Protection of Photosynthesis by Halotolerant Staphylococcus sciuri ET101 in Tomato (Lycoperiscon esculentum) and Rice (Oryza sativa) Plants During Salinity Stress: Possible Interplay Between Carboxylation and Oxygenation in Stress Mitigation.

Dinakar Challabathula,Zarin Taj

doi:10.3389/fmicb.2020.547750

Abstract

Tomato (Lycoperiscon esculentum) and rice (Oryza sativa) are the two most important agricultural crops whose productivity is severely impacted by salinity stress. Soil salinity causes an irreversible damage to the photosynthetic apparatus in plants at all developmental stages leading to significant reduction in agricultural productivity. Reduction in photosynthesis is the primary response that is observed in all glycophytic plants during salt stress. Employment of salt-tolerant plant growth-promoting bacteria (PGPB) is an economical and viable approach for the remediation of saline soils and improvement of plant growth. The current study is aimed towards investigating the growth patterns and photosynthetic responses of rice and tomato plants upon inoculation with halotolerant PGPB Staphylococcus sciuri ET101 under salt stress conditions. Tomato and rice plants inoculated with PGPB showed increased growth rate and stimulated root growth, along with higher transpiration rates (E), stomatal conductance (gs), and intracellular CO2 accumulation (Ci). Additionally, correlation of relative water content (RWC) to electrolyte leakage (EL) in tomato and rice plants showed decreased EL in inoculated plants during salt stress conditions, along with higher proline and glycine betaine content. Energy dissipation by non-photochemical quenching (NPQ) and increased photorespiration of 179.47% in tomato and 264.14% in rice plants were observed in uninoculated plants subjected to salinity stress. Furthermore, reduced photorespiration with improved salinity tolerance is observed in inoculated plants. The higher rates of photosynthesis in inoculated plants during salt stress were accompanied by increased quantum efficiency (ΦPSII) and maximum quantum yield (Fv/Fm) of photosystem II. Furthermore, inoculated plants showed increased carboxylation efficiency of RuBisCO, along with higher photosynthetic electron transport rate (ETR) (J) during salinity stress. Although the total cellular ATP levels are drastically affected by salt stress in tomato and rice plants along with increased reactive oxygen species (ROS) accumulation, the restoration of cellular ATP levels in leaves of inoculated plants along with decreased ROS accumulation suggests the protective role of PGPB. Our results reveal the beneficial role of S. sciuri ET101 in protection of photosynthesis and amelioration of salinity stress responses in rice and tomato plants.

Highlights

Salinity stress is the major environmental problem all over the world due to which the cultivable land area is decreased, and drastic reduction in root length, biomass, and growth is observed causing a decline in crop yields (Deinlein et al, 2014; Janda et al, 2016; Kumar et al, 2020)
S. sciuri ET101 was further characterized for the production of various plant growthpromoting substances in the absence and presence of NaCl
The results from the current study indicated that the isolated halotolerant bacteria S. sciuri ET101 plays a crucial role in protecting the tomato and rice plants against damaging effects of salt stress

Summary

Introduction

Salinity stress is the major environmental problem all over the world due to which the cultivable land area is decreased, and drastic reduction in root length, biomass, and growth is observed causing a decline in crop yields (Deinlein et al, 2014; Janda et al, 2016; Kumar et al, 2020). The limitation of plant growth under salinity conditions is primarily due to reduction in photosynthesis rate and high intracellular accumulation of Na+ ions, which interfere with various physiological processes (Assaha et al, 2017; Analin et al, 2020). Decrease in intracellular CO2 concentration and photosynthesis during salinity stress due to stomatal closure leads to lesser availability of CO2 to the RuBisCO enzyme binding, thereby enhancing the rate of photorespiration (Igamberdiev, 2015). The key photosynthetic processes including RuBisCO enzyme activity, ATP generation, electron transport rate (ETR), and efficiency of light capture in the photosystems are seriously affected by salt stress (Chaves et al, 2009). The prevalence of hypoxia/anoxia conditions in root zone due to hindrance of O2 diffusion in soil leads to reduction of ATP formation and diminished growth (Kozlowski, 1997; Barrett-Lennard, 2003). The downregulation of the photochemical linear electron transport during salt stress conditions limits the oxidative stress, and increased cyclic electron flow increases the photoprotective energy dissipation (Stepien and Johnson, 2009)

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Discussion

Conclusion