An evaluation of the role of cytokinins in the development of abnormal inflorescences in oil palms (Elaeis guineensis Jacq.) regenerated from tissue culture

Abstract

Tissue cultures and regenerant plants from cell lines producing palms with normal and abnormal flowers were analyzed for cytokinin content and compared with zygotic embryos and seedlings. Immature inflorescences at the critical stage of flower development dissected from normal and abnormal palms were also analyzed. High performance liquid chromatography (HPLC)/radioimmunoassay and HPLC/enzyme-linked immunosorbent assay methods were used over a period of several years to measure the isoprenoid cytokinins. The results of analyses of endogenous aromatic cytokinins, present at comparable levels, will be reported separately. Oil palm cultures and regenerant plants contained relatively high concentrations of the 9-glucosides of isopentenyladenine ([9G]iP) and zeatin ([9G]Z). The predominant biologically active isoprenoid cytokinin present was zeatin riboside ([9R]Z), with lesser amounts of isopentenyladenine (iP) and isopentenyladenosine ([9R]iP). There was evidence of small amounts of dihydrozeatin compounds, but high concentrations (mainly as dihydrozeatin-9-glucoside ([9G]DHZ)) were confined to the haustorium of the zygotic embryo. Callus tissue contained very low concentrations of cytokinin. Frequently only [9G]iP could be detected, at about 1 pmol · g-1 fresh weight, with [9R]Z at less than 0.05 pmol · g-1. In comparison, nodular embryogenic tissues in vitro contained between 30 and 1,500 pmol · g-1 of [9G]iP, 5–50 pmol · g-1 of [9G]Z, and up to 12 pmol · g-1 of [9R]Z. Shoots of regenerant plantlets and seedlings contained lower concentrations of [9G]iP (3–30 pmol · g-1), although this was still the predominant cytokinin. [9R]Z and [9G]Z were present at between 2 and 15 pmol · g-1, with iP at 1–5 pmol · g-1 and [9R]iP at between 1 and 12 pmol · g-1. Seedlings contained similar amounts with the exception of a lower [9G]iP content (5–10 pmol · g-1) and more [9R]iP (10–20 pmol · g-1). Root tissues of ramets contained significantly higher concentrations of [9G]iP than shoots. Comparison of two isogenic lines of one clone giving rise to normal and abnormal palms showed significantly higher concentrations of [9R]Z and [9G]Z in the normal than in the abnormal line and, in embryoids only, higher [9G]iP in the normal line. In all other cases the between-done differences were greater than any normal/abnormal differences. There was a general tendency for increased concentrations of [9G]iP in abnormal lines and for this compound to be in a higher concentration in embryoids and plants derived from culture than in zygotic embryos and seedlings. Analysis of cytokinins in immature female inflorescences of normal and abnormal palms of a single clone showed the abnormal inflorescences to have higher concentrations of [9R]Z and [9R]DHZ and less [9G]Z than the normal inflorescences at comparable stages of development.