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Öğe Abscisic acid cross-talking with hydrogen peroxide and osmolyte compounds may regulate the leaf rolling mechanism under drought(Springer Heidelberg, 2018) Sezgin, Asiye; Altuntaş, Cansu; Sağlam, Aykut; Terzi, Rabiye; Demiralay, Mehmet; Kadıoğlu, AsımLeaf rolling observed in some crops such as maize, rice, wheat and sorghum is an indicator of decreased water status. Moderate leaf rolling not tightly or early increases the photosynthesis and grain yield of crop cultivars under environmental stresses. Moreover, the effects of exogenous abscisic acid (ABA) on stomatal conductance, water status and synthesis of osmotic compounds are a well-known issue in plants subjected to water deficit. However, it is not clear how the cross-talk of ABA with H2O2 and osmolyte compounds affects the leaf rolling mechanism. Regulation mechanism of leaf rolling by ABA has been first studied in maize seedlings under drought stress induced by polyethylene glycol 6000 (PEG 6000) in this study. ABA treatment under drought stress reduced hydrogen peroxide (H2O2) content and the degree of leaf rolling (%) while the treatment-induced ABA synthesis, osmolyte levels (proline, polyamine and total soluble sugars) and some antioxidant enzyme activities in comparison to the plants that were not treated with ABA. Furthermore, exogenous ABA up-regulated the expression levels of arginine decarboxylase (ADC) and pyrroline-5-carboxylate synthase (P5CS) genes and down-regulated polyamine oxidase (PAO), diamine oxidase (DAO) and proline dehydrogenase (ProDH) gene expressions. When endogenous ABA content was decreased by the treatment of fluoridone (FLU) that is an ABA inhibitor, leaf rolling degree (%), H2O2 content and antioxidant enzyme activities increased, but osmolyte levels, ADC and P5CS gene expressions decreased. Finally, the treatment of ABA to maize seedlings exposed to drought stress resulted in the stimulation of the antioxidant system, osmotic adjustment and reduction of leaf rolling. We concluded that ABA can be a signal compound cross-talking H2O2, proline and polyamines and thus involved in the leaf rolling mechanism by providing osmotic adjustment. The results of this study can be used to provide data for the molecular breeding of maize hybrids with high grain yield by means of moderately rolled leaves.Öğe Alpha lipoic acid application promotes water-deficit tolerance by modulating osmoprotectant metabolism-related genes in maize(Pleiades journals, 2021) Saruhan Güler, Neslihan; Öztürk, Kamil; Sezgin, Asiye; Altuntaş, Cansu; Kadıoğlu, AsımAbstract: Alpha lipoic acid (ALA) is a potent antioxidant molecule that has positive effects on plant growth and the adaptation of plants to environmental stresses. However, the physiological and molecular mechanisms of the effect of exogenous ALA on the tolerance of plants to environmental stresses associated with osmolyte metabolism are not yet known. Therefore, this study was designed to assess the potential role of exogenous ALA in the water-deficit tolerance mechanism related to the osmolyte metabolism of maize (Zea mays L.) seedlings in hydroponic conditions. Three-week-old maize seedlings were treated or not treated with ALA (12 ?M) and exposed to water-deficit stress generated by addition of 10% polyethylene glycol (PEG6000). The results showed that exogenous ALA enhanced the proline content and the transcript level of the pyrroline-5-carboxylate synthetase (P5CS) gene while decreasing the transcript level of the proline dehydrogenase (ProDH) gene under PEG-induced water-deficit stress. With ALA treatment, the contents of polyamines and transcript level of the S-adenosylmethionine decarboxylase (SAMDC) gene increased while the transcript level of the diamine oxidase (DAO) gene decreased. In addition, the content of soluble sugar and transcript level of the sucrose synthase (SUS) gene increased in ALA-treated maize seedlings under the PEG-free and PEG-induced water-stress conditions but the transcript level of sucrose phosphate synthase (SUPS) did not change. These findings provide evidence that ALA application to plants under water deficit can be a useful strategy for enhancing their stress tolerance by regulating the metabolism of some osmolytes or signal intermediate compounds such as proline, soluble sugar, and polyamine and thus by reducing water loss.Öğe Application of proline to root medium is more effective for amelioration of photosynthetic damages as compared to foliar spraying or seed soaking in maize seedlings under short-term drought(TUBITAK Scientific & Technical Research Council Turkey, 2017) Demiralay, Mehmet; Altuntaş, Cansu; Sezgin, Asiye; Terzi, Rabiye; Kadıoğlu, AsımExogenous proline (PRO) at low concentrations can enhance drought stress tolerance in different application modes such as application to rooting medium, foliar spray, and seed soaking. However, there is no information about which application mode is more effective for increasing the drought tolerance. Comparative effects of 1, 10, and 20 mM PRO applications through three application modes to hydroponically grown seedlings were examined under short-term drought stress in maize seedlings. Effects on leaf water potential, membrane damage, chlorophyll content, proline level, and gas exchange parameters such as net photosynthetic rate (Pn), transpiration rate (E), stomatal conductance (gs), and substomatal CO2 concentration (Ci) were compared. Results indicated that PRO pretreatments raised the water potential, chlorophyll content, Pn, E, gs, and Ci but lowered the malondialdehyde content in the three application modes as compared to the untreated plants. Of the three different modes of PRO pretreatment, rooting medium treatment at 1 mM concentration was also more effective in alleviating stress-induced damages in maize seedlings. Moreover, effectively applied PRO increased the maximum quantum efficiency of PS II, quantum yield of PS II photochemistry, photochemical quenching, and electron transport rate but decreased nonphotochemical quenching of chlorophyll fluorescence under short-term drought stress. In conclusion, exogenous PRO was markedly more effective in the root-treated mode than in foliar spray or seed soaking mode, suggesting that PRO had a different ameliorating effect in different application modes. Proline application in an effective mode can induce photochemical efficiency under short-term drought in maize.Öğe Application of sucrose modulates the expressions of genes involved in proline and polyamine metabolism in maize seedlings exposed to drought(ACAD Sciences Czech Republic, 2019) Altuntaş, Cansu; Sezgin, Asiye; Demiralay, Mehmet; Terzi, Rabiye; Sağlam, Aykut; Kadıoğlu, AsımSucrose, proline, and polyamines are compatible solutes accumulating in plant tissues and increasing cellular osmolarity under environmental stresses. These compatible solutes and hydrogen peroxide can function as signaling molecules in plants. There has been very little evidence how the supply of sucrose changes the biosynthesis of compatible solutes. This study aimed to assess the cross-talk among sucrose, H2O2, and compatible solutes on the expression of genes encoding key enzymes in the pathways of proline and polyamine metabolism in drought stressed maize seedlings. Drought stress (induced by polyethylene glycol solution) increased the expressions of genes encoding pyrroline-5-carboxylate synthetase (P5CS), arginine decarboxylase (ADC), and S-adenosylmethionine decarboxylase (SAMDC), while decreased proline dehydrogenase (ProDH), diamine oxidase (DAO), and polyamine oxidase (PAO) expressions. Addition of sucrose to the stressed seedlings increased the P5CS, ADC and SAMDC expressions more than drought stress alone and reduced more the ProDH, DAO, and PAO expressions. Moreover, exogenous sucrose increased leaf water potential and the content of proline, polyamines, and total soluble sugars, whereas decreased H2O2 content and membrane damages under the drought stress conditions. Consequently, exogenous sucrose contributed to the preservation of water status and the amelioration of damage in maize seedlings under the drought stress.Öğe 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(Elsevier GMBH, 2019) Sezgin, Asiye; Altuntaş, Cansu; Demiralay, Mehmet; Cinemre, Salih; Terzi, RabiyeProtective 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 ?M) 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 (MgCHLI) 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.
