ABSTRACT
The nucleotide sequence of 3.2 kbp of pea chloroplast DNA located upstream from the petA gene for cytochrome f, and previously reported to contain the gene for a photosystem I polypeptide, has been determined. Three open reading frames of 587, 40 and 157 codons have been identified. Orf40 encodes a highly conserved, hydrophobic, membrane-spanning polypeptide, and is identified as the gene psaI for the 4 kDa subunit of photosystem I. Orf587 is an extended version of the gene zfpA previously identified as encoding a conserved putative zinc-finger protein. The product of orf587 shows extensive homology to an unidentified open reading frame cotranscribed with a gene for folate metabolism in Escherichia coli and local homology to a region of the beta subunit of rat mitochondrial propionyl-CoA carboxylase. It is suggested that the product of orf587 is an enzyme of C1 metabolism and is unlikely to be a regulatory DNA-binding protein. Orf157 potentially encodes an unidentified basic protein, but the protein sequence is not conserved in other plants.
Subject(s)
Chloroplasts , Fabaceae/genetics , Photosynthetic Reaction Center Complex Proteins/genetics , Plants, Medicinal , Amino Acid Sequence , Base Sequence , Biological Evolution , Blotting, Western , DNA/genetics , Molecular Sequence Data , Open Reading Frames , Photosystem I Protein Complex , Restriction Mapping , Sequence Homology, Nucleic AcidABSTRACT
The aim of this work was to discover if there is enough ATP citrate lyase (EC 4.1.3.8) in the cytosol of the leaves of Pisum sativum L. to catalyse the synthesis of the acetyl CoA needed for terpenoid synthesis. Estimates of the maximum catalytic activity of the enzyme in leaves of 7-d-old peas gave values of 113 nmol min(-1) g(-1) fresh weight. The rate of carotenoid accumulation in these leaves corresponded to a requirement for acetyl CoA of 0.7 nmol min(-1) g(-1) fresh weight. The distribution of marker enzymes during fractionation of homogenates of leaves from 7 to 10-d-old peas showed that differential centrifugation led to the isolation in reasonable yields of chloroplasts, mitochondria, peroxisomes and the endomembrane system. None of the above components of the leaf contained appreciable detectable activity of ATP citrate lyase, the distribution of which closely paralleled that of the cytosolic marker. It was concluded that in young leaves of pea most of the ATP citrate lyase is in the cytosol.
ABSTRACT
Using liposomes, some possible consequences of auxin-stimulated proton secretion in plant tissues are modelled. Liposomes, made specifically permeable to protons and potassium ions, but containing at least one impermeant, swell at a rate which is proportional to the availability and hydration rate of carbon dioxide; the gas functions as a source of proton and dehydrated anion and this enables a net transfer of KHCO3 to take place.
