Albuquerque Caetano, Scoffoni Christine, Brodersen Craig R, Buckley Thomas N, Sack Lawren, McElrone Andrew J
Department of Viticulture and Enology, University of California, Davis, 595 Hilgard Lane, Davis, CA, USA.
Department of Biological Sciences, California State University, Los Angeles, 5151 State University Drive, Los Angeles, CA, USA.
J Exp Bot. 2020 Dec 31;71(22):7286-7300. doi: 10.1093/jxb/eraa392.
Drought decreases water transport capacity of leaves and limits gas exchange, which involves reduced leaf leaf hydraulic conductance (Kleaf) in both the xylem and outside-xylem pathways. Some literature suggests that grapevines are hyper-susceptible to drought-induced xylem embolism. We combined Kleaf and gas exchange measurements, micro-computed tomography of intact leaves, and spatially explicit modeling of the outside-xylem pathways to evaluate the role of vein embolism and Kleaf in the responses of two different grapevine cultivars to drought. Cabernet Sauvignon and Chardonnay exhibited similar vulnerabilities of Kleaf and gs to dehydration, decreasing substantially prior to leaf xylem embolism. Kleaf and gs decreased by 80% for both cultivars by Ψ leaf approximately -0.7 MPa and -1.2 MPa, respectively, while leaf xylem embolism initiated around Ψ leaf = -1.25 MPa in the midribs and little to no embolism was detected in minor veins even under severe dehydration for both cultivars. Modeling results indicated that reduced membrane permeability associated with a Casparian-like band in the leaf vein bundle sheath would explain declines in Kleaf of both cultivars. We conclude that during moderate water stress, changes in the outside-xylem pathways, rather than xylem embolism, are responsible for reduced Kleaf and gs. Understanding this mechanism could help to ensure adequate carbon capture and crop performance under drought.
干旱会降低叶片的水分运输能力并限制气体交换，这涉及木质部和木质部外途径中叶片水力传导率（Kleaf）的降低。一些文献表明，葡萄极易受到干旱诱导的木质部栓塞的影响。我们结合了Kleaf和气体交换测量、完整叶片的微观计算机断层扫描以及木质部外途径的空间明确建模，以评估叶脉栓塞和Kleaf在两种不同葡萄品种对干旱响应中的作用。赤霞珠和霞多丽在Kleaf和气孔导度（gs）对脱水的脆弱性方面表现相似，在叶片木质部栓塞之前大幅下降。两个品种的Kleaf和gs在叶片水势（Ψleaf）分别约为-0.7 MPa和-1.2 MPa时下降了80%，而在两个品种中，即使在严重脱水的情况下，叶片木质部栓塞在中脉约Ψleaf = -1.25 MPa时开始，在小叶脉中几乎没有检测到栓塞。建模结果表明，与叶脉维管束鞘中类似凯氏带相关的膜通透性降低可以解释两个品种Kleaf的下降。我们得出结论，在中度水分胁迫期间，木质部外途径的变化而非木质部栓塞是导致Kleaf和gs降低的原因。了解这一机制有助于确保在干旱条件下有足够的碳捕获和作物表现。
