A cell system for symplastic transport of photoassimilate between meristoderm and sieve elements in Alaria teniufolia

Prior to long-distance assimilate transport in the blades of Laminariales, photoassimilate from the meristoderm (source tissue) must first be transferred across the cortex before it can be loaded into the sieve elements. This radial assimilate transfer seems to be a symplastic parenchyma transport. The wings of Alaria tenuifolia Setchell are only a few cell layers thick and reveal a continuous cell system interconnecting the meristoderm with the sieve elements. This cell system probably provides an uninterrupted route for the symplastic transverse assimilate transfer and loading. The tissue topography of the wings, the anatomy of the composing cell types, and the micromorphology of the cellular network channelling assimilate to the sieve element system are described. The anatomical results are discussed with regard to the transport physiology of Laminariales in general and the possible mode of sieve element loading.