Short-term control of root: shoot partitioning

We present data showing that the fraction of the available photosynthatepartitioned between the root and the shoot of a barley seedlingis affected by the supply of photosynthate from the source leaf:an increased fraction of the exported photosynthate goes tothe shoot when supply is reduced. Also, if the roots are cooleda short time before reducing the supply of photosynthate, thenthe effect of a reduced supply upon partitioning is reversedwith an increased fraction then going to the root. We concludethat the distribution of available photosynthate between competingsinks is influenced by source supply as well as sink function.The reported source-sink interactions are consistant with thepredictions of a recently pro posed model of source-sink interaction(Minchin et al., 1993). The concept of marginal partitioningis introduced to describe the distribution, between all of thesinks, of a small change in photosynthate supply. Key words: Carbohydrate partitioning, shoot : root ratio, source-sink interactions