Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå, Sweden.
Physiol Plant. 2021 May;172(1):201-217. doi: 10.1111/ppl.13319. Epub 2021 Jan 7.
Autumn senescence in aspen (Populus tremula) is precisely timed every year to relocate nutrients from leaves to storage organs before winter. Here we demonstrate how stem girdling, which leads to the accumulation of photosynthates in the crown, influences senescence. Girdling resulted in an early onset of senescence, but the chlorophyll degradation was slower and nitrogen more efficiently resorbed than during normal autumn senescence. Girdled stems accumulated or retained anthocyanins potentially providing photoprotection in senescing leaves. Girdling of one stem in a clonal stand sharing the same root stock did not affect senescence in the others, showing that the stems were autonomous in this respect. One girdled stem with unusually high chlorophyll and nitrogen contents maintained low carbon-to-nitrogen (C/N) ratio and did not show early senescence or depleted chlorophyll level unlike the other girdled stems suggesting that the responses depended on the genotype or its carbon and nitrogen status. Metabolite analysis highlighted that the tricarboxylic acid (TCA) cycle, salicylic acid pathway, and redox homeostasis are involved in the regulation of girdling-induced senescence. We propose that disrupted sink-source relation and C/N status can provide cues through the TCA cycle and phytohormone signaling to override the phenological control of autumn senescence in the girdled stems.
秋季，欧洲山杨（Populus tremula）会精确地将养分从叶片转移到冬季贮藏器官中，以完成衰老过程。本研究展示了茎环割（stem girdling）如何影响衰老过程，茎环割会导致冠层中光合产物的积累。结果表明，环割导致衰老提前发生，但叶绿素降解速度较慢，氮素的再吸收效率更高，与正常秋季衰老过程不同。环割的茎积累或保留花色素苷，可能为衰老叶片提供光保护。在克隆种群中，对一根茎进行环割不会影响其他茎的衰老，表明这些茎在这方面是自主的。一根环割的茎表现出异常高的叶绿素和氮含量，同时保持低的碳氮比（C/N），并且没有表现出早期衰老或叶绿素水平降低，这与其他环割的茎不同，表明这些反应取决于基因型或其碳氮状态。代谢物分析突出表明，三羧酸（TCA）循环、水杨酸途径和氧化还原稳态参与了环割诱导衰老的调节。我们提出，破坏源库关系和 C/N 状态可以通过 TCA 循环和植物激素信号提供线索，从而超越环割茎秋季衰老的物候控制。
