The tonoplast sucrose transporter PtaSUT4 is well expressed in leaves of Populus tremula × Populus alba (INRA 717‐IB4), and its inhibition by RNA‐interference (RNAi) alters leaf sucrose homeostasis. Whether sucrose partitioning between the vacuole and the cytosol is modulated by PtaSUT4 for specific physiological outcomes in Populus remains unexplored. In this study, partial defoliation was used to elicit compensatory increases in photosynthesis and transpiration by the remaining leaves in greenhouse‐grown poplar. Water uptake, leaf gas exchange properties, growth and nonstructural carbohydrate abundance in source and sink organs were then compared between wild‐type and SUT4‐RNAi lines. Partial defoliation increased maximum photosynthesis rates similarly in all lines. There was no indication that source leaf sugar levels changed differently between wild‐type and RNAi plants following partial defoliation. Sink levels of hexose (glucose and fructose) and starch decreased similarly in all lines. Interestingly, plant water uptake after partial defoliation was not as well sustained in RNAi as in wild‐type plants. While the compensatory increase in photosynthesis was similar between genotypes, leaf transpiration increased less robustly in RNAi than wild‐type plants. SUT4‐RNAi and wild‐type source leaves differed constitutively in their bulk modulus of elasticity, a measure of leaf turgor, and storage water capacitance. The data demonstrate that reduced sucrose partitioning due to PtaSUT4‐RNAi altered turgor control and compensatory transpiration capacity more strikingly than photosynthesis and sugar export. The results are consistent with the interpretation that SUT4 may control vacuolar turgor independently of sink carbon provisioning.

中文翻译：

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SUT4-RNAi 杨中落叶诱导的补偿性蒸腾受到损害


液泡膜蔗糖转运蛋白 PtaSUT4 在欧洲山杨×白杨(INRA 717-IB4) 的叶子中良好表达，并且 RNA 干扰 (RNAi) 对其的抑制会改变叶子蔗糖稳态。在杨属中，液泡和细胞质之间的蔗糖分配是否受到 PtaSUT4 的调节以实现特定的生理结果仍有待探索。在这项研究中，部分落叶用于引起温室种植的杨树剩余叶子的光合作用和蒸腾作用的补偿性增加。然后比较野生型和SUT4 ‐RNAi 系之间的水吸收、叶气体交换特性、源器官和库器官中的生长和非结构碳水化合物丰度。部分落叶在所有品系中均类似地增加了最大光合作用速率。没有迹象表明部分落叶后野生型和 RNAi 植物的源叶糖水平变化不同。所有品系中己糖（葡萄糖和果糖）和淀粉的吸收水平均类似地下降。有趣的是，部分落叶后植物水分吸收在 RNAi 中的持续性不如野生型植物。虽然基因型之间光合作用的补偿性增加相似，但 RNAi 中叶片蒸腾作用的增加不如野生型植物强劲。 SUT4-RNAi 和野生型源叶在体积弹性模量（叶子膨压的测量值）和储存水容量方面存在本质差异。数据表明， PtaSUT4 ‐RNAi 导致的蔗糖分配减少比光合作用和糖输出更显着地改变了膨压控制和补偿蒸腾能力。 结果与 SUT4 可以独立于库碳供应控制液泡膨胀的解释一致。