Physiological and photosynthesis-related gene expression analysis of seagress enhalus acoroides (L.f.) royle under salt stress

Abstract

This study aims to examine physiological responses (photophy- siological and osmotic responses) and photosynthesis-related gene expression in seedlings of the seagrass Enhalus acoroides after exposure to different salinity levels. Seagrass seedlings were grown for 20 days in control (salinity 30), hyposaline (salinity 10 and 20) and hypersaline (salinity 40 and 50) conditions. The present study showed that both hypo- and hypersaline conditions affected the photophysiology of E. acoroides seedlings, reducing the maximum quantum yield of photosystem II (F/Fm) and total chlorophyll content. The photosynthetic system appeared to be more sensitive to hyposaline than to hypersaline conditions as shown by immediate declines in F/Fm and total chlorophyll content. Hyposaline conditions increased the water content in roots. The increase in tissue Na* content induced by hypersalinity did not affect photosynthetic integrity and was more pronounced in leaves than in roots. It is concluded that the ionic homeostasis of E. acoroides seedlings is less affected by shortterm hypersalinity than by hyposalinity. The K/Na* ratios in leaves with hypersalinity decreased by 20 days after treatment. Additionally, the photosynthetic efficiency (F/Fm and total chlorophyll content) is highly sensitive to salinity shifts and can be used as a marker for short-term acclimation to salinity stress in this seagrass species. The photosynthesis-related gene expression showed that hypo- and hypersalinity conditions unclearly changed LHCB gene expression in E. acoroides leaves. The decline trend of LHCB transcript might correspond to the chlorophyll content and photosynthesis decreases in the physiological study. At the late experiment, RCA, psbA and psbD gene were up-regulated which are possibly related to the repair of occurred photodamage in photosystem II.