Abstract
Plant responses to salinity have been extensively studied over the last decades. Despite the vast accumulated knowledge, the ways Arabidopsis lateral roots (LR) cope with lethal salinity has not been fully resolved. Here we compared the primary root (PR) and the LR responses during events leading to lethal salinity (NaCl 200 mM) in Arabidopsis. We found that the PR and young LR responded differently to lethal salinity: While the PR died, emerging and young LR’s remained strikingly viable. Moreover, “age acquired salt tolerance” (AAST) was observed in the PR. During the 2 days after germination (DAG) the PR was highly sensitive, but at 8 DAG there was a significant increase in the PR cell survival. Nevertheless, the young LR exhibited an opposite pattern and completely lost its salinity tolerance, as it elongated beyond 400 µm. Examination of several cell death signatures investigated in the young LR showed no signs of an active programmed cell death (PCD) during lethal salinity. However, Autophagic PCD (A-PCD) but not apoptosis-like PCD (AL-PCD) was found to be activated in the PR during the high salinity conditions. We further found that salinity induced NADPH oxidase activated ROS, which were more highly distributed in the young LR compared to the PR, is required for the improved viability of the LR during lethal salinity conditions. Our data demonstrated a position-dependent resistance of Arabidopsis young LR to high salinity. This response can lead to identification of novel salt stress coping mechanisms needed by agriculture during the soil salinization challenge.
Highlights
The ongoing process of soil salinization negatively affects many plant species, including staple crops, imposing a major threat for global food production[1,2]
By using several vital staining assays, we found that emerging and young lateral roots (LR) survived longer than the primary root (PR) in the lethal salinity conditions (Figs. 1–3)
This is the first report demonstrating that phenomena in Arabidopsis roots that were challenged with prolonged toxic salt concentrations
Summary
The ongoing process of soil salinization negatively affects many plant species, including staple crops, imposing a major threat for global food production[1,2]. The above study focused on cells from the tip zone of the primary root (PR) and did not include cells from the branching lateral roots (LR), whose salt induced transcriptome has not yet been determined. It is thought that PR and LR differential growth dynamics are essential for plant adaptation to various environmental conditions[27] Cell death processes such as apoptosis-like programmed cell death (AL-PCD) and Autophagic PCD (A-PCD) were studied in roots of several species during salt stress[28,29,30]. These studies focused mainly on the PR, while events leading to salinity induced cell death in Arabidopsis LR are still obscure. To the best of our knowledge, salinity induced ROS which was well documented in Arabidopsis PR12,13,31,32, has not been previously studied in Arabidopsis LR during high-lethal salt treatments
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