Return of Fire as a Restoration Tool: Long‐Term Effects of Burn Severity on Habitat Use by Mexican Fox Squirrels

After decades of suppression, fire is returning to forests of the western United States through wildfires and prescribed burns. These fires may aid restoration of vegetation structure and processes, which could improve conditions for wildlife species and reduce severe wildfire risk. Understanding response of wildlife species to fires is essential to forest restoration because contemporary fires may not have the same effects as historical fires. Recent fires in the Chiricahua Mountains of southeastern Arizona provided opportunity to investigate long‐term effects of burn severity on habitat selection of a native wildlife species. We surveyed burned forest for squirrel feeding sign and related vegetation characteristics to frequency of feeding sign occurrence. We used radio‐telemetry within fire‐influenced forest to determine home ranges of Mexican fox squirrels, Sciurus nayaritensis chiricahuae, and compared vegetation characteristics within home ranges to random areas available to squirrels throughout burned conifer forest. Squirrels fed in forest with open understory and closed canopy cover. Vegetation within home ranges was characterized by lower understory density, consistent with the effects of low‐severity fire, and larger trees than random locations. Our results suggest that return of low‐severity fire can help restore habitat for Mexican fox squirrels and other native wildlife species with similar habitat affiliations in forests with a historical regime of frequent, low‐severity fire. Our study contributes to an understanding of the role and impact of fire in forest ecosystems and the implications for forest restoration as fire returns to the region.     

Detection and identification of gibberellins in Douglas fir (Pseudotsuga menziesii) shoots

Extracts of Douglas fir ( Pseudotsuga menziesii [Mirb.] Franco) shoots were purified by reversed and normal phase HPLC; gibberellin (GA)-like compounds detected by radioimmunoassay with antibodies against GA₄ and the Tan-ginbozu dwarf rice micro-drop biossay were analyzed by GC-MS. Three major components were identified as GA₄, GA₇, and GA₉ while smaller amounts of GA¹, GA₃ and putative GA⁹-glucosyl ester were also present.     

Quantification of GA1, GA3, GA4, GA7, GA8, GA9, GA19 and GA20; and GA20 metabolism in dormant and non-dormant beechnuts

The endogenous levels of GA₁, GA₃, GA₄, GA₇, GA₈, GA₉, GA₁₉ and GA₂₀ were determined in beech seeds (Fagus sylvatica L.) treated with different dormancy breaking treatments. Gibberellins were analysed separately in cotyledons and embryo axes. After purification of the extracts, GAs were quantified by GC-MS-selected ion monitoring (GC-MS-SIM) with deuterated GAs as internal standards. The results showed that GAs corresponding to the 13-OH pathway seemed to be involved in dormancy breaking. Strong differences in GA₁, GA₃, GA₈, GA₁₉ and GA₂₀ levels between embryo axes and cotyledons of dormant and non-dormant beechnuts were detected with less pronounced differences for GA₄, GA₇ and GA₉ levels. Both the quantitative differences between dormant and non-dormant seeds in the analysed GAs corresponding to the 13-OH pathway, and the capacity of non-dormant seeds to carry out metabolic conversions when labelled GA₂₀ was injected into the seeds, reveal a dynamic role of GAs in dormancy release.     

Use of a proteome strategy for tagging proteins present at the plasma membrane

A plasma membrane (PM) fraction was purified from Arabidopsis thaliana using a standard procedure and analyzed by two-dimensional (2D) gel electrophoresis. The proteins were classified according to their relative abundance in PM or cell membrane supernatant fractions. Eighty-two of the 700 spots detected on the PM 2D gels were microsequenced. More than half showed sequence similarity to proteins of known function. Of these, all the spots in the PM-specific and PM-enriched fractions, together with half of the spots with similar abundance in PM fraction and supernatant, have previously been found at the PM, supporting the validity of this approach. Extrapolation from this analysis indicates that (i) approximately 550 polypeptides found at the PM could be resolved on 2D gels; (ii) that numerous proteins with multiple locations are found at the PM; and (iii) that approximately 80% of PM-specific spots correspond to proteins with unknown function. Among the later, half are represented by ESTs or cDNAs in databases. In this way, several unknown gene products were potentially localized to the PM. These data are discussed with respect to the efficiency of organelle proteome approaches to link systematically genomic data to genome expression. It is concluded that generalized proteomes can constitute a powerful resource, with future completion of Arabidopsis genome sequencing, for genome-wide exploration of plant function.     

Cytokinins act directly on lateral root founder cells to inhibit root initiation

In Arabidopsis thaliana, lateral roots are formed from root pericycle cells adjacent to the xylem poles. Lateral root development is regulated antagonistically by the plant hormones auxin and cytokinin. While a great deal is known about how auxin promotes lateral root development, the mechanism of cytokinin repression is still unclear. Elevating cytokinin levels was observed to disrupt lateral root initiation and the regular pattern of divisions that characterizes lateral root development in Arabidopsis. To identify the stage of lateral root development that is sensitive to cytokinins, we targeted the expression of the Agrobacterium tumefaciens cytokinin biosynthesis enzyme isopentenyltransferase to either xylem-pole pericycle cells or young lateral root primordia using GAL4-GFP enhancer trap lines. Transactivation experiments revealed that xylem-pole pericycle cells are sensitive to cytokinins, whereas young lateral root primordia are not. This effect is physiologically significant because transactivation of the Arabidopsis cytokinin degrading enzyme cytokinin oxidase 1 in lateral root founder cells results in increased lateral root formation. We observed that cytokinins perturb the expression of PIN genes in lateral root founder cells and prevent the formation of an auxin gradient that is required to pattern lateral root primordia.     

Metabolic activation by adrenal tissue in rats of a liver carcinogen: safrole]

In vivo and in vitro metabolisms by the rat adrenal tissue of safrol, a natural hepatocarcinogen, were studied by gas chromatography-mass spectrometry and compared to the hepatic metabolism. In the adrenals the epoxide-diol pathway was found besides demethylase and hydroxylase activities, suggesting that the adrenal cortex may participate to the metabolic activation of a procarcinogen.     

New synthesis of immunogenic N6-isopent-2-enyladenosine-protein conjugate. Preparation, purification, and specificity of related antibodies.

An original procedure which preserves the structure of the sugar ring is described to link a plant hormone as N6-isopent-2-enyladenosine [( 9R]iP) onto a protein carrier to prepare a more specific immunogen. This cytokinin is bound to bovine serum albumin (BSA) and ovalbumin by a five-step procedure. These [9R]iP-protein conjugates have a maximal absorption at 269 nm and show molar ratios of hormone bound to proteins in the range of 12:1 and 18:1 for BSA and ovalbumin, respectively. Polyclonal antibodies were raised in rabbits against [9R]iP-BSA and were purified by affinity chromatography. Titers and specificity of the antisera and purified antibodies were determined by ELISA and RIA. These antibodies are highly specific for [9R]iP and do not cross-react with zeatin and ribosylzeatin. An immunoaffinity matrix was prepared with a capacity of 1 microgram of [9R]iP/mL of gel.