Chloroplast ultrastructure of sugar beet (Beta vulgaris L.) cultivated in normal and elevated CO2 concentrations with two contrasted nitrogen supplies

Sugar beet (Beta vulgaris L., cultivar Celt) plants were grownunder simulated field conditions in pots and supplied with adequateor deficient nitrogen (HN and LN, respectively) combined withtwo CO₂ concentrations, ambient (c. 350µmol mol^–1C0₂—AC), or elevated CO₂ (c. 600 µmol mol^–1CO₂—HC). Chloroplast structure in mesophyll palisade cellsof mature leaves (leaf number 19 in HN and 9 in LN), sampledat midday on 16 August 1993 was studied by transmission electronmicroscopy and quantified stereologically. The ultrastructureof palisade parenchyma chloroplasts was affected by the elevatedCO₂ concentration and strikingly affected by nitrogen supply.Chloroplast diameter (cross-sectional length) was slightly,but not significantly, greater in HC than AC treatments withinan N treatment, but was smaller in LN than HN; chloroplast cross-sectionalarea also increased with HC in both N treatments, but only significantlyso in LN. Elevated CO₂ reduced the proportion of total thylakoids(significant at 5% and 0.1% in HN and LN, respectively) dueto decreased granal thylakoids, but the proportion of inter-granal(stromal) thylakoid membranes was not affected compared to chloroplastsfrom plants grown with ambient CO₂. Chloroplast stroma increasedas a proportion of chloroplast volume with elevated comparedto ambient CO₂ with HN but not LN. Starch inclusions were notsignificantly different with elevated compared to ambient CO₂at HN, but the proportion of starch increased considerably atelevated compared to ambient C0₂ at LN, indicating an over-productionof assimilates. Plastoglobuli in chloroplasts increased withdeficient N, but decreased with elevated CO₂. Larger chloroplastswith a greater proportion of stroma, but a smaller proportionof granal thylakoids, suggest increased CO² assimilating capacityand decreased light harvesting/PSII capacity with elevated CO₂. Key words: Chloroplast, ultrastructure, elevated CO₂ concentration, nitrogen deficiency, sugar beet, Beta vulgaris     

Reduction in phosphoribulokinase activity by antisense RNA in transgenic tobacco: effect on CO2 assimilation and growth in low irradiance

To quantify the importance of the Calvin cycle enzyme phosphoribulokinase (PRK) in photosynthesis and to perturb photosynthesis without large direct reductions in leaf protein content, tobacco plants (Nicotiana tabacum L.) were transformed with an inverted cDNA encoding tobacco PRK. A population of plants expressing antisense RNA and a range of PRK activities from wild-type to less than 5% of wild-type were obtained. CO₂ assimilation under the growing conditions (330 µmol photons m^?2 sec^?1, 350 µbar CO₂, 25°C) was not inhibited until more than 85% of PRK activity had been removed. With reduction in PRK activity of between 85 and 95%, assimilation rates and amounts of chlorophyll compared with wild-type were reduced by up to half. Decreased absorption of light by leaves with less chlorophyll accounte0d for only a small part of the reduction in assimilation rate. When PRK activity was below 15% of wild-type, amounts of ribulose-5-phosphate, ribose-5-phosphate, ATP and fructose-6-phosphate were 1.5- to fivefold higher and levels of ribulose-1,5-bisphosphate, 3-phosphoglyceric acid and ADP 1.5- to fourfold lower than in wild-type. It is estimated that these changes maintained flux through PRK to realise the assimilation rates observed. A possible shift of control within the Calvin cycle towards fructose-1,6-bisphosphatase in plants with low PRK is discussed. Amounts of hexoses and starch in particular were reduced in plants expressing the lowest PRK activities; amounts of sucrose were little affected. Lower CO₂ assimilation in plants with low PRK activity correlated with reduced relative growth rate of shoots and delayed flowering, but there was no effect on specific leaf area. It is concluded that (i) in wild-type plants grown in constant low light, PRK has a flux-control coefficient for CO₂ assimilation of zero, and that even when amounts of PRK are reduced 20-fold relative to wild-type, altered amounts of metabolites compensate for much of the reduction in PRK protein; (ii) in plants where there is a 95% reduction in amounts of PRK, photosynthesis was reduced twofold without large changes in leaf protein content or leaf geometry.     

A transposable epitope of HLA-137, B40 molecules

The monoclonal antibody M1340.2 defines a novel subtype of HLA-1340 that is expressed by the Sweig cell line. This molecule, called HLA-B40^*, lacks an antigenic determinant that is common to HLA-137 and the HLA-Bw60 subtype of HLA-1340. Genes encoding HLA-B40^* and HLA-BW60 have now been isolated and the amino acid sequences of these proteins compared with other HLA-13 locus molecules. These results show that HLA-B40^* is a unique protein which differs from HLA-BW60 by eight amino acid substitutions. Comparison of the sequences for HLA-B40^*, -Bw60, and -B7 localizes the MB40.2 epitope to a cluster of three substitutions at positions 177, 178, and 180 at the end of the ₂ domain. Gene conversion or reciprocal recombination are postulated to have transferred this cluster of substitutions, and their associated epitope, during the evolution of HLA-B locus genes. The epitope may consist of an a helical segment which is exclusively found on MB40.2-positive molecules.     

Does Childhood Sexual Abuse Predict Young Adult's BMI? A Birth Cohort Study

Objective: The objective was to identify the extent to which childhood sexual abuse (CSA) is associated with BMI and overweight status in young adulthood and to examine whether any associations differ by gender. Research Methods and Procedures: The Mater‐University of Queensland Study of Pregnancy is a prospective birth cohort from a population‐based sample involving 7223 singletons whose mothers were enrolled in the 1980s at the first antenatal visit. The present cohort consisted of a subgroup of 2461 young adults who had both self‐reported CSA data and measured BMI at 21 years. Results: Of 1273 men, 10.5% reported non‐penetrative and 7.5% reported penetrative CSA before age 16 years. Of 1305 women, 20.6% reported non‐penetrative and 7.9% reported penetrative CSA by age 16 years. We found young women's BMI and the prevalence of overweight at age 21 were greater in those who experienced penetrative CSA. This association was robust to adjustment for a variety of potential confounders. However, there was no association between non‐penetrative CSA and BMI in women and no association between either category of CSA and BMI in men. There was statistical evidence for a gender difference in the association of CSA with mean BMI at age 21 (p value for statistical interaction <0.01 in all models). Discussion: These findings suggest that among women, penetrative CSA is associated with greater BMI and increased odds of being overweight in later life, whereas in men, this association does not hold. This gender difference may reflect differences between women and men in the relationship between psychological trauma and body image or may be a chance subgroup finding.