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ULTRASTRUCTURE OF P. PATENS TIP CAULONEMATA CELLS: UNTREATED, COLD GROWN, SEVERED, ORYZALIN TREATED, UV-A TREATED.    Edward B. Tucker¹, Vinoud Sookhdeo¹, and Lucy Yin².   ¹Natural Sciences, Baruch College, CUNY, New York, NY and ²Biology Department, University of Massachusetts, Amherst MA.

The apical cells of P. Patens caulonemata are tip growing and in the dark they are negatively gravitropic.  Our data indicated that sedimentation of chloro-amyloplasts preceded gravi-curvature, similar to that previously reported for Ceratodon (Walker and Sack, 1990; Planta 181: 71-77).  Gravi-curvature occurred if cells were grown at 5^o C, and was temporarily inhibited if cells were either treated with oryzalin or exposed to a flash of UV-A light.  Gravi-curvature did not occur if cells were severed from the sub-apical cells. 

Cells were grown on agar plates, wrapped in foil and placed vertically.  They were not gravi-stimulated.  Treatments were: untreated, grown at 5^oC, severed, treated for 5 min with 0.1% oryzalin, or exposed to UV-A for 10s.  Cells were fixed in the dark with 4% paraformaldehyde, 2% glutaraldehyde in 100 mM PIPES pH 6.8 and post-fixed with 2% OSO₄ plus 0.8% potassium ferricyanide.  Tissue was en bloc stained with 2% uranyl acetate and embedded in Spurr resin.  Sections were post stained with lead citrate. The ultrastructure of the apical cell demonstrated organelle domains: an apical ER zone, a chloro-amyloplast free zone,  a chloro-amyloplast  zone, a nuclear zone, and a vacuolar zone.  Changes in organelle ultrastructure and distribution were observed on electron micrographs of the treated cells.  For example, in untreated cells chloro-amyloplasts aligned in rows seemingly outlined by endoplasmic reticulum.  In cold grown cells chloro-amyloplasts were larger while in severed cells they were smaller.  Chloro-amyloplasts of oryzalin treated cells accumulated in the tip region.  With all of these treatments the normal alignment of chloro-amyloplasts was altered.  

(Supported by NASA grant NAG5-3743.)