Peter Melcher. Invited seminar speaker. "The risky business of moving water long-distances under negative pressure in plant." Hamilton College's Biology Department Seminar Series. October 2012.
Abstract
Plants move water from the soil to the leaf rather great distances without using a positive force pump, such as a heart. Understanding this phenomena stimulated scientific inquiries dating back 500 years with Leonardo Da Vinci. How do plants move water long distances? Plants use the dry atmosphere to evaporate water from internal leaf spaces, thus pulling water against the forces of gravity and hydraulic resistance. However, this means that the continuous water columns are put under negative pressures, and this makes them vulnerable to the formation of bubbles or embolisms. Embolisms disrupt the liquid continuity and impeded the flow of water through the plant. Recently, we have discovered that many plants have evolved mechanisms to remove embolisms and I will present observations using hydraulic methods and Magnetic Resonance Imaging that show refilling of embolisms while water is at negative pressure potentials. Mechanisms that allow plants to refill embolisms while under tension will also be discussed.
https://www.ithaca.edu/intercom/article.php/20121002112115802