The Effects of Benzylaminopurine on Growth and ¹⁴Carbon Translocation in Excised Mustard Cotyledons

When localized areas of blades of recently excised mustard cotyledons were fed with 14 CO 2 it was found that the fixation products passed rapidly into the veins and then were translocated to the petiole. Since other cotyledons similarly treated subsequently rooted at the petiole base, this suggested that it acted as a sink for assimilates. Treatment of excised cotyledons with benzylaminopurine (BAP) resulted in the enhancement of blade growth and the suppression of root initiation and development. Quantitative determinations of labelled assimilate in both the cotyledon blade and the terminal 2 mm portion of the petiole were made. It was found that cotyledons treated with BAP at a concentration high enough to suppress completely root initiation had a higher level of radioactivity in the petiole base than the terminal segments in untreated petioles, whether expressed as specific activity or as a percentage of the total radiocarbon fixed. BAP‐treated cotyledons also fixed consistently higher levels of 14 CO 2 , probably due to an increase in photosynthetic area. The results suggest that BAP alters the pattern of differentiation at the base of the petiole rather than the polarity of movement of assimilates to the petiole base.