Tissue layer specific regulation of leaf length and width in Arabidopsis as revealed by the cell autonomous action of ANGUSTIFOLIA

In vascular plants the shoot apical meristem consists of three tissue layers, L1, L2 and the L3, that are kept separate during organ formation and give rise to the epidermis (L1) and the subepidermal tissues (L2, L3). For proper organ development these different tissue layers must interact with each other, though their relative contributions are a matter of debate. Here we use ANGUSTIFOLIA (AN), which controls cell polarity and leaf shape, to study its morphogenetic function in the epidermis and the subepidermis of Arabidopsis thaliana. We show that ANGUSTIFOLIA expression in the subepidermis cannot rescue epidermal cell polarity defects, indicating a cell‐autonomous molecular function. We demonstrate that leaf width is only rescued by subepidermal AN expression, whereas leaf length is also rescued by epidermal expression. Strikingly, subepidermal rescue of leaf width is accompanied by increased cell number in the epidermis, indicating that AN can trigger cell divisions in a non‐autonomous manner.     

Multiple forms of human glutathione S-transferase and their affinity for bilirubin.

The initial enzymic step in mercapturic acid formation is catalyzed by glutathione S-transferase. Several species of this enzyme, designated as transferases alpha, beta, gamma, delta and epsilon on the basis of increasing isoelectric points, were isolated from human liver. Evidence is presented that each of the purified species is homogeneous with respect to sodium dodecylsulfate-gel electrophoresis. Transferases alpha, beta and epsilon each appear as a single band on gel electrofocusing; transferases gamma and delta are present as two and three bands, respectively, with each band catalytically active. Amino acid analysis indicated the five transferases to be either very closely related or identical in this respect. All enzyme species have a molecular weight of about 48500 and consist of two apparently identical subunits. The spectrum of substrates is the same for each although the enzymes differ slightly in specific activity. As is the case for the rat liver enzymes, each of the human transferases binds bilirubin although this compound is not a substrate.     

Aryl sulfotransferase IV from rat liver

A group of aryl sulfotransferases has been identified that catalyzes sulfate ester formation with simple phenols at an acidic pH and with several physiological metabolites at a more alkaline pH. One enzyme, aryl sulfotransferase IV, has been purified to homogeneity and found to be a protein of 61,000 daltons composed of two subunits of apparent equal size. Homogeneous preparations are active with simple phenols, organic hydroxylamines, and catecholamines as well as serotonin and its metabolites. The enzyme is also active with tyrosine methyl ester and with those peptide hormones e.g., cholecystokinin heptapeptide and some of the enkephalins, which have N-terminal tyrosine residues.     

Methinin: A peptide inhibitor of methylation

Five enzymes, active in the transfer of a methyl group to either oxygen, nitrogen or sulfur atoms, were inhibited competitively by a peptide isolated from rabbit liver. The peptide, named methinin, appears to have a chromophore that resembles pyridinoline, a cross linking amino acid found in elastin and collagen.