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. 2020 Sep 21;20(1):434.
doi: 10.1186/s12870-020-02624-9.

Responses of leaf gas exchange attributes, photosynthetic pigments and antioxidant enzymes in NaCl-stressed cotton (Gossypium hirsutum L.) seedlings to exogenous glycine betaine and salicylic acid

Abdoul Kader Mounkaila Hamani  1   2 , Guangshuai Wang  1 , Mukesh Kumar Soothar  1   2 , Xiaojun Shen  1 , Yang Gao  3 , Rangjian Qiu  4 , Faisal Mehmood  1   2
Affiliations

Responses of leaf gas exchange attributes, photosynthetic pigments and antioxidant enzymes in NaCl-stressed cotton (Gossypium hirsutum L.) seedlings to exogenous glycine betaine and salicylic acid

Abdoul Kader Mounkaila Hamani et al. BMC Plant Biol. .

Abstract

Background: Application of exogenous glycine betaine (GB) and exogenous salicylic acid (SA) mitigates the adverse effects of salinity. Foliar spraying with exogenous GB or SA alleviates salt stress in plants by increasing leaf gas exchange and stimulating antioxidant enzyme activity. The effects of foliar application of exogenous GB and SA on the physiology and biochemistry of cotton seedlings subjected to salt stress remain unclear.

Results: Results showed that salt stress of 150 mM NaCl significantly reduced leaf gas exchange and chlorophyll fluorescence and decreased photosynthetic pigment quantities and leaf relative water content. Foliar spray concentrations of 5.0 mM exogenous GB and 1.0 mM exogenous SA promoted gas exchange and fluorescence in cotton seedlings, increased quantities of chlorophyll pigments, and stimulated the antioxidant enzyme activity. The foliar spray also increased leaf relative water content and endogenous GB and SA content in comparison with the salt-stressed only control. Despite the salt-induced increase in antioxidant enzyme content, exogenous GB and SA in experimental concentrations significantly increased the activity of glutathione reductase, ascorbate peroxidase, superoxide dismutase, catalase and peroxidase, and decreased malondialdehyde content under salt stress. Across all experimental foliar spray GB and SA concentrations, the photochemical efficiency of photosystem II (FV/FM) reached a peak at a concentration of 5.0 mM GB. The net photosynthetic rate (Pn) and FV/FM were positively correlated with chlorophyll a and chlorophyll b content in response to foliar spraying of exogenous GB and SA under salt stress.

Conclusions: We concluded, from our results, that concentrations of 5.0 mM GB or 1.0 mM SA are optimal choices for mitigating NaCl-induced damage in cotton seedlings because they promote leaf photosynthesis, increase quantities of photosynthetic pigments, and stimulate antioxidant enzyme activity. Among, 5.0 mM GB and 1.0 mM SA, the best performance in enhancing endogenous GB and SA concentrations was obtained with the foliar application of 1.0 mM SA under salt stress.

Keywords: Antioxidant; Cotton; Gas exchange; Glycine betaine; Salicylic acid; Salt stress.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Response of (a) net photosynthetic rate (Pn), b stomatal conductance (gs), c transpiration rate (Tr) and d intracellular CO2 concentration (Ci) to exogenous glycine betaine (GB) and salicylic acid (SA) under 150 mM NaCl regime. CK = Control; GB2.5 = 2.5 mM GB; GB5.0 = 5.0 mM GB; GB7.5 = 7.5 mM GB; SA1.0 = 1.0 mM SA; SA1.5 = 1.5 mM SA; SA2.0 = 2.0 mM SA; and ST = saline treatment (150 mM NaCl). All data are mean ± standard deviation. Differences between treatments having different letters above the error bars are significant at P < 0.05
Fig. 2
Fig. 2
Response of (a) D-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), b phosphoenolpyruvate carboxylase (PEPC), c malondialdehyde (MDA), and d leaf relative water content (LRWC) to exogenous glycine betaine (GB) and exogenous salicylic acid (SA) treatments under salt stress. CK = Control; GB2.5 = 2.5 mM GB; GB5.0 = 5.0 mM GB; GB7.5 = 7.5 mM GB; SA1.0 = 1.0 mM SA; SA1.5 = 1.5 mM SA; SA2.0 = 2.0 mM SA; and ST = saline treatment (150 mM NaCl). All data are mean ± standard deviation. Differences between treatments having different letters above the error bars are significant at P < 0.05
Fig. 3
Fig. 3
Response to exogenous glycine betaine (GB) and salicylic acid (SA) treatments under salt stress of (a) maximal photochemical efficiency of photosystem II (FV/FM), b quantum efficiency of photochemical transports used for photosynthesis (ΦPSII), c quantum efficiency of thermal dissipation promoted by the photoprotective non-photochemical quenching via the xanthophyll cycle (ΦNPQ), and d combined quantum efficiency of fluorescence and constitutive thermal dissipation (Φf,D). CK = Control; GB2.5 = 2.5 mM GB; GB5.0 = 5.0 mM GB; GB7.5 = 7.5 mM GB; SA1.0 = 1.0 mM SA; SA1.5 = 1.5 mM SA; SA2.0 = 2.0 mM SA; and ST = saline treatment (150 mM NaCl). All data are mean ± standard deviation. Differences between treatments having different letters above the error bars are significant at P < 0.05
Fig. 4
Fig. 4
Response to exogenous glycine betaine (GB) and salicylic acid (SA) treatments under salt stress of (a) chlorophyll a (chlp a), b chlorophyll b (chlp b), and c carotenoid (crtn) content. CK = Control; GB2.5 = 2.5 mM GB; GB5.0 = 5.0 mM GB; GB7.5 = 7.5 mM GB; SA1.0 = 1.0 mM SA; SA1.5 = 1.5 mM SA; SA2.0 = 2.0 mM SA; and ST = saline treatment (150 mM NaCl). All data are mean ± standard deviation. Differences between treatments having different letters above the error bars are significant at P < 0.05
Fig. 5
Fig. 5
Response of (a) ascorbate peroxidase (APX), b catalase (CAT), c peroxidase (POD), d superoxide dismutase (SOD) and e glutathione reductase (GR) to exogenous glycine betaine (GB) and salicylic acid (SA) treatments under salt stress. CK = Control; GB2.5 = 2.5 mM GB; GB5.0 = 5.0 mM GB; GB7.5 = 7.5 mM GB; SA1.0 = 1.0 mM SA; SA1.5 = 1.5 mM SA; SA2.0 = 2.0 mM SA; and ST = saline treatment (150 mM NaCl). All data are mean ± standard deviation. Differences between treatments having different letters above the error bars are significant at P < 0.05
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