Phytosulfokine-alpha, a sulfated pentapeptide, stimulates the proliferation of rice cells by means of specific high- and low-affinity binding sites.
Peptide growth factors were isolated from conditioned medium derived from rice (Oryza sativa L.) suspension cultures and identified to be a sulfated pentapeptide [H-Tyr(SO3H)-Ile-Tyr(SO3H)-Thr-Gln-OH] and its C-terminal-truncated tetrapeptide [H-Tyr(SO3H)-Ile-Tyr(SO3H)-Thr-OH]. These structures were identical to the phytosulfokines originally found in asparagus (Asparagus officinalis L.) mesophyll cultures. The pentapeptide [phytosulfokine-alpha (PSK-alpha)] very strongly stimulated colony formation of rice protoplasts at concentrations above 10(-8) M, indicating a similar mode of action in rice of phytosulfokines. Binding assays using 35S-labeled PSK-alpha demonstrated the existence of both high- and low-affinity specific saturable binding sites on the surface of rice cells in suspension. Analysis of [35S]PSK-alpha binding in differential centrifugation fractions suggested association of the binding with a plasma membrane-enriched fraction. The apparent Kd values for [35S]PSK-alpha binding were found to be 1 x 10(-9) M for the high-affinity type and 1 x 10(-7) M for the low-affinity type, with maximal numbers of binding sites of 1 x 10(4) sites per cell and 1 x 10(5) sites per cell, respectively. Competition studies with [35S]PSK-alpha and several synthetic PSK-alpha analogs demonstrated that only peptides that possesses mitogenic activity can effectively displace the radioligand. These results suggest that a signal transduction pathway mediated by peptide factors is involved in plant cell proliferation.
Matsubayashi
Y
Y
Laboratory of Bioactive Natural Products Chemistry, School of Agricultural Sciences, Nagoya University, Chikusa, Japan. i95d307d@nucc.cc.nagoya-u.ac.jp
Takagi
L
L
Sakagami
Y
Y
D001665:Binding Sites; D002455:Cell Division / Q000187:drug effects*; D002851:Chromatography, High Pressure Liquid; D017077:Culture Media, Conditioned; D013058:Mass Spectrometry / Q000379:methods; D012275:Oryza / Q000166:cytology*; D036361:Peptide Hormones; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010940:Plant Proteins / Q000494:pharmacology*; D013462:Sulfur Radioisotopes
D017077:Culture Media, Conditioned; C100975:PSK-alpha protein, plant; D036361:Peptide Hormones; D010937:Plant Growth Regulators; D010940:Plant Proteins; D013462:Sulfur Radioisotopes