Salt tolerance in indica rice cell cultures depends on a fine tuning of ROS signalling and homeostasis.

Bushra Ijaz,Fiorella Lo Schiavo,Vittoria Locato,Muhammad Zeeshan Hyder,Tayyaba Yasmin,Elisabetta Barizza,Elide Formentin,Beatrice Ronci,Keqiang Wu

doi:10.1371/journal.pone.0213986

Bushra Ijaz, Fiorella Lo Schiavo + Show 7 more

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https://doi.org/10.1371/journal.pone.0213986

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Abstract

Among cereal crops, salinity tolerance is rare and complex. Multiple genes control numerous pathways, which constitute plant’s response to salinity. Cell cultures act as model system and are useful to investigate the salinity response which can possibly mimic a plant’s response to stress. In the present study two indica rice varieties, KS-282 and Super Basmati which exhibited contrasting sodium chloride (NaCl) stress response were used to establish cell cultures. The cell cultures showed a contrasting response to salt stress at 100 mM NaCl. High level of intracellular hydrogen peroxide (H2O2) and nitric oxide (NO) were observed in sensitive cell culture for prolonged period as compared to the tolerant cells in which an extracellular H2O2 burst along with controlled intracellular H2O2 and NO signal was seen. To evaluate the role of NO in inducing cell death under salt stress, cell death percentage (CDP) was measured after 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) pre-treatment. CDP was reduced significantly in both tolerant and sensitive cell cultures emphasizing NO’s possible role in programmed cell death. Expression analysis of apoplastic NADPH oxidase, i.e. OsRbohA and recently characterised OSCA family members i.e. OsOSCA 1.2 and OsOSCA 3.1 was done. Intracellular H2O2/NO levels displayed an interplay between Ca2+ influx and ROS/RNS signal. Detoxifying enzyme (i.e. ascorbate peroxidase and catalase) activity was considerably higher in tolerant KS-282 while the activity of superoxide dismutase was significantly prominent in the sensitive cells triggering greater oxidative damage owing to the prolonged presence of intracellular H2O2. Salt stress and ROS responsive TFs i.e. OsSERF1 and OsDREB2A were expressed exclusively in the tolerant cells. Similarly, the expression of genes involved in maintaining high [K+]/[Na+] ratio was considerably higher and earlier in the tolerant variety. Overall, we suggest that a control over ROS production, and an increase in the expression of genes important for potassium homeostasis play a dynamic role in salinity tolerance in rice cell cultures.

Highlights

Aerobic metabolic processes such as respiration, photosynthesis and photorespiration unavoidably produce reactive oxygen species (ROS) in the mitochondria, chloroplast, and peroxisomes respectively [1,2]
No significant difference in the growth rate of KS-282 cell cultures under control and at 75mM NaCl stress was observed, the rate of cell division was significantly affected at 100 and 150 mM NaCl starting from day 6
We propose that OSCA 1.2 and OSCA3.1 channels are modulated by H2O2 and may be related to systemic signaling by increasing an influx of Ca2+

Summary

Introduction

Aerobic metabolic processes such as respiration, photosynthesis and photorespiration unavoidably produce reactive oxygen species (ROS) in the mitochondria, chloroplast, and peroxisomes respectively [1,2]. These ROS are produced in a controlled amount under optimal conditions. Under abiotic stress their level increases dramatically. Overproduction of ROS caused by abiotic stress in plants highly damages proteins, lipids, and nucleic acids leading to cell injury and death [2]. ROS are generated across the plasma membrane and apoplastic region [1,2,3] Under abiotic stress these apoplastic ROS might act as signal molecules for the activation of stress responsive pathways [4]

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