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A genomic DNA containing a rice (Oryza sativa L., cv. Norin-8) gene coding for a pullulanase-type starch debranching enzyme (EC 3.2.1. 41) was sequenced (EMBL/GenBank/DDBJ accession number AB012915). Along the 15, 248 bp DNA, the pullulanase gene is split into 26 exons. The four pullulanase consensus regions are positioned in the middle portion of the sequence and are separated by long introns and 1-3 exons. Comparison of the rice cv. Norin-8 pullulanase genomic structure with that of barley pullulanase (limit dextrinase) (F. Lok et al., EMBL/GenBank/DDBJ accession number AF022725) indicates that most of the pullulanase exons are highly conserved. Alignment of the nucleotide bases of rice exon 8 with those of barley exon 8-intron 8-exon 9 fragment suggests that the 85 bp internal sequence of rice exon 8 was originally an intron, a possibility further indicated by the absence in barley and spinach (A. Renz et al., EMBL/GenBank/DDBJ accession number X83969) pullulanases of amino acid residues encoded by the 85 bp fragment.

The effects of amino acid medium (AA medium) on the dissociation of rice callus tissues were examined in suspension-cultured cells, because a finely dispersed cell suspension had been obtained previously from rice callus tissues in this medium. The level of extracellular polysaccharides formed in cultured AA medium was much higher than that of those formed in cultured B5 medium. The polysaccharides were mainly composed of higher levels of arabinose, xylose, and galactose, suggesting the solubilization of arabinoxylan and (arabino)galactan. Nevertheless, wall polysaccharides in cells cultured in AA medium contained the same levels of arabinosyl-, xylosel-, and galactosyl-linkages as those in B5 medium. Based on amino acid analysis, rice cells in AA medium incorporated the amino acids in 3 days and formed ornithine and urea during the early stages of cultivation, and secreted urea into the culture medium. Transfer of rice tissue cultured in AA medium to B5 medium composed of inorganic nitrogen source caused...

Two isoforms of starch branching enzyme (Q-enzyme), QEI and QEII, have been purified to honlogeneity from developing rice endosperm. QEI and QEII, with molecular weights of about 80 and 85 kDa, respectively, could be fully separated by anion-exchange or hydrophobic chromatography. The peptide maps obtained after V8 proteinase digestion were quite different between the two enzymes. Antibodies prepared against QEI showed no immunological cross-reaction with the QEII protein in Western blot experiments, and anti-QEII serum did not react with the QEI protein. The data indicate that QEI and QEII are distinct proteins encoded by different genes in rice plants.