Photosynthetic response of clusterbean chloroplasts to UV-B radiation: Energy imbalance and loss in redox homeostasis between QA and QB of photosystem II

The effects of ultraviolet-B (UV-B: 280-320 nm) radiation on the photosynthetic pigments, primary photochemical reactions of thylakoids and the rate of carbon assimilation (P_n) in the cotyledons of clusterbean (Cyamopsis tetragonoloba) seedlings have been examined. The radiation induces an imbalance between the energy absorbed through the photophysical process of photosystem (PS) II and the energy consumed for carbon assimilation. Decline in the primary photochemistry of PS II induced by UV-B in the background of relatively stable P_n, has been implicated in the creation of the energy imbalance_. The radiation induced damage of PS II hinders the flow of electron from Q_A to Q_B resulting in a loss in the redox homeostasis between the Q_A to Q_B leading to an accumulation of Q_A⁻. The accumulation of Q_A⁻ generates an excitation pressure that diminishes the PS II-mediated O₂ evolution, maximal photochemical potential (F_v/F_m) and PS II quantum yield (Φ_{PS II}). While UV-B radiation inactivates the carotenoid-mediated protective mechanisms, the accumulation of flavonoids seems to have a small role in protecting the photosynthetic apparatus from UV-B onslaught. The failure of protective mechanisms makes PS II further vulnerable to the radiation and facilitates the accumulation of malondialdehyde (MDA) indicating the involvement of reactive oxygen species (ROS) metabolism in UV-B-induced damage of photosynthetic apparatus of clusterbean cotyledons.     

Nitric oxide content is associated with tolerance to bicarbonate-induced chlorosis in micropropagated Prunus explants

Iron (Fe) chlorosis is a common nutritional deficiency in fruit trees grown in calcareous soils. Grafting on tolerant rootstocks is the most efficient practice to cope with it. In the present work, three Prunus hybrid genotypes, commonly used as peach rootstocks, and one peach cultivar were cultivated with bicarbonate in the growth medium. Parameters describing oxidative stress and the metabolism of reactive nitrogen species were studied. Lower contents of nitric oxide and a decreased nitrosoglutathione reductase activity were found in the most sensitive genotypes, characterized by higher oxidative stress and reduced antioxidant defense. In the peach cultivar, which behaved as a tolerant genotype, a specifically nitrated polypeptide was found.     

White monkey syndrome and presumptive copper deficiency in wild savannah baboons

In immature wild savannah baboons (Papio cynocephalus), we observed symptoms consistent with copper (Cu) deficiency and, more specifically, with a disorder referred to as white monkey syndrome (WMS) in laboratory primates. The objectives of this study were to characterize this pathology, and test three hypotheses that (1) Cu deficiency may have been induced by zinc (Zn) toxicity, (2) it may have been induced by molybdenum (Mo) toxicity, and (3) cumulative rainfall during the perinatal period and particularly during gestation is an ecological factor distinguishing infants afflicted with WMS from non-WMS infants. During 2001-2009, we observed 22 instances of WMS out of a total 377 live births in the study population. Visible symptoms exhibited by WMS infants included whitening of the animal's fur and/or impaired mobility characterized by an apparent "stiffening" of the hindlimbs. Occurrence of WMS did not vary significantly by gender. However, among individuals that survived at least 180 days, WMS males had a significantly lower survivorship probability than non-WMS males. Zn/Cu ratios assessed from hair samples of adult female baboons were higher in females who had produced at least one WMS offspring relative to females who had not had a WMS offspring. This was true even when the hair sample was collected long after the birth of the female's afflicted infant. We consider this potentially indicative of a robust tendency for low Cu levels induced by elevated Zn intake in some individuals. No significant differences of Mo/Cu ratios were observed. Cumulative rainfall during gestation (～179 days) was 50% lower for WMS infants relative to non-WMS infants. In contrast, rainfall for the two classes of infants did not differ in the 180 days before conception or in the 180 days following birth. This finding highlights the importance of prenatal ecological conditions in healthy fetal development with regard to WMS.     

Glycosylation of the OCTN2 carnitine transporter: Study of natural mutations identified in patients with primary carnitine deficiency

Primary carnitine deficiency is caused by impaired activity of the Na⁺-dependent OCTN2 carnitine/organic cation transporter. Carnitine is essential for entry of long-chain fatty acids into mitochondria and its deficiency impairs fatty acid oxidation. Most missense mutations identified in patients with primary carnitine deficiency affect putative transmembrane or intracellular domains of the transporter. Exceptions are the substitutions P46S and R83L located in an extracellular loop close to putative glycosylation sites (N57, N64, and N91) of OCTN2. P46S and R83L impaired glycosylation and maturation of OCTN2 transporters to the plasma membrane. We tested whether glycosylation was essential for the maturation of OCTN2 transporters to the plasma membrane. Substitution of each of the three asparagine (N) glycosylation sites with glutamine (Q) decreased carnitine transport. Substitution of two sites at a time caused a further decline in carnitine transport that was fully abolished when all three glycosylation sites were substituted by glutamine (N57Q/N64Q/N91Q). Kinetic analysis of carnitine and sodium-stimulated carnitine transport indicated that all substitutions decreased the Vmax for carnitine transport, but N64Q/N91Q also significantly increased the Km toward carnitine, indicating that these two substitutions affected regions of the transporter important for substrate recognition. Western blot analysis confirmed increased mobility of OCTN2 transporters with progressive substitutions of asparagines 57, 64 and/or 91 with glutamine. Confocal microscopy indicated that glutamine substitutions caused progressive retention of OCTN2 transporters in the cytoplasm, up to full retention (such as that observed with R83L) when all three glycosylation sites were substituted. Tunicamycin prevented OCTN2 glycosylation, but it did not impair maturation to the plasma membrane. These results indicate that OCTN2 is physiologically glycosylated and that the P46S and R83L substitutions impair this process. Glycosylation does not affect maturation of OCTN2 transporters to the plasma membrane, but the 3 asparagines that are normally glycosylated are located in a region important for substrate recognition and turnover rate.     

Tissue-specific distribution of aberrant DNA methylation associated with maternal low-folate status in human neural tube defects

This study compares the density and tissue-specific distribution of 5-methyl cytosine (5mC) in genomic DNA from human fetuses with or without neural tube defects (NTD) and examines whether low maternal serum folate is a possible correlate and/or risk factor for NTD. The results demonstrate significant hypomethylation of brain genomic DNA in NTD fetuses relative to controls (P<.01), as well as relative hypermethylation of skin and heart in NTD fetuses. In normal fetuses, the level of 5mC in liver genomic DNA decreased from fetal week 18 to 28 and increased over the same developmental period in kidney genomic DNA, but these trends were absent in genomic DNA from NTD fetuses. Mean maternal serum folate was significantly lower in NTD fetuses than in controls (P<.01), and maternal serum folate correlated with density of 5mC in genomic brain DNA from NTD fetuses (r=0.610). The results indicate that aberrant DNA methylation in NTD may be due to maternal folate deficiency and may be involved in the pathogenesis of NTD in humans.     

Roles of reactive oxygen and nitrogen species in pain

Peroxynitrite (PN; ONOO⁻) and its reactive oxygen precursor superoxide (SO; O₂^•−) are critically important in the development of pain of several etiologies including pain associated with chronic use of opiates such as morphine (also known as opiate-induced hyperalgesia and antinociceptive tolerance). This is now an emerging field in which considerable progress has been made in terms of understanding the relative contributions of SO, PN, and nitroxidative stress in pain signaling at the molecular and biochemical levels. Aggressive research in this area is poised to provide the pharmacological basis for development of novel nonnarcotic analgesics that are based upon the unique ability to selectively eliminate SO and/or PN. As we have a better understanding of the roles of SO and PN in pathophysiological settings, targeting PN may be a better therapeutic strategy than targeting SO. This is because, unlike PN, which has no currently known beneficial role, SO may play a significant role in learning and memory [1]. Thus, the best approach may be to spare SO while directly targeting its downstream product, PN. Over the past 15 years, our team has spearheaded research concerning the roles of SO and PN in pain and these results are currently leading to the development of solid therapeutic strategies in this important area.     

A polymorphic position in electron transfer flavoprotein modulates kinetic stability as evidenced by thermal stress

The electron transfer flavoprotein (ETF) is a hub interacting with at least 11 mitochondrial flavoenzymes and linking them to the respiratory chain. Here we report the effect of the ETFα-T/I171 polymorphism on protein conformation and kinetic stability under thermal stress. Although variants have comparable thermodynamic stabilities, kinetically their behavior is rather distinct as ETFα-T171 displays increased susceptibility to cofactor flavin adenine dinucleotide (FAD) loss and enhanced kinetics of inactivation during thermal stress. Mimicking a fever episode yields substantial activity loss. However, the presence of substoichiometric concentrations of GroEL is sufficient to act as an effective buffer against long-term thermal denaturation. Our investigations are compatible with the notion that the ETFα-T171 variant displays an altered conformational landscape that results in reduced protein function under thermal stress.     

REGULATION OF BIOSYNTHESIS OF DIMETHYLSULFONIOPROPIONATE AND ITS UPTAKE IN STERILE MUTANT OF ULVA PERTUSA (CHLOROPHYTA)1

It has been shown that marine algae produce the compatible solute dimethylsulfoniopropionate (DMSP) from methionine (Met) via four enzymatic reactions in which the third step, synthesis of 4‐dimethylsulfonio‐2‐hydroxy‐butyrate (DMSHB) from 4‐methylthio‐2‐hydroxybutyrate (MTHB), is the committing step. However, regulation of the biosynthetic pathways and transport properties of DMSP is largely unknown. Here, the effects of sulfur and sodium concentrations on the uptake and synthesis of DMSHB and DMSP were examined in a sterile mutant of Ulva pertusa Kjellm. Sulfur deficiency increased the activity of the sulfur assimilation enzyme O‐acetyl serine sulfhydrylase but decreased the MTHB S‐methyltransferase activity, suggesting the preferential utilization of sulfur atoms for Met metabolites other than DMSP. Uptake of DMSP and DMSHB was enhanced by S deficiency. High salinity enhanced the MTHB S‐methyltransferase activity as well as the uptake of DMSHB. The MTHB S‐methyltransferase activity was inhibited by its product DMSP. These data demonstrate the importance of MTHB S‐methyltransferase activity and uptake of DMSHB for the regulation of DMSP.     

Effect of cytokinins on oxidative stress in tobacco plants under nitrogen deficiency

Wild type and transgenic tobacco plants expressing isopentenyltransferase, a gene coding the rate-limiting step in cytokinin synthesis, were grown under limited nitrogen (N) conditions. Our results indicated that the WT plants subjected to N deficiency displayed reduced biomass and relative growth rates, increased levels of oxidative damage and reduced foliar concentrations of the different N forms. However, the transgenic plants expressing P_SARK∷IPT, in spite of showing a significant decline in all the N forms in the leaf, avoided the alteration of the oxidative metabolism and maintained biomass and the relative growth rates at control levels, under suboptimal N conditions. These results suggest that the increased cytokinin synthesis in the transgenic plants is an effective mechanism to improve N-use efficiency.     

EFFECTS OF SELENIUM DEFICIENCY ON THE MORPHOLOGY AND ULTRASTRUCTURE OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

The effects of selenium deficiency on the siliceous and nonsiliceous components of the planktonic marine diatom Thalassiosira pseudonana (Hust.) Hasle and Heimdal (clone 3H) are examined using light and electron microscopy. Selenium deficiency induces elongation along the pervalvar axis initially as a result of chain formation caused by the failure of sibling cells to separate and subsequently by cell elongation via the production of hyaline girdle bands. In Se-deficient cultures cell elongation involves the blockage of both mitotic and cytokinetic components of cell division. Selenium deficiency results in ultrastructural alterations in the reticular membrane system and in mitochondrial and chloroplast membranes. Various types of inclusions are seen in vacuolar areas and the accumulation of lipid reserves is evident in Se-deficient cells. These results provide indirect evidence for a metabolic Se requirement in this algal species.