CHANGES IN CELL COMPOSITION AND LIPID METABOLISM MEDIATED BY SODIUM AND NITROGEN AVAILABILITY IN THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

The effects of nitrogen starvation in the presence or absence of sodium in the culture medium were monitored in batch cultures of the marine diatom Phaeodactylum tricornutum Bohlin. During nitrogen starvation in the presence of sodium, cell nitrogen and chlorophyll a decreased, mainly as a consequence of continued cell division. These decreases were accompanied by decreases in the rates of photosynthesis and respiration. There was no change in either cell volume or carbohydrate, but both carbon and lipid increased. During nitrogen starvation in the absence of sodium, cell division ceased. Cell nitrogen and chlorophyll a remained constant, and respiration did not decrease, but the changes in the photosynthetic rate and the lipid content per cell were similar to cultures that were nitrogen-starved in the presence of sodium. The carbon-to-nitrogen ratio increased in both cultures. Nitrogen, in the form of nitrate, and sodium were resupplied to cultures that had been preconditioned in nitrogen- and sodium-deficient medium for 5 d. Control cultures to which neither nitrate or sodium were added remained in a static state with respect to cell number, volume, and carbohydrate but showed slight increases in lipid. Cells in cultures to which 10 mM nitrate alone was added showed a similar response to cultures where no additions were made. Cells in cultures to which 50 mM sodium alone was added divided for 2 d, with concomitant small decreases in all measured constituents. Cell division resumed in cultures to which both sodium and nitrate were added. The lipid content fell dramatically in these cells and was correlated to metabolic oxidation via measured increases in the activity of the glyoxylate cycle enzyme, isocitrate lyase. We conclude that lipids are stored as a function of decreased growth rate and are metabolized to a small extent when cell division resumes. However, much higher rates of metabolism occur if cell division resumes in the presence of a nitrogen source.     

Efficient transgenic plant regeneration throughAgrobacterium-mediated transformation of Chickpea (Cicer arietinum L.)

Three genotypes of chickpea ICCV-1, ICCV-6 and a Desi (local) variety were tested for plant regeneration through multiple shoot production. The embryo axis was removed from mature seeds, the root meristem and the shoot apex were discarded. These explants were cultured on medium containing MS macro salts, 4X MS micro salts, I35 vitamins, 3.0 mg/1 BAP, 0.004 mg/1 NAA, 3% (w/v) sucrose and incubated at 26⁰C. The explants were transformed withAgrobacterium tumefaciens strain LBA4404 with binary vector pBI121 containing theuidA andnptIl genes. Multiple shoots were repeatedly selected with kanamycin. The selected kanamycin resistant shoots were rooted on MS medium supplemented with 0.05 mg/1 113A. The presumptive transformants histochemically stained positive for GUS. Additionally, nptll assay confirmed the expression ofnptII in kanamycin resistant plants. Transgenic plants were transferred to soil and grown in the green house.Abbreviations BAP 6-benzylamino purine - 2,4-D 2,4dichlorophenoxy acetic acid - IAA Indole acetic acid - IBA Indole butaric acid - NAA Naphthalene acetic acid     

Cold requirement for maximal activity of the bacterial ice nucleation protein INAZ in transgenic plants

The bacterial ice nucleation gene inaZ confers production of ice nuclei when transferred into transgenic plants. Conditioning of the transformed plant tissue at temperatures near 0°C greatly increased the ice nucleation activity in plants, and maximum ice nucleation activity was achieved only after low-temperature conditioning for about 48 h. Although the transgenic plants contain similar amounts of inaZ mRNA at both normal and low temperatures, low temperatures are required for accumulation of INAZ protein. We propose that the stability of the INAZ protein and thus ice nucleation activity in the transgenic plants is enhanced by low-temperature conditioning.     

Biased gene conversion is not occurring among rDNA repeats in the Brassica triangle.

Hybridization is a common phenomenon that results in complex genomes. How ancestral genomes interact in hybrids has long been of great interest. Recombination among ancestral genomes may increase or decrease genetic variation. This study examines rDNA from members of the Brassica triangle for evidence of gene conversion across ancestral genomes. Gene conversion is a powerful force in the evolution of multigene families. It has previously been shown that biased gene conversion can act to homogenize rDNA repeats within hybrid genomes. Here, we find no evidence for biased gene conversion or unequal crossing over across ancestral genomes in allotetraploid Brassica species. We suggest that, while basic genomic processes are shared by all organisms, the relative frequency of these processes and their evolutionary importance may differ among lineages. Key words : Brassica, rDNA, gene conversion, allotetraploids.     

Disparate modulation of plasma membrane protein lateral mobility by various cell permeabilizing agents

The mobility of a cell surface protein on cells osmotically swollen by treatment with several different cell permeabilizing agents retains specific restraints despite detachment of the plasma membrane from the cortical cytoskeleton. Fluorescence photobleaching recovery experiments indicate that the lateral diffusion constants of immunoglobulin E (IgE)-receptor complexes on the surface of rat basophilic leukemia cells increase 2–5 × following permeabilization with streptolysin O or digitonin, with little change in their mobile fractions. Swelling by hypo-osmotic treatment in water enhances lateral diffusion of IgE-receptor complexes and raises the mobile fractions to near 100%. In contrast, swelling by treatment with filipin arrests lateral diffusion, although rotational mobility remains unhindered. Lateral mobility of a fluorescent lipid analogue remains unchanged under these conditions. Crosslinking by anti-IgE antibodies redistributes the IgE-receptor complexes into large patches on untreated cells and on cells swollen by permeabilization with streptolysin O or digitonin, but rot on cells swollen by treatment with filipin. The results indicate a diversity of effects of the various permeabilizing agents on the mobility of membrane proteins. In particular, treatment with filipin appears to reorganize the plasma membrane into a network of fluid domains on a scale smaller than the bleaching spot size used (～1.5 μm). © 1994 Wiley-Liss, Inc.     

The functional units of a peptostreptococcal protein L

Protein L is a cell-surface protein from Peptostreptococcus which interacts with immunoglobulin kappa light chains. A gene from Peptostreptococcus strain 3316 coding for protein L and fragments thereof were expressed in Escherichia coli. The peptides were examined for binding to immunoglobulin and serum albumin. The four C units were shown to be responsible for binding to immunoglobulin and the four D units for binding to albumin. This protein L molecule therefore binds to albumin at a site separate from that involved in binding to immunoglobulin. The albumin-binding units have high amino acid sequence identity with the albumin-binding units of streptococcal cell-surface proteins. The gene contains three sites available for internal initiation of translation resulting in three active proteins. The protein L molecule presented in this report was compared with a previously reported protein from Peptostreptococcus strain 312. The two proteins differ in several respects, including size and the number and types of repeat units.