Vitamin E biosynthesis and its regulation in plants

Vitamin E is one of the 13 vitamins that are essential to animals that do not produce them. To date, six natural organic compounds belonging to the chemical family of tocochromanols—four tocopherols and two tocotrienols—have been demonstrated as exhibiting vitamin E activity in animals. Edible plant-derived products, notably seed oils, are the main sources of vitamin E in the human diet. Although this vitamin is readily available, independent nutritional surveys have shown that human populations do not consume enough vitamin E, and suffer from mild to severe deficiency. Tocochromanols are mostly produced by plants, algae, and some cyanobacteria. Tocochromanol metabolism has been mainly studied in higher plants that produce tocopherols, tocotrienols, plastochromanol-8, and tocomonoenols. In contrast to the tocochromanol biosynthetic pathways that are well characterized, our understanding of the physiological and molecular mechanisms regulating tocochromanol biosynthesis is in its infancy. Although it is known that tocochromanol biosynthesis is strongly conditioned by the availability in homogentisate and polyprenyl pyrophosphate, its polar and lipophilic biosynthetic precursors, respectively, the mechanisms regulating their biosyntheses are barely known. This review summarizes our current knowledge of tocochromanol biosynthesis in plants, and highlights future challenges regarding the understanding of its regulatio

Metabolic origins and transport of vitamin e biosynthetic precursors

Tocochromanols are organic compounds mostly produced by photosynthetic organisms that exhibit vitamin E activity in animals. They result from the condensation of homogentisate with four different polyprenyl side chains derived all from geranylgeranyl pyrophosphate. The core tocochromanol biosynthesis has been investigated in several photosynthetic organisms and is now well characterized. In contrast, our current knowledge of the biosynthesis and transport of tocochromanol biosynthetic precursors is much more limited. While tocochromanol synthesis occurs in plastids, converging genetic data in Arabidopsis and soybean demonstrate that the synthesis of the polar precursor homogentisate is located in the cytoplasm. These data implies that tocochromanol synthesis involves several plastidic membrane transporter(s) that remain to be identified. In addition, the metabolic origin of the lipophilic isoprenoid precursor is not fully elucidated. While some genetic data exclusively attribute the synthesis of the prenyl component of tocochromanols to the plastidic methyl erythritol phosphate pathway, multiple lines of evidence provided by feeding experiments and metabolic engineering studies indicate that it might partially originate from the cytoplasmic mevalonate pathway. Although this question is still open, these data demonstrate the existence of membrane transporter(s) capable of importing cytosolic polyprenyl pyrophosphate such as farnesyl pyrophosphate into plastids. Since the availability of both homogentisate and polyprenyl pyrophosphates are currently accepted as major mechanisms controlling the type and amount of tocochromanols produced in plant tissues, we summarized our current knowledge and research gaps concerning the biosynthesis, metabolic origins and transport of tocochromanol biosynthetic precursors in plant cells

Current strategies for vitamin E biofortification of crops

Vitamin E refers to four tocopherols and four tocotrienols that are exclusively synthesized by photosynthetic organisms. While α-tocopherol is the most potent vitamin E compound, it is not the main form consumed since the composition of most major crops is dominated by γ-tocopherol. Nutritional studies show that populations of developed countries do not consume enough vitamin E and that a large proportion of individuals exhibit plasma α-tocopherol deficiency. Following the identification of vitamin E biosynthetic genes, several strategies including metabolic engineering, classic breeding and mutation breeding, have been undertaken to improve the vitamin E content of crops. In addition to providing crops in which vitamin E content is enhanced, these studies are revealing the bottlenecks limiting its biosynthesis

Valuable carcasses: postmortem preservation of fatty acid composition in heart tissue

In order to effectively conserve species, we must understand the structure and function of integral mechanisms at all levels of organismal organisation, from intracellular biochemistry to whole animal ecophysiology. The accuracy of biochemical analyses depend on the quality and integrity of the samples analysed. It is believed that tissue samples collected immediately postmortem provide the most reliable depiction of the living animal. Yet, euthanasia of threatened or protected species for the collection of tissue presents a number of ethical complications. Polyunsaturated fatty acids (PUFA) are essential to the cardiovascular system of all animals and the structure of PUFA can be degraded by peroxidation, potentially modifying the fatty acid composition of the tissue over postmortem time. Here, we assessed the composition of PUFA in cardiac tissue of bats (Carollia perspicillata) over the course of 12-h postmortem. We show that PUFA are resistant to naturally occurring postmortem degradation in heart tissue, with no difference in the overall composition of fatty acids across all time classes (0, 3, 6 or 12-h postmortem). Our results suggest that carcasses that would otherwise be discarded may actually be viable for the assessment of fatty acid composition in a number of tissues. We hope to spur further investigations into the viability of carcasses for other biochemical analyses as they may be an untapped resource available to biologists

Efficiency of natural substances to protect Beauveria bassiana conidia from UV radiation

Solar radiation is assumed to be a major factor limiting the efficacy of entomopathogenic fungi used as biocontrol agents in open field applications. We evaluated 12 natural UV‐protective co‐formulants for their effect on the survival of UV‐ exposed Beauveria bassiana spores on agar plates, colza leaf discs and in the field.RESULTS: Colony‐forming unit (CFU) counts of unformulated conidia on agar plates and leaf discs dropped to ≤ 50% after exposure to UV radiation. The highest UV protection was achieved with humic acid, which provided > 90% protection of UV‐ B‐exposed conidia in laboratory experiments. In the field, 10% humic acid increased spore persistence up to 87% at 7 days after application. Sesame and colza oil also provided high UV protection in both assays (> 73% and > 70%, respectively).CONCLUSIONS: This study shows that it is possible to increase the persistence of B. bassiana spores under exposure to UV radiation by formulation with natural UV‐protective additives. UV protectants might, therefore, increase the efficacy of entomopathogenic fungi as biocontrol agents in open field applications

Yeast Integral Membrane Proteins Apq12, Brl1, and Brr6 Form a Complex Important for Regulation of Membrane Homeostasis and Nuclear Pore Complex Biogenesis

Proper functioning of intracellular membranes is critical for many cellular processes. A key feature of membranes is their ability to adapt to changes in environmental conditions by adjusting their composition so as to maintain constant biophysical proper- ties, including fluidity and flexibility. Similar changes in the biophysical properties of membranes likely occur when intracellular processes, such as vesicle formation and fusion, require dramatic changes in membrane curvature. Similar modifications must also be made when nuclear pore complexes (NPCs) are constructed within the existing nuclear membrane, as occurs during in- terphase in all eukaryotes. Here we report on the role of the essential nuclear envelope/endoplasmic reticulum (NE/ER) protein Brl1 in regulating the membrane composition of the NE/ER. We show that Brl1 and two other proteins characterized previous- ly—Brr6, which is closely related to Brl1, and Apq12—function together and are required for lipid homeostasis. All three trans- membrane proteins are localized to the NE and can be coprecipitated. As has been shown for mutations affecting Brr6 and Apq12, mutations in Brl1 lead to defects in lipid metabolism, increased sensitivity to drugs that inhibit enzymes involved in lipid synthesis, and strong genetic interactions with mutations affecting lipid metabolism. Mutations affecting Brl1 or Brr6 or the absence of Apq12 leads to hyperfluid membranes, because mutant cells are hypersensitive to agents that increase membrane flu- idity. We suggest that the defects in nuclear pore complex biogenesis and mRNA export seen in these mutants are consequences of defects in maintaining the biophysical properties of the NE

Kinetic Monte Carlo (KMC) Algorithm for Nanocrystals

This thesis uses the kinetic Monte Carlo (KMC) algorithm to examine the growth morphology and structure of nanocrystals. Crystal growth in a supersaturated gas of atoms and in an undercooled binary melt is investigated. First, in the gas phase, the interplay of the deposition and surface diffusion rates is studied. Then, the KMC algorithm is refined by including solidification events and finally, by adding diffusion in the surrounding liquid. A new algorithm is developed for modelling solidification from an undercooled melt. This algorithm combines the KMC method, which models the change in shape of the crystal during growth, with a macroscopic continuum method that tracks the diffusion of material through solution towards the crystal. For small length and time scales, this approach provides simple, effective front tracking with fully resolved atomistic detail of the crystal-melt interface. Anisotropy is included in the model as a surface diffusion process and the growth rate of the crystal is found to increase monotonically with increase in the surface anisotropy value. The method allows for the study of multiple crystal nuclei and Ostwald ripening. This method will aid researchers to explain why certain crystal shapes form under particular conditions during growth, and may enable nanotechnologists to design techniques for growing nanocrystals with specific shapes for a variety of applications, from catalysis to the medicine field and electronics industry. This will lead to a better understanding of the atomistic process of crystal growth at the nanoscale