Cernusak Lucas A, Wong S Chin, Farquhar Graham D
Environmental Biology Group and Cooperative Research Centre for Greenhouse Accounting, Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia. Corresponding author; email:
Environmental Biology Group and Cooperative Research Centre for Greenhouse Accounting, Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
Funct Plant Biol. 2003 Nov;30(10):1059-1070. doi: 10.1071/FP03137.
We measured the oxygen isotope composition of both the water and dry matter components of phloem sap exported from photosynthesising Ricinus communis L. leaves. The O / O composition of exported dry matter matched almost exactly that expected for equilibrium with average lamina leaf water (leaf water exclusive of water associated with primary veins) with an isotope effect of α=1.027, where α=R / R , and R and R are O / O of organic molecules and water, respectively. Average lamina leaf water was enriched by 14-22‰ compared with source water under our experimental conditions, and depleted by 4-7‰, compared with evaporative site water. This showed that it is the average lamina leaf water O / O signal that is exported from photosynthesising leaves rather than a signal more closely related to that of evaporative site water or source water. Additionally, we found that water exported in phloem sap from photosynthesising leaves was enriched compared with source water; the mean phloem water enrichment observed for leaf petioles was 4.0 ± 1.5‰ (mean ± 1 s.d., n = 27). Phloem water collected from stem bases was also enriched compared with source water. However, the enrichment was approximately 0.8 times that observed for leaf petioles, suggesting some mixing between enriched phloem water and unenriched xylem water occurred during translocation. Results validated the assumption that organic molecules exported from photosynthesising leaves are enriched by 27‰ compared with average lamina leaf water. Furthermore, results suggest that the potential influence of enriched phloem water should be considered when interpreting the O / O signatures of plant organic material and plant cellulose.
我们测量了从进行光合作用的蓖麻（Ricinus communis L.）叶片输出的韧皮部汁液中水和干物质成分的氧同位素组成。输出干物质的O / O组成几乎与与平均叶片水（不包括与主脉相关的水的叶片水）达到平衡时预期的组成完全匹配，同位素效应α = 1.027，其中α = R / R ，R 和R 分别是有机分子和水的O / O。在我们的实验条件下，平均叶片水比源水富集14 - 22‰，比蒸发部位水贫化4 - 7‰。这表明从进行光合作用的叶片输出的是平均叶片水的O / O信号，而不是与蒸发部位水或源水的信号更密切相关的信号。此外，我们发现从进行光合作用的叶片的韧皮部汁液中输出的水比源水富集；观察到叶叶柄的韧皮部水平均富集为4.0 ± 1.5‰（平均值±1标准差，n = 27）。从茎基部收集的韧皮部水也比源水富集。然而，富集程度约为叶叶柄观察值的0.8倍，这表明在运输过程中富集的韧皮部水和未富集的木质部水之间发生了一些混合。结果验证了从进行光合作用的叶片输出的有机分子比平均叶片水富集27‰的假设。此外，结果表明在解释植物有机物质和植物纤维素的O / O特征时应考虑富集的韧皮部水的潜在影响。
