Skelton Robert P, Brodribb Timothy J, Choat Brendan
School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS, 7001, Australia.
Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW, 2753, Australia.
New Phytol. 2017 Apr;214(2):561-569. doi: 10.1111/nph.14450. Epub 2017 Jan 26.
Finding thresholds at which loss of plant functionality occurs during drought is critical for predicting future crop productivity and survival. Xylem resistance to embolism has been suggested as a key trait associated with water-stress tolerance. Although a substantial literature exists describing the vulnerability of woody stems to embolism, leaves and roots of herbaceous species remain under-represented. Also, little is known about vulnerability to embolism at a whole-plant scale or propagation of embolism within plants. New techniques to view the process of embolism formation provide opportunities to resolve long-standing questions. Here, we used multiple visual techniques, including X-ray micro-computed tomography and the optical vulnerability method, to investigate the spread of embolism within intact stems, leaves and roots of Solanum lycopersicum (common tomato). We found that roots, stems and leaves of tomato plants all exhibited similar vulnerability to embolism, suggesting that embolism rapidly propagates among tissues. Although we found scarce evidence for differentiation of xylem vulnerability among tissues at the scale of the whole plant, within a leaf the midrib embolized at higher water potentials than lower order veins. Substantial overlap between the onset of cavitation and incipient leaf damage suggests that cavitation represents a substantial damage to plants, but the point of lethal cavitation in this herbaceous species remains uncertain.
确定干旱期间植物功能丧失的阈值对于预测未来作物生产力和存活率至关重要。木质部对栓塞的抗性被认为是与水分胁迫耐受性相关的关键性状。尽管有大量文献描述了木本茎干对栓塞的脆弱性，但草本物种的叶片和根系在这方面的研究仍较少。此外，对于全株尺度上的栓塞脆弱性或植物体内栓塞的传播了解甚少。观察栓塞形成过程的新技术为解决长期存在的问题提供了机会。在此，我们使用了多种可视化技术，包括X射线显微计算机断层扫描和光学脆弱性方法，来研究栓塞在完整的番茄植株茎、叶和根中的传播情况。我们发现番茄植株的根、茎和叶对栓塞均表现出相似的脆弱性，这表明栓塞在组织间迅速传播。尽管我们在全株尺度上几乎没有发现木质部脆弱性在不同组织间存在差异的证据，但在叶片内部，中脉在比低阶叶脉更高的水势下发生栓塞。空化起始与叶片初期损伤之间存在大量重叠，这表明空化对植物造成了严重损害，但这种草本物种的致死空化点仍不确定。
