Developmental phase-dependent photosynthetic responses to ultraviolet-B radiation: damage, defence, and adaptation of primary leaves of wheat seedlings

Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280–320 nm; 60 μmol m⁻² s⁻¹) exposure alone and in combination with photosynthetically active radiation (PAR; 400–800 nm; 200 μmol m⁻² s⁻¹) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O₂ evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples.     

Methylphenidate decreased the amount of glucose needed by the brain to perform a cognitive task

The use of stimulants (methylphenidate and amphetamine) as cognitive enhancers by the general public is increasing and is controversial. It is still unclear how they work or why they improve performance in some individuals but impair it in others. To test the hypothesis that stimulants enhance signal to noise ratio of neuronal activity and thereby reduce cerebral activity by increasing efficiency, we measured the effects of methylphenidate on brain glucose utilization in healthy adults. We measured brain glucose metabolism (using Positron Emission Tomography and 2-deoxy-2[18F]fluoro-D-glucose) in 23 healthy adults who were tested at baseline and while performing an accuracy-controlled cognitive task (numerical calculations) given with and without methylphenidate (20 mg, oral). Sixteen subjects underwent a fourth scan with methylphenidate but without cognitive stimulation. Compared to placebo methylphenidate significantly reduced the amount of glucose utilized by the brain when performing the cognitive task but methylphenidate did not affect brain metabolism when given without cognitive stimulation. Whole brain metabolism when the cognitive task was given with placebo increased 21% whereas with methylphenidate it increased 11% (50% less). This reflected both a decrease in magnitude of activation and in the regions activated by the task. Methylphenidate's reduction of the metabolic increases in regions from the default network (implicated in mind-wandering) was associated with improvement in performance only in subjects who activated these regions when the cognitive task was given with placebo. These results corroborate prior findings that stimulant medications reduced the magnitude of regional activation to a task and in addition document a "focusing" of the activation. This effect may be beneficial when neuronal resources are diverted (i.e., mind-wandering) or impaired (i.e., attention deficit hyperactivity disorder), but it could be detrimental when brain activity is already optimally focused. This would explain why methylphenidate has beneficial effects in some individuals and contexts and detrimental effects in others.     

Occult medullary carcinoma of thyroid with lymph node metastases: a case report

BACKGROUND: Occult thyroid malignancies presenting with secondary neck masses as the first clinical manifestation is well known. Although rare, medullary carcinoma serves a potential source for lymph node metastases. The characteristic cytomorphology of medullary thyroid carcinoma (MTC) should clinch the diagnosis. Further, fine needle aspiration cytology (FNAC) of the ultrasonography-detected occult nodules in thyroid serves as a useful preoperative diagnostic tool. CASE: A 22-year-old man presented with left-sided neck masses of 1 year duration. FNAC smears of the neck masses revealed cytomorphology characteristic of MTC. Ultrasonography of the thyroid led to ruling out the presence of an occult nodule and detected an 8-mm nodule in the left thyroid lobe. Ultrasound-guided FNAC of the nodule showed features similar to those with FNAC of the neck masses. Surgical resection of thyroid and neck masses further confirmed the diagnosis of a primary occult MTC with lymph node metastases. CONCLUSION: FNAC smears of lymph node masses showing the distinct cytomorphology of MTC should prompt suspicion for occult primary in thyroid. Ultrasound-guided FNAC of these occult nodules, if detected, further serves a diagnostic tool for accurate preoperative diagnosis when metastasis presents as the first clinical manifestation of an occult primary.     

CXXC domain of human DNMT1 is essential for enzymatic activity

DNA cytosine methylation is one of the major epigenetic gene silencing marks in the human genome facilitated by DNA methyltransferases. DNA cytosine-5 methyltransferase 1 (DNMT1) performs maintenance methylation in somatic cells. In cancer cells, DNMT1 is responsible for the aberrant hypermethylation of CpG islands and the silencing of tumor suppressor genes. Here we show that the catalytically active recombinant DNMT1, lacking 580 amino acids from the amino terminus, binds to unmethylated DNA with higher affinity than hemimethylated or methylated DNA. To further understand the binding domain of enzyme, we have used gel shift assay. We have demonstrated that the CXXC region (C is cysteine; X is any amino acid) of DNMT1 bound specifically to unmethylated CpG dinucleotides. Furthermore, mutation of the conserved cysteines abolished CXXC mediated DNA binding. In transfected COS-7 cells, CXXC deleted DNMT1 (DNMT1 (DeltaCXXC)) localized on replication foci. Both point mutant and DNMT1 (DeltaCXXC) enzyme displayed significant reduction in catalytic activity, confirming that this domain is crucial for enzymatic activity. A permanent cell line with DNMT1 (DeltaCXXC) displayed partial loss of genomic methylation on rDNA loci, despite the presence of endogenous wild-type enzyme. Thus, the CXXC domain encompassing the amino terminus region of DNMT1 cooperates with the catalytic domain for DNA methyltransferase activity.     

Copper removal by immobilized Microcystis aeruginosa in continuous flow columns at different bed heights: study of the adsorption/desorption cycle

Microcystis aeruginosa immobilized in a natural polymer was tested for its potential to remove Cu²⁺ ions from aqueous solution in a continuous, downflow packed columnar reactor. Various parameters like flow rate, bed height and contact time required for maximum removal of test metals by the immobilized Microcystis aeruginosa were optimized. An increase in bed height from 2 to 10 cm resulted in an apparent decrease in biosorption capacity from 8.94 to 5.34 mg g^–1, but more Cu²⁺ solution was purified at the higher bed height. Efficiency of metal recovery from Cu²⁺-loaded biomass and its subsequent regeneration was also determined. Immobilized M. aeruginosa was found to be effective in Cu²⁺ removal from solution for up to 10 cycles of adsorption–desorption and 1 M HCl is very efficient desorbent for regeneration of Microcystis biomass for reuse.     

Photochemical labeling of membrane hydrophobic core of human erythrocytes using a new photoactivable reagent 2-[3H]diazofluorene

Photoactivable reagents have been useful for studying the structural aspects of membrane hydrophobic core. We have reported earlier (Anjaneyulu, P.S.R., and Lala, A. K. (1982) FEBS Lett. 146, 165-167) the use of diazofluorene as a probe for fluorescent photochemical labeling of hydrophobic core in artificial membranes. To quantitate and enhance the monitoring ability of this probe, we have synthesized 2-[3H]diazofluorene of high specific activity. This reagent rapidly partitions into phosphatidylcholine vesicles and selectively labels the fatty acyl chains of phosphatidylcholine. The insertion yield (13%) is not affected by the presence of scavengers like reduced glutathione. 2-[3H]Diazofluorene also readily partitions into erythrocyte membranes and on photolysis labels the membrane. The overall insertion was 48% with 9.7% in protein fraction and the rest in lipids. The distribution of radioactivity in labeled protein fraction was restricted to integral membrane proteins with Band 3 being the major protein labeled. There is little or no labeling associated with extrinsic proteins like spectrin. Further analysis of labeled Band 3 by treatment with chymotrypsin indicated that the labeling was restricted to the membrane spanning CH-17 and CH-35 fragments. No labeling of the cytoplasmic fragment of Band 3 could be observed. 2-[3H]Diazofluorene should prove useful for studying integral membrane proteins and their membrane-spanning regions.