Assimilation and Translocation in Perennial Grasses

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Abstract
Single leaves, ears, or shoots of timothy (Phleum pratense L.) were exposed in light to 14CO2, then left overnight, after which the plants were autoradiographed. The following conclusions were drawn. Actively growing leaves retain all their assimilates and import from older ones. Fully expanded leaves export but do not import assimilates. Export begins before leaf expansion is complete, so import and export may for a time be simultaneous. Exports go at first to younger leaves and to roots, accumulating at meristems. At later stages, exports move downwards rather than upwards. Buds and small tillers import from older shoots, but large tillers do not import from other shoots or export to other large ones. Ears assimilate while still green, and import assimilates from their associated flag leaves. Exports from other leaves on flowering stems move downwards. These findings agree in general with those from other plants: they are discussed in relation to the vascular system of the grass plant, and the need for further studies, particularly quantitative ones, is emphasized.