Inhibition of carnation petal inrolling by growth retardants and cytokinins

Excised carnation petals induced to senescence by ethrel (an ethylene-releasing compound) exhibited morphological changes that closely resembled those of senescing petals in situ in cut flowers. The sensitivity of the excised petals to ethylene was reduced by exogenous cytokinin and this type of hormonal interaction in the control of plant development is discussed. Using the excised petals, a number of known and potential growth inhibitors were compared for ability to prevent petal inrolling induced by ethrel. Cycloheximide and 6-methylpurine were the most effective and inhibited inrolling almost completely, but purine, purine riboside, lauric acid, L-azetidine-2-carboxylic acid and n-decyl alcohol were also very effective. All these compounds were considerably more effective than any cytokinin tested. When supplied through the transpiration stream to short-stemmed carnations, cycloheximide, 6-methylpurine and purine inhibited inrolling nearly completely and the flowers finally senesced by water loss. 6-Methylpurine inhibited ethylene production in cut flowers and RNA synthesis in excised petals very markedly. Degradation of exogenous zeatin riboside by cytokinin oxidase, and the level of activity of the enzyme in petals, were reduced by 6-methylpurine. These biochemical changes probably account for the strong inhibition of inrolling induced by this compound.