Boron (B) is an essential micronutrient for the survival of vascular plants. The most severe effect derived from a deficiency of B is the alteration of cell wall biogenesis and pollen germination. We investigated pollen of plant species that require B for germination (Zea may L. and Nicotiana tabacum L.), as well as those that can germinate without B (Pinus sp, Lilum longiflorum, Impatiens sp.). In both groups, B addition in the growth medium increased the length of the pollen tube after germination. Hydroxyproline Rich Glycoproteins (HRGPs) are the most abundant cell wall structural proteins of dicotyledonous plants and the sexual tissues of monocotyledonous plants. Here, we show that maize pollen accumulated a significant pool of hydroxyproline (Hyp) and 63% of this amino acid was localized in the pollen tube wall. Maize pollen germinated in the presence of B accumulated soluble (48%) and non-soluble (16%) Hyp in the pollen tube wall in contrast to maize pollen germinated without B. In addition, B seems to modify the amount of HRGPs that become cross-linked to the wall. Immunolocalization of HRGPs showed that these glycoproteins were preferentially localized in the pollen tube of maize, not in the pollen grain itself. Hence, B might affect the assembling of HRGPs in the wall of pollen tubes grown in vitro.
cell wall; HRGPs; hydroxyproline; pollen tube
