POSTPHLOEM, NONVASCULAR TRANSFER IN CITRUS - KINETICS, METABOLISM, AND SUGAR GRADIENTS
POSTPHLOEM, NONVASCULAR TRANSFER IN CITRUS - KINETICS, METABOLISM, AND SUGAR GRADIENTS
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DOI：
10.1104/pp.93.4.1405
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发表时间：
1990-08-01
期刊：
影响因子：
7.4
通讯作者：
AVIGNE, WT
中科院分区：
文献类型：
--
作者：
KOCH, KE;AVIGNE, WT
韧皮部后，非维管同化物运输发生在一个不寻常的长面积在柑橘类水果，从而有利于调查这一过程相对于糖进入许多库结构。标记的光合细菌进入葡萄柚汁组织（Citrus paradisi Macf.）在进入韧皮部后的运输路径（薄壁细胞，节表皮的狭窄部分，和毛状的，薄壁组织的汁囊柄）后，速度急剧减慢。动力学，代谢和成分的数据表明，通过非维管区域的转移被延迟了许多小时的临时存储和/或平衡与糖在隔室沿着的postphloem path. Labeled同化物一般回收蔗糖在整个路径，和程度的己糖形成enroute孔没有明显的关系同化物转移过程。即使在24小时后，放射性标记也仅限于直接位于维管束和汁囊之间的离散、高度局部化的区域。 韧皮部后转移发生在幼果蔗糖浓度梯度上升，而下降的梯度（有利于扩散/细胞质流）只在成熟后期。在本例中，由于汁囊通过蒸腾作用或液体回流而损失的水分极其有限，韧皮部后大量流动的参与变得复杂。尽管如此，组织扩张可以在大部分汁囊发育过程中每天至少1.0毫升的集体水流入，从而提供适度但潜在重要的非血管溶液流动手段。总的来说，数据表明韧皮部后转移（a）可以沿着高度局部化的路径通过相当大的非维管区域（总共高达3.0厘米），（B）似乎涉及暂时储存和/或途中与区室化糖的平衡，（c）可发生在总体上坡糖梯度（年轻组织）或沿着下降梯度（接近完全扩张），以及（d）似乎涉及由组织扩张调节的非血管质量流的至少一些贡献。
Postphloem, nonvascular assimilate transport occurs over an unusually long area in citrus fruit and thus facilitates investigation of this process relative to sugar entry into many sink structures. Labeled photosynthates moving into juice tissues of grapefruit (Citrus paradisi Macf.) slowed dramatically after entering the postphloem transport path (parenchyma cells, narrow portions of segment epidermis, and hair-like, parenchymatous stalks of juice sacs). Kinetic, metabolic, and compositional data indicated that transfer through the nonvascular area was delayed many hours by temporary storage and/or equilibration with sugars in compartments along the postphloem path. Labeled assimilates were generally recovered as sucrose throughout the path, and extent of hexose formation enroute bore no apparent relationship to the assimilate transfer process. Even after 24 hours, radiolabel was restricted to discrete, highly localized areas directly between vascular bundles and juice sacs. Postphloem transfer occurred against an ascending sucrose concentration gradient in young fruit, whereas a descending gradient (favoring diffusion/cytoplasmic streaming) developed only later in maturation. Involvement of a postphloem bulk flow is complicated in the present instance by the extremely limited water loss from juice sacs either via transpiration or fluid backflow. Nonetheless, tissue expansion can account for a collective water inflow of at least 1.0 milliliter per day throughout the majority of juice sac development, thus providing a modest, but potentially important means of nonvascular solution flow. Overall, data indicate postphloem transfer (a) can follow highly localized paths through sizable nonvascular areas (up to 3.0 centimeters total, (b) appears to involve temporary storage and/or equilibration with compartmentalized sugars enroute, (c) can occur either against an overall up-hill sugar gradient (young tissues) or along a descending gradient (near full expansion), and (d) appears to involve at least some contribution by nonvascular mass flow accomodated by tissue expansion.