ROS-mediated abiotic stress-induced programmed cell death in plants

Abstract

During the course of their ontogenesis plants are continuously exposed to a large variety of abiotic stress factors which can damage tissues and jeopardize the survival of the organism unless properly countered. While animals can simply escape and thus evade stressors, plants as sessile organisms have developed complex strategies to withstand them. When the intensity of a detrimental factor is high, one of the defense programs employed by plants is the induction of programmed cell death (PCD). This is an active, genetically controlled process which is initiated to isolate and remove damaged tissues thereby ensuring the survival of the organism. The mechanism of PCD induction usually includes an increase in the levels of reactive oxygen species (ROS) which are utilized as mediators of the stress signal. Abiotic stress-induced PCD is not only a process of fundamental biological importance, but also of considerable interest to agricultural practice as it has the potential to significantly influence crop yield. Therefore, numerous scientific enterprises have focused on elucidating the mechanisms leading to and controlling PCD in response to adverse conditions in plants. This knowledge may help develop novel strategies to obtain more resilient crop varieties with improved tolerance and enhanced productivity. The aim of the present review is to summarize the recent advances in research on ROS-induced PCD related to abiotic stress and the role of the organelles in the process.

Keywords: abiotic stress; programmed cell death; reactive oxygen species; signal transduction; stress adaptation.

FIGURE 1

An overview of the central role of ROS in the responses towards abiotic stress factors. Different abiotic cues either directly or indirectly (through the action of other signals and hormones) lead to the production of ROS. In turn, ROS may influence a variety of signal transduction systems, thus providing positive or negative feedback control mechanisms (red arrow). The function of the antioxidant machinery is to prevent dangerous elevations of ROS levels. The outcome of ROS signaling depends mainly on the ROS concentration, but other factors like the site of ROS synthesis, previous stress exposure, developmental stage, and interaction with other signals like reactive nitrogen species (RNS) and Ca²⁺ are also integrated into the response. In general relatively weak stressors cause only a slight rise in ROS quantities which leads to adaptation. At more intensive abiotic stimuli the price for adaptation may be impaired growth and development of the plant. Severe stress usually causes massive accumulation of ROS and the initiation of PCD, or in extreme cases even necrosis of the tissue.