Betula Neoalaskana

Betula neoalaskana (syn. B. resinifera) or Alaska birch, also known as Alaska paper birch or resin birch, is a species of birch native to Alaska and northern Canada. Its range covers most of interior Alaska, and extends from the southern Brooks Range to the Chugach Range in Alaska, including the Turnagain Arm and northern half of the Kenai Peninsula, eastward from Norton Sound through the Yukon, Northwest Territories, British Columbia, Alberta, Saskatchewan, Manitoba, southern Nunavut, and into northwestern Ontario.

betula neoalaskana

Notes This species can be easily confused with Betula papyrifera. The key to differentiating the two species is a close examination of the twigs. Betula neoalaskana twigs are densely covered in bumpy resin glands.Erratum: this information on the Alaska paper birch was added October 2003 to the on-line version of the Tree Book and is not available in the printed version or any other version.1 Majority of information and all images (except location map) are copied with permission from Trees in Canada. Farrar, J.L. , Trees in Canada. 1995. Canadian Forestry Service; Fitzhenry & Whiteside Limited, Markham, Ontario. Previous Next

Chromosome numbers in Betula are variable, but appear to build on a base haploid number of 14 (Woodworth, 1929; Taper and Grant, 1973). Following the FNA treatment (Furlow, 1997), B. papyrifera is known with 2n = 56, 70, and 84; B. neoalaskana has 2n = 28; and B. kenaica with 2n = 70. However, given the variation within species with multiple counts, and the wide geographic ranges involved, it is likely that additional cytogenetic variation exists.

Papyriferic acid (PA) is a triterpene that is secreted by glands on twigs of the juvenile ontogenetic phase of resin producing tree birches (e.g., Betula neoalaskana, B. pendula) and that deters browsing by mammals such as the snowshoe hare (Lepus americanus). We investigated the pharmacology of PA as a first step in understanding its antifeedant effect. After oral administration to rats, PA and several metabolites were found in feces but not urine, indicating that little was absorbed systemically. Metabolism involved various combinations of hydrolysis of its acetyl and malonyl ester groups, and hydroxylation of the terpene moiety. The presence of a malonyl group suggested a possible interaction with succinate dehydrogenase (SDH), a mitochondrial enzyme known to be competitively inhibited by malonic acid. The effect of PA on the oxidation of succinate by SDH was examined in mitochondrial preparations from livers of ox, rabbit, and rat. In all three species, PA was a potent inhibitor of SDH. Kinetic analysis indicated that, unlike malonate, PA acted by an uncompetitive mechanism, meaning that it binds to the enzyme-substrate complex. The hydrolysis product of PA, betulafolienetriol oxide, was inactive on SDH. Overall, the evidence suggests that PA acts as the intact molecule and interacts at a site other than the succinate binding site, possibly binding to the ubiquinone sites on complex II. Papyriferic acid was potent (K(iEIS) ranged from 25 to 45 microM in the three species) and selective, as malate dehydrogenase was unaffected. Although rigorous proof will require further experiments, we have a plausible mechanism for the antifeedant effect of PA: inhibition of SDH in gastrointestinal cells decreases mitochondrial energy production resulting in a noxious stimulus, 5-HT release, and sensations of nausea and discomfort. There is evidence that the co-evolution of birches and hares over a large and geographically-diverse area in Northern Europe and America has produced marked differences in the formation of PA by birches, and the tolerance of hares to dietary PA. The present findings on the metabolic fate and biochemical effects of PA provide a rational basis for investigating the mechanisms underlying differences among populations of hares in their tolerance of a PA-rich diet. 041b061a72