Symposium IV: Sensing and responding to water
Abs #
40003: Sensing and responding to water: the role of the hydraulic system
Plants are fundamentally decentralized organisms, yet function in a highly integrated manner. The absence of specialized tissues for information transmission and processing requires that issues of coordination and control be viewed in an unorthodox fashion. One of the major challenges for land plants is to balance the evaporative demand imposed by the atmosphere with the ability to acquire water from the soil. The classical view holds that stomata are the only control point for water uptake and transport – and indeed in a strict sense stomata can be said to regulate the flow of water through the plant. However, the information used by stomata to assess the balance between supply and demand is markedly influenced by the liquid phase pathway, allowing one to think of the vascular tissues as forming a distributed control system. Recently we have begun to discover how the hydraulic path that links supply (soil) and demand (transpiration and growth) plays a role in sensing and responding to water availability at the whole plant level. Demonstration of the role of evaporative demand on fine tuning leaf expansion and thus fine vein density, as well as the effects of xylem sap ion concentration, temperature, cavitation/refilling dynamics, and aquaporin activity on water transport capacity illustrates how the liquid phase pathway contributes to the mesoscale management of water resources. Because short-term changes in water uptake and redistribution are directly linked to the suitability of conditions for photosynthesis, they provide a decentralized way of integrating information at the whole plant level. In addition, reversible and localized changes in hydraulic conductivity provide plants with a mechanism for combining local responses into a global strategy that is appropriately tuned to the substantial spatial and temporal environmental heterogeneity experienced both above and belowground.
