HISTOCHEMISTRY OF LIGNIN DEPOSITION DURING SCLERENCHYMA DIFFERENTIATION IN ALFALFA STEMS

The spatial deposition of lignin within the cell walls layer of sclere nchyma is distinct from the lignification pattern of secondary xylem c ell walls. Histochemical staining and autofluorescence of the cell wal ls during alfalfa internode ageing clearly showed that lignin depositi on first occurs in the secondary cell walls of the differentiating scl erenchyma. This is in contrast to the widely reported lignification pa ttern in secondary xylem where lignins are incorporated in the primary cell walls prior to the secondary walls. Spatial variations in the on set of lignin deposition are accompanied by differences in the frequen cy of the di-methoxylated lignin monolignol (i.e. syringyl unit) depen ding on the nature of the tissue. Modifications of the lignin composit ion are also related to the physiological stage of alfalfa internodes. (C) Annals of Botany Company