THIDIAZURON-INDUCED SOMATIC EMBRYOGENESIS IN INTACT SEEDLINGS OF PEANUT (ARACHIS-HYPOGAEA) - ENDOGENOUS GROWTH-REGULATOR LEVELS AND SIGNIFICANCE OF COTYLEDONS

The regulatory role of thidiazuron (TDZ) and explant factors in imparting somatic embryogenic potential was assessed in relation to endogenous growth regulator levels in peanut (Arachis hypogaea L. cv. Tango). TDZ induced somatic embryogenesis over a range of concentrations (0.5 to 10 mu M). Culture of seedlings for just 2 days on TDZ-supplemented medium was sufficient to induce somatic embryogenesis. Seedling age and retention or removal of cotyledons during culture influenced morphogenic potential significantly. The younger the seedlings, the better was the embryogenic response to TDZ treatment. The embryogenic potential of seedlings was limited for explants with no cotyledons and they did not respond to increasing levels of TDZ. In contrast, retention of at least one or both the cotyledons resulted in increased response to TDZ. Endogenous levels of cytokinins, auxins and abscisic acid were influenced by TDZ treatment, white TDZ itself was detected only in the cotyledons. The cytokinin N-6-(2-iso-pentenyl)adenine (2iP) fluctuated on a 10-day cycle in the cotyledons; TDZ treatment suppressed this change and caused an overall decrease in the pool of available 2iP in the tissue. It appeared that TDZ induced somatic embryogenesis in peanut by influencing endogenous levels of both auxin and cytokinins.