Biology Faculty and Student Presentations

10/05/2004

Contributed by Nancy Pierce

Peter Melcher presented the following posters with Andrew McGraw '05 and Eleanor Lahr '04 at the second annual Symposium in Plant Biology.

The meeting was sponsored by the University of Massachusetts, Amherst, and held at Smith College.

Poster 1: "Ions and Bordered Pit Strength". Andrew McGraw and Peter Melcher.
Tension driven water transport through the xylem of plants is powered by evaporation of water from internal leaf spaces. Pulling water through the xylem under negative pressures requires that the water columns within the xylem remain continuous. Thus plants depend on the ability of water to withstand substantial negative pressures during tension driven sap flow. However, water under negative pressure is considered metastable and thus susceptible to cavitation and embolism (bubble formation). Because of this, we would expect plants to have evolved strategies to tolerate embolized xylem conduits. It has been suggested that bordered pit membranes aid in protecting the continuity of the xylem sap by isolating embolisms to discrete regions within the xylem. More recently, these membranes have been shown to respond to small changes in ion concentrations in the transpiration stream resulting in altered xylem hydraulic conductance's. But only a few studies have investigated the effect of ions on xylem cavitation thresholds. Here we investigated the ability of bordered pit membranes to withstand air-injection pressures measured on an individual vessel level. We found that Calcium ions increase the strength of bordered pit membranes located in older xylem to withstand increased air injection pressures compared to newer xylem.

Poster 2: "A test of the Segmentation Hypothesis". Eleanor Lahr and Peter Melcher
It is known that the xylem on many plant species are divided up into smaller chambers that are separated by primary cell wall material known as bordered pit membranes. Martin Zimmermann proposed the segmentation hypothesis that describes how bordered pit membranes may act as safety "valves" that preserve the hydraulic network in plants by containing embolism (bubbles), that are considered catastrophic in maintaining overall plant health, to expendable plant parts such as leaves and petioles and thus preserving the main branches and trunks. Here we present data using an individual vessel approach that support the segmentation hypothesis.

Contributed by Nancy Pierce

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