Physiological relationships between auxin, cytokinin, and a peptide growth factor, phytosulfokine-α, in stimulation of asparagus cell proliferation

The aim of this research was to determine whether the production of the mitogenic peptide, phytosulfokine-α (PSK-α), is affected by auxin and/or cytokinin, and whether the expression of the biological activity of PSK-α requires the presence of these plant hormones. We developed a competition enzyme-linked immunosorbent assay system that measures the amount of PSK-α using a polyclonal antibody. In suspension-cultured mesophyll cells of Asparagus officinalis L., the production of PSK-α was first detected after 48 h of culture, prior to the first cell division which was generally observed after 96 h of culture when both 1-napthaleneacetic acid and N⁶-benzyladenine were present in the medium. No significant amount of PSK-α was, however, produced when one of these plant hormones was eliminated from the medium. We also characterized the progression of the cell cycle triggered by PSK-α using a fluorescent dye and microdensitometry. Asparagus mesophyll cells immediately after isolation were arrested in G₀/G₁, and the cell cycle proceeded only when all three factors, 1-naphthaleneacetic acid, N⁶-benzyladenine, and PSK-α, existed in the medium. These results show that the production and the expression of biological activity of PSK-α is closely correlated with the signal transduction pathway mediated by auxin and cytokinin. Received: 26 June 1998 / Accepted: 11 November 1998