Trifil Patrizia, Nardini Andrea, Raimondo Fabio, Lo Gullo Maria A, Salleo Sebastiano
Dipartimento di Scienze della Vita, Università di Messina, Salita Sperone 31, 98166 Messina S Agata, Italy.
Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italy.
Funct Plant Biol. 2011 Jul;38(7):606-613. doi: 10.1071/FP10233.
Xylem cavitation is a common occurrence in drought-stressed plants. Cavitation-induced embolism reduces xylem hydraulic conductivity (kxylem) and may lead to stomatal closure and reduction of photosynthetic rates. Recent studies have suggested that plants may compensate for kxylem loss through ion-mediated enhancement of the residual water transport capacity of functioning conduits. To test this hypothesis, field-grown laurel (Laurus nobilis L.) plants were subjected to mild drought stress by suspending irrigation. Drought treatment induced a significant increase in xylem embolism compared with control (well watered) plants. Xylem sap potassium concentration ([K+]) increased during the day both in control and water stressed plants. Midday values of sap [K+] were significantly higher in water stressed plants. The recorded increase in sap potassium concentration induced significant enhancement of residual kxylem when solutions with different [K+] were perfused through excised stems sampled in the field and measured in the laboratory. In planta measurements of stem hydraulic conductance revealed no change between water stressed plants and controls. Our data suggest that ion-mediated enhancement of residual kxylem buffered the actual loss of hydraulic conductance suffered by plants during the warmest hours of the day as well as under mild drought stress conditions.
木质部空化在遭受干旱胁迫的植物中很常见。空化引发的栓塞会降低木质部水力传导率（kxylem），并可能导致气孔关闭和光合速率下降。最近的研究表明，植物可能通过离子介导增强功能导管的剩余水分运输能力来补偿kxylem的损失。为了验证这一假设，对田间种植的月桂（Laurus nobilis L.）植株停止灌溉，使其遭受轻度干旱胁迫。与对照（充分浇水）植株相比，干旱处理导致木质部栓塞显著增加。对照植株和水分胁迫植株的木质部汁液钾浓度（[K+]）在白天均有所增加。水分胁迫植株的汁液[K+]中午值显著更高。当将不同[K+]的溶液灌注通过田间采集并在实验室测量的离体茎段时，所记录的汁液钾浓度增加导致剩余kxylem显著增强。对植株茎干水力导度的原位测量表明，水分胁迫植株与对照植株之间没有变化。我们的数据表明，离子介导的剩余kxylem增强缓冲了植物在一天中最热时段以及轻度干旱胁迫条件下实际遭受的水力导度损失。
