Daloso Danilo M, Williams Thomas C R, Antunes Werner C, Pinheiro Daniela P, Müller Caroline, Loureiro Marcelo E, Fernie Alisdair R
Departamento de Biologia Vegetal, Universidade Federal de Viçosa, Viçosa, MG, 36570-000, Brazil.
Max-Planck-Institut für Molekulare Pflanzenphysiologie, Potsdam-Golm, 14476, Germany.
New Phytol. 2016 Mar;209(4):1470-83. doi: 10.1111/nph.13704. Epub 2015 Oct 15.
Isoform 3 of sucrose synthase (SUS3) is highly expressed in guard cells; however, the precise function of SUS3 in this cell type remains to be elucidated. Here, we characterized transgenic Nicotiana tabacum plants overexpressing SUS3 under the control of the stomatal-specific KST1 promoter, and investigated the changes in guard cell metabolism during the dark to light transition. Guard cell-specific SUS3 overexpression led to increased SUS activity, stomatal aperture, stomatal conductance, transpiration rate, net photosynthetic rate and growth. Although only minor changes were observed in the metabolite profile in whole leaves, an increased fructose level and decreased organic acid levels and sucrose to fructose ratio were observed in guard cells of transgenic lines. Furthermore, guard cell sucrose content was lower during light-induced stomatal opening. In a complementary approach, we incubated guard cell-enriched epidermal fragments in (13) C-NaHCO3 and followed the redistribution of label during dark to light transitions; this revealed increased labeling in metabolites of, or associated with, the tricarboxylic acid cycle. The results suggest that sucrose breakdown is a mechanism to provide substrate for the provision of organic acids for respiration, and imply that manipulation of guard cell metabolism may represent an effective strategy for plant growth improvement.
蔗糖合酶3（SUS3）的同工型3在保卫细胞中高度表达；然而，SUS3在这种细胞类型中的具体功能仍有待阐明。在此，我们对在气孔特异性KST1启动子控制下过表达SUS3的转基因烟草植株进行了表征，并研究了从黑暗到光照转变期间保卫细胞代谢的变化。保卫细胞特异性SUS3过表达导致SUS活性增加、气孔孔径增大、气孔导度增大、蒸腾速率增大、净光合速率增大以及生长加快。虽然在全叶代谢物谱中仅观察到微小变化，但在转基因株系的保卫细胞中观察到果糖水平升高、有机酸水平降低以及蔗糖与果糖的比率降低。此外，在光诱导气孔开放期间保卫细胞蔗糖含量较低。在一种互补方法中，我们将富含保卫细胞的表皮片段在¹³C-NaHCO₃中孵育，并追踪从黑暗到光照转变期间标记物的重新分布；这揭示了三羧酸循环的代谢物或与之相关的代谢物中标记增加。结果表明，蔗糖分解是为呼吸作用提供有机酸底物的一种机制，这意味着对保卫细胞代谢的调控可能是改善植物生长的一种有效策略。
