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

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.

OSCA1 is an osmotic specific sensor: a method to distinguish Ca2+‐mediated osmotic and ionic perception

“…Previously, we have shown that [Ca 2+ ] i increases induced by salt stress and H 2 O 2 are similar, although aequorin imaging of lower temporal resolution was used (Jiang et al ., 2013; Liu et al ., 2018), in contrast to the drastic difference between those induced by abiotic vs biotic stress (Cao et al ., 2017). Superficially similar responses of whole seedling [Ca 2+ ] i to 200 mM sorbitol and 100 mM NaCl have been observed previously, although the concentrations used were relatively low compared to those commonly used (Tracy et al ., 2008).…”

“…There are a few key steps to determine the selectivity between Stimulus A and Stimulus B (S‐B) in the s‐a mutant using the method developed here as well our previous studies (Jiang et al ., 2013; Cao et al ., 2017; Liu et al ., 2018). Similar Ca 2+ signaling levels induced by S‐A and S‐B, which are obtained from their dose curves, should be used for comparison in the wild‐type, such as NaCl and H 2 O 2 (Jiang et al ., 2013) (Fig.…”

“…For a given Stimulus A (S-A) and its Ca 2+ -genetic mutant (s-a), several criteria should be met to verify its Ca 2+ signaling phenotype: no mutation in aequorin transgene; no alteration in aequorin dischargefor instance, the Arabidopsis ecotype Landsberg erecta could not be used in aequorin-imaging possibly due to dark leaf structures preventing aequorin bioluminescence emission (Yuan et al, 2014); similar Ca 2+ phenotype detected using another Ca 2+ indicator, such as Yellow Cameleon and GCaMP variants (Walia et al, 2018;Grenzi et al, 2021); Ca 2+ phenotype occurring in a dosedependent manner; and finally having stimulus-related physiological phenotypes. There are a few key steps to determine the selectivity between Stimulus A and Stimulus B (S-B) in the s-a mutant using the method developed here as well our previous studies (Jiang et al, 2013;Cao et al, 2017;Liu et al, 2018). Similar Ca 2+ signaling levels induced by S-A and S-B, which are obtained from their dose curves, should be used for comparison in the wild-type, such as NaCl and H 2 O 2 (Jiang et al, 2013) (Fig.…”

NADPH oxidases and the evolution of plant salinity tolerance

“…One of the earliest events found in salinity stressed plant cells is an elevation in cytosolic free Ca 2+ (Liu et al, 2018;Tracy, Gilliham, Dodd, Webb, & Tester, 2008;Wang, Teng, Zhu, Zhang, & Liu, 2019). NADPH oxidase possesses two Ca 2+ -binding sites at the N-terminal of its EF-hand (Marino, Dunand, Puppo, & Pauly, 2012).…”

Modulation of Ethylene and Ascorbic Acid on Reactive Oxygen Species Scavenging in Plant Salt Response

“…One of these regulators is calmodulins-like 10, which interacts with AsA biosynthesis enzyme phosphomannomutase (PMM) to modulate enzyme activities and AsA pool ( Cho et al, 2016 ), which suggested the role of calcium (Ca 2+ ) in AsA biosynthesis. It has been known that Ca 2+ signaling is triggered by ROS accumulation ( Rentel and Knight, 2004 ) and Ca 2+ wave is induced under salt stress ( Choi et al, 2014 ; Liu et al, 2018 ). A chloroplast protein, QUASIMODO1 (QUA1), functions upstream of a thylakoid-localized Ca 2+ sensor, CAS, to mediate Ca 2+ signaling under salt stress ( Zheng et al, 2017 ).…”