Pratt R Brandon, Jacobsen Anna L
California State University, Bakersfield, Department of Biology, Bakersfield, CA, 93311, USA.
Plant Cell Environ. 2017 Jun;40(6):897-913. doi: 10.1111/pce.12862. Epub 2016 Dec 21.
The secondary xylem of woody plants transports water mechanically supports the plant body and stores resources. These three functions are interdependent giving rise to tradeoffs in function. Understanding the relationships among these functions and their structural basis forms the context in which to interpret xylem evolution. The tradeoff between xylem transport efficiency and safety from cavitation has been carefully examined with less focus on other functions, particularly storage. Here, we synthesize data on all three xylem functions in angiosperm branch xylem in the context of tradeoffs. Species that have low safety and efficiency, examined from a resource economics perspective, are predicted to be adapted for slow resource acquisition and turnover as characterizes some environments. Tradeoffs with water storage primarily arise because of differences in fibre traits, while tradeoffs in carbohydrate storage are driven by parenchyma content of tissue. We find support for a tradeoff between safety from cavitation and storage of both water and starch in branch xylem tissue and between water storage capacity and mechanical strength. Living fibres may facilitate carbohydrate storage without compromising mechanical strength. The division of labour between different xylem cell types allows for considerable functional and structural diversity at multiple scales.
木本植物的次生木质部负责运输水分、为植物体提供机械支撑并储存资源。这三种功能相互依存，导致了功能上的权衡。理解这些功能之间的关系及其结构基础，构成了解释木质部进化的背景。木质部运输效率与抗气穴安全性之间的权衡已得到仔细研究，而对其他功能，尤其是储存功能的关注较少。在此，我们在权衡的背景下综合了被子植物枝木质部所有三种功能的数据。从资源经济学角度来看，具有低安全性和低效率的物种预计适应于缓慢的资源获取和周转，这是某些环境的特征。与水分储存的权衡主要源于纤维性状的差异，而碳水化合物储存的权衡则由组织的薄壁细胞含量驱动。我们发现枝木质部组织中抗气穴安全性与水分和淀粉储存之间以及水分储存能力与机械强度之间存在权衡的证据。活纤维可能有助于碳水化合物储存而不损害机械强度。不同木质部细胞类型之间的分工在多个尺度上允许相当大的功能和结构多样性。
