Abscisic‐acid‐induced turion formation in Spirodela polyrrhiza L. I. Production and development of the turion

Abstract

Abstract The production, growth, and development of the abscisic‐acid‐induced turion (a small dormant bud) of Spirodela polyrrhiza were investigated. Addition of ABA to a culture of S. polyrrhiza resulted in growth inhibition at concentrations as low as 10−6molm−3, growth being completely arrested at 10−2 mol m. Over a single order of magnitude range around I0−4molm−3, ABA also induced the production of turions. The range of turion‐producing concentrations of ABA was found to be much narrower than previously reported, turion production having a clearly defined threshold, optimum, and upper limit. The possibility that growth inhibition and turion formation are integrally linked aspects of a single response is discussed. Only primordia ≤0.7 mm long at the time of ABA addition could be induced to develop into turions and the events leading to turion formation were found to be reversible up to 72 h in ABA. It is concluded that in terms of turion formation there is a sensitivity window to abscisic acid lasting some 4–20h in the normal developmental life of frond cells. Providing cells experience the appropriate signal in this sensitivity window they initiate a new programme which eventually leads to turion formation. Microscopical analysis showed that the cells within this sensitivity window were still actively dividing. It is suggested that the developmental switch‐over to rapid cell expansion and separation marks the end of this ABA sensitivity window.