Translocation from leaves to fruits of a legume, studied by a phloem bleeding technique: Diurnal changes and effects of continuous darkness
Translocation from leaves to fruits of a legume, studied by a phloem bleeding technique: Diurnal changes and effects of continuous darkness
复制标题
通过韧皮部出血技术研究豆科植物从叶子到果实的易位：昼夜变化和持续黑暗的影响
作者：
P. Sharkey;J. S. Pate
根据叶片和果实碳水化合物的日变化以及果实韧皮部的糖和氨基酸的流出，对白羽扇豆种群进行连续采样。植物。从附生果实的远端切下的韧皮部汁液收集标准的5分钟。叶片干物质的日波动主要是由淀粉和糖的变化引起的。叶糖在下午达到最大值，淀粉在黄昏或之后不久达到最大值。从黄昏到黎明，树叶失去了糖和淀粉。韧皮部出血率在一天的周期内变化不大，但蔗糖水平在中午最高12-13%(w/v)到黎明最低9-10%之间波动。韧皮部含糖量的节律与果实和叶片的节律基本一致。韧皮部氨基酸水平与蔗糖同步波动：在一天的周期中，氨基酸组分的相对组成没有明显变化。在光周期的不同时间脉冲给予源叶14CO_2，可以研究标记的光合作用产物释放到果实韧皮部的方式和叶片中14C淀粉的积累和消耗。转入持续黑暗的植株表现出韧皮部汁液溶质的产量和浓度迅速下降，向果实中转移氮素的速度仅为自然光照下对照植株的四分之一。实验的综合数据表明，水果切段韧皮部的产糖率与叶片中当前的糖分水平直接相关。当叶片含糖量较低时(5~10mgml组织水-1)，韧皮部含糖量是源叶含糖量的10~11倍，而当含糖量较高时(25~30mgml-1)，韧皮部含糖量相差仅为原叶含糖量的3~4倍。
Diurnal changes in the carbohydrates of leaf laminae and fruits and in the bleeding of sugar and amino acids from fruit phloem were followed by successive sampling from a population ofLupinus albusL. plants. Phloem sap was collected for a standard 5 min period from cut distal tips of attached fruits. Daily fluctuations in leaf dry matter resulted largely from changes in starch and sugar. Leaf sugar rose to a maximum in the afternoon, starch to a maximum at, or shortly after, dusk. Leaves lost sugar and starch from dusk to dawn. Phloem bleeding rate varied little over a daily cycle but sucrose levels fluctuated from a noon maximum of 12–13% (w/v) to a dawn minimum of 9–10%. The rhythm of phloem sugar levels matched closely those of fruit and leaf. Phloem amino acid levels fluctuated in phase with that of sucrose: the relative composition of the amino fraction did not vary significantly over the daily cycle. Pulse feeding of source leaves with14CO2at different times in the photoperiod allowed study of the pattern of release of labelled photosynthate to the fruit phloem and the build up and depletion of14C starch in leaves. Plants transferred to continuous darkness showed a rapid decline in output and concentration of phloem sap solutes, and translocated nitrogen to their fruits at only one quarter of the rate of control plants retained in natural daylight. The combined data from the experiments showed that the rate of output of sugar from cut phloem of a fruit was directly related to the current level of sugar in leaves. When leaf sugar levels were low (5–10 mg ml tissue water-1) sugar in phloem was 10–11 times more concentrated than in source leaves, but at high leaf sugar levels (25–30 mg ml-1) this concentration difference was only 3–4 fold.