Cross-Resistance of a Chlorsulfuron-Resistant Biotype of Stellaria media to a Triazolopyrimidine Herbicide

A biotype of Stellaria media (L.) Vill. has been identified that is highly resistant to the herbicide chlorsulfuron. Resistance is due to an altered acetolactate synthase (ALS) that is much less sensitive to chlorsulfuron than the ALS from the susceptible (S) biotype. The S biotype was extremely sensitive to D489 (N-[2,6-dichlorophenyl]-5,7-dimethyl-1,2,4-triazolo[1,5a] pyrimidine-2-sulfonamide), a member of a new class of triazolopyrimidine herbicides, while the chlorsulfuron-resistant biotype exhibited complete cross-resistance at both the whole plant and enzyme levels. ALS activity of the S biotype was reduced by approximately 90% in the presence of 0.1 micromolar D489, while that of the R biotype was reduced by less than 10%. This result suggests that the two herbicides share a common binding site on ALS. Only very slight cross-resistance at the ALS level was found to imazamethabenz, an imidazolinone herbicide.     

Protein D is differentially expressed and regulated in the rat epididymis.

We report the use of a sensitive and specific enyzme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) to study the expression of protein D, a major androgen-regulated sperm-binding glycoprotein at the protein and mRNA level in different anatomical regions of the rat epididymis. The concentration of protein D in the caput, corpus and cauda region of the epididymis was 10.2 +/- 0.67, 7.3 +/- 0.61 and 22.8 +/- 1.34 ng/micrograms total protein, respectively. The total RNA extracted from the caput, corpus and cauda regions of the rat epididymis was amplified by PCR with oligonucleotide primers specific for the 5' and 3' portion of protein D cDNA. Compared to the caput and cauda region, a significant reduction (greater than 82 +/- 3%) in the expression of protein D mRNA levels was observed for corpus epididymal RNA. This data demonstrates regional differences in the concentration of protein D and suggests that protein D expression may be regulated at the level of mRNA within the corpus epididymidis.     

Non-photochemical quenching of Fo in leaves is emission wavelength dependent: consequences for quenching analysis and its interpretation

The effects of light-induced non-photochemical quenching on the minimal F_o, and variable F_v, fluorescence emissions at 690 and 730 nm in leaves were determined. Non-photochemical quenching of F_o, but not F_v, was found to be dependent upon the wavelength of emission, and was greater at 690 nm than at 730 nm. For emission at 730, compared to at 690 nm, approx. 30% of F_o was not affected by non-photochemical quenching processes in leaves of C3 plants; in maize leaves this was found to be approx. 50%. The data indicate that a substantial proportion of the pigments contributing to F_o emission at 730 nm are not quenched by light-induced, non-photochemical quenching processes and that there are large differences in the pigment matrices contributing to F_o and F_v emissions at 730 nm, compared to those at 690 nm. These findings have important implications for the accurate estimation and interpretation of non-photochemical quenching of fluorescence parameters and their use in the calculation of photochemical efficiencies in leaves. Measurements of fluorescence emissions at wavelengths above 700 nm are likely to give rise to significant errors when used for determinations of photochemical and non-photochemical quenching parameters.     

Mechanisms of amoeboid chemotaxis: an evaluation of the cortical expansion model

In this work we evaluate the cortical expansion model for amoeboid chemotaxis with regard to new information about molecular events in the cytoskeleton following chemotactic stimulation of Dictyostelium amoebae. A rapid upshift in the concentration of chemoattractant can be used to synchronize the motile behavior of a large population of cells. This synchrony presents an opportunity to study the biochemical basis of morphological changes such as pseudopod extension that are required for amoeboid chemotaxis. Changes in the composition and activity of the cytoskeleton following stimulation can be measured with precision and correlated with important morphological changes. Such studies demonstrate that activation of actin nucleation is one of the first and most crucial events in the actin cytoskeleton following stimulation. This activation is followed by incorporation of specific actin cross-linking proteins into the cytoskeleton, which are implicated in the extension of pseudopods and filopods. These results, as well as those from studies with mutants deficient in myosin, indicate that cortical expansion, driven by focal actin polymerization, cross-linking and gel osmotic swelling, is an important force for pseudopod extension. It is concluded that whereas three forces, frontal sliding, tail contraction, and cortical expansion may cooperate to produce amoeboid movement, the cortical expansion model offers the simplest explanation of how focal stimulation with a chemoattractant causes polarized pseudopod extension.     

Altered function of pulmonary surfactant in fatty acid lung injury

To determine whether acute fatty acid lung injury impairs pulmonary surfactant function, we studied anesthetized ventilated rabbits given oleic acid (55 mg/kg iv, n = 11) or an equivalent volume of saline (n = 8). Measurements of pulmonary mechanics indicated a decrease in dynamic compliance within 5 min of injury and a decrease in lung volume that was disproportionately large at low pressures, consistent with diminished surfactant activity in vivo. Bronchoalveolar lavage fluid obtained 1 h after injury had significantly increased erythrocytes and total leukocytes, largely polymorphonuclear cells. The phospholipid content and composition of the cell-free fraction had only minor changes from those of controls, but the protein content was increased 35-fold. Measurements of lavage surface activity in vitro showed an increase in average minimum surface tension from 1.3 +/- 0.4 (SE) dyn/cm in controls to 20.2 +/- 3.9 dyn/cm in injured animals. The alterations in static pressure-volume curves and decrease in lavage surface activity suggest a severe alteration of surfactant function in this form of lung injury that occurs despite the presence of normal amounts of surfactant phospholipids.     

Compensatory growth response of the legume, Medicago sativa, to defoliation and denodulation

A laboratory study was conducted to determine the effects of defoliation and denodulation on compensatory growth of Medicago sativa (L.). Plants grown hydroponically in clear plastic growth pouches were subjected to 0 and 50% nodule pruning, and 0, 25, 50, and 75% defoliation by clipping trifoliate leaves. An additional experiment was conducted to determine if clipping leaves simulated herbivory by Hypera postica (Gyllenhal) larvae. Previously, we determined that nodule pruning accurately simulated herbivory by Sitona hispidulus (L.) larvae (Quinn & Hall, 1992). Results indicated that denodulation stimulated nodule growth and caused exact compensation in standing and total number of nodules per plant within 15 days and in standing nodule biomass within 22 days of treatment. Denodulation caused a significant reduction (13%) in final shoot biomass, but did not affect significantly final root biomass. Percentage of change in number of trifoliate leaves per plant increased with the level of defoliation. Within 22 days of treatment, total number of trifoliate leaves per plant was similar to controls. However, final standing shoot biomasses were significantly less that controls, indicating undercompensatory growth. Shoot biomasses of the 25-, 50-, and 75%-defoliated plants were 18, 20, and 36% lower than controls, respectively. Nodule biomass per plant was reduced by 24 and 32% in 50- and 75%-defoliated plants, respectively, but was not affected significantly by 25% defoliation. Root biomass was affected by all levels of defoliation. Clipping trifoliate leaves accurately simulated defoliation by H. postica larvae. Our results indicated that partial defoliation affected shoot, root, and nodule biomass of M. sativa, but that partial denodulation only affected shoot biomass.