Quantitative and qualitative changes of cell wall polysaccharides during somatic embryogenesis and plantlet development of asparagus (Asparagus officinalis L.)

Abstract

Quantitative and qualitative changes in cell wall polysaccharides of asparagus (Asparagus officinalis L.) during somatic embryogenesis and plantlet development were determined by methylation analysis. The globular embryos developed from the stable embryogenic calli in suspension culture for 15 d. The embryos developed into plantlets on a solid (2.5% agar) medium in 50 d. The root and other parts were separately sampled from the plantlet for sugar analysis of the cell walls. The percentage of cellulose was maintained at a low level (20%) during somatic embryogenesis and increased in the root and shoot after plantlet development (40-50%), while that of pectic polysaccharides decreased from 45 to 20-30% after embryogenesis. Hemicellulose was maintained at a constant percentage (30-40%) throughout the experiment. Methylation analysis of hemicelluloses revealed that 5- and 3,5-linked arabinose transiently increased during embryogenesis and then steadily decreased during plantlet development. The contents of 4-linked xylose, the main component of xylan, and 4- and 4,6-linked glucose, found in the glucan backbone of xyloglucans, increased after plantlet development. These results suggested that branched arabinan was actively synthesized in embryonic calli but degraded during the course of differentiation, while xylan and xyloglucan were massively synthesized in the root and shoot as plantlet developed.