Sugar loading is not required for phloem sap flow in maize plants
Sugar loading is not required for phloem sap flow in maize plants
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DOI：
10.1038/s41477-022-01098-x
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发表时间：
2022-02-01
期刊：
影响因子：
18
通讯作者：
Jensen, Kaare H.
中科院分区：
文献类型：
--
作者：
Babst, Benjamin A.;Braun, David M.;Jensen, Kaare H.
韧皮部将同化物从叶片运输到非光合器官，如根和茎尖以及生殖器官，对植物生长和产量至关重要。近90年来，证据一直与韧皮部运输的压力-流动机制理论基本一致。这一假说的核心是渗透调节剂，主要是糖，进入韧皮部产生的渗透压，推动整体流动。在这里，我们使用遗传和光操作，以测试是否需要糖输入到韧皮部作为韧皮部液流的驱动力。使用碳-11放射性示踪剂，我们表明，玉米蔗糖转运蛋白1（sut 1）功能丧失突变体已严重减少出口的碳从光合叶片（只有类似于野生型水平的4%）。然而，突变体显著地保持韧皮部压力在野生型的100%和液流速度在野生型的50-75%。Sut 1突变体叶片韧皮部钾（K+）丰度升高。流体动力学模型支持的结论，增加K+负载补偿减少蔗糖负载，以保持韧皮部压力，从而保持韧皮部运输通过压力-流动机制。此外，这些结果表明，液流和其他韧皮部移动的营养物质和信号分子的运输可以独立调节糖加载到韧皮部，可能会影响碳营养的稳态和信号分子在植物中遇到不同的环境条件下的分布。
Phloem transport of photoassimilates from leaves to non-photosynthetic organs, such as the root and shoot apices and reproductive organs, is crucial to plant growth and yield. For nearly 90 years, evidence has been generally consistent with the theory of a pressure-flow mechanism of phloem transport. Central to this hypothesis is the loading of osmolytes, principally sugars, into the phloem to generate the osmotic pressure that propels bulk flow. Here we used genetic and light manipulations to test whether sugar import into the phloem is required as the driving force for phloem sap flow. Using carbon-11 radiotracer, we show that a maize sucrose transporter1 (sut1) loss-of-function mutant has severely reduced export of carbon from photosynthetic leaves (only similar to 4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at similar to 100% and sap flow speeds at similar to 50-75% of those of wild type. Potassium (K+) abundance in the phloem was elevated in sut1 mutant leaves. Fluid dynamic modelling supports the conclusion that increased K+ loading compensated for decreased sucrose loading to maintain phloem pressure, and thereby maintained phloem transport via the pressure-flow mechanism. Furthermore, these results suggest that sap flow and transport of other phloem-mobile nutrients and signalling molecules could be regulated independently of sugar loading into the phloem, potentially influencing carbon-nutrient homoeostasis and the distribution of signalling molecules in plants encountering different environmental conditions.