Both NaCl and H2O2 Long-Term Stresses Affect Basal Cytosolic Ca2+ Levels but Only NaCl Alters Cytosolic Ca2+ Signatures in Arabidopsis.

Lulu Liu,Hongyan Zhao,Zhen-Ming Pei,James N. Siedow,Shu Zhang,Weiguang Yang,Zhonghao Jiang

doi:10.3389/fpls.2018.01390

Abstract

Salinity is one of the formidable environmental factors that affect plant growth and development and constrain agricultural productivity. Experimentally imposed short-term NaCl treatment triggers a transient increase in cytosolic free Ca2+ concentration ([Ca2+]i) via Ca2+ influx across the plasma membrane. Salinity stress, as well as other stresses, induces the production of reactive oxygen species (ROS), such as H2O2. It is well established that short-term H2O2 treatment also triggers a transient increase in [Ca2+]i. However, whether and how long-term NaCl and H2O2 treatments affect the basal levels of [Ca2+]i as well as plant responses to additional NaCl and H2O2 stresses remain poorly understood. Using an aequorin-based Ca2+ imaging assay, we found that the long-term treatment of Arabidopsis seedlings with both moderate NaCl and H2O2 in the growth media reduced the basal [Ca2+]i levels. Interestingly, we found that the long-term treatment with NaCl, but not H2O2, affected the responses of plants to additional NaCl stress, and remarkably the roots displayed enhanced responses while the leaves showed reduced responses. These findings suggest that plants adapt to the long-term NaCl stress, while H2O2 might be an integrator of many stresses.

Highlights

Soil salinization impacts nearly every aspect of plant growth and development and causes enormous agricultural production losses all over the world (Hasegawa et al, 2000; Zhu, 2002, 2016)
Since a failure in the regulation of basal [cytosolic free Ca2+ concentration (Ca2+]i) leads to a vast array of severe diseases in humans, including cancers, neuron degeneration diseases, and cardiovascular diseases, the maintenance of adequate basal [Ca2+]i seems to be essential for all organisms (Roderick and Cook, 2008; Sammels et al, 2010)
We observed significant variations of the basal [Ca2+]i levels in these seedlings, when we used NaCl media-grown seedlings of the ecotype Col-0 expressing cytosolic apoaequorin detective in stimulus-induced [Ca2+]i increases, similar to the osmo-sensing mutant osca1, for aequorin-based Ca2+ imaging analyses, we observed remarkably significant variations of the basal [Ca2+]i levels in these seedlings. This observation trigged us to ask a question regarding whether the long-term treatments of NaCl and H2O2 affect the basal [Ca2+]i, which is in line with our previous study on the [Ca2+]i signatures with short-term salt and reactive oxygen species (ROS) stresses (Jiang et al, 2013)

Summary

Introduction

Soil salinization impacts nearly every aspect of plant growth and development and causes enormous agricultural production losses all over the world (Hasegawa et al, 2000; Zhu, 2002, 2016). High salinity affects almost a quarter to one-third of global agricultural land, especially in irrigated areas. Previous studies show that high salinity led us to lose about 10 million hectares of agricultural land per year (Zhu, 2001; Munns and Tester, 2008; Deinlein et al, 2014). An additional challenge that compounded these losses is that agriculture needs to provide enough food for a rapidly expanding population in the world and stave off large-scale food shortages (Schroeder et al, 2013). It is vital to understand how plants perceive and respond to salt stress

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Conclusion