Sink-Source Transition in Leaves: A Model

随着叶子的发育，它从碳水化合物的净使用者转化为碳水化合物的净使用者。 成为净出口国。 这一事件影响了增长模式， 生产力 糖从叶向韧皮部的转移称为 韧皮部装载 这一过程的公认模式是， 蔗糖通过选择性载体转移穿过细胞膜。 提出了一种替代机制，其中蔗糖从 细胞间通过胞间连丝、微小的原生质 连接，提供细胞之间的细胞质连续性。 在 在韧皮部中，较小的蔗糖分子被转化为较大的蔗糖分子。 不能通过胞间连丝返回的糖分子。 糖因此被困在韧皮部细胞中。 形态和 胞间连丝的尺寸将与酶一起沿着研究 参与将蔗糖转化为更大的糖。//

As a leaf develops it is converted from a net user of carbohydrate to a net exporter. This event influences patterns of growth and productivity. The transfer of sugars form leaf to phloem is called phloem loading. The accepted model for this process is that surcose is transferred across cell membranes by selective carriers. An alternative mechanism is proposed in which sucrose passes from cell to cell to the phloem through plasmodesmata, tiny protoplasmic connections that provide cytoplasmic continuity between cells. In the phloem, the smaller sucrose molecules are converted to larger sugar molecule that cannot pass back through the plasmodesmata. The sugar is thus trapped in the phloem cells. The morphology and dimensions of plasmodesmata will be studied along with the enzymes involved in converting sucrose into larger sugars.//