title: Peptide growth factor phytosulfokine-alpha contributes to the pollen population effect.
abstract: Density-dependent pollen germination and tube growth in vitro is a well-documented phenomenon, termed the pollen population effect, but far less is known about its molecular basis. We present evidence to support phytosulfokine-alpha [Y(SO3H)IY(SO3H)TQ; PSK-alpha] as a native bioactive factor contributing to this effect. Mature pollen grains of Nicotiana tabacum L. var. macrophylla were incubated in liquid medium for 2 h. Pollen germination frequency increased in a density-dependent manner from 625 to 46,000 grains/ml. Conditioned medium, obtained from the medium of pollen cultured at a density of 10,000 pollen grains/ml for 12 h, promoted the germination of pollen cultured at a low density (625 grains/ml). A rabbit antiserum against PSK-alpha specifically inhibited the promotive effect of conditioned medium. Quantification by enzyme-linked immunosorbent assay showed that the conditioned medium contained 0.4 nM of PSK-alpha. Exogenous PSK-alpha also stimulated pollen germination in the low-density culture. These results indicate that PSK-alpha is an important regulator involved in the pollen population effect.
authors.affiliation: Laboratory of Bioactive Natural Products Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Japan.
authors.forename: Y F
authors.initials: YF
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Matsubayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Sakagami
mesh_terms: D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D007700:Kinetics; D036361:Peptide Hormones; D010937:Plant Growth Regulators / Q000494:pharmacology / Q000502:physiology*; D010940:Plant Proteins / Q000494:pharmacology / Q000502:physiology*; D010947:Plants, Toxic; D011058:Pollen / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D014026:Nicotiana / Q000166:cytology / Q000502:physiology*
chemical_list: D017077:Culture Media, Conditioned; C100975:PSK-alpha protein, plant; D036361:Peptide Hormones; D010937:Plant Growth Regulators; D010940:Plant Proteins