Poster: Root biology

Abs # 703: The role of pH in root hair apical growth

Presenter:	Bibikova, Tatiana N, txb119@psu.edu
Authors	Bibikova, Tatiana N (A)   Gilroy, Simon  (A)   Weisenseel, Manfred  (B)   Monshausen, Gabriele  (B)
Affiliations:	(A): Penn State University (B): Universitaet Karlsruhe

Cytosolic Ca2+ and cell wall pH are known to be important determinants of root hair development. Thus, a tip–focused Ca2+ gradient drives apical growth but not the initial events of root hair initiation, whereas an acidification of the cell wall is a key component of the initiation process. The role of wall pH in tip growth remains undefined. We have monitored surface pH and extracellular proton fluxes during root hair growth and identified three modes of proton fluxes associated with distinct phases of root hair development. Root hair initiation is characterized by a stable efflux of protons from the bulging site, consistent with the wall acidification required for initiation. During the developmental switch from initiation to tip growth the previously stable efflux changes to large oscillating extracellular fluxes and corresponding alkalinization of the surface of the growing tip. Tip alkalinization ceases upon termination of growth. Interestingly, buffering cell wall pH to alkaline values reversibly inhibits root hair growth, whereas treatment with acidic buffers causes bursting. Monitoring cytosolic pH with pH sensitive GFP reveals no changes in cytosolic pH associated with these treatments suggesting that pH might affect cell wall extensibility either by stiffening the wall at alkaline pH values, or loosening it at acidic pH. The oscillatory character of extracellular pH changes may reflect periodic stiffening and relaxation of the wall that are presumably associated with apical growth. We are currently investigating possible mechanisms whereby the spatio-temporal changes in cytosolic Ca2+ may be generating these oscillating proton fluxes through modulation of the transport activities that support proton flux in the wall. This work was supported by NASA and NSF.