Ditylenchus dipsaci Infestation of Trifolium repens. I. Temperature Effects,Seedling Invasion,and a Field Survey

Rates of development of stem nematode (Ditylenchus dipsaci) in white clover (Trifolium repens) seedlings were found to be linearly related to temperature. Basal developmental temperature (T_b) was 3 °C, and the thermal constant (S) for development of gravid adult females from freshly laid eggs was 270 accumulated day-degrees above the T_b. Only 12% at 20 °C and 4% at 4 °C of the gravid female nematodes inoculated into seedling axils successfully penetrated seedling epidermis. These nematodes slowly migrated within the seedling and after a lag of 5 days at 20 °C started to lay eggs. The maximal rate of egg production was temperature-dependent, being 0.8 and 3.1 eggs female⁻¹ day⁻¹ at 10 and 20 °C, respectively. Nematodes emigrated rapidly from infested stolons when they were immersed in water, with rates being highest at 25 °C and lowest at 4 °C. The sensitivity to temperature of many of the parameters that govern nematode population dynamics indicates that climatic changes will have a marked effect upon this host-parasite system. A study of infested stolons from the field indicated that nematode numbers increased up to 3,000 or more before tissue senesence, triggered by nematode damage, caused a mass emigration of nematodes from the stolon.     

Proteinases produced by pseudomonads isolated from sheep fleece

Fifty-nine pseudomonads isolated from sheep fleece were able to grow on a minimal salts medium with glycerol as the sole source of carbon and energy. Many of these isolates showed additional growth when collagen-based or wool-based substrates were included in the medium. After several days of incubation with these substrates, the nature of soluble proteins present in the growth medium was investigated by using polyacrylamide gel electrophoresis. Up to four major bands of protein with proteinase activity and with widely different electrophoretic mobilities were detected in the gels; one of the bands appeared as a doublet at times. The electrophoretic mobilities of each class of proteinase were similar for the different pseudomonads examined, but the proteinase (or combination of proteinases) induced depended on the protein substrate and strain or species of pseudomonad used.     

Characterization of pseudomonads isolated from diseased fleece.

A total of 59 Pseudomonas isolates was obtained from 11 samples of diseased fleece taken from live sheep. All but four of the isolates could be assigned to one of nine Pseudomonas species, of which P. aeruginosa, P. alcaligenes, P. mendocina , and P. putida were the most common. P. aeruginosa was found in four of the fleece samples and, when present, appeared to predominate. Although several of the isolates of P. aeruginosa lacked the ability to produce pyocyanin (and some produced neither pyocyanin nor fluorescein), nearly all produced several virulence factors. Of the other pseudomonads, many produced proteinase, esterase, and catalase, several were able to grow at 42 degrees C and reduce nitrate, and some also produced lipase and hemolysin and, like P. aeruginosa, might serve to initiate (or sustain) the dermatitis frequently associated with fleece rot in sheep.     

Accumulation of Plastoquinone A during Low Temperature Growth of Winter Rye

Chloroplasts isolated from rye (Secale cereale L. cv Puma) grown at 5°C (RH) accumulated 260% more plastoquinone A (PQA) per plastid than chloroplasts isolated from rye grown at 20°C (RNH). The number of plastoglobuli increased by 270% in RH chloroplasts compared with RNH plastids. When RH plastids were lysed and washed, the number of plastoglobuli associated with thylakoid membranes decreased significantly, yet the PQA levels remained high. Room temperature fluorescence induction indicated that (a) there is no change in the size of the PQA pool immediately available for photochemistry in RNH and RH thylakoids and (b) there is a pool of oxidized PQA present in RNH and RH thylakoids which is not available for photochemistry. The accumulated PQA in RH thylakoids may reflect an increased nonphotochemical function such as regulation of thylakoid protein phosphorylation or protection against photoinhibition.     

Tissue fixation by osmium tetroxide. A possible role for proteins.

The osmiophilia, under the conditions of normal tissue fixation, of the histidine, lysine, tryptophan, cysteine and methionine side chain of proteins is suggested by in vitro studies on blocked amino acids representative of such protein side chains, and the chemical nature of the reaction products elucidated. The chemical feasibility of inter- or intramolecular cross-linking of protein by OsO4 at these and other sites is demonstrated, as in the cross-linking of protein with unsaturated lipids such as methyl oleate, methyl linoleate and linolenate, and cholesteryl acetate. The relevance of these results to the process of tissue fixation by OsO4 is discussed.     

Evidence for actin filament-microtubule interaction mediated by microtubule-associated proteins

We have used low shear viscometry and electron microscopy to study the interaction between pure actin filaments and microtubules. Mixtures of microtubules having microtubule-associated proteins (MAPs) with actin filament have very high viscosities compared with the viscosities of the separate components. MAPs themselves also cause a large increase in the viscosity of actin filaments. In contrast, mixtures of actin filaments with tubulin polymers lacking MAPs have low viscosities, close to the sum of the viscosities of the separate components. Our interpretation of these observations is that there is an interaction between actin filaments and microtubules which requires MAPs. This interaction is inhibited by ATP and some related compounds. Electron micrographs of thin sections through mixtures of actin and microtubules show numerous close associations between the two polymers which may be responsible for their high viscosity.