Author index for volume 219

Proteinase inhibitors I and II were purified to electrophoretic homogeneity from leaves of tomato plants induced by either wounding intact plants or by supplying excised plants with the proteinase inhibitor inducing factor. Affinity chromatography with chymotrypsin-Sepharose was employed as a final purification step for each inhibitor. The tomato leaf inhibitors are very similar to potato tuber inhibitors I and II in subunit molecular weight, composition, and inhibitory activities against chymotrypsin, trypsin, and subtilisin. However, unlike the potato tuber which contains multiple isoinhibitors by isoelectric focusing, the tomato leaf exhibits only two isoinhibitor forms of inhibitor I and a single form of inhibitor II. The molecular weight of native potato inhibitor I was reevaluated by rigorous ultracentrifugal analysis and compared with data from previous analyses. The data confirm that native inhibitor I has a native M_r of about 41,000 and is a pentamer. Inhibitor II has a molecular weight of near 23,000 and is a dimer.     

Antagonistic and synergistic interactions between aluminum and manganese on growth of Vigna unguiculata at low ionic strength

Concentrations of soluble aluminum (Al) and manganese (Mn) frequently reach phytotoxic levels in acid soils. While dose response relationships for these metals are well documented, the effects of combined exposure have received less attention. We have examined the effect of combinations of Al and Mn on growth and metal accumulation in Vigna unguiculata (L.) Walp. grown in solution culture under conditions of low ionic strength (conductivities typically < 100 µS cm⁻¹). The nature of interaction between these metals varied with the specific physiological response, the part of the plant investigated, and the relative amount of stress imposed. Analysis of growth data provided evidence for amelioration of metal toxicity (antagonistic effects), although this effect was dose dependent. Analysis of metal content data provided evidence for antagonistic and synergistic (exacerbation of toxicity) effects, again depending on dose. Analysis of foliar symptoms also provided evidence for antagonisms and synergisms, with the nature of the response dependent on the specific physiological response and specific plant part investigated. In contrast with previous reports, evidence for antagonistic, synergistic, and multiplicative effects on growth, metal uptake, and expression of foliar symptoms have been obtained under physiologically and environmentally relevant conditions. These results suggest a more detailed analysis of the potential for interactions between metals in the environment is required.     

Dimorphism in methane seep-dwelling ecotypes of the largest known bacteria

We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization.