Clermont Université, Université Blaise Pascal, UMR 547 PIAF, F-63177 Aubière, France.
Plant Physiol. 2010 Aug;153(4):1932-9. doi: 10.1104/pp.110.155200. Epub 2010 Jun 14.
Xylem vulnerability to cavitation is a key parameter in the drought tolerance of trees, but little is known about the control mechanisms involved. Cavitation is thought to occur when an air bubble penetrates through a pit wall, and would hence be influenced by the wall's porosity. We first tested the role of wall-bound calcium in vulnerability to cavitation in Fagus sylvatica. Stems perfused with solutions of oxalic acid, EGTA, or sodium phosphate (NaPO(4)) were found to be more vulnerable to cavitation. The NaPO(4)-induced increase in vulnerability to cavitation was linked to calcium removal from the wall. In contrast, xylem hydraulic conductance was unaffected by the chemical treatments, demonstrating that the mechanisms controlling vulnerability to cavitation and hydraulic resistance are uncoupled. The NaPO(4) solution was then perfused into stems from 13 tree species possessing highly contrasted vulnerability to cavitation. Calcium was found to be a major determinant of between-species differences in vulnerability to cavitation. This was evidenced in angiosperms as well as conifer species, thus supporting the hypothesis of a common mechanism in drought-induced cavitation.
木质部对空化的脆弱性是树木耐旱性的一个关键参数，但人们对此知之甚少。当气泡穿透纹孔壁时，就会发生空化，因此纹孔壁的孔隙率会对此产生影响。我们首先测试了细胞壁结合钙在欧洲山毛榉易空化性中的作用。结果发现，用草酸、EGTA 或磷酸钠（NaPO(4)）溶液灌注的茎更容易发生空化。NaPO(4)诱导的易空化性增加与壁中钙的去除有关。相比之下，化学处理对木质部水力传导率没有影响，这表明控制易空化性和水力阻力的机制是解耦的。然后将 NaPO(4)溶液灌注到 13 种具有明显易空化性差异的树种的茎中。发现钙是易空化性种间差异的主要决定因素。这在被子植物和针叶树物种中都得到了证实，因此支持了干旱诱导空化中存在共同机制的假设。
