Abadie Cyril, Lamothe-Sibold Marlène, Gilard Françoise, Tcherkez Guillaume
Research School of Biology, ANU College of Medicine, Biology and Environment, Australian National University, Canberra, ACT 2601, Australia.
Université Paris-Sud, Institute of Plant Sciences Paris-Saclay IPS2 (Bâtiment 630), UMR CNRS-INRA 9213, Université Paris-Saclay, 91405 Orsay, France.
Funct Plant Biol. 2016 Mar;43(3):298-306. doi: 10.1071/FP15187.
Many plant species or cultivars form variegated leaves in which blades are made of green and white sectors. On the one hand, there is little photosynthetic CO2 assimilation in white tissue simply because of the lack of functional chloroplasts and thus, leaf white tissue is heterotrophic and fed by photosynthates exported by leaf green tissue. On the other hand, it has been previously shown that the white tissue is enriched in nitrogenous compounds such as amino acids and polyamines, which can, in turn, be remobilised upon nitrogen deficiency. However, the origin of organic nitrogen in leaf white tissue, including the possible requirement for N-reduction in leaf green tissue before export to white tissue, has not been examined. Here, we took advantage of isotopic methods to investigate the source of nitrogen in the white tissue. A survey of natural isotope abundance (δ15N) and elemental composition (%N) in various variegated species shows no visible difference between white and green tissues, suggesting a common N source. However, there is a tendency for N-rich white tissue to be naturally 15N-enriched whereas in the model species Pelargonium×hortorum, white sectors are naturally 15N-depleted, indicating that changes in metabolic composition and/or N-partitioning may occur. Isotopic labelling with 15N-nitrate on illuminated leaf discs clearly shows that the white tissue assimilates little nitrogen and thus relies on nitrate reduction and metabolism in the green tissue. The N-sink represented by the white tissue is considerable, accounting for nearly 50% of total assimilated nitrate.
许多植物物种或栽培品种会形成杂色叶片，其叶片由绿色和白色部分组成。一方面，白色组织中几乎没有光合二氧化碳同化作用，仅仅是因为缺乏功能性叶绿体，因此，叶片白色组织是异养的，由叶片绿色组织输出的光合产物提供养分。另一方面，先前的研究表明，白色组织富含含氮化合物，如氨基酸和多胺，这些化合物在缺氮时又可以被重新利用。然而，叶片白色组织中有机氮的来源，包括在输出到白色组织之前叶片绿色组织中可能对氮还原的需求，尚未得到研究。在这里，我们利用同位素方法来研究白色组织中氮的来源。对各种杂色物种的天然同位素丰度（δ15N）和元素组成（%N）的调查表明，白色组织和绿色组织之间没有明显差异，这表明它们有共同的氮源。然而，富含氮的白色组织有自然富集15N的趋势，而在模式物种天竺葵中，白色部分自然贫化15N，这表明可能发生了代谢组成和/或氮分配的变化。用15N-硝酸盐对光照下的叶盘进行同位素标记清楚地表明，白色组织吸收的氮很少，因此依赖于绿色组织中的硝酸盐还原和代谢。白色组织所代表的氮库相当大，占总同化硝酸盐的近50%。
