Physiological relationships between auxin, cytokinin, and a peptide growthfactor, phytosulfokine-alpha, in stimulation of asparagus cell proliferation

The aim of this research was to determine whether the production of the mit ogenic peptide, phytosulfokine-alpha (PSK-alpha), is affected by auxin and/ or cytokinin, and whether the expression of the biological activity of PSK- alpha requires the presence of these plant hormones. We developed a competi tion enzyme-linked immunosorbent assay system that measures the amount of P SK-alpha using a polyclonal antibody. In suspension-cultured mesophyll cell s of Asparagus officinalis L., the production of PSK-alpha was first detect ed after 48 h of culture, prior to the first cell division which was genera lly observed after 96 h of culture when both 1-napthalene-acetic acid and N -6-benzyladenine were present in the medium. No significant amount of PSK-a lpha was, however, produced when one of these plant hormones was eliminated from the medium. We also characterized the progression of the cell cycle t riggered by PSK-alpha using a fluorescent dye and microdensitometry. Aspara gus mesophyll cells immediately after isolation were arrested in G(0)/G(1), and the cell cycle proceeded only when all three factors, 1-naphthaleneace tic acid, N-6-benzyladenine, and PSK-alpha, existed in the medium. These re sults show that the production and the expression of biological activity of PSK-alpha is closely correlated with the signal transduction pathway media ted by auxin and cytokinin.