Sidhu Parminder, Singh Rangil
Department of Biochemistry, Punjab Agricultural University, Ludhiana 141 004, India.
Indian J Exp Biol. 2002 Sep;40(9):1060-6.
Mobilization of free sugars from vegetative tissues to grain and their transformation to starch in relation to activities of some relevant enzymes during growth and development were investigated in wheat (Triticum aestivum L.). Vegetative tissues, viz. flag-leaf, flag-leaf sheath, nodes and internodes contained high concentration of free sugars from 70 DAS to 18 DPA and that was in the order of accumulation--flag-leaf sheath> flag-leaf and internodes > nodes. In these tissues, major portion of 14C appeared in endogenous sucrose, irrespective of the nature of (U-14C]-sugars supplied. In photosynthetic structures above flag-leaf node, namely peduncle, rachis and bracts, the free sugar make-up was maximum at anthesis (90 DAS). Activity of soluble acid invertase (EC 3.2.1.26) was high in these tissues during early stages of grain growth but reverse was true for soluble neutral invertase (EC 3.2.1.27) activity. In apical and basal portions of grain, free sugars were more or less similarly distributed in concentration. Linear and rapid accumulation of starch in endosperm paralleled with a decline in accumulation of this polymer in pericarp-aleurone. In the latter tissue, the activities of starch hydrolyzing enzymes, i.e alpha- and beta-amylases (3.2.1.1 and 3.2.1.2) were high during initial stages of grain growth. During active grain-filling, alkaline inorganic pyrophosphatase (EC 3.6.1.1) seemed to play a vital role during starch accumulation in endosperm, whereas the involvement of 3-PGA phosphatase (EC 3.1.3.38) was almost confined to pericarp-aleurone. Impairement of ear head photosynthesis by shading depressed starch synthesis (approximately 50%) indicating, thereby, the significant role of current photosynthates during grain-filling. The results suggested that grain growth in wheat was influenced by an efficient operation of source as well as regulatory factors, including enzymes, constituting intrinsic potential of grain sink.
对小麦（Triticum aestivum L.）生长发育过程中营养组织中游离糖向籽粒的转运及其与一些相关酶活性的关系转化为淀粉进行了研究。营养组织，即旗叶、旗叶鞘、节和节间，在开花后70天至18天期间含有高浓度的游离糖，其积累顺序为——旗叶鞘>旗叶和节间>节。在这些组织中，无论供应的（U-14C）-糖的性质如何，14C的大部分都出现在内源性蔗糖中。在旗叶节以上的光合结构，即穗轴、小穗轴和苞片，游离糖组成在开花期（开花后90天）最高。在籽粒生长早期，这些组织中可溶性酸性转化酶（EC 3.2.1.26）的活性较高，但可溶性中性转化酶（EC 3.2.1.27）的活性则相反。在籽粒的顶端和基部，游离糖的浓度分布大致相似。胚乳中淀粉的线性快速积累与果皮-糊粉层中这种聚合物积累的下降平行。在后者组织中，淀粉水解酶，即α-淀粉酶和β-淀粉酶（3.2.1.1和3.2.1.2）的活性在籽粒生长初期较高。在籽粒灌浆活跃期，碱性无机焦磷酸酶（EC 3.6.1.1）似乎在胚乳淀粉积累过程中起重要作用，而3-磷酸甘油酸磷酸酶（EC 3.1.3.38）的作用几乎局限于果皮-糊粉层。遮光对穗部光合作用的损害抑制了淀粉合成（约50%），从而表明当前光合产物在籽粒灌浆过程中的重要作用。结果表明，小麦籽粒生长受源的有效运转以及包括酶在内的调节因子的影响，这些因子构成了籽粒库的内在潜力。
