Higuchi Kyoko, Iwase Jun, Tsukiori Yoshifumi, Nakura Daiki, Kobayashi Nahoko, Ohashi Hidenori, Saito Akihiro, Miwa Eitaro
Department of Applied Biology and Chemistry, Laboratory of Plant Production Chemistry, Tokyo University of Agriculture, Tokyo, 156-8502, Japan.
Physiol Plant. 2014 Jul;151(3):313-22. doi: 10.1111/ppl.12175. Epub 2014 Mar 20.
Barley (Hordeum vulgare), which tolerates iron (Fe) deficiency, secretes a large amount of phytosiderophores from its roots. However, how barley is able to allocate resources for phytosiderophore synthesis when the carbon assimilation rate is reduced by Fe deficiency is unknown. We previously suggested that the acceleration of senescence in older leaves triggered by Fe deficiency may allow the recycling of assimilates to contribute to phytosiderophore synthesis. In this work, we show the relationship between an increase in the C/N ratio in older leaves and Fe-deficiency tolerance among three barley cultivars. The increase in the C/N ratio suggests an enhanced capacity for the retranslocation of carbohydrates or amino acids from older leaves to the sink organs. An increase in the sucrose concentration in Fe-deficient barley also suggests active redistribution of assimilates. This metabolic modulation may be supported by accelerated senescence of older leaves, as Fe deficiency increased the expression of senescence-associated genes. The older leaves of Fe-deficient barley maintained CO2 assimilation under Fe deficiency. Barley that had been Fe-deficient for 3 days preferentially allocated newly assimilated (13) C to the roots and nutrient solution. Interestingly, the oldest leaf of Fe-deficient barley released more (13) C into the nutrient solution than the second oldest leaf. Thus, the balance between anabolism and catabolism in older leaves, supported by highly regulated senescence, plays a key role in metabolic adaptation in Fe-deficient barley.
耐缺铁的大麦（Hordeum vulgare）会从其根部分泌大量植物铁载体。然而，当缺铁导致碳同化率降低时，大麦如何为植物铁载体合成分配资源尚不清楚。我们之前曾提出，缺铁引发的老叶衰老加速可能使同化物得以循环利用，从而有助于植物铁载体的合成。在这项研究中，我们展示了三个大麦品种老叶中碳氮比增加与耐缺铁性之间的关系。碳氮比的增加表明碳水化合物或氨基酸从老叶向库器官重新转运的能力增强。缺铁大麦中蔗糖浓度的增加也表明同化物的积极重新分配。这种代谢调节可能得到老叶加速衰老的支持，因为缺铁增加了衰老相关基因的表达。缺铁大麦的老叶在缺铁条件下维持二氧化碳同化。缺铁3天的大麦优先将新同化的（13）C分配到根部和营养液中。有趣的是，缺铁大麦最老的叶片向营养液中释放的（13）C比第二老的叶片更多。因此，在高度调控的衰老支持下，老叶中合成代谢与分解代谢之间的平衡在缺铁大麦的代谢适应中起关键作用。
