Einfluß einer abgestuften Wasserversorgung auf CO2-Assimilation,Transpiration, Substanzproduktion und Wasserverbrauch vonAvena sativa

Zusammenfassung Gefäßkulturen von Hafer in Sand und Erde mit abgestuftem, jeweils gleichbleibend gehaltenem Wasserangebot von 100, 75, 50, 30 und 15% der Boden wasserkapazität ergaben die höchsten Erträge an Gesamttrockenmasse in der Regel bei voller Wassersättigung des Bodens in Verbindung mit gleichzeitig maximalem Wasserverbrauch (bestimmt durch tägliches Wägen der Gefäße). Abnehmende Wasserversorgung verringerte auch Trockenmasse und Wasserverbrauch der Pflanzen. In trockenem Boden und bei reichlicher Wasserzufuhr entwickelte sich die Wurzelmasse im Vergleich mit den oberirdischen Organen stärker als bei mittlerer Bodenfeuchtigkeit. Klimatische Einflüsse, Aussaatzeit und Witterung sowie die Bodenart modifizierten die vom Wasserzustand des Bodens ausgehenden Wirkungen auf Trockenmasseproduktion und Wasserverbrauch, z. B. wurde bei Sommeraussaat gegenüber der Frühjahrsaussaat die Blattentwicklung bedeutend gefördert.Mit registrierenden Infrarot-Gasanalysatoren wurden Tagesgänge von CO₂-Aufnahme, Nachtatmung und Transpiration unter natürlichen Bedingungen gemessen. Bei trockenem Boden war die photosynthetische Leistung der Pflanzen zu Beginn ihrer Entwicklung deutlich gehemmt; sie steigerte sich allmählich und war später merklich größer als bei hohen Wassergaben. Die Transpiration verlief im allgemeinen gleichsinnig wie die Netto-Assimilationsrate, wurde jedoch auch nachts meist auf einer gewissen Höhe fortgesetzt. Die Nachtatmung der sehr trocken gehaltenen Pflanzen war gegenüber den anderen Wasserstufen meist erhöht. Die Trockenkulturen zeigten einen größeren Lichtbedarf; der Lichtkompensationspunkt wurde gewöhnlich erst bei höherer Beleuchtungsstärke erreicht als bei guter Wasserversorgung. Daraus wird auf erhöhten Energiebedarf der sehr trocken kultivierten Pflanzen geschlossen. Das Verhältnis zwischen CO₂-Aufnahme und Transpiration wurde durch unterschiedliche Bodenwasserversorgung meist nur wenig beeinflußt. Die Ergebnisse der CO₂-Assimilationsmessungen stehen im großen und ganzen mit dem wöchentlich festgestellten Trockensubstanzgewinn in Einklang.

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Summary Cultures ofAvena sativa L. grown in pots with sand or garden soil with a graduated, in each case fairly constant water supply of 100, 75, 50, 30, and 15% of field capacity yielded maximum total dry weight, as a rule, in fully water-saturated soils combined with maximum water consumption (measured by daily weighing). Decreasing water supply reduced dry matter production and water consumption of plants. In dry soil and at high degrees of water saturation roots developed more dry matter in comparison to the shoots than at medium soil moisture. Results in dry matter production and water consumption, as caused by water relations in soil, are modified additionally by climatic factors, sowing date and weather, and soil type, e.g. sowing in summer considerably favoured leaf development, compared with the spring seed.Daily courses of CO₂-uptake, night respiration and transpiration were registered by infrared-gasanalyzers. In very dry soil photosynthetic activity of plants was distinctly hampered during the first weeks of development; it gradually increased, and at a later stage photosynthetic activity was markedly higher than at abundant water supply. In general transpiration followed the net assimilation rate, it was continued, however, even over night on a certain level. Night respiration of plants growing in dry soil was higher in relation to the other water stages. Those plants, too, required more light for dry matter production; their light compensation point arrived at higher light intensity than under abundant water supply. This behaviour seems to indicate higher energy requirement of plants distinctly influenced by water stress. Relations between CO₂-uptake and transpiration were but slightly influenced by different soil water level. Results of gas exchange measurements on CO₂-assimilation agreed, as a rule, with the weekly dry matter measurements by weighting.

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Tim50 maintains the permeability barrier of the mitochondrial inner membrane

Transport of metabolites across the mitochondrial inner membrane is highly selective, thereby maintaining the electrochemical proton gradient that functions as the main driving force for cellular adenosine triphosphate synthesis. Mitochondria import many preproteins via the presequence translocase of the inner membrane. However, the reconstituted Tim23 protein constitutes a pore remaining mainly in its open form, a state that would be deleterious in organello. We found that the intermembrane space domain of Tim50 induced the Tim23 channel to close. Presequences overcame this effect and activated the channel for translocation. Thus, the hydrophilic cis domain of Tim50 maintains the permeability barrier of mitochondria by closing the translocation pore in a presequence-regulated manner.     

Nonvolatiles of commercial lime and grapefruit oils separated by high-speed countercurrent chromatography

The nonvolatile fractions of cold-pressed peel oils of Key and Persian lime as well as grapefruit were separated by high-speed countercurrent chromatography (HS-CCC). In addition to the isolation of the main coumarins, psoralens and polymethoxyflavones, a number of minor constituents were enriched and successfully characterized by GC-MS and HPLC-UV. 5,7,8-Trimethoxycoumarin and the cyclical acetals of oxypeucedanin hydrate with citral were determined as new nonvolatile trace constituents of lime oils and confirmed by NMR spectroscopy. The citral oxypeucedaninyl acetals were found particularly in Key lime oil type A, which as a result of the juice-oil contact, is exposed to acidic conditions during industrial processing. Some of the confirmed minor constituents, such as pabulenol, isooxypeucedanin, and oxypeucedanin methanolate in lime as well as auraptenol in grapefruit, may have been generated by hydrolysis-sensitive precursors during CCC separation or their respective industrial processing techniques.     

ATP release guides neutrophil chemotaxis via P2Y2 and A3 receptors

Cells must amplify external signals to orient and migrate in chemotactic gradient fields. We find that human neutrophils release adenosine triphosphate (ATP) from the leading edge of the cell surface to amplify chemotactic signals and direct cell orientation by feedback through P2Y2 nucleotide receptors. Neutrophils rapidly hydrolyze released ATP to adenosine that then acts via A3-type adenosine receptors, which are recruited to the leading edge, to promote cell migration. Thus, ATP release and autocrine feedback through P2Y2 and A3 receptors provide signal amplification, controlling gradient sensing and migration of neutrophils.     

BKCa-Cav channel complexes mediate rapid and localized Ca2+-activated K+ signaling

Large-conductance calcium- and voltage-activated potassium channels (BKCa) are dually activated by membrane depolarization and elevation of cytosolic calcium ions (Ca2+). Under normal cellular conditions, BKCa channel activation requires Ca2+ concentrations that typically occur in close proximity to Ca2+ sources. We show that BKCa channels affinity-purified from rat brain are assembled into macromolecular complexes with the voltage-gated calcium channels Cav1.2 (L-type), Cav2.1 (P/Q-type), and Cav2.2 (N-type). Heterologously expressed BKCa-Cav complexes reconstitute a functional "Ca2+ nanodomain" where Ca2+ influx through the Cav channel activates BKCa in the physiological voltage range with submillisecond kinetics. Complex formation with distinct Cav channels enables BKCa-mediated membrane hyperpolarization that controls neuronal firing pattern and release of hormones and transmitters in the central nervous system.     

Biogenic potassium salt particles as seeds for secondary organic aerosol in the Amazon

The fine particles serving as cloud condensation nuclei in pristine Amazonian rainforest air consist mostly of secondary organic aerosol. Their origin is enigmatic, however, because new particle formation in the atmosphere is not observed. Here, we show that the growth of organic aerosol particles can be initiated by potassium-salt-rich particles emitted by biota in the rainforest. These particles act as seeds for the condensation of low- or semi-volatile organic compounds from the atmospheric gas phase or multiphase oxidation of isoprene and terpenes. Our findings suggest that the primary emission of biogenic salt particles directly influences the number concentration of cloud condensation nuclei and affects the microphysics of cloud formation and precipitation over the rainforest.     

Compartmentalized control of skin immunity by resident commensals

Intestinal commensal bacteria induce protective and regulatory responses that maintain host-microbial mutualism. However, the contribution of tissue-resident commensals to immunity and inflammation at other barrier sites has not been addressed. We found that in mice, the skin microbiota have an autonomous role in controlling the local inflammatory milieu and tuning resident T lymphocyte function. Protective immunity to a cutaneous pathogen was found to be critically dependent on the skin microbiota but not the gut microbiota. Furthermore, skin commensals tuned the function of local T cells in a manner dependent on signaling downstream of the interleukin-1 receptor. These findings underscore the importance of the microbiota as a distinctive feature of tissue compartmentalization, and provide insight into mechanisms of immune system regulation by resident commensal niches in health and disease.