Harvard University, Department of Organismic and Evolutionary Biology, 26 Oxford Street, Cambridge, MA 02138, USA.
Harvard University, Department of Organismic and Evolutionary Biology, 26 Oxford Street, Cambridge, MA 02138, USA.
Curr Opin Plant Biol. 2018 Jun;43:101-107. doi: 10.1016/j.pbi.2018.04.007. Epub 2018 Apr 25.
Current conceptions of sucrose export largely neglect the effect of transpiration-induced water potential gradients within leaf mesophyll, even as the mix of convection and diffusion in the pre-phloem path remains uncertain. It is also generally held that the relative importance of convection and diffusion in the pre-phloem path is controlled by the ratio of their respective mass transfer coefficients. Here, we consider pre-phloem sucrose transport in the presence of adverse water potential gradients, finding that whether convection impedes or aids sucrose delivery to the phloem is independent of the permeability of the plasmodesmata to bulk flow, and depends only on assimilation rate, path-length, and the diffusivity. For most tissues subject to transpiration, convection through plasmodesmata pushes sugar away from the phloem.
当前关于蔗糖输出的概念在很大程度上忽略了蒸腾作用引起的叶片叶肉内水势梯度的影响，尽管韧皮部前质流中的对流和扩散的混合仍然不确定。人们普遍认为，在韧皮部前质流中对流和扩散的相对重要性取决于它们各自传质系数的比值。在这里，我们考虑了在存在不利水势梯度的情况下韧皮部前质流中的蔗糖运输，发现对流是否阻碍或有助于蔗糖输送到韧皮部与胞间连丝对体相流的通透性无关，而仅取决于同化速率、路径长度和扩散性。对于大多数受蒸腾作用影响的组织来说，通过胞间连丝的对流将糖从韧皮部推开。
