Ultrarapid endocytotic uptake of large molecules in Dunaliella species

This paper describes the uptake of Lucifer Yellow carbohydrazide and fluore scent dextrans labeled with fluorescein isothiocyanate or Sodium Green (mol ecular masses ranging from 522 to 2 x 10(6) De) by Dunaliella spp. halotole rant unicellular green algae isolated from salt pools in the Sinai peninsul a. The fluorescent dyes were taken up into a set of vesicles around the nuc leus and just above the chloroplast. It proved impossible to inhibit uptake of the fluorescent compounds in cells treated with a large variety of meta bolic and other inhibitors. Cell labeling was complete within half a minute of addition of fluorescent compounds to the outside medium; efflux was equ ally rapid. The results are interpreted in terms of an endocytotic process whereby the outside medium, together with any substance dissolved in it, re mains within vesicles enclosed within the cell body but cycles rapidly betw een the plasma membrane and the interior of the cell. The outside medium do es not pass across the vesicular membrane, nor enters the cytosol.