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Plant Physiology 2017年11月10日文章:SHORTROOT-mediated increase in stomatal density has no impact on photosynthetic efficiency


叶脉,叶肉细胞和气孔在叶片上的协调定位对于有效的气体交换和蒸腾以及整体功能是至关重要的。在单子叶植物叶片中,气孔细胞位于下方的纵向叶脉的侧翼,而不是正上方或下方。这种模式表明,气孔的形成在与叶脉直接接触的表皮细胞中被抑制,或者在叶脉之外的细胞中被诱导。 SHORTROOT途径在根和芽的下表皮层中的脉管系统周围指定不同的细胞类型,通过与叶脉的距离确定细胞类型的一致性。为了检测该途径是否具有类似的确定表皮细胞类型的潜力,我们研究了水稻OsSHR2基因的表达域,结果显示其表达仅限于发育叶脉,包括包绕着叶脉的束鞘细胞。在使用直向同源ZmSHR1基因,以避免OsSHR2的潜在沉默的转基因株系中,在正常位置和距离叶脉更远的位置都观察到气孔细胞。与理论预测相反,以及在双子叶植物叶片中观察到的表型,气孔密度的增加不提高光合能力或增加叶肉细胞密度。总的来说,这些结果表明SHORTROOT途径可以协调静脉和气孔在单子叶植物叶片中的定位,并且在单子叶和双子叶植物中可能具有不同的机制来协调气孔构型与叶肉细胞的发育。


The co-ordinated positioning of veins, mesophyll cells and stomata across a leaf is crucial for efficient gas exchange and transpiration, and therefore for overall function. In monocot leaves, stomatal cell files are positioned at the flanks of underlying longitudinal leaf veins, rather than directly above or below. This pattern suggests either that stomatal formation is inhibited in epidermal cells directly in contact with the vein, or that specification is induced in cells files beyond the vein. The SHORTROOT pathway specifies distinct cell-types around the vasculature in sub-epidermal layers of both root and shoots, with cell-type identity determined by distance from the vein. To test whether the pathway has the potential to similarly pattern epidermal cell-types, we expanded the expression domain of the rice OsSHR2 gene, which we show is restricted to developing leaf veins, to include bundle sheath cells encircling the vein. In transgenic lines, which were generated using the orthologous ZmSHR1 gene to avoid potential silencing of OsSHR2, stomatal cell files were observed both in the normal position and in more distant positions from the vein. Contrary to theoretical predictions, and to phenotypes observed in eudicot leaves, the increase in stomatal density did not enhance photosynthetic capacity or increase mesophyll cell density. Collectively these results suggest that the SHORTROOT pathway may co-ordinate the positioning of veins and stomata in monocot leaves, and that distinct mechanisms may operate in monocot and eudicot leaves to co-ordinate stomatal patterning with the development of underlying mesophyll cells.



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