Abstract
Summary In Ipomoea we observed that various growth retardants (CCC, B-nine and Phosfon) inhibited the expansion of isolated cotyledons while 2,4-dichloro-phenoxy acetic acid, gibberellin, cytokin ins and certain fluorene-9-carboxylic acid derivatives (morphactins) acted as stimulators of this process (1, 2). Further, gibberellin when used in combination with CCC or B-nine successfully reversed the inhibition of expansion caused by the former growth substances. In contrast, morphactin and 2,4-dichloro-phenoxyacetic acid, in combination, acted synergistically in influencing expansion. A synergism was also found to exist between morphactins and cytokinins (2). Recently, K ursanov et al., (3) have shown that in isolated cotyledons of pumpkin all the three phytohormones tested viz., 6-benzylaminopurine gibberellin and 3-indoleacetic acid can promote expansion. However, the resulting effect depended on the concentration of the particular growth regulator and on its quantitative ratio in respect to other phytohormones. These evidences apparently suggest that like many other physiological processes expansion of cotyledons is also regulated by endogenous levels of bio-regulants and their interactions.
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