engleski

Gibberellin biosynthesis in developing fruit of the Christmas rose (Helleborus niger L.)

In the Christmas rose (Helleborus niger L.) the, initially white or rose, perianth persists and turns green after fertilization, a process which depends on the presence of developing fruit or can, in their absence, be induced by the application of gibberellins. The pistils and fruit were thus analyzed for endogenous presence of the common, biologically active, gibberellins, GA1, GA3, GA4 and GA7. The freeze-dried plant material was extracted with aqueous methanol, in the presence of deuterated internal standards, and the extracts were, after purification and derivatization, subjected to gas chromatography-mass spectrometry-selected ion monitoring. The presence of the respective molecular ion and two (per GA) characteristic fragment ions suggested the presence of all four of the above gibberellins as endogenous compounds. GA4 was most abundant, followed by GA1, while GA3 and GA7 were minor gibberellins. The size of the pool of bioactive gibberellins in the fruit started to increase markedly, when chlorophyll formation in the perianth was initiated, suggesting a role for fruit gibberellins in the induction and maintenance of photosynthetic capacity in the perianth. The concentration of GA4 reached top levels during early anthesis and embryo initiation, to decrease only slightly until about two weeks before fruit ripening (most advanced stage investigated). The GA1 concentration peaked after pollination, decreased during embryo initiation, and rose again as the fruit approached maturity. To explore the possible role of tissue-specific GA biosynthesis in fruit development and perianth greening, a partial GA 20-oxidase cDNA clone was isolated from developing Helleborus seeds by RT-PCR using a pair of degenerate primers. The corresponding sequence of amino acid residues showed 70 - 80% identity with GA 20-oxidases which were already characterized from other dicots.

Helleborus niger L.; Christmas rose; Ranunculaceae; Gibberellin analysis; flower; fruit and seed development; chlorophyll induction; GA1; GA3; GA4; GA7; GA 20-oxidase

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