Genetic and biochemical analyses suggest that the developmental program of catalase (H 2 O 2 :H 2 O 2 oxidoreductase, EC 1.11.1.6) activity in maize scutella is controlled by a temporal regulatory gene ( Car1 ) that is distinct from the structural genes thus far identified. Recombination data show that Car1 is located about 37 map units from the Cat2 structural gene on the chromosome 1S. Turnover studies indicate that Car1 may act by regulating the rate of catalase synthesis.

Thirty lines from a cross between VPM/ Moisson 421 and Selection 101 were used in the study to determine whether strawbreaker foot rot resistance derived from Aegilops ventricosa was associated with an allele for endopeptidase. The progeny examined for foot rot lesions represented F2 derived F5 lines and enzyme assays were done on F6 seedlings. The results indicate that the wheat and 'VPM/Moisson 421' endopeptidase alleles are distinctly different. The endopeptidase allele frequencies of 30 lines were compared with strawbreaker foot rot resistance as measured by the lesion severity index. The results demonstrate a close association between the gene for strawbreaker foot rot resistance and the endopeptidase allele derived from Ae. ventricosa.

Three separate sets of polymerase chain reaction primers were designed to specifically detect the presence of a toxin A gene fragment, a toxin B gene fragment, and the entire toxin B gene. In addition toxin gene fragments that were amplified from well characterized toxic strains were tagged fluorescently and used as hybridization probes to screen C. difficile strains. A survey of 37 toxic strains and 10 non-toxic strains demonstrated that toxic strains normally contain the genetic composition for toxin A and toxin B simultaneously; whereas, non-toxic strains typically did not contain detectable toxin determinants. The only exception found was strain 39, which had the genetic composition for toxins A and B, but was not cytotoxic under the conditions tested.

Clostridium difficile is the causative agent for pseudomembranous colitis in humans. Toxic strains of C. difficile produce two toxins, toxin A and toxin B. A reliable and definitive method of typing the toxic strains of C. difficile is needed since nosocomial cross infection is a primary concern in hospitals and other health care facilities. A method for typing toxic strains of Clostridium difficile using arbitrary polymerase chain reaction (PCR) primers is presented in this study. The C. difficile strains were initially characterized for the toxin A genetic determinant using specific PCR primers which differentiate toxin positive from toxin negative strains. These toxic strains were then PCR typed using six arbitrary primers which generated DNA patterns that were unique for all toxic strains examined. The use of this typing scheme in clinical applications is discussed.

Six inbred lines of Zea mays expressing different soluble (cytosolic) malate dehydrogenase (sMDH) zymogram phenotypes were analyzed genetically. sMDH was found to be coded for by unlinked duplicated loci in four of these inbred lines. The remaining two lines were found not to possess these duplicated loci. Furthermore, the duplicated loci, sMdhl and sMdh2, have been found to be located on different chromosomes: sMdhl on chromosome IL linked to Ampl, and sMdh2 on chromosome 5S linked to Catl and Amp3. The importance of finding sMDH encoded by duplicated loci is discussed in relation to the role of chromosomal rearrangements, the relationshi between the cytoplasmic and mitochondrial enzymes, andde evolution of Z. mays. Multiple molecular forms of malate dehydrogenase (MDH) occur in the mitochondria, glyoxysomes, and cytoplasm of Zea mays (1, 2). Mitochondrial MDH (mMDH) participates in the mitochondrial half of the malate shuttle and is an essential enzyme of the tricarboxylic acid cycle (3). Extensive biochemical analysis of mMDH in Z. nwys has been described (1). Genetic analysis has shown that mMDH in maize is coded for by nuclear genes (4) on unlinked, duplicated chromosome segments (5). Soluble MDH (sMDH) is involved in transporting NADH equivalents, in the form of malate, from the cytoplasm across the mitochondrial membrane. Therefore, sMDH and mMDH are intimately related by means of their individual roles in the malate shuttle. This close relationship and the fact that mMDEI was found to be coded for by duplicated loci led to the question of whether or not selection might favor duplication of the sMDH loci as well. The present study found extensive genetic evidence that sMDH is coded for by unlinked duplicated loci in some inbred lines of maize; in other inbred lines of maize, the duplication does not exist. The significance of this finding is discussed in relation to mMDH duplications, gene evolution, and the evolution of Z. mays. MATERIALS AND METHODSGenetic Stocks. The inbred lines used in this study are listed first by our own laboratory designation followed by the breeder's designation in parentheses. Inbred The extracts were applied to 5 X 7 mm Whatman 3MM filter paper sections which were inserted into vertical slots cut into 12% starch gels. Horizontal starch gel electrophoresis and specific staining for MDH were conducted as described (6). Mitochondrial Isolation. Six-day-old dark grown maize scutella (10 g) was minced (razor blade) in a petri dish with 8 ml of cold grinding medium. The grinding medium was modified from that used by Briedenbach and Beevers (7). Instead of 0.4 M sucrose in Tris buffer, g5% sucrose in 0.05 M Hepes buffer (pH 7.5) was used. The homogenate was passed through four layers of Miracloth and the filtrate was centrifuged at 1500 X g for 15 min. The supernatant was layered into a 25-60% continuous sucrose gradient and centrifuged at 113,000 X g in an SW 27 rotor for 4 hr. After centrifugation, the bottom of the tube was punctured with a dissecting needle and 0.5-m...