The role of ribonucleoproteins in the production of mitotic abnormalities

Summary Immersion of growing roots of onion and lily in aerated solutions of ribonuclease affected their pattern of growth and altered the structure and mitotic distribution of the chromosomes. Action of the enzyme on meristematic cells caused enlargement of nucleoli, excessive contraction, stickiness, adhesion, and clumping of chromosomes, and production of aneuploid and polyploid chromosome complexes, tripolar and multipolar spindles, binucleate and multinucleate cells. Very few cases of chromosome fragmentation were observed.Accumulation of abnormalities accompanied the passage of ribonuclease across the root as determined by alterations in stainability of the cells with pyronin and fast green. There was no visible modification of stainability of the chromosomes with methyl green or the Feulgen reagent.These results, when compared with those produced by control solutions, indicate that ribonuclease enters the living cell and degrades ribonucleoproteins essential for maintenance of structural and functional integrity. The implications of these results, with respect to the production of aberrations by other agents, are discussed.This study was supported by a research grant (RG-149) from the National Institutes of Health, U.S. Public Health Service.     

The role of molybdenum in agricultural plant production

BACKGROUND: The importance of molybdenum for plant growth is disproportionate with respect to the absolute amounts required by most plants. Apart from Cu, Mo is the least abundant essential micronutrient found in most plant tissues and is often set as the base from which all other nutrients are compared and measured. Molybdenum is utilized by selected enzymes to carry out redox reactions. Enzymes that require molybdenum for activity include nitrate reductase, xanthine dehydrogenase, aldehyde oxidase and sulfite oxidase. SCOPE: Loss of Mo-dependent enzyme activity (directly or indirectly through low internal molybdenum levels) impacts upon plant development, in particular, those processes involving nitrogen metabolism and the synthesis of the phytohormones abscisic acid and indole-3 butyric acid. Currently, there is little information on how plants access molybdate from the soil solution and redistribute it within the plant. In this review, the role of molybdenum in plants is discussed, focusing on its current constraints in some agricultural situations and where increased molybdenum nutrition may aid in agricultural plant development and yields. CONCLUSIONS: Molybdenum deficiencies are considered rare in most agricultural cropping areas; however, the phenotype is often misdiagnosed and attributed to other downstream effects associated with its role in various enzymatic redox reactions. Molybdenum fertilization through foliar sprays can effectively supplement internal molybdenum deficiencies and rescue the activity of molybdoenzymes. The current understanding on how plants access molybdate from the soil solution or later redistribute it once in the plant is still unclear; however, plants have similar physiological molybdenum transport phenotypes to those found in prokaryotic systems. Thus, careful analysis of existing prokaryotic molybdate transport mechanisms, as well as a re-examination of know anion transport mechanisms present in plants, will help to resolve how this important trace element is accumulated.     

The role of birds in sustainable food production

Birds (Class Aves) are already an important source of food in most parts of the world. Only a few species have been successfully domesticated but many others are harvested from the wild. There is potential for greater use of birds as a food source. Existing domesticated species, especially galliforms, need to be better utilized. Certain new species could be brought into domestication. The efficiency and sustainability of harvesting methods for free-living birds might be improved and the harvesting of new species should be considered. These measures could be compatible with improved conservation of wild birds and their habitats, but careful planning and surveillance are essential prerequisites.     

The role of iron in the production of hemolysin byListeria monocytogenes

The in vitro production of hemolysin byListeria monocytogenes, a facultative intracellular bacterial pathogen, was examined as a function of medium iron. There was an inverse relationship between iron and hemolysin production: Hemolysis increased as medium iron concentration decreased. This study offers the first evidence that the in vitro production of hemolysin byListeria monocytogenes is under the control of external iron in growth medium.     

The role of metabolic engineering in the production of secondary metabolites

In the production of secondary metabolites yield and productivity are the most important design parameters. The focus is therefore to direct the carbon fluxes towards the product of interest, and this can be obtained through metabolic engineering whereby directed genetic changes are introduced into the production strain. In this process it is, however, important to analyze the metabolic network through measurement of the intracellular metabolites and the flux distributions. Besides playing an important role in the optimization of existing processes, metabolic engineering also offers the possibility to construct strains that produce novel metabolites, either through the recruitment of heterologous enzyme activities or through introduction of specific mutations in catalytic activities.     

The role of thrombin in the regulation of the endothelial prostaglandin production

Prostaglandin synthesis in endothelial cells may be initiated by the addition of exogenous substrate (arachidonic acid) or by addition of thrombin or the CA2+-ionophore A23187, which leads to prostacyclin formation from endogenous substrates. We noticed that endothelial cells produce more than twice the amount of prostacyclin when incubated with thrombin and arachidonic acid together than with arachidonic acid alone. In addition, it was found that the thrombin-induced conversion of endogenous substrates was inhibited by exogenous arachidonic acid. This means that the conversion of exogenous added arachidonic acid to prostacyclin was stimulated by thrombin. This activation of the enzymes involved in prostacyclin synthesis lasted about 5 min and could be inhibited by phospholipase inhibitors such as mepacrine and p-bromophenyl-acylbromide but not by the cAMP analogue dibutyryl cAMP, an inhibitor of arachidonic acid release from cellular phospholipids. These data demonstrate that, in addition to causing release of endogenous substrate, thrombin and the Ca2+-ionophore also activate the enzyme system involved in the further transformation of arachidonic acid.     

The role of short-lived DNA lesions in the production of chromosome-exchange aberrations

Human lymphocytes were treated with combined UVC radiation and X-rays or they were X-irradiated and incubated for 60–90 min in the presence of DNA-repair inhibitor ara-C. The X-ray induced chromosome exchange aberration yield was enhanced both by UVC and ara-C by approximately a factor of two in the linear (low dose) portion of the dose-response curve. The enhancement was small in the dose squared (high dose) portion where previous dose-fractionation experiments have shown that X-ray-induced lesions leading to aberrations exist for several hours. The yield of aberrations in lymphocytes incubated after irradiation in the presence of ara-C reaches a saturation level almost immediately after irradiation (5–15 min). These cytogenetic observations together with a previous finding (Holmberg and Strausmanis, 1983) give direct and indirect evidence that the enhanced aberration yield is due to short-lived DNA breaks formed immediately after X-irradiation.

Measurements on the repair kinetics of the DNA breaks induced by X-irradiation show that ara-C strongly impairs the repair of short-lived X-ray-induced DNA breaks. It was also observed that the DNA breaks generated after UVC irradiation occur almost immediately after irradiation and the level of these transient DNA breaks reaches saturation even for short incubation times. Thus, the repair of these breaks can compete with the repair of short-lived X-ray-induced DNA-breaks in combined irradiation with UVC and X-rays.

The experimental results can be explained on the assumption that X-ray-induced aberrations originate from exchange complexes formed in interactions between both short-lived DNA breaks. The short-lived DNA breaks give rise to exchange complexes mainly within single ionization tracks where the DNA breaks are close together. The time between irradiation and exchange complex formation is of the order of 5–15 min within such a track, and short-lived breaks might be repaired before complexes have been formed. If the DNA repair of these breaks is delayed by UVC or ara-C treatment this results in a higher probability of exchange-complex formation. In contrast, interactions between breaks in different tracks originate from long-lived DNA breaks and the probability for complex formation from these breaks is not markedly affected by UVC or ara-C.