All complex, multicellular organisms face the challenge of developing and maintaining a safe and efficient system for long distance transport of materials. In vascular plants, water absorbed by roots is transported up the plant in the dead remains of xylem cells. Plants are capable of rapidly transporting water to heights in excess of 100 m, and can extract water from dry soils and saline substrates. To achieve this, plants have evolved a transport system that relies on water sustaining a tensile force, such that the xylem sap is at negative absolute pressures. This mechanism is made possible by the intricate plumbing system that constitutes the xylem tissue of plants. However, this transport mechanism comes with its own set of problems. Most notably, water under tension is prone to cavitation, which results in the formation of a gas bubble (embolism). Embolism reduces the capacity of the xylem tissue to deliver water to the canopy, eventually causing dieback and whole plant mortality. Xylem embolism is exacerbated by environmental stresses and is now considered one of the leading causes of plant mortality resulting from drought stress. Progress in our understanding of plant water transport has been hampered by the inherent difficulty in observing and experimentally manipulating a transport system containing a metastable liquid. Non-invasive imaging techniques such as micro computed tomography (microCT) offer the potential to make direct observations on intact plants at high resolution and in real time. We utilised synchrotron based x-ray microCT to examine xylem function during drought stress in a range of woody plant species. These observations provided unprecedented spatial and temporal resolution of (a) the patterns of embolism spread in the xylem network during dehydration, and (b) refilling of embolised xylem conduits during recovery from drought. These results were compared with widely used techniques that require destructive sampling.
Brendan Choat obtained his BSc (Hons) in 1997 (JCU) and his PhD in 2003 (JCU). From 2003-2005 he worked as a Post Doctoral Fellow at Harvard University in the Department of Organismic and Evolutionary Biology. He held a second Post Doctoral Fellowship in the Department of Viticulture and Enology at the University of California, Davis from 2005-2008. In 2008 he returned to Australia to take up a Research Fellowship at ANU before moving to a Senior Research Lectureship at the Hawkesbury Institute for the Environment (UWS). He is an editor for the PrometheusWiki Project and on the editorial review board of Tree Physiology. In 2010 he was awarded an Alexander von Humboldt Fellowship for Experienced Researchers. In 2013, Dr Choat was awarded an ARC Future Fellowship for his work in mapping drought responses in plants.