Changes of Cell Wall Composition and Polymer Size in Primary Roots of Cotton 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 seedlings (Gossypium hirsutum L. cv. Acala SJ-2) grown in saline environments, in order to relate the interaction between high salinity and root growth to possible changes in cell wall metabolism. Cotton seedlings were grown in modified Hoagland nutrient solution with various combinations of NaCl and CaCl2. Cell walls were fractionated into four fractions (pectin, hemicellulose 1 and 2, cellulose), and analysed for their total sugar content, neutral sugar composition and size of polysaccharides. At 1 mol m−3 Ca, 150 mol m−3 NaCl resulted in a significant increase in the cell wall uronic acid content, but a reduction in cellulose content on a per unit dry weight basis. Supplemental Ca overcame the inhibitory effect of high Na on cellulose content. The neutral sugar composition of the cell wall fractions showed no major changes caused by varied Na/Ca ratios. Determinations of polysaccharide polymer size showed 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 inhibition of polysaccharide degradation by high Na. This change was not observed in the 10 mol m−3 Ca treatments. The results reveal a relationship between the effects of high salinity on root growth and cell wall metabolism, particularly in regard to cellulose biosynthesis