Microelement Research Center, Huazhong Agricultural University, Wuhan 430070, China.
Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, China.
J Exp Bot. 2022 Jun 2;73(11):3686-3698. doi: 10.1093/jxb/erac060.
Carbon and water are two main factors limiting leaf expansion. Restriction of leaf growth by low availability of carbon or water is among the earliest visible effects of potassium (K) deficiency. It is not known how K is involved in regulating the rhythmic supply of these two substrates, which differ remarkably across the day-night cycle, affecting leaf expansion. We investigated the effects of different K regimes on the time courses of leaf expansion, carbon assimilation, carbohydrates, and hydraulic properties of Brassica napus. Potassium supply increased leaf area, predominantly by promoting night-time leaf expansion (>60%), which was mainly associated with increased availability of carbohydrates from photosynthetic carbon fixation and import from old leaves rather than improvement of leaf hydraulics. However, sufficient K improved leaf hydraulic conductance to balance diurnal evaporative water loss and increase the osmotic contribution of water-soluble carbohydrates, thereby maintaining leaf turgor and increasing the daytime expansion rate. The results also indicated an ontogenetic role of K in modifying the amplitude of circadian expansion; almost 80% of the increase in leaf area occurred before the area reached 66.9% of the mature size. Our data provide mechanistic insight into K-mediated diel coordination of rhythmic carbon supply and water balance in leaf expansion.
碳和水是限制叶片扩张的两个主要因素。钾（K）缺乏时，叶片生长受到限制是最早可见的现象之一。目前尚不清楚 K 是如何参与调节这两种底物的节律性供应的，这两种底物在昼夜周期中差异显著，影响叶片扩张。我们研究了不同 K 处理对油菜叶片扩张、碳同化、碳水化合物和水力特性时间进程的影响。K 的供应增加了叶片面积，主要是通过促进夜间叶片扩张（超过 60%），这主要与光合作用固定的碳同化和从老叶中导入的碳水化合物的可用性增加有关，而不是叶片水力特性的改善。然而，充足的 K 提高了叶片水力传导率，以平衡白天的蒸散失水，并增加水溶性碳水化合物的渗透压贡献，从而维持叶片膨压并增加白天的扩张率。结果还表明 K 在改变昼夜扩张幅度方面具有个体发育作用；在叶片面积达到成熟大小的 66.9%之前，叶片面积增加了近 80%。我们的数据为 K 介导的昼夜节律性碳供应和叶片扩张中水平衡的协调提供了机制上的见解。
