[72]

OXYGEN EFFECTS ON POLLEN GERMINATION AND TUBE ORIENTATION.    J. Blasiak, D. Mulcahy and M. Musgrave.    Biology Department, University of Massachusetts, Amherst MA 01002.

                Chemical gradients and structural features within the pistil have been previously proposed as factors determining the directionality of pollen tube growth. In this study, we examine the behavior of pollen of eight species germinated in a dynamic oxygen gradient.  While the germination rates of some species decreased directly with decreasing oxygen tension, other species showed no decrease in germination at oxygen tensions as low as 2 kPa.  In one species, germination was consistently greater at decreased oxygen tensions than at ambient atmospheric levels.  In three of the eight species tested, the developing pollen tube showed clear directional growth away from the more oxygenated regions of the growth medium, while in one species growth was towards the more oxygenated region.  The remaining four species showed random tube growth. The pattern of oxytropic responses among the taxa suggests that this tropic behavior is both widespread and phylogenetically unpredictable. 

(Supported by NASA: NAG2-1020 and NAG2-1375.)