Externally supplied [3H]myo-inositol and [14C]glucose were incorporated in cell-wall fractions of segments of etiolated squash hypocotyl. The extent of incorporation of [14C]glucose into cell-wall fractions was very much greater than that of [3H]myo-inositol. Radioactivity from [14C]-glucose was effectively incorporated into hemicellulose B and cellulose fractions and was incorporated uniformly into hexose, pentose and uronic acid residues, but radioactivity from [3H]myo-inositol was incorporated predominantly into uronic acid and pentose residues in the pectin and hemicellulose B fractions. Exogenously applied ABA significantly suppressed the elongation of segments of squash hypocotyl and the incorporation of radioactivity from [l4C]glucose and [3H]myo-inositol into the segments. Furthermore, ABA significantly inhibited the distribution of incorporated radioactivity from [14C]glucose into the cellulose fraction, but did not affect distribution into the pectic fraction. By contrast, ABA only slightly inhibited the distribution of the incorporated radioactivity from [3H]myo-inositol into the pectic fraction. These results suggest that most of the cell-wall polysaccharides in segments of squash hypocotyl are synthesized via the UDP-sugar pathway, and that ABA significantly inhibits the synthesis of cellulose but not the synthesis of pectic polysaccharides when ABA suppresses the elongation of the segments.
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Wakabayashi et al. (1989) studied this question.