Absence of arabinan in the side chains of the pectic polysaccharides strongly associated with cell walls of Nicotiana plumbaginifolia non-organogenic callus with loosely attached constituent cells

Abstract.

When leaf disks from haploid plants of Nicotiana plumbaginifolia Viv. were transformed with T-DNA and cultured on shoot-inducing medium, non-organogenic callus, designated nolac (for non-organogenic callus with loosely attached cells), appeared on approximately 7% of leaf disks. In contrast, normal callus was generated on T-DNA-transformed leaf disks from diploid plants and on non-transformed leaf disks from haploid and diploid plants. Transmission electron microscopy revealed that the middle lamellae and the cell walls of one line of mutant callus (nolac-H14) were barely stained by ruthenium red, even after demethylesterification with NaOH, whereas the entire cell wall and the middle lamella were strongly stained in normal callus. In cultures of nolac-H14 callus, the level of sugar components of pectic polysaccharides in the hemicellulose fraction was reduced and that in the culture medium was elevated, as compared with cultures of normal callus. These results indicate that pectic polysaccharides are not retained in the cell walls and middle lamellae of nolac-H14 callus. In nolac-H14, the ratio of arabinose to galactose was low in the pectic polysaccharides purified from all cell wall fractions and from the medium, in particular, in the hemicellulose fractions. The low levels of arabinofuranosyl (T-Ara_f, 5-Ara_f, 2,5-Ara_f and 3,5-Ara_f) residues in the pectic polysaccharides of the hemicellulosic fraction of nolac-H14 indicated that no neutral-sugar side chains, composed mainly of linear arabinan, were present in nolac-H14. Arabinose-rich pectins, which are strongly associated with cellulose-hemicellulose complexes, might play an important role in intercellular attachment in the architecture of the cell wall.