Diurnal patterns of gas‐exchange and metabolic pools in tundra plants during three phases of the arctic growing season

Arctic tundra plant communities are subject to a short growing season that is the primary period in which carbon is sequestered for growth and survival. This period is often characterized by 24‐h photoperiods for several months a year. To compensate for the short growing season tundra plants may extend their carbon uptake capacity on a diurnal basis, but whether this is true remains unknown. Here, we examined in situ diurnal patterns of physiological activity and foliar metabolites during the early, mid, and late growing season in seven arctic species under light‐saturated conditions. We found clear diurnal patterns in photosynthesis and respiration, with midday peaks and midnight lulls indicative of circadian regulation. Diurnal patterns in foliar metabolite concentrations were less distinct between the species and across seasons, suggesting that metabolic pools are likely governed by proximate external factors. This understanding of diurnal physiology will also enhance the parameterization of process‐based models, which will aid in better predicting future carbon dynamics for the tundra. This becomes even more critical considering the rapid changes that are occurring circumpolarly that are altering plant community structure, function, and ultimately regional and global carbon budgets.     

Effects of curcumin on methyl methanesulfonate damage to mouse kidney

Methylmethane sulfonate (MMS) is an alkylating agent that may react with DNA and damage it. We investigated histological changes and apoptosis caused by MMS and the effects of curcumin on MMS treated mouse kidneys. Twenty-four mice were divided into four equal groups: controls injected with saline, a group injected with 40 mg/kg MMS, a group injected with 40 mg/kg MMS and given 100 mg/kg curcumin by gavage, and a group given 100 mg/kg curcumin by gavage. MMS caused congestion and vacuole formation, and elevated the apoptotic index significantly, but had no other effect on kidney tissue. Curcumin improved the congestion and vacuole formation caused by MMS and decreased the apoptotic index. Curcumin administered with MMS appears to decrease the deleterious effects of MMS on the kidney.     

Ecophysiological analysis of two arctic sedges under reduced root temperatures

Shoot physiological activity in arctic vascular plants may be controlled by low soil temperatures. While leaves may be exposed to moderate temperatures during the growing season, root temperatures often remain near freezing. In this study, two tundra sedges, Eriophorum vaginatum and Carex bigellowii , were subjected to reduced soil temperatures, and photosynthetic parameters (light saturated photosynthesis A _max, variable to maximal fluorescence and F _v/ F _m stomatal conductance) and abscisic acid concentrations were determined. Stomatal conductance and A _max for both E. vaginatum and C. bigellowii strongly decreased with declining soil temperatures. Decreasing soil temperature, however, impacted F _v/ F _m to a much lesser degree. Root and leaf ABA concentrations increased with decreasing root temperature. These observations support the contention that soil temperature is a significant photosynthetic driving factor in arctic sedges exposed to variable root and shoot temperatures. Because these two species comprise approximately 30% of the vascular ground cover of wet tussock tundra, the soil temperature responses of these sedges potentially scale up to significant effects on ecosystem carbon exchange.     

Thymocyte sensitivity and supramolecular activation cluster formation are developmentally regulated: a partial role for sialylation

TCR reactivity is tuned during thymic development. Immature thymocytes respond to low-affinity self-ligands resulting in positive selection. Following differentiation, T cells no longer respond to low-affinity ligands, but respond well to high-affinity (foreign) ligands. We show in this study that this response includes integrin activation, supramolecular activation cluster formation, Ca(2+) flux, and CD69 expression. Because glycosylation patterns are known to change during T cell development, we tested whether alterations in sialylation influence CD8 T cell sensitivity to low affinity TCR ligands. Using neuraminidase treatment or genetic deficiency in the ST3Gal-I sialyltransferase, we show that desialylation of mature CD8 T cells enhances their sensitivity to low-affinity ligands, although these treatments do not completely recapitulate the dynamic range of immature T cells. These studies identify sialylation as one of the factors that regulate CD8 T cell tuning during development.     

Functional expression cloning reveals proapoptotic role for protein phosphatase 4

Functional expression cloning strategies are highly suitable for the analysis of the molecular control of apoptosis. This approach has two critical advantages. Firstly, it eliminates prior assumptions about the properties of the proteins involved, and, secondly, it selectively targets proteins that are causally involved in apoptosis control and which affect the crucial cellular decision between survival and death. The application of this strategy to the isolation of cDNAs conferring resistance to dexamethasone and gamma-irradiation resulted in the isolation of a partial cDNA for the catalytic subunit of protein phosphatase 4 (PP4). Cells transfected with this partial cDNA in an expression vector downregulated PP4 and were resistant to both dexamethasone and UV radiation, as demonstrated by both membrane integrity and colony-forming assays. These observations suggest that PP4 plays an important proapoptotic role in T lymphocytes.     

Resistance of Interspecific Arachis Breeding Lines to Meloidogyne javanica and an Undescribed Meloidogyne Species

Resistance to a peanut-parasitic population of Meloidogyne javanica and an undescribed Meloidogyne sp. in peanut breeding lines selected for resistance to Meloidogyne javanica was examined in greenhouse tests. The interspecific hybrid TxAG-7 was resistant to reproduction of Meloidogyne javanica, M. javanica, and Meloidogyne sp. An Meloidogyne javanica-resistant selection from the second backcross (BC) of TxAG-7 to the susceptible cultivar Florunner also was resistant to M. javanica but appeared to be segregating for resistance to the Meloidogyne sp. When reproduction of M. javanica and Meloidogyne javanica were compared on five BC4F3 peanut breeding lines, each derived from Meloidogyne javanica-susceptible BC4F2 individuals, all five lines segregated for resistance to M. javanica, whereas four of the lines appeared to be susceptible to Meloidogyne javanica. These data indicate that several peanut lines selected for resistance to Meloidogyne javanica also contain genes for resistance to populations of M. javanica and the undescribed Meloidogyne sp. that are parasitic on peanut. Further, differences in segregation patterns suggest that resistance to each Meloidogyne sp. is conditioned by different genes.