Symplasmic mass flow and sieve tubes in algae and plants
Knoblauch, Michael; Peters, Winfried S.
Abstract Most organisms made of cells with walls, including land plants, algae, and fungi, maintain plasmatic cell-to-cell connections through pores in the cell walls. The resulting symplasmic nature of the tissues establishes a structural condition for osmotically-driven cytoplasmic bulk flow, a biophysical phenomenon that cannot be avoided in walled cells and symplasmic tissues if intra- or extracellular gradients of osmolarity exist. The sieve tubes known from land plants and brown algae consist of cells that have differentiated to maximize the efficiency of this ubiquituous transport mechanism. We argue that due to their ‘biophysical relatedness’ and despite their phylogenetic distance, brown algae can provide valid experimental models for certain aspects of long-distance transport in tracheophytes, and discuss recent experimental progress in a wider context.