Analysis of alternative transcripts of the flax L6 rust resistance gene.

The L6 rust resistance gene from flax generates at least four transcript classes by alternative splicing of the third intron. The most abundant transcript class encodes a resistance protein containing domains that include nucleotide binding site motifs and a leucine-rich repeat region (NBS-LRR). The remaining three transcript classes encode truncated products which lack most of the C-terminal part of the protein containing the leucine-rich region (LRR). The four transcript classes occur in all plant organs examined and no induction of L6 expression was observed following infection of resistant plants with an avirulent rust strain expressing the corresponding A-L6 avirulence gene. Flax plants transgenic for an intronless L6 gene, incapable of encoding truncated resistance proteins by alternative splicing, expressed L6 resistance indistinguishable from that of the wild-type gene. Therefore, a definitive role for alternative transcripts and their predicted truncated products could not be assigned in the flax/flax rust system.

What do losses in selenium and arsenic bioavailability signify for health?

Levels of As and Se in human foods and animal feeds respectively have decreased in recent years as a result of official limits and other factors. The reduction of SeO2 by SO2 to Se0 results in less bioavailability in the food cycle. Acid rain further reduces the pH of Se-depleted soils and soluble forms of Se are bound by metal ions in fallout from burning of fossil fuels. However, there is evidence that Se and As act as essential nutrients with anticancer value. The need for As in nutrition was shown by three laboratories in four mammalian species. Selenium inadequacies among people, as well as animals, are being recognized worldwide in the form of Se-responsive diseases. Reported data indicate that we have yet to learn the optimal intake levels for Se or As and how their decreased bioavailabilities affect human health.

Selenium in biology.

The role of Se in biology appears from the evidence now at hand to be as a catalyst par excellence. As unique prosthetic group of a variety of enzymes, presumably as Se(2-), Se functions with tocopherol to protect cell and organelle membranes from oxidative damage, to facilitate the union between oxygen and hydrogen at the end of the metabolic chain, and to transfer ions across cell membranes, in protein synthesis in erythrocytes and in liver organelles, in immunoglobulin synthesis, and in ubiquinone syntheses. As perhaps the most versatile and rapid nucleophile, Se is thought to amplify and orient SH in equilibrium -S-S-interactions involving glutathione and proteins. Its toxicity appears to be due to overaccumulation of selenite ions, which act as oxidants to inhibit SH interactions. Such toxicity is readily avoided or reversed in many ways. Although not yet recognized as essential for man, Se is clearly essential for many animal species and some microorganisms. As the active selenide, Se emerged as the target for many heavy metal toxicities; contrariwise, as a specific antidote against heavy metal toxicities. Despite all this, its unusual toxicity and the many preconceived notions about Se continue to confuse attitudes toward the safe uses of selenicals. From a suspected cause of cancer, Se metamorphosed, via evidence over many years, into something of possible anticancer value. Interrelations between Se, Vitamin E, the ubiquinones, and various chronic diseases appear as beckoning research areas. The reported veterinary values of Se-tocopherol combinations in animals, together with clinical evidence, plus human and animal evidence for safety, offer promise for intensive medical investigation. The historical confusion and misunderstandings regarding Se must be corrected, however, before advantage can be taken of its potential for human welfare. The many misjudgments about Se, ever since 1900 and more obviously since the 1930s, have involved other trace elements. Unrealistic regulations stemming from these misunderstandings prevail worldwide. Evidence suggests that, once the nutrition biochemistry and toxicology of Se is sufficiently understood and appreciated, major breakthroughs in agriculture, medicine, and public health can result. Much has been accomplished along these lines in New Zealand in animal agriculture, in the US and other countries in veterinary medicine, and in Mexico in human medicine.