Characterization of Peroxidase Changes in Tolerant and Susceptible Soybeans Challenged by Soybean Aphid (Hemiptera: Aphididae).

Changes in protein content, peroxidase activity, and isozyme profiles in response to soybean aphid feeding were documented at V1 (fully developed leaves at unifoliate node, first trifoliate leaf unrolled) and V3 (fully developed leaf at second trifoliate node, third trifoliate leaf unrolled) stages of soybean aphid-tolerant (KS4202) and -susceptible (SD76R) soybeans. Protein content was similar between infested and control V1 and V3 stage plants for both KS4202 and SD76R at 6, 16, and 22 d after aphid introduction. Enzyme kinetics studies documented that control and aphid-infested KS4202 V1 stage and SD76R V1 and V3 stages had similar levels of peroxidase activity at the three time points evaluated. In contrast, KS4202 aphid-infested plants at the V3 stage had significantly higher peroxidase activity levels than control plants at 6 and 22 d after aphid introduction. The differences in peroxidase activity observed between infested and control V3 stage KS4202 plants at these two time points suggest that peroxidases may be playing multiple roles in the tolerant plant. Native gels stained for peroxidase were able to detect differences in the isozyme profiles of aphid-infested and control plants for both KS4202 and SD76R.

Orthogonally-oriented nanotube arrays: experiment I.

Recently a new type of self-assembling surface has been proposed that, in theory, possesses a number of desirable tribological, electrical, and thermal characterstics. The surface consists of arrays of carbon nanotubes partially embedded lengthwise in a substrate such that when two arrayed surfaces are brought together orthogonally, the areal contact between them is small, limited to a lattice of nearly point-like contacts. These orthogonally-oriented nanotube arrays (ONAs) are predicted to exhibit: (i) surface adhesion (stiction) 10-100 times less than for Teflon or other advanced perfluorocarbons; (ii) frictional coefficients up to 1000 times less than for conventional solids; (iii) ultra-low wear; and (iv) superior thermal and electrical conductivity. In this paper, laboratory methods are described for embedding nanotubes in trenched substrates. Using microscopically trenched substrates and a custom ultrasonic atomization source, experiments show that individual nanotubes can spontaneously and controllably entrench themselves via interfacial forces (capillary and surface tension). Results indicate ONAs might be relatively simply and inexpensively fabricated. More decisive experiments are proposed.

Subcellular Localization of Oxygen Defense Enzymes in Soybean (Glycine max [L.] Merr.) Root Nodules.

Soybean (Glycine max [L.] Merr.) root nodules contain the enzymes of the ascorbate-glutathione pathway to minimize oxidative damage. In the present study, fractionation and immunocytochemistry were used to determine the subcellular location of the enzymes of this pathway. All four enzymes (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase) were present in the soluble fraction from nodule plant cells and in isolated mitochondria. No activity was detected in peroxisomes. Bacteroids contained glutathione reductase but not the other enzymes of this pathway. Immunogold localization indicated that ascorbate peroxidase was present in the cytosol of infected and uninfected cells but not in the peribacteroid space. Results of immunogold and immunofluorescence studies indicated that monodehydroascorbate reductase was located primarily in the cell wall, suggesting that ascorbate regeneration in the cytoplasm may proceed primarily through the action of dehydroascorbate reductase. The possible roles of monodehydroascorbate reductase in cell wall metabolism are discussed.

Varicella-zoster virus infection in Australia.

OBJECTIVE: To determine the epidemiology of varicella-zoster virus (VZV) infection in Australia using currently available data sources. DESIGN: Analysis of national death data (23 years), congenital and neonatal cases (one year) and attendances at sentinel general practices (two years); hospital admissions in NSW and SA (six years); serological studies in 1995 involving antenatal clinics in Sydney and Brisbane and child-care centre staff and refugees in Sydney; and case-ascertainment in 1995 in South Western Sydney among public hospital staff, child-care centre staff and the community. RESULTS: In Australia, there have been an average of 3.5 deaths from chickenpox (mostly children) and 11 from herpes zoster (mostly older people) each year since 1980. The crude death rate for chickenpox has declined (p > 0.05). In 1995, there were 14 cases of neonatal and two of congenital varicella. Average annual admission rates for NSW and SA showed 1,200 hospital bed-days used for chickenpox, more than 20% with complications, and more than 7,300 bed days for zoster; annually more than 880 in-patient admissions were complicated by VZV. Most people encounter the virus in their first 15 years, but some remain susceptible into their 20s; 25% of cases and 37% of hospital admissions for chickenpox occur in people > or = 15 years of age. CONCLUSION: VZV infection involves people of all ages. It causes substantial morbidity and mortality, particularly at the extremes of life. The death rate from chickenpox but not zoster has fallen since the introduction of acyclovir in the 1980s. Surveillance of VZV infection must be given priority once vaccines become available, to monitor changes in morbidity and mortality.

Salt tolerance in cultured cells of Spartina pectinata.

Suspension cultures with cell doubling times of ca. 2 days were developed from the halophytic grass Spartina pectinata. Maximum rates of exponential growth measured by direct cell counts and by total culture packed-cell-volume were not significantly reduced by NaCl up to 200 mM but dropped beyond this point. In contrast, total cell production over a one week culture cycle, by both measures, was reduced in a roughly linear fashion between 0 and 500 mM NaCl. The pattern of growth in relation to NaCl is very similar to that of previously described cell suspensions derived from another halophyte, Distichlis spicata. In the field the latter is much more salt tolerant. The basis for the whole plant differences is not clear. They do not appear to reflect effectiveness of cell based salt tolerance or the presence of salt glands, which are reported here for the first time in S. pectinata and are found on the leaves of both species.

Stress-induced legume root nodule senescence. Physiological, biochemical, and structural alterations.

Nitrate-fed and dark-stressed bean (Phaseolus vulgaris) and pea (Pisum sativum) plants were used to study nodule senescence. In bean, 1 d of nitrate treatment caused a partially reversible decline in nitrogenase activity and an increase in O(2) diffusion resistance, but minimal changes in carbon metabolites, antioxidants, and other biochemical parameters, indicating that the initial decrease in nitrogenase activity was due to O(2) limitation. In pea, 1 d of dark treatment led to a 96% decline in nitrogenase activity and sucrose, indicating sugar deprivation as the primary cause of activity loss. In later stages of senescence (4 d of nitrate or 2-4 d of dark treatment), nodules showed accumulation of oxidized proteins and general ultrastructural deterioration. The major thiol tripeptides of untreated nodules were homoglutathione (72%) in bean and glutathione (89%) in pea. These predominant thiols declined by approximately 93% after 4 d of nitrate or dark treatment, but the loss of thiol content can be only ascribed in part to limited synthesis by gamma-glutamylcysteinyl, homoglutathione, and glutathione synthetases. Ascorbate peroxidase was immunolocalized primarily in the infected and parenchyma (inner cortex) nodule cells, with large decreases in senescent tissue. Ferritin was almost undetectable in untreated bean nodules, but accumulated in the plastids and amyloplasts of uninfected interstitial and parenchyma cells following 2 or 4 d of nitrate treatment, probably as a response to oxidative stress.