The presence of very low concentrations of ethylene had dramatic effects on the opening of cut flowers of rose (Rosa hybrida L.). Depending on cultivar, the rate of opening was unaffected (e.g., ‘Gold Rush’), accelerated (e.g., ‘Sterling Silver’), or inhibited (e.g., ‘Lovely Girl’). The Km for the inhibition of opening of ‘Lovely Girl’ by ethylene was 4 ppb. Flowers of some cultivars (e.g., ‘Royalty’) had an abnormal shape when opened in the presence of ethylene. The effects of exogenous ethylene could be overcome by pretreatment of the flowers with 0.5 μmol silver thiosulfate per stem. No phytotoxicity was observed in flowers treated with 2 μmol per stem. Examination of the kinetics of the ethylene/Ag+ interaction in inhibition of opening of ‘Lovely Girl’ flowers indicated that the Ag+/ethylene interaction was competitive.
Rhythmic pulses of irreversible petal expansion in rose (Rosa hybrida L. ‘Sonia’) petals cause diurnal changes in the rate of flower opening. Time-lapse cinematography revealed a transient increase in the rate of rose flower opening that commenced shortly before the onset of a light period and lasted for a few hours. Petal expansion, which occurred sequentially from the outer to the innermost whorl, involved rhythmic increases in fresh and dry weights. The amount of expansion was greatest in the distal portion of each petal and least near the petal base. Periods of rapid expansion were accompanied by decreases in starch and increases in soluble sugars in the petals, but the total carbohydrate content of the petals remained constant during a light–dark cycle. During expansion, the osmotic potential of the outer petal increased from −790 to −690 kPa. Starch hydrolysis during petal growth appears to be important for maintenance of cell size, but it is not the factor controlling cell expansion.
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