No.42 - è¾²æ¥çç©è³æºç 究æ
No.42 - è¾²æ¥çç©è³æºç 究æ
No.42 - è¾²æ¥çç©è³æºç 究æ
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Gamma Field Symposia, No. 42, 2003 Institute of Radiation Breeding<br />
NIAS, Japan<br />
PEPTIDE PLANT HORMONE, PHYTOSULFOKINE<br />
67<br />
PEPTIDE PLANT HORMONE, PHYTOSULFOKINE<br />
Yoshikatsu MATSUBAYASHI<br />
Graduate School of Bio-Agricultural Sciences, Nagoya University<br />
Chikusa, Nagoya, 464-8601, Japan<br />
e-mail: matsu@agr.nagoya-u.ac.jp<br />
Key words: phytosulfokine, peptide hormone, receptor kinase, dedifferentiation, proliferation<br />
Abstract<br />
Plant cells retain features characteristic of totipotent stem cells. That is, they have the<br />
potential to dedifferentiate, re-differentiate, and give rise to all the organs of a new plant. However,<br />
relative rates of these cellular processes are strictly dependent on initial cell density, suggesting<br />
that cell-to-cell communication is necessary for these processes. Recent biochemical purification<br />
studies have demonstrated that phytosulfokine (PSK), a small sulfated peptide, acts as an<br />
extracellular ligand involved in the initial step of cellular dedifferentiation, proliferation and redifferentiation.<br />
Furthermore, a 120-kD leucine-rich repeat receptor kinase, specifically interacting<br />
with PSK, has been purified from plasma membranes using ligand-based affinity chromatography.<br />
Lines of evidence suggest that this ligand-receptor pair confers competence for dedifferentiation<br />
and re-differentiation to individual cells, rather than directly determining cellular fate. In this<br />
article, I review what is known about PSK signaling.<br />
Introduction<br />
A high proportion of plant cells, even at a fully differentiated stage, can dedifferentiate and<br />
proliferate in vitro as totipotent stem cells, forming a structure called a callus, after treatment with<br />
plant hormones such as auxin and cytokinin. (Skoog F & Miller CO 1967) Callus cells can<br />
differentiate into various organs and give rise to a new plant, indicating that plant cells from<br />
specific adult tissues are capable of differentiating into cells of all tissues. However, relative rates<br />
of cellular dedifferentiation and growth in vitro generally depend on initial cell density. Cellular<br />
dedifferentiation and growth progress efficiently under high cell density, but are significantly<br />
suppressed under low cell density. To promote cellular growth at low cell density, several<br />
researchers have used specialized culture techniques such as nurse cultures, in which target cells
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