The Effects of Osmotic Tissue Dehydration and Air Drying on Morphology and Energy Transfer in Two Species of Porphyra

Abstract

Studies were conducted to document the effects on morphology and energy transfer in photosynthesis of severe tissue dehydration induced either by air-drying or by immersing the tissues of two Porphyra species in hyperosmotic solutions. These studies showed that the dehydrationtolerant intertidal alga, Porphyra perforata J.Ag., was almost unaffected by either of these treatments, while the dehydration-sensitive Porphyra nereocystis Anders. was damaged similary by both treatments. Damage to that sensitive species was characterized by ruptured organelles as seen by interference microscopy as well as by increased fluorescence emission at 682 nanometers emanating from allophycocyanin. These results suggest that a disruption of energy transfer between allophycocyanin and chlorophyll a occurs because of the damage to membranes following tissue dehydration, and that the increase in the yield of phycobilin fluorescence is a good indicator of these phenomena. Thus, air-drying and osmotic-dehydration appear to have similar physiological consequences in a dehydration-sensitive alga but almost no effect in a tolerant species.Macrophytic marine algae are distributed in distinct zones in coastal regions from intertidal areas that are rarely wetted by incoming waves to subtidal areas that are never exposed by low tides. The algae in these communities differ in their physiological tolerance ofair-drying, and these differences explain in part their observed zonation (4,15,18). Those species adapted to live in the intertidal region are tolerant of severe dehydration that can be induced by air-drying (4, 16). Intertidal species are also tolerant of osmotic dehydration, but subtidal and low tidal species are intolerant of both kinds of dehydrations (1, 15, see also 2).Because air-drying of algal tissues to a specific water content is difficult, a new approach was needed to study the basis of adaptation made by marine algae to dehydration. We considered the possibility that immersing algal tissues in hyperosmotic solutions may parallel the buildup of salts in the extracellular water of air-dried algae, and may be an effective means of experimentally dehydrating tissues. Providing that algal cells are impermeable to NaCl, exposure to a solution with increased salt concen- by the concentration of salts in the external medium. Because of the lack ofa cuticle, algal tissues rapidly equilibrate with solutions of different water potentials. Thus, hyperosmotic dehydration allows greater reproducibility for replicate dehydrations than is possible with air-drying.Studies of the characteristics of fluorescence emission in fully hydrated and in air-dried tissues of Porphyra perforata (5, 1 1) revealed alterations in distributions of light energy upon dehydration. In this study, fluoresence emission was used to follow changes in energy transfer resulting from air-dehydration and osmotically induced dehydration in the intertidal species, P. perforata, and the subtidal species, Porphyra nereocystis. Nomarski interference micrography was us...

Fluorescence Characteristics of Photoinhibition and Recovery in a Sun and a Shade Species of the Red Algal Genus Porphyra

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