Morphogenesis of potato plants in vitro. II. Endogenous levels,distribution, and metabolism of IAA and cytokinins

The levels of endogenous IAA and cytokinins (zeatin, zeatin riboside, isopentenyladenine, and isopentenyladenosine) were determined in potato plants cultured in vitro under red light (R) and blue light (B) on medium with or without hormones. On medium without hormones in B, plants contained much higher cytokinin levels, particularly in leaves and roots, and also slightly elevated IAA levels. Kinetin in the medium in B changed the distribution of cytokinins and significantly increased IAA level in roots. In R, the presence of kinetin led to an increased cytokinin level in the whole plant, while the IAA level was slightly lower. IAA in the medium in B decreased cytokinin level in all plant parts, while the IAA level did not change significantly. In R, the presence of IAA in the medium led to a moderate increase of CK level and to a significant increase in IAA level, especially in roots. Uptake of 1-¹⁴C-IAA and of ³H-zeatin was generally higher in B than in R. Higher percentage of IAA taken up in B was converted to conjugates in the roots. Metabolism of ³H-zeatin was similar in R and B with only slight differences in metabolite amounts.Thus, in all experimental situations in which tuber formation was stimulated, IAA level in roots and stolons rose significantly, stressing the importance of an IAA gradient for tuber formation.     

A surplus no more? Variation in krill availability impacts reproductive rates of Antarctic baleen whales

The krill surplus hypothesis of unlimited prey resources available for Antarctic predators due to commercial whaling in the 20th century has remained largely untested since the 1970s. Rapid warming of the Western Antarctic Peninsula (WAP) over the past 50 years has resulted in decreased seasonal ice cover and a reduction of krill. The latter is being exacerbated by a commercial krill fishery in the region. Despite this, humpback whale populations have increased but may be at a threshold for growth based on these human-induced changes. Understanding how climate-mediated variation in prey availability influences humpback whale population dynamics is critical for focused management and conservation actions. Using an 8-year dataset (2013–2020), we show that inter-annual humpback whale pregnancy rates, as determined from skin-blubber biopsy samples (n = 616), are positively correlated with krill availability and fluctuations in ice cover in the previous year. Pregnancy rates showed significant inter-annual variability, between 29% and 86%. Our results indicate that krill availability is in fact limiting and affecting reproductive rates, in contrast to the krill surplus hypothesis. This suggests that this population of humpback whales may be at a threshold for population growth due to prey limitations. As a result, continued warming and increased fishing along the WAP, which continue to reduce krill stocks, will likely impact this humpback whale population and other krill predators in the region. Humpback whales are sentinel species of ecosystem health, and changes in pregnancy rates can provide quantifiable signals of the impact of environmental change at the population level. Our findings must be considered paramount in developing new and more restrictive conservation and management plans for the Antarctic marine ecosystem and minimizing the negative impacts of human activities in the region.     

Citrulline metabolism in normal and citrullinemic human lymphocyte lines

Citrullinemia is one of the five aminoacidurias associated with the Krebs-Henseleit urea cycle. A long-term lymphocyte line (UM-21) derived from a patient with this disease and nine of ten clones of this line were found to have no activity for the enzyme argininosuccinate synthetase (AS), as demonstrated by their inability to grow in medium in which citrulline had been substituted for arginine, by their inability to incorporate arginine-C14 derived from citrulline-C14 into cellular protein, and by direct enzyme assay. One clone had normal or nearly normal argininosuccinate synthetase activity, as demonstrated by the same criteria. Nutritional "variants" able to grow logarithmically in medium containing citrulline were isolated from UM-21 and three clones. The apparent Kms of AS for citrulline in UM-21, the ten clones, the variant lines, and a normal line were measured and fell into three groups: AS in UM-21 and nine clones had no measurable apparent Km for citrulline; AS in the variant cells had apparent Kms for citrulline of approximately 20 mM; and AS in the normal cell line and one clone had apparent Kms for citrulline of 0.2 mM. The data suggest that the defect in the citrullinemic cell lines is due to a mutation in the structural gene coding for argininosuccinate synthetase.     

Peptide Mimetic of the S100A4 Protein Modulates Peripheral Nerve Regeneration and Attenuates the Progression of Neuropathy in Myelin Protein P0 Null Mice

We recently found that S100A4, a member of the multifunctional S100 protein family, protects neurons in the injured brain and identified two sequence motifs in S100A4 mediating its neurotrophic effect. Synthetic peptides encompassing these motifs stimulated neuritogenesis and survival in vitro and mimicked the S100A4-induced neuroprotection in brain trauma. Here, we investigated a possible function of S100A4 and its mimetics in the pathologies of the peripheral nervous system (PNS). We found that S100A4 was expressed in the injured PNS and that its peptide mimetic (H3) affected the regeneration and survival of myelinated axons. H3 accelerated electrophysiological, behavioral and morphological recovery after sciatic nerve crush while transiently delaying regeneration after sciatic nerve transection and repair. On the basis of the finding that both S100A4 and H3 increased neurite branching in vitro, these effects were attributed to the modulatory effect of H3 on initial axonal sprouting. In contrast to the modest effect of H3 on the time course of regeneration, H3 had a long-term neuroprotective effect in the myelin protein P₀ null mice, a model of dysmyelinating neuropathy (Charcot-Marie-Tooth type 1 disease), where the peptide attenuated the deterioration of nerve conduction, demyelination and axonal loss. From these results, S100A4 mimetics emerge as a possible means to enhance axonal sprouting and survival, especially in the context of demyelinating neuropathies with secondary axonal loss, such as Charcot-Marie-Tooth type 1 disease. Moreover, our data suggest that S100A4 is a neuroprotectant in PNS and that other S100 proteins, sharing high homology in the H3 motif, may have important functions in PNS pathologies.     

Synthesis and Application of Negatively Charged PNA Analogues

Negatively charged DNA mimics containing phosphonate analogues of peptide nucleic acids were designed, and their physicochemical and biological properties were evaluated in the comparison with natural oligonucleotides, classical peptide nucleic acids, and morpholino phosphorodiamidate oligonucleotide analogues. The results obtained revealed a high potential of phosphonate-containing PNA derivatives for a number of biological applications, such as diagnostic, nucleic acids analysis, and inhibition of gene expression.     

Veillonella,Firmicutes: Microbes disguised as Gram negatives

The Firmicutes represent a major component of the intestinal microflora. The intestinal Firmicutes are a large, diverse group of organisms, many of which are poorly characterized due to their anaerobic growth requirements. Although most Firmicutes are Gram positive, members of the class Negativicutes, including the genus Veillonella, stain Gram negative. Veillonella are among the most abundant organisms of the oral and intestinal microflora of animals and humans, in spite of being strict anaerobes. In this work, the genomes of 24 Negativicutes, including eight Veillonella spp., are compared to 20 other Firmicutes genomes; a further 101 prokaryotic genomes were included, covering 26 phyla. Thus a total of 145 prokaryotic genomes were analyzed by various methods to investigate the apparent conflict of the Veillonella Gram stain and their taxonomic position within the Firmicutes. Comparison of the genome sequences confirms that the Negativicutes are distantly related to Clostridium spp., based on 16S rRNA, complete genomic DNA sequences, and a consensus tree based on conserved proteins. The genus Veillonella is relatively homogeneous: inter-genus pair-wise comparison identifies at least 1,350 shared proteins, although less than half of these are found in any given Clostridium genome. Only 27 proteins are found conserved in all analyzed prokaryote genomes. Veillonella has distinct metabolic properties, and significant similarities to genomes of Proteobacteria are not detected, with the exception of a shared LPS biosynthesis pathway. The clade within the class Negativicutes to which the genus Veillonella belongs exhibits unique properties, most of which are in common with Gram-positives and some with Gram negatives. They are only distantly related to Clostridia, but are even less closely related to Gram-negative species. Though the Negativicutes stain Gram-negative and possess two membranes, the genome and proteome analysis presented here confirm their place within the (mainly) Gram positive phylum of the Firmicutes. Further studies are required to unveil the evolutionary history of the Veillonella and other Negativicutes.     

Heavy metal-induced oxidative damage, defense reactions, and detoxification mechanisms in plants

Heavy metal (HMs) contamination is widespread globally due to anthropogenic, technogenic, and geogenic activities. The HMs exposure could lead to multiple toxic effects in plants by inducing reactive oxygen species (ROS), which inhibit most cellular processes at various levels of metabolism. ROS being highly unstable could play dual role (1) damaging cellular components and (2) act as an important secondary messenger for inducing plant defense system. Cells are equipped with enzymatic and non-enzymatic defense mechanisms to counteract this damage. Some are constitutive and others that are activated only when a stress-specific signal is perceived. Enzymatic scavengers of ROS include superoxide dismutase, catalase, glutathione reductase, and peroxidase, while non-enzymatic antioxidants are glutathione, ascorbic acid, α-tocopherol, flavonoids, anthocyanins, carotenoids, and organic acids. The intracellular and extracellular chelation mechanisms of HMs are associated with organic acids such as citric, malic and oxalic acid, etc. The important mechanism of detoxification includes metal complexation with glutathione, amino acids, synthesis of phytochelatins and sequestration into the vacuoles. Excessive stresses induce a cascade, MAPK (mitogen-activated protein kinase) pathway and synthesis of metal-detoxifying ligands. Metal detoxification through MAPK cascade and synthesis of metal-detoxifying ligands will be of considerable interest in the field of plant biotechnology. Further, the photoprotective roles of pigments of xanthophylls cycle under HMs stress were also discussed.     

Human CCT4 and CCT5 Chaperonin Subunits Expressed in Escherichia coli Form Biologically Active Homo-oligomers

Chaperonins are a family of chaperones that encapsulate their substrates and assist their folding in an ATP-dependent manner. The ubiquitous eukaryotic chaperonin, TCP-1 ring complex (TRiC), is a hetero-oligomeric complex composed of two rings, each formed from eight different CCT (chaperonin containing TCP-1) subunits. Each CCT subunit may have distinct substrate recognition and ATP hydrolysis properties. We have expressed each human CCT subunit individually in Escherichia coli to investigate whether they form chaperonin-like double ring complexes. CCT4 and CCT5, but not the other six CCT subunits, formed high molecular weight complexes within the E. coli cells that sedimented about 20S in sucrose gradients. When CCT4 and CCT5 were purified, they were both organized as two back-to-back rings of eight subunits each, as seen by negative stain and cryo-electron microscopy. This morphology is consistent with that of the hetero-oligomeric double-ring TRiC purified from bovine testes and HeLa cells. Both CCT4 and CCT5 homo-oligomers hydrolyzed ATP at a rate similar to human TRiC and were active as assayed by luciferase refolding and human γD-crystallin aggregation suppression and refolding. Thus, both CCT4 and CCT5 homo-oligomers have the property of forming 8-fold double rings absent the other subunits, and these complexes carry out chaperonin reactions without other partner subunits.