IDENTIFICATION OF 3 CDNA CLONES EXPRESSED IN THE LEAF EXTENSION ZONE AND WITH ALTERED PATTERNS OF EXPRESSION IN THE SLENDER MUTANT OF BARLEY - A TONOPLAST INTRINSIC PROTEIN, A PUTATIVE STRUCTURAL PROTEIN AND PROTOCHLOROPHYLLIDE OXIDOREDUCTASE

Three cDNA clones have been isolated on the basis of altered patterns of expression in the leaf extension zone of the developmental mutant, slender barley, compared with the wild type. mRNAs corresponding to tw o of the cDNAs, 7s and 8s, are increased in slender compared with norm al. 7s encodes a putative gamma-TIP and is expressed throughout the el ongation zone. gamma-TIPs form transmembrane channels which allow the passive transfer of water. Although expression of 7s was increased in slender leaf tissue, the increase was much less extreme than that show n by Phillips and Huttly (1994) following the application of GA to an extreme dwarf of Arabidopsis. 8s is maximally expressed in the region of early cell elongation and has 66% encoded protein identity with MFS 18, a cDNA encoding a putative cell wall structural protein isolated f rom male flowers of maize. Both 8s and MFS18 encode small (128 amino a cids) basic proteins rich in glycine, alanine, proline and serine. mRN A corresponding to the third cDNA, 24n, is present at a greatly reduce d level in slender compared with normal and encodes protochlorophyllid e oxidoreductase (POR). POR catalyses the conversion of protochlorophy llide into chlorophyllide. The reduced level of POR mRNA is not correl ated with a similar reduction in expanded leaf blade chlorophyll level s. Western analysis identified two POR proteins present in light-grown seedlings. Whilst the larger of the proteins is present throughout mo st of the leaf, the smaller protein mimics the mRNA results, being bot h maximally present in the elongation tissue and present at a reduced level in slender. An antagonistic relationship between chlorophyll bio synthesis and extension growth is suggested.