Sulfonylsemicarbazide derivatives and preservative composition for preserving the freshness of flower of cut flowers

A method for preserving the freshness of flowers of a plant of the florist crop, which comprises treating the cut stem portion or leaves of the cut flowers as obtained by cutting off the root part of the florist plant, or treating roots or leaves of the florist plant under cultivation in a field or a pot, with a sulfonylsemicarbazide derivative having the general formula (I):

• ##STR105## wherein R.sup.1 represents a linear or branched, lower alkyl group having 3 to 4 carbon atoms, or a phenyl group which may optionally be substituted by one or more halogen atoms, lower alkyl groups, hydroxyl groups, alkoxyl groups, carboxyl groups, alkoxycarbonyl groups, nitro groups, amino groups or benzyloxy groups, or R.sup.1 represents a pyridyl group, or a thiophenyl group which may optionally be substituted by one or more carboxyl groups or alkoxycarbonyl groups, and R.sup.2 and R.sup.3 each independently represents a hydrogen atom, a lower alkyl group, an alkoxalyl group, an alkoxyalkyl group, an alkoxycarbonyl group or an alkylthio-thiocarbonyl group represented by the formula --C(X)--X--R.sup.4 where X means an oxygen atom or a sulfur atom and R.sup.4 means a lower alkyl group, or R.sup.2 and R.sup.3 may form a heterocyclic ring having 4 to 5 carbon atoms, as taken with the nitrogen atom to which R.sup.2 and R.sup.3 are bonded, or R.sup.2 and R.sup.3 may form a group of the formula --N.dbd.CR.sup.5 (R.sup.6) where R.sup.5 and R.sup.6 mean lower alkyl groups, respectively, as taken with the nitrogen atom to which R.sup.2 and R.sup.3 are bonded, or salts of said derivatives, or with an aqueous solution of said derivative(s) or said salt(s), and thereby allowing the cut flowers or the florist plant under the cultivation to absorb the compound of the general formula (I) in an amount effective to maintain the freshness of the flower.