The Effect of IAA on Sugar Accumulation and Basipetal Transport of ¹⁴C‐labelled Assimilates in Relation to Root Formation in Phaseolus vulgaris Cuttings

The effect of indol‐3yl‐acetic acid on root formation, accumulation of 80% ethanol‐soluble sugars and basipetal transport of ¹⁴C‐labelled assimilates has been investigated in Phaseolus vulgaris (cv. Canadian Wonder) hypocotyl cuttings. The removal of leaves reduced root formation in the hypocotyl, while excision of the apical bud was less detrimental. The expression of the IAA effect in inducing more roots was dependent on the area of leaves, and was found to be better when all leaves were present. Sugars accumulated slowly at the base of cuttings during a four‐day period after excision, and IAA greatly enhanced this accumulation. By comparing sugar content at the base of green and starved cuttings it was established that IAA greatly increased it concurrently with root formation. IAA applied in solution to the hypocotyl greatly enhanced the basipetal transport of ¹⁴C‐labelled assimilates and their accumulation at the hypocotyl during a 24‐h period. The IAA‐induced accumulation was found to be connected with a greater mobilization of labelled assimilates from upper parts of the cutting. Experiments involving pretreatment with IAA and transport in cuttings already possessing root primordia, suggest a dual effect of IAA: (I) a direct effect on transport, and (2) an increase in the root‐“sink”. It is concluded that both may be operating in inducing basipetal accumulation of labelled assimilates. It is suggested that one of the roles of IAA in promoting rooting of cuttings is to increase sugar availability at the site of root formation.