Experimental fluid flow through plasmodesmata of Laminaria digitata

Electron-microscopy (EM) revealed that the conducting filaments in the medulla of the cauloid are interconnected by numerous plasmodesmata in sieve plates. The filaments contain a vesicular ground plasm with a nucleus, mitochondria, and plastids. After a cauloid had been cut through, an exudate flowed from the medulla. Afterwards longitudinal sections showed an accumulation of cytoplasm on the plates near a wound, both basal and apical. On the side facing the wound cytoplasm was absent. EM confirmed this. The authors argue that, for several reasons, a fluid flow of exudate must pass the plasmodesmata. Cytoplasm moved with the exudate and was sieved out by the plates.