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 Şafak 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 Şafak 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 Şafak 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.

中文翻译：

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脯氨酸刺激的信号转导主要针对叶绿素降解途径和光合作用相关过程，以应对玉米短期缺水。

近年来，脯氨酸水平更高的基因型和缺水条件下用脯氨酸处理过的作物的光合作用效率已有所提高，但该过程的生化和分子机制仍未知。我们检查了光系统II（PSII）的活性，光合酶，核糖1,5-双磷酸羧化酶/加氧酶（rubisco），磷酸烯醇丙酮酸羧化酶（PEPc），rubisco活化酶（RCA）和叶绿素代谢酶，镁螯合酶（Mg-CHLI），和叶绿素酶（Chlase），这将是外源脯氨酸的主要靶标，可在PEG诱导的短期缺水条件下为植物提供光合作用保护。脯氨酸含量高的两种玉米基因型W23 / M14和脯氨酸含量低的afafak基因玉米水培生长21-23天，然后使幼苗经受PEG6000诱导的缺水（-0.75 MPa）0、4和8小时。在幼苗暴露于缺水之前，将脯氨酸（1 mM）施用到afaf基因型的生根培养基上2天。应用的时程效应表明，外源脯氨酸显着提高了PSII效率，PEPc活性，rubisco活性，以及​​在0、4和8小时时PEPc，rubisco大亚基，rubisco小亚基和RCA基因的相对表达水平。在所有时间段，W23 / M14基因型具有比afaf基因型更高的rubisco量。在无压力和PEG条件下进行脯氨酸预处理可降低Chlase的活性和Chlase的基因表达，同时在0、4和8 h增强Mg-CHLI基因的表达。在一起