Effect of Growth Retardants Alar and Meia on Peroxidase and Iaa-oxidase Activity in Stems of Tobacco Seedlings

Plant growth retardants Alar (dimethylhydrazide of succinic acid) and its structural analogue MEIA (β-monomethyl ester of itaconic acid) at a concentration 2000mg/l sprayed at the fourth true leaf stage of tobacco seedlings caused identical retardation in stem growth from the second till the tenth day after treatment. Soluble peroxidase activity in stems of the treated plants increased on the second day after treatment and remained the same until the end of the investigated period. IAA-oxidase activity also increased on the second day after treatment, but later dropped slowly and reached the control level. Alar and MEIA did not influence peroxidase and IAA-oxidase activity in vitro. From the second day till the end of the investigated period an increase in total phenols and in the level of chlorogenic acid in the stems of the treated plants was also observed. The increase of IAAoxidase activity post treatment with growth retardants Alar and MEIA probably took part in the regulation of stem growth of tobacco seedlings. The regulation of enzyme activity might not be direct and could be due to the participation of phenol compounds.