NaCl stress causes changes in photosynthetic pigments, proteins, and other metabolic components in the leaves of a true mangrove,Bruguiera parviflora, in hydroponic cultures

Abstract

We studied salt stress-induced biochemical changes in young, hydroponically grown plants of mangrove, Bruguiera parviflora (Rhizophoraceae). Our focus was on the effect of NaCI (applied at 100, 200, 400, or 500 mM) on leaf pigments, total soluble proteins, total free amino acids, carbohydrates, polyphenols, and proline. The total Chl content increased for 14 d after treatment with 100 m/Vl NaCI, then gradually stabilized. At 400 mM, the total Chl content slowly decreased over the 45-d test period. However, the Chl a:b ratio remained unchanged in isolated chloroplasts and in leaf tissue. Percent changes in the carotenolds content followed the same trend as for Chl, except for a 1.5-fold decrease during the 400-mM NaCI treatment, compared with the control. The total sugar content increased by 2.5-fold by Day 45 after treatment with 400 mM NaCI, whereas the starch content measured in the same treatment decreased by 40 to 45%. Leaf protein content decreased as salinity increased, which suggests either a possible disruption in the protein synthesis mechanism or, more likely, an increase in proteolytic activity. The total amino-acid pool increased steadily, by four-fold, in the 45-d, 400-mM treatment. Both proline and polyphenols accumulated with increasing levels of salinity, which confirms the role of proline as a stress-induced protective metabolite in the adaptive process of this species. Our results showed that a true mangrove such as B. parviflora can easily be sustained and propagated under low-salinity conditions. At high levels of salinity (-400 mM, beyond which they could not survive), the plants became adapted to salt stress after two to three weeks. During this adaptive period, changes in pigment and protein levels also occurred. The accumulation of proline and polyphenols played a key role in the plant's stressinduced adjustment to NaCI under hydroponic culture conditions. Keywords: Bruguiera parviflora, hydroponic culture, mangrove, proline accumulation, salt-stressThe rich biological diversity in the mangrove ecosystems of tropical and subtropical inter-tidal zones constitutes an economic resource for coastal people. The mangrove is an ecologically important component that protects the adjacent land from erosion by tidal waves, cyclones, and storms (Banijbatana, 1957). These trees also prevent the accumulation of terrigenous nutrients that affect nearby reefs (Dubinsky and Stambier, 1996). The survival of most of these mangroves is now threatened, largely due to human interference that has resulted in changes in tidal patterns and salinity gradients. Investigations of salinization and desalinization are likely to yield valuable information on salt adaptability by mangroves.Bruguiera parviflora (Rhizophoraceae) is a major member in the tropical mangrove ecosystem. This family of mangrove has a viviparous mode of germination and is tolerant to changes in salinity gradients. *Corresponding author; fax +91-674-550274 e-mail a b das@hotmaiI.comThe effects of salt on mangroves have been studied in relation to ...

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