Department of Botany, University of Toronto, Toronto M5S 1A1 Canada.
Plant Physiol. 1979 Feb;63(2):367-74. doi: 10.1104/pp.63.2.367.
A theory is presented to explain the phloem mobility of certain systemic xenobiotics that are not weak acids. It is shown that there is a theoretically optimum permeability that permits optimum circulation through the symplasm and apoplast (including the phloem and xylem) of Solanum tuberosum plants. The optimum permeability is large enough to permit substantial passive permeation into sieve cells in the source leaf and yet is small enough to permit phloem transport with some retention. The optimum permeability is a function of the velocity of sap flow in sieve tubes, the radius of the sieve tube, the over-all length of the plant, and the length of the carbohydrate and xenobiotic sources. It is argued that the nematicide, oxamyl, is near the optimum permeability under some experimental conditions. It is shown that depending on the strength of the carbohydrate sink in roots or growth points and depending on the permeability of the xenobiotic, there can be passive accumulation of xenobiotics in the sieve tubes in the carbohydrate sink regions.
提出了一个理论来解释某些不是弱酸的系统性外源物质在韧皮部中的移动性。结果表明，对于某些外源物质，在理论上存在一个最佳的通透性，使它们能够在马铃薯植株的共质体和质外体（包括韧皮部和木质部）中进行最佳循环。最佳通透性大到足以允许大量被动渗透进入源叶的筛管细胞，但又小到足以允许有一定保留的韧皮部运输。最佳通透性是筛管中汁液流速、筛管半径、植物总长度和碳水化合物和外源物质源长度的函数。有人认为，在某些实验条件下，杀线虫剂 Oxamyl 接近最佳通透性。结果表明，取决于根部或生长点碳水化合物汇的强度以及外源物质的通透性，外源物质可以在碳水化合物汇区域的筛管中被动积累。
