Sodium, potassium, chloride and proline concentrations of chloroplasts isolated from a halophyte,Mesembryanthemum crystallinumL.
✍ Scribed by B. Demmig; K. Winter
- Book ID
- 104753019
- Publisher
- Springer-Verlag
- Year
- 1986
- Tongue
- English
- Weight
- 568 KB
- Volume
- 168
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
Concentrations of four major solutes (Na +, K +, CI-, proline) were determined in isolated, intact chloroplasts from the halophyte Mesembryanthemum crystallinum L. following longterm exposure of plants to three levels of NaC1 salinity in the rooting medium. Chloroplasts were obtained by gentle rupture of leaf protoplasts. There was either no or only small leakage of inorganic ions from the chloroplasts to the medium during three rapidly performed washing steps involving precipitation and re-suspension of chloroplast pellets. Increasing NaC1 salinity of the rooting medium resulted in a rise of Na + und C1in the total leaf sap, up to approximately 500 and 400 mM, respectively, for plants grown at 400 mM NaC1. However, chloroplast levels ofNa + und C1did not exceed 160-230 and 40-60 mM, respectively, based upon a chloroplast osmotic volume of 20-30 pl per mg chlorophyll. At 20 mM NaC1 in the rooting medium, the Na +/K + ratio of the chloroplasts was about 1; at 400 mM NaC1 the ratio was about 5. Growth at 400mM NaC1 led to markedly increased concentrations of proline in the leaf sap (8 mM) compared with the leaf sap of plants grown in culture solution without added NaC1 (proline 0.25 mM). Although proline was fivefold more concentrated in the chloroplasts than in the total leaf sap of plants treated with 400 mM NaC1, the overall contribution of proline to the osmotic adjustment of chloroplasts was small. The capacity to limit chloroplast C1-concentrations under conditions of high external salinity was in contrast to an apparent affinity of chloroplasts for C1-under conditions of low C1-availability.