School of Biology and Environmental Sciences, University College Dublin, Belfield, Republic of Ireland.
School of Minerals Processing and Bioengineering, Central South University, Changsha, China.
Ann Bot. 2018 Dec 31;122(7):1131-1141. doi: 10.1093/aob/mcy110.
Limited supply of mineral nutrients often reduces plant growth and transpirational water flow while increasing the ratio of water-absorbing root to water-losing shoot surface. This could potentially lead to an imbalance between water uptake (too much) and water loss (too little). The aim of the present study was to test whether, as a countermeasure, the hydraulic properties (hydraulic conductivity, Lp) of roots decrease at organ and cell level and whether any decreases in Lp are accompanied by decreases in the gene expression level of aquaporins (AQPs) or increases in apoplastic barriers to radial water movement.
Barley plants were grown hydroponically on complete nutrient solution, containing 2 mm K+ (100 %), or on low-K solution (0.05 mm K+; 2.5 %), and analysed when they were 15-18 d old. Transpiration, fresh weight, surface area, shoot water potential (ψ), K and Ca concentrations, root (exudation) and cortex cell Lp (cell pressure probe), root anatomy (cross-sections) and AQP gene expression (qPCR) were analysed.
The surface area ratio of root to shoot increased significantly in response to low K. This was accompanied by a small decrease in the rate of water loss per unit shoot surface area, but a large (~50 %) and significant decrease in Lp at root and cortex cell levels. Aquaporin gene expression in roots did not change significantly, due to some considerable batch-to-batch variation in expression response, though HvPIP2;5 expression decreased on average by almost 50 %. Apoplastic barriers in the endodermis did not increase in response to low K.
Barley plants that are exposed to low K adjust to an increased ratio of root (water uptake) to shoot (water loss) surface primarily through a decrease in root and cell Lp. Reduced gene expression of HvPIP2;5 may contribute to the decrease in Lp.
矿物质养分的供应有限通常会降低植物的生长和蒸腾水流，同时增加吸水根系与失水茎表面的比例。这可能导致水分吸收（过多）和水分损失（过少）之间的不平衡。本研究的目的是测试作为一种对策，根系的水力特性（水力传导度，Lp）是否在器官和细胞水平上降低，以及任何 Lp 的降低是否伴随着水通道蛋白（AQP）基因表达水平的降低或径向水分运动的质外体屏障的增加。
大麦植株在完全营养液（含 2mm K+（100%））或低钾溶液（0.05mm K+；2.5%）上水培生长，在 15-18 天时进行分析。蒸腾作用、鲜重、表面积、茎水势（ψ）、K 和 Ca 浓度、根系（渗出）和皮层细胞 Lp（细胞压力探针）、根系解剖结构（横截面）和 AQP 基因表达（qPCR）进行了分析。
低 K 处理显著增加了根与茎的表面积比。这伴随着单位茎表面积水分损失率的轻微下降，但根系和皮层细胞水平的 Lp 大幅（~50%）和显著下降。由于表达反应存在相当大的批次间变异，根系中 AQP 基因表达没有显著变化，尽管 HvPIP2;5 的表达平均下降了近 50%。低 K 处理并没有导致内皮层质外体屏障的增加。
暴露于低钾的大麦植株通过降低根系和细胞 Lp 来适应根系（水分吸收）与茎（水分损失）表面比例的增加。HvPIP2;5 的基因表达减少可能有助于 Lp 的降低。
