Effect of Benzyladenine on Membrane Synthesis in Excised Watermelon Cotyledons

Abstract

Summary We have examined the effect of benzyladenine (BA) on the incorporation of labelled choline or galactose into membrane fractions isolated from darkgrown, 2-day-old watermelon ( Citrullus vulgaris Schrad.) cotyledons by means of differential and sucrose gradient centrifugation. The cotyledons were fed with the labelled precursors for 2 h and then treated with 10 −4 M BA for 2 h. An increased incorporation of choline into the microsomal fraction (105 000 × g , 90 min) can be observed 3 h after end of treatment with BA. This is the fastest response to BA we were able to observe in watermelon cotyledons. Also the labelling of the crude particulate fraction (10 800 × g , 10 min) with choline is increased by BA, but after a lag time of 6 h. Most of the choline label found in the crude particulate fraction is found in the mitochondria, but the stimulation by BA seems to depend on an increased incorporation into plastids and microbodies. BA also enhances the incorporation of galactose into the microsomal and crude particulate fraction, but the enhancement is much smaller than in the case of choline. Most of the galactose incorporated in the crude particulate fraction remains on top of a 32–60% sucrose gradient. Therefore galactose does not seem to be a suitable marker for organelle membranes in our conditions.