Salt tolerance and exclusion in the mangrove plant Avicennia marina in relation to root apoplastic barriers

Salt tolerance and the possible functions of suberization on salt exclusion and secretion were examined in a dominant mangrove plant, Avicennia marina. The results showed that low salinities (10 parts per thousand and 20 parts per thousand) almost has no negative effect on A. marina, however significant growth inhibitions were observed in the seedlings grown in higher salinities (30 parts per thousand and 40 parts per thousand). With the increases of salinity, increased tissue Na+ content and enhanced salt secretion by glands were observed. Obvious suberization thickening were detected both in the exodermis and endodermis of the roots after salt pretreatment when compared to the roots without salt treatment. More importantly, the present data further confirmed that these root apoplastic barriers would directly decrease Na+ loading into xylem. Higher salt tolerance was observed in the seedlings pre-cultivated by salty tide when compared to fresh water cultivated A. marina. In summary, this study suggests a barrier property of suberization in dealing with salt exclusion in mangroves, a moderate salt pre-treatment may benefit plant withstanding high salinity.