Physiological aspects of photosynthesis and organic acid accumulation in alkali-resistant transgenic alfalfa containing the GsPPCK1 and GsPPCK3 genes

doi:10.11686/cyxb2017391

Abstract

Abstract: Photosynthesis affects the growth and development of plants including their response to salt and alkali stress. Previous studies have shown that over-expression of GsPPCK1 or GsPPCK3 from Glycine soja in alfalfa resulted in enhanced plant tolerance to alkali stress. Here, physiological and biochemical indexes and gene expression related traits were investigated to explore the physiological mechanism of alkali-resistant transgenic alfalfa from the perspective of photosynthesis and organic acid accumulation. The chlorophyll content of transgenic lines P1-5 and P3-8 were not different from untreated plants after 9 days of alkali exposure, decreasing by 11.27% and 13.30% respectively, while that of non-transgenic lines decreased by 39.11%. The photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s) and intercellular CO₂ concentration (C_i) of transgenic lines P1-5 and P3-8 all decreased after alkali exposure, but the decreased was half that of non-transgenic plants. NADP-malate dehydrogenase, NADP-malic enzyme, phosphoenolpyruvate carboxylase, pyruvate orthophosphate dikinase, ribulose-1,5-bisphosphate carboxylase enzyme activity and organic acid content (malic acid, citric acid, oxaloacetic acid and phosphoenolpyruvate) trended upward after alkali treatment. The photosynthetic enzyme activity and organic acid content of transgenic lines P1-5 and P3-8 were significantly different (P<0.01) from non-transgenic plants. The expression of PEPC (Medtr4g079860.1), NADP-ME (Medtr8g014390.1), NADP-MDH (Medtr1g043040.1), PPDK (Medtr4g118350.1) and Rubisco (Medtr4g021210.1) were induced under alkali stress and subsequently declined, the expression level in transgenic lines was greater than non-transgenic lines. The results indicated that under normal conditions, the overexpression of GsPPCK1 or GsPPCK3 did not improve photosynthesis of transgenic lines, but photosynthesis in transgenic alfalfa was less affected by alkali stress. This process may be related to the activity of PEPC. In addition, a significant increase in organic acid content played an important role in stabilizing intracellular pH.

Key words: GsPPCKs, alkali stress, transgenic alfalfa, photosynthetic efficiency, organic acid

CAI Hua, XU Hui-hui, SUN Na, SONG Ting-ting, REN Yong-jing, YANG Sheng-qiu. Physiological aspects of photosynthesis and organic acid accumulation in alkali-resistant transgenic alfalfa containing the GsPPCK1 and GsPPCK3 genes[J]. Acta Prataculturae Sinica, 2018, 27(8): 107-117.

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