Gray Var Research Articles

Relative Thermal Stability of Malic Dehydrogenase From Heat‐Hardened and Unhardened Phaseolus Sp.1

Malic dehydrogenase was extracted from heat‐hardened and unhardened plants of two varieties of Phaseolus vulgaris L., ‘Harvester’ and ‘G.N. Nebraska #1’ and P. acutifolius, Gray var. latifolius Freeman, ‘Tepary Buff.’ The leaf disc heat tests showed that Tepary was significantly the most heat‐tolerant variety and that Harvester was significantly more heat‐tolerant than Nebraska #1. Purified fractions of malic dehydrogenase were exposed to temperatures of 52 to 62 C for 15 min. This thermostability test showed that the enzyme from Harvester was significantly the most thermal stable, and the enzyme extracted from Tepary was significantly the least thermostable for both the heat‐hardened and unhardened plants. Heat hardening increased the thermal stability of malic dehydrogenase extracted from all three varieties. Other data indicate that the leaf disc heat test correctly ranked the varieties for heat tolerance. Since the varieties were not properly ranked for heat tolerance by the thermal stability of extracted malic dehydrogenase, malic dehydrogenase does not appear to be a key enzyme in heat tolerance. The enzyme stability test ranked the two P. vulgaris varieties properly, but Tepary, a variety of P. acutifolius, did not appear to be correctly ranked. Enzyme variation based on species difference may tend to account for the discrepancy in ranking.

Some Boleti from Alaska

Reported here are 12 species, subspecies or varieties of boletes—one each in Suillus, Xerocomus and Boletus, and nine in Leccinum. Described as new are one of Boletus, and four species of Leccinum.

A Review of the Cruciferous Genus Selenia

Selenia, established by Nuttall in 1825, for thirteen years included only its original element, S. aurea. A variety, /3, was diagnosed by Torrey and Gray in the Flora of North America in 1838. Collections by Captain Pope's Expedition added a second species, S. dissecta, described by the same authors in their botanical report of the expedition, published in 1855. In Watson's review of Selenia for the Synoptical Flora, 1895, the genus remained unchanged in concept, and except for the substitution of var. aperta S. Wats. for Torrey and Gray's var. /3 of S. aurea, no change in nomenclature was made. In the first edition of Small's Flora of the Southeastern United States this variety became S. aperta (S. Wats.) Small. The three species, S. aurea, dissecta and aperta, then comprised the total content of Selenia for twentyeight years, or until 1931, when Cory described S. Jonesii. There followed S. mexicana Standl., 1937, and the next year S. grandis Martin and S. Oinosepala Steyermark appeared.