salt-stressed plants (Kovács et al 2012). …”

Effects of Salicylic Acid on the Metabolism of Mitochondrial Reactive Oxygen Species in Plants

“…Loss of mitochondrial integrity and cyt c release from mitochondria takes place before cell death execution [45,92]. This cyt c release can activate various cysteine proteases in the cytosol whose activities and the expression of its coding sequences were elevated by SA [97,101,[113][114][115][116]. Cell death in plant organs is preceded by various cytological and biochemical features ( Figure 1): specific morphological changes, rupture of vacuole membrane tonoplast, activation of proteases and nucleases, chromatin aggregation and DNA fragmentation [42][43][44][45][46]117], which hallmarks of PCD were also detected upon SA treatments [97,101].…”