Calcium, pH and the Cytoskeleton in Pollen Tube Growth

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

Pollen tube growth is the process by which flowering plants deliver the male gamete to the egg apparatus for fertilization, a necessary prerequisite to seed production. Characterized by rapid rates and a high degree of polarity, the elongation process is of great interest, both because of its economic implications and its relevance to fundamental aspects of plant cell growth and development. This project focuses on the role of calcium (Ca2+), protons (H+), and the actin cytoskeleton, and builds upon the recent demonstration that pollen tube growth rate oscillates, and that there are underlying oscillations in both ions and cytoskeletal activity. Using pollen tubes of both lily and tobacco, an attempt will be made to correlate at high temporal resolution the oscillations in intracellular Ca2+ and H+ with those in the growth rate. In addition, an exploration will be made on how these oscillations are changed when cell wall properties are modified by various agents, e.g., Ca2+, H+, boron, pectin methyl esterase, or Yariv phenyl glycoside. By determining if and how these agents modify the oscillatory behavior, and its relationship to both the intracellular gradients of Ca2+ and H+ as well as the extracellular fluxes of these ions, it seems possible that a temporal hierarchy can be developed for the activity of factors that control growth. Techniques involved here include ratiometric imaging for intracellular Ca2+ and H+, and ion selective vibration probe analysis to determine the magnitude and direction of extracellular fluxes. In studies on the cytoskeleton, attention will be given to the structure and dynamic distribution of F-actin in the clear zone, where rapid turnover and formation of these elements is presumed to occur. It will be particularly interesting to correlate these turnover processes with the oscillatory pattern of growth, again with the view of determining which events precede the rapid growth phases and which events follow. For these studies the newly developed GFP-talin fusion will be used to fluorescently label F-actin in living pollen tubes. When taken together it is anticipated that these studies will provide insight into the physiological and molecular factors that control growth and development of the pollen tube. To the extent that other tip growing cells, e.g., root hairs, fungal hyphae, fern and moss protonemata, use similar mechanisms, the results from pollen tubes could be pertinent, and help us gain a general understanding of basic mechanisms involved in cell growth.