Relations between Light Level, Sucrose Concentration, and Translocation of Carbon 11 in Zea mays Leaves.
Relations between Light Level, Sucrose Concentration, and Translocation of Carbon 11 in Zea mays Leaves.
复制标题
光照水平、蔗糖浓度和玉米叶中碳 11 易位之间的关系。
DOI：
10.1104/pp.59.5.808
复制
发表时间：
1977
期刊：
影响因子：
7.4
通讯作者：
F. Chang
中科院分区：
文献类型：
--
作者：
J. Troughton;B. Currie;F. Chang
利用半衰期短（20.4 min）的正电子发射同位素碳11研究了玉米叶片中碳的转运机制。湮灭过程中产生的伽马辐射允许对同位素进行体内或非破坏性测量，而短的半衰期允许在同一天内对同一片叶子进行多次易位测量。由（10）B (d,n)(11)C核反应产生的碳11转化为（11）CO(2)，作为短脉冲供给叶片，并在光合作用中被同化。利用计数器在多个位置同时监测放射性脉冲沿韧皮部叶片的运动过程。计数器是带有光电倍增管的NaI晶体，输出被放大，传递到单通道分析仪，计数每30秒累积20秒。用计算机对半衰期和本底辐射进行了校正，并将结果显示在高速绘图仪上。从校正后的数据中得到的信息包括转运的速度、放射性碳脉冲的形状，以及光和叶片距离对这些参数的影响。在所有测量过程中，植物都保持在受控的环境条件下。速度是由脉冲前端中点的时间位移得出的，沿着叶片在两个位置测量。这是表观平均移位速度因为它是速度随距离变化的平均值，筛管之间或筛管内部的速度变化的平均值，它是脉冲中所有粒子的平均速度的平均值。在0.25 - 11 cm min（-1）的大范围内观察到转运速度，但大部分变异是由于叶片可用光的变化。例如，转运的速度与整个植株或单个叶片的光照水平成正比。叶片的阴影确定了光效既不局限于喂食区域，也不局限于测量的叶片部分。提出了速度取决于叶片在最后一个计数器上游的光中的比例。转运速度相对独立于植株的生长阶段、叶龄和昼夜光照周期的时间。叶片中还原糖、淀粉和蔗糖的含量与转运速度有关。转速与叶片中蔗糖浓度呈双相关系，实验中测得的高速只发生在叶片中蔗糖浓度超过干重的8%时。根据脉冲的半宽估计了进入韧皮部和在韧皮部移位的脉冲的形状。半宽主要是由加载现象决定的，加载现象导致半宽从叶片上的2分钟增加到韧皮部的40分钟以上。在许多例子中，脉冲继续随着离fed区域的距离而变宽。半宽度与速度无关，但高度依赖于光的水平。
The mechanism of carbon transport in Zea mays leaves was investigated using carbon 11 which is a short lived (half-life 20.4 min) positronemitting isotope. The gamma radiation produced on annihilation allows in vivo or nondestructive measurement of the isotope and the short half-life allows many measurements of translocation to be made on the same leaf within the same day.Carbon 11 produced by the (10)B (d,n)(11)C nuclear reaction was converted to (11)CO(2), fed to a leaf as a short pulse, and assimilated during photosynthesis. The progress of the radioactive pulse along the leaf in the phloem was monitored in several positions simultaneously with counters. The counters were NaI crystals with photomultipliers and the output was amplified, passed to single channel analyzers, and the counts accumulated for 20 seconds every 30 seconds. Corrections were made for the half-life and background radiation by computer, and the results were displayed on a high speed plotter. Information derived from the corrected data included the speed of translocation, the shape of the radioactive carbon pulse, and the influence of light and distance along the leaf on these parameters. The plants were kept under controlled environment conditions during all measurements.A speed was derived from the time displacement of the midpoint of the front of the pulse, measured at two positions along the leaf. This was an apparent mean speed of translocation because it averaged a variation in speed with distance, variation in speed between or within sieve tubes, and it averaged the mean speed of all of the particles in the pulse.A wide range of speeds of translocation from 0.25 to 11 cm min(-1) was observed but most of the variability was due to the variation in light available to the leaf. For example, the speed of translocation was proportional to the light level on either the whole plant or individual leaf. Shading of the leaf established that the light effect was not localized in either the feeding area or in the portion of the leaf on which the measurements were made. It was proposed that the speed was dependent on the proportion of the leaf in the light upstream from the last counter. The speed of translocation was relatively independent of the stage of growth of the plant, age of the leaf, and the time during the diurnal light cycle.Data obtained on the level of the reducing sugars, starch, and sucrose in the leaf were related to the speed of translocation. A biphasic relationship between speed and sucrose concentration in the leaf was established and the high speeds measured during experiments only occurred when sucrose concentrations in the leaf exceeded 8% of the dry weight.The shape of the pulse loaded into and translocated in the phloem was estimated from the half-width of the pulse. The half-width was primarily determined by loading phenomena which resulted in an increase in the half-width from 2 minutes when fed to the leaf to more than 40 minutes in the phloem. In many examples, the pulse continued to broaden with distance along the leaf from the fed region. The half-width was independent of the speed but highly dependent on the light level.