The Export and Distribution of 14C-labelled Assimilates from each Leaf on the Shoot of Lolium temulentum during Reproductive and Vegetative Growth

In both reproductive and vegetative plants of Lolium temulentum L., the export of 14C-labelled assimilates from each healthy leaf on the main shoot to terminal meristem, stem, tillers, and roots was measured each time a new leaf was expanded, for a period of 5 to 6 weeks. Some labelled assimilates moved from each leaf on the main shoot to every meristem in the same shoot, as well as to the tops and roots of adjacent organically attached tillers. The terminal meristem of the reproductive shoot, which included the developing inflorescence, received 70–80 per cent of the carbon assimilated by the emerged portion of the growing leaf, 15–25 per cent of the carbon assimilated by the two youngest expanded leaves, and 5–10 per cent of that from each of the older leaves. A similar pattern of carbon supply to the terminal meristem was found in vegetative shoots, except that older leaves on young vegetative shoots supplied even less of their carbon to the terminal meristem. The general conclusion is that developing leaves at the tip of the shoot receive about the same proportion of carbon from each leaf as does a developing inflorescence. Young expanded leaves provided most labelled assimilates for stem growth; during both reproductive and vegetative growth, expanded leaves increased their export of labelled carbon to stem, and exported less of their 14C to roots and sometimes to tillers. In these reproductive and vegetative shoots, grown in a constant external environment, the major changes in the pattern of distribution of labelled assimilates appeared to be the result of increased meristematic activity in stem internodes; the development of an inflorescence had no obvious direct effect on the carbon economy of shoots.