Vulnerability to drought-induced cavitation of riparian cottonwoods in Alberta: a possible factor in the decline of the ecosystem?

Vulnerability of xylem to loss of hydraulic conductivity caused by drought-induced cavitation was determined for three riparian cottonwood species in Lethbridge, Alberta: Populus deltoides Bartr., P. balsamifera L., and P. angustifolia James. These species suffered 50% loss of hydraulic conductivity in one-year-old stem segments when xylem pressure potential fell to -0.7 MPa for P. deltoides and -1.7 MPa for P. balsamifera and P. angustifolia, making them the three most vulnerable tree species reported so far in North America. The possible contribution of drought-induced xylem dysfunction to the decline of riparian ecosystems in dammed rivers is discussed.     

新造林中的防火隔离带建设

新造林中防火隔离带分为天然防火隔离带;植物防火隔离带;防火林道,人工防火线等4种。在具体布设上则分为林中防火、林线防火、山脊防火、境界防火、铁路沿线、林区房屋隔离带6种。     

Comment on "Deep mixing of 3He: reconciling Big Bang and stellar nucleosynthesis"

Eggleton et al. (Reports, 8 December 2006, p. 1580) reported on a deep-mixing mechanism in low-mass stars caused by a Rayleigh-Taylor instability that destroys all of the helium isotope 3He produced during the star's lifetime. Observations of 3He in planetary nebulae, however, indicate that some stars produce prodigious amounts of 3He. This is inconsistent with the claim that all low-mass stars should destroy 3He.     

Gibberellins: a phytohormonal basis for heterosis in maize

Four commercially important maize parental inbreds and their 12 F(1) hybrids were studied to investigate the role of the phytohormone gibberellin (GA) in the regulation of heterosis (hybrid vigor). All hybrids grew faster than any inbred. In contrast, all inbreds showed a greater promotion of shoot growth after the exogenous application of GA(3). Concentrations of endogenous GA(1), the biological effector for shoot growth in maize, and GA(19), a precursor of GA(1), were measured in apical meristematic shoot cylinders for three of the inbreds and their hybrids by gas chromatography-mass spectrometry with selected ion monitoring; deuterated GAs were used as quantitative internal standards. In 34 of 36 comparisons, hybrids contained higher concentrations of endogenous GAs than their parental inbreds. Preferential growth acceleration of the inbreds by exogenous GA(3) indicates that a deficiency of endogenous GA limits the growth of the inbreds and is thus a cause of inbreeding depression. Conversely, the increased endogenous concentration of GA in the hybrids could provide a phytohormonal basis for heterosis for shoot growth.     

A QUANTITATIVE STUDY OF THE FIBRINOLYSIN-ANTIFIBRINOLYSIN REACTION

The results of a study of the streptococcal fibrinolysin reaction and its inhibition by sera containing specific antibody are presented. It was possible to devise a quantitative antifibrinolysin test by controlling the various factors influencing the reaction. In man, the antifibrinolysin response was found to vary according to the strain of streptococcus responsible for the infection.     

Gas chromatographic analysis of milk for deoxynivalenol and its metabolite DOM-1

A gas chromatographic method is described for the determination of deoxynivalenol (DON) and its metabolite DOM-1 in milk. Milk samples were extracted with ethyl acetate on a commercially available disposable extraction column, followed by hexane-acetonitrile partitioning. Final purification was accomplished on a reverse phase C-18 cartridge. The trimethylsilyl ether (TMS) derivatives of DON were prepared, chromatographed on an OV-17 column, and quantitated with an electron capture detector. Chromatography of the TMS derivatives of milk extracts was compared to that of the corresponding heptafluorobutyryl derivatives. The limit of detection using TMS derivatives was 1 ng/mL for both toxins with recoveries averaging 82% +/- 9% at 2.5 and 10 ng/mL milk for DON and 85% +/- 6% at 10 ng/mL for DOM-1.