Yoneyama T, Handley L L, Scrimgeour C M, Fisher D B, Raven J A
National Agriculture Research Center, Kannondai 3-1-1, Tsukuba, Ibaraki 305, Japan.
The Scottish Crop Research Institute, Invergowrie, Dundee, Scotland DD2 5DA, UK.
New Phytol. 1997 Oct;137(2):205-213. doi: 10.1046/j.1469-8137.1997.00809.x.
This work explored whether the natural abundances of carbon and nitrogen isotopes could be used to describe the movement of C and X within wheat plants; we also considered whether isotopic analyses of aphids or their honeydew would substitute for direct analysis of phloem exudate. The δ C of ears and roots (sinks) most closely matched those of the sugars + organic acids fraction (sources) in both growth stages; phloem δ C matched that of leaf blade sugars. Xylem exudate δ C matched no other putative (and measured) source in the ear-forming stage and matched that of whole roots and ears in the grain-filling stage. The δ N of grain and roots (sinks) resembled that of leaf amino acids (sources) in the ear-forming stage. In the gram-filling stage, ear δ N continued to resemble that of leaf amino acids, and δ N of roots most closely resembled that of whole leaves. In the grain-filling stage, phloem δ N fell between that of leaf blade amino acids and that of whole leaves and was X-depleted relative to internal and external NO, -N. In both growth stages, xylem exudate δ N was less than that of soil NO -N and more than that of residual soil N after mineral N extraction. The isotopic values are generally in agreement with data from other approaches, such as isotope labelling; they show NO -N reduction in both shoots and roots of wheat and significant N recycling (root-shoot-phloem-root) and C movement. Aphids might serve as a substitute for isotopic analysis of phloem δ N. having the same value as their food source. Their excreta was N-enriched relative to phloem.
本研究探讨了碳和氮同位素的自然丰度是否可用于描述碳和X在小麦植株内的移动；我们还考虑了对蚜虫或其蜜露进行同位素分析是否能替代对韧皮部渗出液的直接分析。在两个生长阶段，穗和根（库）的δC与糖 + 有机酸部分（源）的δC最为匹配；韧皮部δC与叶片糖分的δC相匹配。木质部渗出液δC在穗形成阶段与其他假定（及测量）的源均不匹配，而在灌浆阶段与整个根和穗的δC相匹配。在穗形成阶段，籽粒和根（库）的δN与叶片氨基酸（源）的δN相似。在灌浆阶段，穗的δN继续与叶片氨基酸的δN相似，而根的δN与整叶的δN最为相似。在灌浆阶段，韧皮部δN介于叶片氨基酸和整叶的δN之间，且相对于内部和外部的NO₃⁻-N呈X亏损。在两个生长阶段，木质部渗出液δN均低于土壤NO₃⁻-N且高于矿质氮提取后残留土壤氮的δN。同位素值总体上与其他方法（如同位素标记）的数据一致；它们显示了小麦地上部和根部的NO₃⁻-N减少以及显著的氮循环（根-地上部-韧皮部-根）和碳移动。蚜虫可作为韧皮部δN同位素分析的替代物，其δN值与其食物源相同。其排泄物相对于韧皮部而言氮含量较高。
