Laterals take it better – Emerging and young lateral roots survive lethal salinity longer than the primary root in Arabidopsis

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. The ongoing process of soil salinization negatively affects many plant species, including staple crops, imposing a major threat for global food production 1,2. Therefore, it is not surprising that over the last decades numerous studies have been dedicated to the understanding of plant responses to salt stress. These studies include those conducted from the organismic (whole plant) level to the cellular and molecular levels, deciphering both osmotic and ionic nature of salt 3-7. Since the root is the primary tissue that directly interacts with the rhizosphere's saline environment, special attention has been given to root tissue. In many of the past but also present studies, salt stress responses were determined in whole root samples without differentiating between the root's various developmental zones and cell types, mainly while being compared to the shoot 8,9. Nevertheless, it is well established by now that each of the root's different developmental zones responds to salt in a different manner. For example, the canonical Sodium/ Proton antiporter NHX1 was found in Arabidopsis roots to be expressed during salt stress in the elongation zone but excluded from the root tip meristem, whereas SOS1 exhibited the opposite expression pattern 10. Moreover, in a milestone study Dinneny et al. isolated several types of Arabidopsis root cells and showed that their transcriptomes differed significantly during salt stress 11. Therefore, it is necessary to spec...

Age-Dependent Abiotic Stress Resilience in Plants

“…When roots were confronted with salt or iron deficiency, most transcriptional changes were observed in the oldest two zones [137]. The limited capacity of primary root tip meristems to respond to stress is also reflected by their poor survival rate in high-salt media, whereas protruding lateral primordia perform well [138]. Drought induces a similar response, causing root tip death and lateral meristem outgrowth upon recovery [139].…”

Cyclin B1;1 activity is observed in lateral roots but not in the primary root during lethal salinity and salt stress recovery

“…Recently, we have shown in Arabidopsis that emerging and young lateral roots (LR) survive lethal salinity (200 mM NaCl) significantly longer than the primary root (PR). 1 We showed that autophagy mediated programmed cell death (A-PCD) and not apoptosis-like PCD (AL-PCD) takes place in the PR but not in the young LR. In addition, we found that as the young LR elongates, it loses its salt tolerance and tends to behave like the PR.…”

“…Moreover, we have also shown that NADPH Oxidase activated ROS is required for the young LR improved salt tolerance. 1 Since the young LR remained alive during extended exposure to lethal salinity, we wanted to find whether acclimation and growth occurred in that position. Thus, we monitored root growth parameters in Arabidopsis WT (Col-0) young seedlings that were treated with 200 mM NaCl for several days.…”

“…Images were captured by Inverted light microscope (Motic AE2000) as mentioned in methods. The seedlings were grown and treated as reported earlier 1. GUS histochemical staining and quantification was done as described in the methods.…”

Gibberellins regulate lateral root development that is associated with auxin and cell wall metabolisms in cucumber

“…The root system constitutes the essential part of the higher plant body. The plant root system performs various functions, such as anchorage, absorption and as the major interface between the plant and various stress factors in the soil environment [1,2]. Root system architecture is an integrative result of lateral root (LR) initiation, morphogenesis and growth.…”