David J. Bonfil

A putative HCO−3 transporter in the cyanobacterium Synechococcus sp. strain PCC 79421

Cyanobacteria possess an inducible mechanism which enables them to concentrate inorganic carbon (Ci) within the cells. An inactivation library was used to raise the high‐CO2‐requiring mutant of Synechococcus PCC 7942, IL‐2, impaired in HCO− 3 transport. Analysis of the relevant genomic DNA detected several modifications, probably due to the single crossover recombination, leading to inactivation of ORF467 (designated ictB) in IL‐2. IctB contains 10 trans‐membrane regions and is homologous to several transport‐related proteins from various organisms. Kinetic analyses of HCO− 3 uptake in the wild type and IL‐2 suggested the presence of two or three HCO− 3 carriers exhibiting different affinities to HCO− 3.

Changes in wheat seed storage protein fingerprint due to soil mineral content

Wheat seed storage protein fingerprint is used to determine the gluten protein pattern in studies aimed at improving flour quality. Wild wheat with high seed protein content is used extensively in wheat breeding programs. Although the wild wheat growth and protein content may be influenced by environmental conditions, the gluten-protein pattern is generally considered as indicative of a genotype, without the superimposition of environmental influences. The effects of soil type, habitat, and deficiencies of N, P, K and S on seed storage protein composition were examined in nine accessions of wild wheat (Triticum turgidum var. dicoccoides) and three varieties (two T. aestivum and one T. durum). Soil from ten natural habitats of the wild wheat that had not previously received any fertilizers or manures was sampled and used to grow wheat in a greenhouse. Seed storage protein composition was characterized by SDS-PAGE. Although deficiencies in soil nutrient caused variations in the seed storage proteins, the genotype was the main factor determining the seed storage protein composition. Seed storage protein composition of genotypes varied when grown under different mineral nutrient conditions. Only one genotype was stable showing almost identical protein patterns under all growing conditions studied without any qualitative change in fingerprint pattern. In the other genotypes, as well as the cultivars, the seed storage protein was affected at least to some extent by the soil. The ‘soil effect’ is summarized in terms of three main quantitative changes in the seeds: 1 – the relative amounts of the high-molecular-weight proteins; 2 – the relative amounts of proteins in the range of 45 and 65 kD; 3 – the percentage distribution of the HMW glutenin and other groups of seed storage proteins. The soild induced also qualitative differences in the composition of seed storage proteins, mostly in those of 45–65 kD. These differences were observed whenever a deficiency of S, N, P, K or Mg was identified. Therefore, in breeding programs that use seed storage protein fingerprints of wild wheat germplasms should be exercise caution when the germplasms selected from wild habitats.

Cyanobacterial Mutants Defective in HCO 3 - Uptake

Photosynthetic microorganisms are capable of adapting to a wide range of CO2 concentrations. When cyanobacterial cells are transferred from high to low concentrations of CO2, they undergo an adaptation process. This includes modulation of the expression of certain genes, some of which are involved in the operation of the inorganic carbon (Ci)-concentrating mechanism (CCM, see Miller et al. 1990; Kaplan et al. 1991; Raven 1991; Badger, Price 1992; Ogawa 1993 and Kaplan et al. 1994 for recent reviews and literature citations). The active accumulation of Ci to levels as high as 50-100 mM Ci, consequent on the activity of the CCM, enables the cells to perform efficient photosynthesis in spite of the relatively low affinity of their ribulose 1,5- bisphosphate carboxylase (rubisco) for CO2. Moreover, the elevated concentration of CO2 in close proximity to rubisco, within the carboxysomes, activates the enzyme, reduces competition by O2 and inhibits photorespiration (Schwarz et al. 1995)

The Inorganic Carbon-Concentrating Mechanism of Cyanobacteria

In this chapter we briefly present and discuss recent progress in the elucidation of certain physiological and molecular aspects of the cyanobacterial inorganic carbon (Ci)-concentrating mechanism (CCM). The reader is referred to earlier chapters and reviews [1—14] for a comprehensive account of other important aspects, including the acclimation of cyanobacteria to changing CO2 concentration.