Chromosomal localization of a tandemly repeated DNA sequence in Trifolium repens L

INTRoDUCTIoNlYho1iumrePensL,whiteclover,isaneconomicallyimportantplantspeciesintemperatepastures.Asbrieflyreportedby[1],ithas16pairsofchromosomes(2n=32).Asyet,nodetailedcytologicalexaminationofthisspecies,suchasC-banding,hasbeenrep0rted.Inthelastdecade,thetechnique0fC-bandinghasbeenusedt0examinehighlyrepeatedsequencesinplantchrom0s0mesandhasprovidedausefultoolf0rtheanalysis0fcyt0geneticstructureincr0pplants[2-71.Inplants,thechr0m0s0mall0calizationofhighlyrepeatedDNAsequencesbyinsituhybr…     

Induced and normal crystalline inclusions in plastids revealed by freeze-fracturing

Summary Aggregations of approximately 11 nm spaced spherical particles are described in both freeze-fractured and chemically fixed bean and spinach leaf plastids. It is suggested that the aggregations were induced as a result of the dehydrating action of the cryoprotectants used. It is tentatively concluded, on the basis of previous reports, that the aggregations consist of Fraction I protein.     

Transposition studies of mini-Mu plasmids constructed from the chemically synthesized ends of bacteriophage Mu

We describe below the chemical synthesis of the right and left ends of bacteriophage Mu and characterize the activity of these synthetic ends in mini-Mu transposition. Mini-Mu plasmids were constructed which carry the synthetic Mu ends together with the Mu A and B genes under control of the bacteriophage λ p_L promoter. Derepression of p_L leads to a high frequency of mini-Mu transposition (5.6 × 10⁻²) which is dependent on the presence of the Mu ends and the Mu A and B proteins. Five deletion mutants in the Mu ends were tested in the mini-Mu transposition system and their effects on transposition are described.     

Composition of the photosystems and chloroplast structure in extreme shade plants

Chloroplasts were isolated from leaves of three species of tropical rainforest plants, Alocasia macrorrhiza, Cordyline rubra and Lomandra longifolia; these species are representative of extreme “shade” plants. It was found that shade plant chloroplasts contained 4–5 times more chlorophyll than spinach chloroplasts. Their chlorophyll a/chlorophyll b ratio was 2.3 compared with 2.8 for spinach. Electron micrographs of leaf sections showed that the shade plant chloroplasts contained very large grana stacks. The total length of partitions relative to the total length of stroma lamellae was much higher in Alocasia than in spinach chloroplasts. Freeze-etching of isolated chloroplasts revealed both the small and large particles found in spinach chloroplasts.

Despite their increased chlorophyll content, low chlorophyll a/chlorophyll b ratio, and large grana, the shade plant chloroplasts were fragmented with digitonin to yield small fragments (D-144) highly enriched in Photosystem I, and large fragments (D-10) enriched in Photosystem II. The degree of fragmentation of the shade plant chloroplasts was remarkably similar to that of spinach chloroplasts, except that the subchloroplast fragments from the shade plants had lower chlorophyll a/chlorophyll b ratios than the corresponding fragments from spinach. The D-10 fragments from the shade plants had chlorophyll a/chlorophyll b ratios of 1.78-2.00 and the D-144 fragments ratios of 3.54–4.07. We conclude that Photosystems I and II of the shade plants have lower proportions of chlorophyll a to chlorophyll b than the corresponding photosystems of spinach. The lower chlorophyll a/chlorophyll b ratio of shade plant chloroplasts is not due to a significant increase in the ratio of Photosystem II to Photosystem I in these chloroplasts.

The extent of grana formation in higher plant chloroplasts appears to be related to the total chlorophyll content of the chloroplast. Grana formation may simply be an means of achieving a higher density of light-harvesting assemblies and hence a more efficient collection of light quanta.     

Localization of Bacteria and Hemoglobin in Root Nodules of Parasponia andersonii Containing Both Bradyrhizobium Strains and Rhizobium leguminosarum biovar trifolii

Dual occupancy of Parasponia andersonii nodules with different Bradyrhizobium strains and Rhizobium leguminosarum biovar trifolii was frequently obtained when two strains were inoculated into plants grown aseptically in tubes. Since reisolates of Bradyrhizobium strains from dually occupied nodules acquired the ability to nodulate Trifolium repens, the spatial relationship of the two species of bacteria during nodule initiation and development was investigated and their proximity was demonstrated. By using light microscopy and electron microscopy and immunogold labeling, R. leguminosarum biovar trifolii NGR66 inoculated alone onto P. andersonii produced small ineffective nodules, with bacteria embedded in matrix material in intercellular spaces and in a few nonliving host cells rather than in infection threads (CP299). In dual infections, the two bacterial species were shown to be adjacent to one another in the matrix of nodule intercellular spaces and in some host nodule cells. However, when two different Bradyrhizobium strains occupied a single nodule, they were located in different lobes of the same nodule. Immunogold labeling showed that Parasponia hemoglobin was localized in the cytoplasm of young infected nodule cells. This suggests that the nitrogen-fixing phase of Parasponia nodule cells is short-lived and correlates with previous acetylene reduction data from nodule slices. Hemoglobin was associated only with areas of nodule tissue infected with the effective nitrogen-fixing strain CP299 and absent from areas infected with R. leguminosarum biovar trifolii.     

Management of "brittle" diabetes with a preprogrammable implanted insulin pump delivering intraperitoneal insulin.

OBJECTIVE--Glycaemic control in a young woman with "brittle" diabetes. DESIGN--Use of a preprogrammable fully implanted pump (Infusaid) to deliver insulin intraperitoneally at variable rates, giving a total dose of about 60 units/24 h. SETTING--Endocrinology department in a teaching hospital. PATIENT--Thirty year old woman with 15 years'' history of "brittle" diabetes. MAIN OUTCOME MEASURES--Glycated haemoglobin concentration; plasma glucose concentration. RESULTS--After implantation of the pump there was an immediate and sustained improvement in diabetic control. The patient''s glycated haemoglobin concentration decreased from 15.2% to 9.2% over seven months. Her daily glucose concentrations were in the range 3.5-12 mmol/l. She has not been admitted to hospital since implantation of the pump, which was eight months before the time of writing. CONCLUSION--The implanted programmable intraperitoneal insulin pump may be of value in the management of patients with "brittle" diabetes in whom other attempts at glycaemic control have failed.