Responses of photosynthesis to NaCl in gametophytes of Acrostichum aureum.

Gametophytes of Acrostichum aureum were cultured in 0.0 to 1.0% NaCl solutions or in NaCl-free solution and then transferred to 1.0% NaCl solution. Photosynthetic light-response curves, efficiency of the primary photochemical reaction, relative electron transport rate, and photochemical and non-photochemical quenching at steady state were determined by photosynthetic O evolution and in vivo chlorophyll fluorescence. Results obtained showed that the chlorophyll fluorescence parameters, F /F and F' /F' and αO (the initial linear slope of the photosynthetic light-response curve) increased in gametophytes grown in NaCl. Linear electron transport rate was stimulated by NaCl. Based on the chlorophyll content, light-saturated photosynthesis in gametophytes grown in 0.2 to 0.7% NaCl increased slightly; it decreased in gametophytes grown in 1.0% NaCl. Photochemical quenching decreased in NaCl-grown gametophytes at all photosynthetic photon flux density (PPFD) levels measured, but there was no increase in non-photochemical quenching. The chlorophyll a/b ratio increased with increasing NaCl concentration in culture solutions. These results indicated that NaCl enhanced photochemical efficiency of photosystem II (PSII) and photosynthetic linear electron transport, thus resulting in the development of an excitation pressure in PSII. Such excitation pressure might act as a signal for photosynthetic acclimation to salt stress, thus allowing the gametophytes to grow in their natural habitats.