Oxytropism: a new twist in pollen tube orientation

Abstract

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.

Pyruvate Decarboxylase Provides Growing Pollen Tubes with a Competitive Advantage in Petunia

“…Such conditions might exist in the style during in vivo pollen tube growth (Linskens and Schrauwen, 1966;Blasiak et al, 2001). To examine the pollen tube growth rate under in vivo conditions, both types of pollen grains were germinated on the stigma of wild-type W115 plants, and the Pollen from wild-type, heterozygous pdc2/þ, and homozygous pdc2/ pdc2 plants were tested.…”

“…Blasiak et al (2001) showed a clear tropic response in pollen tubes of several species to an oxygen gradient in a colloidal medium. Indeed, the existence of an oxygen gradient in the unpollinated style was shown in Hipeastrum hybridum.…”

Profiling of Translatomes of in Vivo–Grown Pollen Tubes Reveals Genes with Roles in Micropylar Guidance during Pollination in Arabidopsis

“…This may reflect the recent finding that heme may participate in pollen tube burst during fertilization. It is known that oxygen content is extremely low in ovules (Linskens and Schrauwen, 1966;Blasiak et al, 2001), which may reduce hemeoxygenase activity and result in heme accumulation in pollen tubes. In pear (Pyrus pyrifolia), pollen tube accumulation of heme restricts potassium channel transport and thereby increases the osmolarity in the pollen tube, resulting in pollen tube burst (Wu et al, 2011).…”

Pollen tube growth: where does the energy come from?

“…A high oxygen pressure could be detected in the stigma and style which decreases at the base of the style and approaches approximately zero in the ovary. It was also observed that pollen tubes of several species show a positive tropic response toward O 2 in an oxygen gradient in a colloidal medium which mimics the stylar environment 49 and that the pollen tube itself additionally creates hypoxic regions within the style. 50 Tobacco and petunia pollen were shown to produce copious amounts of ethanol even in the absence of oxygen stress 51 indicating that fermentation plays an important role during pollenpistil interaction.…”