Dickson R E, Larson P R
North Central Forest Experiment Station, United States Department of Agriculture Forest Service, Institute of Forest Genetics, Rhinelander, Wisconsin 54501.
Plant Physiol. 1975 Aug;56(2):185-93. doi: 10.1104/pp.56.2.185.
The incorporation and distribution of photosynthetically fixed (14)CO(2) was followed for 48 hours in a recently matured source leaf (LPI 7) and in young expanding source and sink leaves (LPI 4) of cottonwood (Populus deltoides Bartr.). The major chemical constituents of leaf laminae and petioles were separated by sequential solvent extractions and enzyme hydrolyses. Two hours after labeling, about 80% of the (14)C was found in water-alcohol-soluble constituents in the mature source lamina as compared to about 45% in those of the young expanding leaf. In both mature and expanding source leaves the water-alcohol-soluble constituents decreased while the CHCl(3)-soluble and -insoluble compounds increased with time. After 48 hours, 7 and 37% of the total (14)C was recovered from structural carbohydrates and from protein + CHCl(3)-soluble fractions, respectively, in the mature source leaf; and 4 and 65%, respectively, in the young source leaf. When the distribution of (14)C among major chemical fractions was calculated on per cent dpm/mg basis, the data showed that a young sink leaf incorporated over twice as much (14)C into structural carbohydrates as a young source leaf (11% versus 4%). However, when calculated on an absolute dpm/mg basis, activity in this fraction of the young source leaf exceeded that in the sink leaf by a ratio of about 11:1 (9528 versus 845 dpm/mg). Thus, most of the material for synthesis of structural carbohydrates was derived from in situ photosynthate.The distribution of (14)C in chemical fractions recovered from petioles was similar to that recovered from their respective laminae, except that petioles incorporated greater amounts (up to 24% of total (14)C) into structural carbohydrates. In contrast to lamina tissue, most of the photosynthate for synthesis of structural carbohydrates in the petioles of young developing leaves was imported from mature leaves farther down the stem.
在三角叶杨（Populus deltoides Bartr.）近期成熟的源叶（叶龄指数7）以及幼嫩的正在伸展的源叶和库叶（叶龄指数4）中，对光合固定的(14)CO(2)的掺入和分布情况进行了48小时的追踪研究。通过连续的溶剂萃取和酶水解，分离出了叶片和叶柄的主要化学成分。标记两小时后，在成熟源叶的水 - 醇溶性成分中发现约80%的(14)C，而在幼嫩伸展叶中这一比例约为45%。在成熟和伸展的源叶中，水 - 醇溶性成分随时间减少，而氯仿溶性和不溶性化合物则增加。48小时后，在成熟源叶中，分别从结构碳水化合物和蛋白质 + 氯仿溶性组分中回收了7%和37%的总(14)C；在幼嫩源叶中分别为4%和65%。当以每毫克每分钟衰变数（dpm/mg）为基础计算(14)C在主要化学成分中的分布时，数据显示幼嫩库叶掺入结构碳水化合物中的(14)C是幼嫩源叶的两倍多（11%对4%）。然而，以绝对dpm/mg计算时，幼嫩源叶该组分中的活性比库叶高出约11:1（9528对845 dpm/mg）。因此，结构碳水化合物合成的大部分物质来源于原位光合产物。从叶柄中回收的化学成分中的(14)C分布与从各自叶片中回收的相似，只是叶柄掺入结构碳水化合物中的量更大（高达总(14)C的24%）。与叶片组织不同，幼嫩发育叶片叶柄中结构碳水化合物合成的大部分光合产物是从茎下部的成熟叶片输入的。
