Matheson N K
Department of Agricultural Chemistry and Soil Science, University of Sydney, NSW, Australia.
Carbohydr Res. 1996 Mar 18;282(2):247-62. doi: 10.1016/0008-6215(95)00381-9.
Starches, isolated from rapidly expanding tobacco leaves four times during the day and night and once from fully expanded leaves, were fractionated with concanavalin A. From an examination of the amounts and properties of amylose, the diurnal decrease in iodine absorption of the starches on illumination appeared to be due to an increase in its branched character, and possibly the presence of unbranched polymer of low dp, combined with a decrease in the proportion of amylose fraction. The increase in apparent amylose content with age was due to an increase in the proportion of amylose. The amylose fractions at different times had only small differences in average mol size in solution and relative mol wt (M(r) near 4 x 10(5)) which were lower than those of storage organs. The average mol size in solution and relative mol wt of the amylopectins decreased during illumination, increased in darkness, and were lower (M(r) 2-2.7 x 10(6)) at all times than those from storage organs. Debranching followed by size-exclusion chromatography [on Fractogel TSK 50(S)] gave similar proportions of long, medium, and short chains for all amylopectin samples, and these proportions differed from those for debranched amylopectin from n-maize seed starch. On debranching and chromatography of the amylopectin beta-limit dextrins (which gives an estimate of the proportions of core chains) differences persisted. Structural characteristics of amylopectin from tobacco leaf starch were similar to those of normal genotypes from storage organs. The proportion of glucosyl units in core chains, the external-to-core chain ratio, and indices of compactness were calculated for a number of (1-->4)(1-->6) alpha-glucans. A plot of the index of compactness for glycogens and amylopectins showed that the decrease in compactness and the increase in total average chain length that occurs from glycogen to normal and then to amylose extender amylopectins involves a proportionate increase in average internal, external, and core chain lengths and not a selective increase in one type of chain.
在白天和夜晚期间从快速生长的烟草叶片中分离四次淀粉，并从完全展开的叶片中分离一次淀粉，然后用伴刀豆球蛋白A对其进行分级分离。通过对直链淀粉的量和性质进行研究，发现淀粉在光照下碘吸收的昼夜减少似乎是由于其支链特性增加，可能还存在低聚合度的无分支聚合物，同时直链淀粉级分的比例降低。随着叶片变老，表观直链淀粉含量的增加是由于直链淀粉比例的增加。不同时间的直链淀粉级分在溶液中的平均分子大小和相对分子量（M(r)接近4×10⁵）只有很小差异，且低于储存器官中的直链淀粉。支链淀粉在溶液中的平均分子大小和相对分子量在光照期间降低，在黑暗中增加，并且在所有时间都低于储存器官中的支链淀粉（M(r)为2 - 2.7×10⁶）。对所有支链淀粉样品进行去分支后再通过尺寸排阻色谱法（在Fractogel TSK 50(S)上）分析，得到的长链、中链和短链比例相似，且这些比例与来自n - 玉米种子淀粉的去分支支链淀粉不同。对支链淀粉β - 极限糊精进行去分支和色谱分析（这可以估计核心链的比例），差异仍然存在。烟草叶片淀粉中支链淀粉的结构特征与储存器官中正常基因型的支链淀粉相似。计算了许多(1→4)(1→6)α - 葡聚糖的核心链中葡萄糖基单元的比例、外链与核心链的比例以及紧密指数。糖原和支链淀粉紧密指数的曲线图表明，从糖原到正常支链淀粉再到直链淀粉延伸支链淀粉，紧密性降低和总平均链长增加涉及平均内部链、外部链和核心链长度的成比例增加，而不是某一种链的选择性增加。
