Ph.D. opportunity
Water plays a key role in the life of plants. The water is taken up by roots and is transported to the leaves. Most of the water is lost through the stomata in exchange for the uptake of carbon dioxide. How does water move up to the top of a tall tree? Evaporation of water at the leaf level creates a pulling force which lifts up the water column. Since water in the xylem is pulled (not pushed) up, it is under tension or negative pressure. This means that water in the xylem is in a metastable state, i.e., it is prone to cavitation. Individual vessels and tracheids may cavitate. This means that they will no longer transport water, unless the plant can refill these conduits. Since xylem is a 3-dimensional network of many vessels or tracheids, water can usually flow around individual conduits that have become air filled as a result of cavitation. Still, if too many conduits cavitate, leaves will not receive sufficient amounts of water. Stomata may close to reduce water loss, but this also reduces carbon uptake and photosynthesis. Eventually, the plant may die of carbon starvation or it may desiccate. Not surprisingly, xylem cavitation can limit plant growth and plant distribution. One of the main causes of cavitation is drought. In areas where climate change is leading to drier conditions, plants will experience more cavitation and/or more stomatal closure. It is therefore important to understand how plants can cope with drought. In the absence of cavitation, the xylem represents a low resistance highway for water molecules. However, before water can enter the xylem of roots, it has to flow through living cells. This radial pathway for water flow in roots is highly variable and is regulated by aquaporins. We are currently learning much about these membrane-spanning proteins, and how they respond to environmental factors including drought. Our lab is studying many aspects of water transport, including xylem structure and development and aquaporin function. Students in the lab have the opportunity to use a variety of modern methods to reach their research objectives. Much of our work involves the model tree poplar. Poplars are ecologically and economically important, they grow fast, and, importantly, their genome has been sequenced. I welcome inquiries by students who are interested in plants and would like to learn more about some of the issues mentioned above.
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