Abstract
Salinity stress-induced production of reactive oxygen species (ROS) and associated oxidative damage is one of the major factors limiting crop production in saline soils. However, the causal link between ROS production and stress tolerance is not as straightforward as one may expect, as ROS may also play an important signaling role in plant adaptive responses. In this study, the causal relationship between salinity and oxidative stress tolerance in two cereal crops—barley (Hordeum vulgare) and wheat (Triticum aestivum)—was investigated by measuring the magnitude of ROS-induced net K+ and Ca2+ fluxes from various root tissues and correlating them with overall whole-plant responses to salinity. We have found that the association between flux responses to oxidative stress and salinity stress tolerance was highly tissue specific, and was also dependent on the type of ROS applied. No correlation was found between root responses to hydroxyl radicals and the salinity tolerance. However, when oxidative stress was administered via H2O2 treatment, a significant positive correlation was found for the magnitude of ROS-induced K+ efflux and Ca2+ uptake in barley and the overall salinity stress tolerance, but only for mature zone and not the root apex. The same trends were found for wheat. These results indicate high tissue specificity of root ion fluxes response to ROS and suggest that measuring the magnitude of H2O2-induced net K+ and Ca2+ fluxes from mature root zone may be used as a tool for cell-based phenotyping in breeding programs aimed to improve salinity stress tolerance in cereals.
Highlights
Salinity stress is one of the major environmental constraints limiting crop production worldwide that results in massive economic penalties, especially in arid and semi-arid regions [1,2,3]
The major efforts were focused on either improving plant capacity to exclude Na+ from uptake by targeting SOS1 [6,7,8] and HKT1 [9,10,11] genes, or increasing de novo synthesis of organic osmolytes for osmotic adjustment [12,13,14]
We have shown that (1) the same trend is applicable to wheat species; (2) larger K+ efflux is mirrored by the higher Ca2+ uptake in H2O2-treated roots; and (3) the correlation between salinity tolerance and H2O2-induced ion flux responses exists only in mature but not elongation root zone
Summary
Salinity stress is one of the major environmental constraints limiting crop production worldwide that results in massive economic penalties, especially in arid and semi-arid regions [1,2,3]. Reported initially for barley roots [73,74,75], a positive correlation between the overall salinity stress tolerance and the ability of a root tissue to retain K+ was later expanded to many other species (reviewed by Shabala [49]) and extrapolated to explain the inter-specific variability in salinity stress tolerance [76,77,78] In roots, this NaCl-induced K+ efflux is mediated predominantly by outward-rectifying K+ channels GORK that are activated by both membrane depolarization [79] and ROS [23], as shown in direct patch-clamp experiments. This indicated that channel activation by H2O2 may be indirect and mediated by its interaction with cell wall transition metals [55,90]
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