Exogenous acetone O-(4-chlorophenylsulfonyl) oxime alleviates Cd stress-induced photosynthetic damage and oxidative stress by regulating the antioxidant defense mechanism in Zea mays.

Cadmium (Cd) toxicity in leaves decreases their photosynthetic efficiency by degrading photosynthetic pigments, reducing the activity of gas exchange parameters and photosystem II (PSII), and producing reactive oxygen species. Although acetone O-(4-chlorophenylsulfonyl) oxime (AO) alleviates stress due to heavy metals in plants, its effects on the photosynthetic apparatus and redox balance under Cd stress are not clear. Herein, the role of AO in modulating the relationship between the antioxidant defense system and photosynthetic performance including chlorophyll fluorescence and gas exchange in mitigating the stress damage caused by Cd in maize seedlings was investigated. Three-week-old maize seedlings were pre-treated with AO (0.66 mM) and exposed to 100 µM Cd stress. Our findings indicated that AO application increased Cd accumulation, thiobarbituric acid-reactive substances (TBARS), photosynthetic rate, hydrogen peroxide (H2O2), total chlorophyll and carotenoid, transpiration, stomatal conductance, maximum photochemical efficiency of PSII (Fv/Fm), effective quantum yield of PSII (ΦPSII), intercellular CO2 concentration, photochemical quenching (qP), superoxide dismutase, electron transport rate, proline, ascorbate peroxidase, catalase, guaiacol peroxidase, 4-hydroxybenzoic acid, catechol, and cinnamic acid in maize seedling under Cd stress. Conversely, AO significantly reduced oxidative damage levels (H2O2, TBARS). It was concluded that exogenous AO can overcome Cd-mediated oxidative damage and hence protect the photosynthetic machinery by providing stress tolerance and regulating the antioxidant defense mechanism, which includes proline, phenolic compounds, and antioxidant enzyme activities. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-022-01258-5.

Increased dehydrin level decreases leaf rolling grade by altering the reactive oxygen species homeostasis and abscisic acid content in maize subjected to osmotic stress.

Dehydrins (DHNs) are stress proteins involved in the development of protective reactions in plants against dehydration. The relationship between DHNs and morphological responses such as leaf rolling in plants exposed to water deficit is not well known. In this study, we detected how variations in DHN levels affect the leaf rolling response in maize exposed to osmotic stress in relation to the antioxidant system and ABA level. In this context, we altered the DHN levels in maize seedlings by treatment with bio-regulators (salicylic acid and abscisic acid) under PEG6000-free and PEG6000-induced osmotic stress. When the DHN levels were increased by the bio-regulators (25 µM SA and 100 µM ABA), the relative expression level of the Zea mays dehydrin COR410 gene increased in the seedlings, while reactive oxygen species (ROS) and leaf rolling grade decreased. Moreover, induction of DHNs caused increases in the antioxidant enzyme activity and content of antioxidant substances, and very high amounts of endogenous abscisic acid. When DHN level was suppressed by a bio-regulator (200 µM SA) in the maize seedlings, dehydrin COR410 expression level decreased, while ROS and the leaf rolling grade increased. Moreover, the antioxidant enzyme activity and content of antioxidant substances decreased in the seedlings, while the amount of abscisic acid increased. Taken all together, an increase in DHN level by bio-regulator treatment can stimulate the antioxidant system, enable abscisic acid regulation, and thus reduce leaf rolling through decreased ROS levels. The results also indicated that DHNs may be involved in the signal pathways inducing expression of some genes related to leaf rolling response, possibly by modulating ROS levels, in maize seedlings exposed to osmotic stress.

Proline-stimulated signaling primarily targets the chlorophyll degradation pathway and photosynthesis associated processes to cope with short-term water deficit in maize.

Increased photosynthetic efficiencies in genotypes with greater proline level and in crops treated with proline under water deficit have been reported in recent years, but the biochemical and molecular mechanisms of this process are still not known. We examined photosystem II (PSII) activity, photosynthetic enzymes, ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco), phosphoenolpyruvate carboxylase (PEPc), rubisco activase (RCA), and chlorophyll metabolic enzymes, magnesium chelatase (Mg-CHLI), and chlorophyllase (Chlase), which would be the primary targets of exogenous proline to provide photosynthetic protection to plants under PEG-induced short-term water deficit. Two maize genotypes W23/M14 with greater proline content and Safak with low proline content were hydroponically grown for 21-23 days, and then the seedlings were subjected to water deficit (- 0.75 MPa) induced by PEG6000 for 0, 4, and 8 h. Before the seedlings were exposed to the water deficit, proline (1 mM) was applied to the rooting medium of the Safak genotype for 2 days. The time course effects of the applications showed that exogenous proline significantly enhanced PSII efficiency, PEPc activity, rubisco activity, and the relative expression levels of PEPc, rubisco large subunit, rubisco small subunit, and RCA genes at 0, 4, and 8 h. The W23/M14 genotype had higher rubisco quantity than the Safak genotype at all time periods. Proline pre-treatment under the stress-free and PEG conditions reduced the activity of Chlase and the gene expressions of Chlase, while it enhanced Mg-CHLI gene expression at 0, 4, and 8 h. Taken together, the results indicated that the primary target of proline-stimulated signaling in maize seedlings exposed to short-term severe water deficit may be to induce PSII efficiency, activities of carbon dioxide fixation enzymes and chlorophyll metabolism and mitigate chlorophyll degradation.

Exogenous alpha lipoic acid can stimulate photosystem II activity and the gene expressions of carbon fixation and chlorophyll metabolism enzymes in maize seedlings under drought.

Protective compounds such as non-enzymatic antioxidants, osmolytes and signal molecules have been applied to plants exposed to various environmental stresses to increase their stress tolerance. However, there are not enough records about the response of plants to alpha lipoic acid (ALA) application with antioxidant properties. Therefore, this study was designed to evaluate the function of exogenous ALA on the photosynthetic performance of maize seedlings grown in hydroponic conditions under drought stress. Three weeks old seedlings were treated with or without ALA (12 µM) and they were subjected to drought stress induced by 10% polyethylene glycol (PEG6000) for 24 h. Chlorophyll content, gas exchange parameters, chlorophyll fluorescence and the expression levels of genes involved in CO2 fixation (ribulose-1,5-bisphosphate carboxylase (rubisco), phosphoenolpyruvate carboxylase (PEPc), Rubisco activase (RCA)) and chlorophyll metabolism (magnesium chelatase (Mg-CHLI) and chlorophyllase (Chlase)) were determined. The application of ALA increased chlorophyll content and the activity of photosystem II in comparison to the untreated seedlings under drought stress. The relative expression levels of Rubisco, PEPc, RCA and Mg-CHLI significantly increased while the Chlase gene expression decreased in seedlings to which ALA was applied in comparison those to which it was not applied under the stress. These results suggest that exogenous ALA can enhance the photosynthetic performance of maize seedlings exposed to drought by inducing photosystem II activity and the gene expressions of carbon fixation and chlorophyll metabolism enzymes.