CHANGES OF CELL-WALL COMPOSITION AND POLYMER SIZE IN PRIMARY ROOTS OFCOTTON SEEDLINGS UNDER HIGH SALINITY

The aim of this study was to investigate changes in cell wall chemical composition and polymer size in the root tip of intact cotton seedlin gs (Gossypium hirsutum L. cv. Acala SJ-2) grown in saline environments , in order to relate the interaction between high salinity and root gr owth to possible changes in cell wall metabolism. Cotton seedlings wer e grown in modified Hoagland nutrient solution with various combinatio ns of NaCl and CaCl2. Cell walls were fractionated into four fractions (pectin, hemicellulose 1 and 2, cellulose), and analysed for their to tal sugar content, neutral sugar composition and size of polysaccharid es. At 1 mol m-3 Ca, 150 mol m-3 NaCl resulted in a significant increa se in the cell wall uronic acid content, but a reduction in cellulose content on a per unit dry weight basis. Supplemental Ca overcame the i nhibitory effect of high Na on cellulose content. The neutral sugar co mposition of the cell wall fractions showed no major changes caused by varied Na/Ca ratios. Determinations of polysaccharide polymer size sh owed that high Na at 1 mol m-3 Ca led to an increase in the amount of polysaccharides of intermediate molecular size and a decrease in that of small size in the hemicellulose 1 fraction, indicating a possible i nhibition of polysaccharide degradation by high Na. This change was no t observed in the 10 mol m-3 Ca treatments. The results reveal a relat ionship between the effects of high salinity on root growth and cell w all metabolism, particularly in regard to cellulose biosynthesis.