Growth and cell wall changes in azuki bean epicotyls I. Changes in wall polysaccharides during intact growth
Nishitani K, Masuda Y
Plant Cell Physiol 20: 63-74
Measurement of endogenous growth rates and the mechanical property of the cell wall in various regions of light-grown azuki bean epicotyls revealed diat the minimum stress-relaxation time (To) was the shortest in the upper region (0-30 mm below the apex) of the epicotyl, where vigorous endogenous growth took place, and became longer toward the basal region, which was mature and not growing. In the upper region of the epicotyl, a lower percentage of a-cellulose and a higher percentage of pectic substances than in the lower region were found. The percentage of hemicellulose content was almost constant over the whole epicotyl. Major components of noncellulosic neutral sugars in the cell wall were galactose and xylose. The percentage of the galactose content to the noncellulosic polysaccharide was highest in the upper region and lowest in the basal region of the epicotyl, and a clearly negative correlation between the galactose composition and the To value was obtained. On the contrary, the percentage of die xylose content was highest in the basal region and lowest in die upper region, and a clearly positive correlation between die xylose composition and the To value was obtained. During die endogenous growth of die intact epicotyl, all die neutral sugars, particularly galactose, increased in die upper region, whereas in die middle and basal regions, only xylose increased. Similar changes in sugar compositions were observed during IAA-induced elongation of die segment excised from various regions of die epicotyl.