Effects of Salinity on Primary Processes of Photosynthesis in the Red Alga Porphyra perforata

Abstract

The effects of salinity on the primary processes of photosynthesis were studied in the red alga Porphyra perforate. The results show that there are at least three sites in the photosynthetic apparatus of this alga that were affected by increased salinity. The first site, photoactivation and dark-inactivation of electron flow on the reducing side of photosystem I, was completely inhibited at high salinity. The second site, electron flow on the oxidizing side (water side) of photosystem II, was inhibited as was the re-oxidation of Q in the presence of 343,4-dichlorophenyl)-1,1-dimethylurea. The third site affected by high salinity was the transfer of light energy probably from pigment system II to I. High salinity reduced the amount of light energy that reached the reaction centers of photosystem II.These effects are discussed in relation to the mechanisms available to this plant to avoid photoinhibition when it is exposed to stresses such as high light and high salinity which are conditions that are commonly found in the intertidal habitat.The intertidal red alga Porphyra perforate lives where, at low tide, the plants are routinely exposed to air-drying. As a result of evaporative water loss, the salt concentration of extracellular water can increase up to about 10 times above normal levels. During desiccation at low tide this alga can lose up to 90% of its fresh weight (23). This air-drying has the effect of slowly increasing external salt concentrations in the small amount of water remaining around the algal tissues. The osmotic stress of airdrying can be experimentally induced by increasing external salt concentrations around algal tissues. This method has the advantage of allowing greater control over tissue dehydration than is possible using air-drying. Upon dehydration either by high salt or by air-drying, the photosynthesis of Porphyra is similarly inhibited (23). Furthermore, this alga is often exposed to high light intensities in combination with tissue dehydration in the field. It is well known that photoinhibition of photosynthesis can take place during experimental conditions under which photosynthesis is inhibited and there is an excess amount of light energy (5,13,15,16,18 6,8). It was observed that below a water content of 20 to 25%, the fluorescence time course became similar to that in the presence of DCMU. When the water content was less than 20%, the variable part of fluorescence (F, became small, whereas at 5% the F, was totally eliminated but F0 was little affected (24). From these and other results, Wiltens et al. (24) suggested that electron flow between the two photosystems was inhibited by low water content. The decrease of F, under conditions of very low water content was attributed to an accelerated back reaction of PSII because of the inhibition of the re-reduction of P680 with electrons normally derived from water. By contrast, Fork and Oquist (4) showed that there still remained relatively large amounts of F, in dark dried Porphyra. It is natural to assume that water oxidati...

Photosynthetic parameters of sexually different parts of Porphyra katadai var. hemiphylla (Bangiales, Rhodophyta) during dehydration and re-hydration

“…3, 4). According to Satoh et al (1983), severe water deficiency inhibits electron flow on the water side of PSII and between the two photosystems of Porphyra perforata. When AWC reached 42%, the effective quantum yield of PSII (YII) became relatively stable (Fig.…”

“…Since photosynthetic electron transport is highly sensitive to environmental conditions, marine seaweeds in shallow coastal waters need mechanisms for acclimation to the fast changes in their environment (Kaiser 1987;Andersson et al 2006). To date, some information has been published regarding the influences of dehydration and re-hydration on the photosynthetic performance of Porphyra sp (Satoh et al 1983;Smith et al 1986;Zou and Gao 2002). It was reported that different Porphyra species may react differently under the same water-deficient conditions: some species being extremely resistant to dehydration, while others are not (Smith et al 1986).…”

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

“…Another study using osmotic dehydration as an experimental tool for testing photosynthetic tolerance of 12 intertidal and subtidal algal species found that the distributions of plants were well correlated with abilities of those species to recover photosynthesis following osmotic dehydration (CM Smith and JA Berry, unpublished results). Moreover, Satoh et al (14) [10] for a recent review). Work by Reed et al (12) and Wiencke and Lauchli (17) shows that changes in concentrations of two intracellular galactosylglycerols, floridoside and isofloridoside, occur with changes in external water potentials when species ofPorphyra are cultured in continuously elevated osmotic conditions.…”

Accumulation of photosynthesis gene transcripts in response to sodium chloride by salt-tolerant alfalfa cells

“…Exposure to saline environments results in loss of chloroplast activity (Kingsbury and Epstein 1986) and leads to increased growth and maintenance costs for plant cells (Stavarek and Rains 1984). Salinity affects at least three primary processes of photosynthesis in red algae (Satoh et al 1983). In some plants, synthesis of osmoprotectants has been localized in chloroplasts (Weigel et al 1988).…”