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1.
2.
In maize leaves nitrogen (N)-deprivation induced a significant decline of chlorophyl and total N contents. On the contrary,
sulphur (S) content increased with N-deprivation. The activities of ATP-sulphurylase and O-acetylserine sulphydrylase also
decreased with N-deprivation, but ATP-sulphurylase activity was more sensitive than O-acetylserine sulphydrylase activity
to N-deficiency both in whole leaf extracts and in isolated leaf cells. Finally, N-deprivation induced higher changes in activity
of the two enzymes in mesophyll protoplasts than in bundle sheath strands.
This research was supported by Consiglio Nazionale delle Ricerche-Special grant I.P.R.A.-Subproject 1. Paper N. 73. 相似文献
3.
We compare the primary sex ratio (proportion of haploid eggs laid by queens) and the secondary sex ratio (proportion of male pupae produced) in the Argentine ant Iridomyrmex humilis with the aim of investigating whether workers control the secondary sex ratio by selectively eliminating male brood. The proportion of haploid eggs produced by queens was close to 0.5 in late winter, decreased to less than 0.3 in spring and summer, and increased again to a value close to 0.5 in fall. Laboratory experiments indicate that temperture is a proximate factor influencing the primary sex ratio with a higher proportion of haploid eggs being laid at colder temperatures. Production of queen pupae ceased in mid-June, about three weeks before that of male pupae. After this time only worker pupae were produced. During the period of production of sexuals, the proportion of male pupae ranged from 0.30 to 0.38. Outside this period no males were reared although haploid eggs were produced all the year round by queens. Workers thus exert a control on the secondary sex ratio by eliminating a proportion of the male brood during the period of sexual production and eliminating all the males during the remainder of the cycle. These data are consistent with workers preferring a more female-biased sex ratio than queens. The evolutionary significance of the production of male eggs by queens all the year round is as yet unclear. It may be a mechanism allowing queen replacement in the case of the death of the queens in the colony. 相似文献
4.
Milford H. Wolpoff Fred H. Smith Mirko Malez Jakov Radov
i Darko Rukavina 《American journal of physical anthropology》1981,54(4):499-545
Human remains excavated from Vindija cave include a large although fragmentary sample of late Mousterian-associated specimens and a few additional individuals from the overlying early Upper Paleolithic levels. The Mousterian-associated sample is similar to European Neandertals from other regions. Compared with earlier Neandertals from south central Europe, this sample evinces evolutionary trends in the direction of Upper Paleolithic Europeans. Compared with the western European Neandertals, the same trends can be demonstrated, although the magnitude of difference is less, and there is a potential for confusing temporal with regional sources of variation. The early Upper Paleolithic-associated sample cannot be distinguished from the Mousterian-associated hominids. We believe that this site provides support for Hrdli?ka's “Neandertal phase” of human evolution, as it was originally applied in Europe. 相似文献
5.
Ulrich Stottmeister Jana Helm Bettina Soltmann Mirko Jechorek Matthias Beck 《Engineering in Life Science》2010,10(2):87-102
Methanotrophic bacteria possess a unique set of enzymes enabling them to oxidize, degrade and transform organic molecules and synthesize new compounds. Therefore, they have great potential in environmental biotechnology. The application of these unique properties was demonstrated in three case studies: (i) Methane escaping from leaky gas pipes may lead to massive mortality of trees in urban areas. Lack of oxygen within the soil surrounding tree roots caused by methanotrophic activity was identified as one of the reasons for this phenomenon. The similarity between metabolic reactions performed by the key enzymes of methanotrophs (methane monooxygenase) and ammonium oxidizers (ammonium monooxygenase) might offer a solution to this problem by applying commercially available nitrification and urease inhibitors. (ii) Methanotrophs are able to co‐metabolically degrade contaminants such as low‐molecular‐weight‐chlorinated hydrocarbons in soil and water in the presence of methane. Batch and continuous trichloroethylene degradation experiments in laboratory‐scale reactors using Methylocystis sp. GB 14 were performed, partly with cells entrapped in a polymer matrix. (iii) Using a short, two‐stage pilot‐scale process, the intracellular polymer accumulation of poly‐β‐hydroxybutyrate (PHB) in methanotrophs reached a maximum of 52%. Interestingly, an ultra‐high‐molecular‐weight PHB of 3.1 MDa was accumulated under potassium deficiency. Under strictly controlled conditions (temperature, pH and methane supply) this process can be nonsterile because of the establishment of a stable microbial community (dominant species Methylocystis sp. GB 25 ≥86% by biomass). The possibility to substitute methane with biogas from renewable sources facilitates the development of a methane‐based PHB production process that yields a high‐quality biopolymer at competitive costs. 相似文献
6.
Bulwin GC Wälter S Schlawinsky M Heinemann T Schulze A Höhne W Krause G Kalka-Moll W Fraser P Volk HD Löhler J Milford EL Utku N 《PloS one》2008,3(2):e1576
Classically, HLA-DR expressed on antigen presenting cells (APC) initiates lymphocyte activation via presentation of peptides to TCR bearing CD4+ T-Cells. Here we demonstrate that HLA-DR alpha 2 domain (sHLA-DRalpha2) also induces negative signals by engaging TIRC7 on lymphocytes. This interaction inhibits proliferation and induces apoptosis in CD4+ and CD8+ T-cells via activation of the intrinsic pathway. Proliferation inhibition is associated with SHP-1 recruitment by TIRC7, decreased phosphorylation of STAT4, TCR-zeta chain & ZAP70, and inhibition of IFN-gamma and FasL expression. HLA-DRalpha2 and TIRC7 co-localize at the APC-T cell interaction site. Triggering HLA-DR - TIRC7 pathway demonstrates that sHLA-DRalpha2 treatment inhibits proinflammatory-inflammatory cytokine expression in APC & T cells after lipopolysaccaride (LPS) stimulation in vitro and induces apoptosis in vivo. These results suggest a novel antiproliferative role for HLA-DR mediated via TIRC7, revise the notion of an exclusive stimulatory interaction of HLA-DR with CD4+ T cells and highlights a novel physiologically relevant regulatory pathway. 相似文献
7.
Grzegorz Garbacz Bartosz Kołodziej Mirko Koziolek Werner Weitschies Sandra Klein 《AAPS PharmSciTech》2013,14(2):517-522
The bicarbonate buffer is considered as the most biorelevant buffer system for the simulation of intestinal conditions. However, its use in dissolution testing of solid oral dosage forms is very limited. The reason for this is the thermodynamic instability of the solution containing hydrogen carbonate ions and carbonic acid. The spontaneous loss of carbon dioxide (CO2) from the solution results in an uncontrolled increase of the pH. In order to maintain the pH on the desired level, either a CO2 loss must be completely avoided or the escaped CO2 has to be replaced by quantitative substitution, i.e. feeding the solution with the respective amount of gas, which re-acidifies the buffer after dissociation. The present work aimed at the development of a device enabling an automatic pH monitoring and regulation of hydrogen carbonate buffers during dissolution tests. 相似文献
8.
Rosangela Catoni Francesco Bracco Mirko U. Granata 《Physiology and Molecular Biology of Plants》2020,26(2):261-270
Mesophyll conductance (gm) has received over time much less attention than stomatal conductance (gs), although it affects leaf photosynthesis to about the same extent as stomatal conductance does. The objective of this study was to analyze the gm trend in five understory herbaceous species growing in a close-canopy forest in the north-west of Italy. In particular, three of analyzed species were monocots: Carex brizoides Lam., Carex pilosa Scop., and Oplismenus undulatifolius P. Beauv and the others dicots species: Circaea lutetiana L., and Pulmonaria officinalis Ced. The results showed, on one hand, the absence of correlation between gm and the considered environmental variables in the forest understory (i.e. air temperature, photosynthetic photon flux density and carbon dioxide concentration). Moreover, we carried out a principal component analysis considering all the analyzed morphological and physiological variables for the five species. The following correlation between the first component, related to the leaf mass per unit of leaf area and the leaf tissue density, and gm seem to suggest a key role of the leaf structural features in determining gm variations across the five species. 相似文献
9.
Integrated requirement of non‐specific and sequence‐specific DNA binding in Myc‐driven transcription