Abstract
Already a short-term Cd treatment induces changes in gene expression in barley root tips via IAA and ROS signaling during mild and severe Cd stress, respectively. Even a short, 30min, Cd treatment of roots induced a considerable alteration in gene expression in the barley root tips within an hour after the treatments. The very early activation of MYB1 transcription factor expression is partially regulated by auxin signaling in mildly stressed seedlings. An increase in allene oxide cyclase and NADPH oxidase expression was a distinguishing feature of root tips response to mild Cd stress and their expression is activated via IAA signaling. Meanwhile, early changes in the level of dehydrin transcripts were detected in moderately and severely stressed root tips, and their induction is related to altered ROS homeostasis in cells. The early activation of glutathione peroxidase expression by mild Cd stress indicates the involvement of IAA in the signaling process. In contrast, early ascorbate peroxidase expression was induced only with Cd treatment causing severe stress and ROS play central roles in its induction. The expression of cysteine protease was activated similarly in both mildly and severely Cd-stressed roots; consequently, both increased IAA and ROS levels take part in the regulation of cysteine protease expression. The Cd-evoked accumulation of BAX Inhibitor-1 mRNA was characteristic for moderately and severely stressed roots. Whereas decreased IAA level did not affect its expression, rotenone-mediated ROS depletion markedly reduced the Cd-induced expression of BAX Inhibitor-1. An early increase of alternative oxidase levels in the root tip cells indicated that the reduction of mitochondrial superoxide generation is an important component of barley root response to severe Cd stress.
Highlights
Cadmium (Cd) is an undesirable environmental pollutant without any known function in higher plants
During moderate Cd -stress (30 μM Cd for 30 min), there is a transient depletion of indole-3-acetic acid (IAA) in the root tips, and its level increases compared to the untreated seedlings, in a similar fashion as observed during mild Cd stress
Transgenic tobacco seedlings overexpressing this gene were more tolerant to Cd or Zn than control seedlings. Expression of both APX1 and GPX1 was upregulated in the root tips of Cd-treated roots in a Cd dosedependent manner, and it increased with incubation time after the transient treatment (Fig. 4)
Summary
Cadmium (Cd) is an undesirable environmental pollutant without any known function in higher plants. RGI has exclusively been considered a toxicity symptom of metal stress; recently, it became widely regarded as a part of mainly auxin-mediated root growth reorientation during different abiotic stress-induced adaptations (Kazan, 2013; Potters et al, 2009). Besides this rapid RGI, due to the reduced cell elongation and cell division, root thickening, twisting, enhanced root hair formation and root branching are the main characteristic features of toxic metal excess-induced changes in root system architecture and morphology.
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