Excised carnation petals induced to senescence by ethrel (an ethylene-relea
sing 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 hor
monal interaction in the control of plant development is discussed. Using t
he excised petals, a number of known and potential growth inhibitors were c
ompared for ability to prevent petal inrolling induced by ethrel. Cyclohexi
mide and 6-methylpurine were the most effective and inhibited inrolling alm
ost completely, but purine, purine riboside, lauric acid, L-azetidine-2-car
boxylic acid and n-decyl alcohol were also very effective. All these compou
nds were considerably more effective than any cytokinin tested. When suppli
ed through the transpiration stream to short-stemmed carnations, cyclohexim
ide, 6-methylpurine and purine inhibited inrolling nearly completely and th
e flowers finally senesced by water loss. 6-Methylpurine inhibited ethylene
production in cut flowers and RNA synthesis in excised petals very markedl
y. Degradation of exogenous zeatin riboside by cytokinin oxidase, and the l
evel of activity of the enzyme in petals, were reduced by 6-methylpurine. T
hese biochemical changes probably account for the strong inhibition of inro
lling induced by this compound.