Changes in Cell Wall Polysaccharides during Sunflower Seed Development

Developing sunflower (Helianthus annuus L.) seeds were analyzed for their fresh and dry weights, water content and wall components viz. low and high molecular weight xyloglucan and pectic polysaccharides. Seeds from two rows (6th and 12th) differing in their final dry weight and position on the capitulum were selected for the investigation. The dry weight of seed from 6th row was 69 mg while that of 12th row was 55 mg. Thus a clear effect of position was observed. Seed having higher dry weight had higher water content and vice versa. The xyloglucans were fractioned into low and high molecular weight fractions by extracting them in 4% and 24% KOH, respectively. Though the level of low molecular weight xyloglucan fraction was more than that of high molecular weight xyloglucan, both showed an inverse correlation with water content. Pectic polysaccharide content was maximum at the beginning of seed growth which decreased as the seed matured thus showing an inverse correlation with water content. It is suggested that pectic polysaccharides may be involved in cell wall loosening and xyloglucan may be a major component that contributes to wall rigidity.