FINE STRUCTURE CHANGES DURING FUNCTION OF THE DIGESTIVE GLAND OF VENUS'S-FLYTRAP

Changes in the structure of the digestive gland cells of Venus's-flytrap during the digestive process have been studied with light and electron microscopy. Large vacuolar lipid-protein inclusions break up and become smaller; however, they never completely disappear during the entire 7-10-day cycle. Dictyosomes in the resting digestive gland are associated with small, inconspicuous vesicles, whereas during the digestive cycle two types of prominent vesicles are observed on the peripheral tubules. Changes in plastid fine structure are complex and involve the disappearance of lipid globules and the tubular complex, followed by the formation of microtubules on the thylakoids and cisternae on the outer plastid membrane. Mitochondrial fine structure changes from the small cristae and light matrix of the resting state to large cristae and a very dense matrix representative of a change to a state where phosphorylation is tightly coupled to electron transport. Pronounced changes which occur in the cell envelope (cell wall and membrane taken together) are apparently associated with secretion of the digestive fluid. Numerous other changes are observed such as polysome formation, multivesicular body formation, mitochondria division, and changes which can be attributed in general to elevated cell activity.     

Solubilization of hen brain neurotoxic esterase in dimethylsulfoxide

Neurotoxic esterase is the putative site of initiation of organophosphorus-induced neuropathy. The protein is membrane-associated and will thus require solubilization before it can be purified. Its enzymic activity was retained in hen brain microsomes suspended in 10-60% (v/v in water) dimethylsulfoxide and 5-20% dimethylacetamide, but lost in 5-20% 1- and 2-propanol as well as higher concentrations of dimethylsulfoxide. Soluble activity (100,000 x g, 60 min supernatant) was not obtained with dimethylacetamide, but 24% of the recovered activity (67%) was solubilized in 40% dimethylsulfoxide, with retention of its native response to inhibitors. Solvent extraction of active enzyme is of intrinsic interest and expands the options for its purification.     

Stromal NADH supplied by PHOSPHOGLYCERATE DEHYDROGENASE3 is crucial for photosynthetic performance

During photosynthesis, electrons travel from light-excited chlorophyll molecules along the electron transport chain to the final electron acceptor nicotinamide adenine dinucleotide phosphate (NADP) to form NADPH, which fuels the Calvin–Benson–Bassham cycle (CBBC). To allow photosynthetic reactions to occur flawlessly, a constant resupply of the acceptor NADP is mandatory. Several known stromal mechanisms aid in balancing the redox poise, but none of them utilizes the structurally highly similar coenzyme NAD(H). Using Arabidopsis (Arabidopsis thaliana) as a C₃-model, we describe a pathway that employs the stromal enzyme PHOSPHOGLYCERATE DEHYDROGENASE 3 (PGDH3). We showed that PGDH3 exerts high NAD(H)-specificity and is active in photosynthesizing chloroplasts. PGDH3 withdrew its substrate 3-PGA directly from the CBBC. As a result, electrons become diverted from NADPH via the CBBC into the separate NADH redox pool. pgdh3 loss-of-function mutants revealed an overreduced NADP(H) redox pool but a more oxidized plastid NAD(H) pool compared to wild-type plants. As a result, photosystem I acceptor side limitation increased in pgdh3. Furthermore, pgdh3 plants displayed delayed CBBC activation, changes in nonphotochemical quenching, and altered proton motive force partitioning. Our fluctuating light-stress phenotyping data showed progressing photosystem II damage in pgdh3 mutants, emphasizing the significance of PGDH3 for plant performance under natural light environments. In summary, this study reveals an NAD(H)-specific mechanism in the stroma that aids in balancing the chloroplast redox poise. Consequently, the stromal NAD(H) pool may provide a promising target to manipulate plant photosynthesis.

PHOSPHOGLYCERATE DEHYDROGENASE 3, an oxidoreductase in leaf chloroplasts with strong preference to reduce the stromal NAD(H) instead of the NADP(H) pool, is required for full photosynthetic capacity.     

Über die Nerven- und Muskelphysiologie des Pferdeegels Haemopis sanguisuga

Zusammenfassung Bei Haemopis sanguisuga ist die Leitungsgeschwindigkeit im ungedehnten Rückenmuskel 48,6 ± 8,4 cm/sec, sie nimmt bei Dehnung proportional der erreichten Länge zu. Die Leitungsgeschwindigkeit im ungedehnten Nervenstrang ist 18,1 ± 7,5 cm/sec.Die Kontraktion des Rückenmuskels bei einer Einzelerregung steigt in 0,50 ± 0,03 Sek an und fällt in 27 ± 8 Sek. ab.Das absolute Refraktärstadium des Rückenmuskels ist etwa 0,012 Sek.Die Länge der Muskelfasern im Rückenmuskel ist übereinstimmend nach Messungen an Zupfpräparaten und nach elektrischen Reizversuchen mit verschiedenem Elektrodenabstand 5–15 mm am ungedehnten Muskel, die Fasern erstrecken sich somit über 1–3 Dissipimente. Die Chronaxie des Rückenmuskels ist im Mittel 0,068 Sek., die der Bauchganglienkette 0,052 Sek.Die Aktionsströme des Muskels haben eine Anstiegszeit von 0,033 und eine Gesamtdauer von 0,09 Sek.Während die bisher genannten Größen bei den verschiedenen tierischen und pflanzlichen Objekten sehr verschieden sind, ist víelfach das Produkt aus zweien von ihnen recht konstant, wie etwa das aus Leitungsgeschwindigkeit und Dauer des Refraktärstadiums, die Refraktärlänge, und insbesondere das aus Leitungsgeschwindigkeit und Anstiegszeit des Aktionsstromes, die Anstiegslänge. Die Daten von Haemopis fügen sich hier den schon bekannten Gesetzmäßigkeiten gut ein.Theoretische Betrachtungen über die elektrische Erregbarkeit und über die Erregungsleitung machen die Zunahme der Leitungsgeschwindigkeit mit der Dehnung verständlich.Im Bauchmark von Haemopis wurden 6 g Acetylcholin je Gramm Gewebe gefunden, im Rückenmuskel 0,03 g/g. Cholinesterase enthält das Bauchmark etwa 800, der Muskel 500 E nach Hellauer. Das Bauchmark verhält sich damit ähnlich wie cholinerge Teile des Zentralnervensystems der Wirbeltiere.Die pulsierenden Seitengefäße der Egel sind nach Gaskell antagonistisch innerviert, wobei der fördernde Nerv adrenerg ist. Untersuchungen an Herpobdella zeigen, daß der Einfluß von Acetylcholin auf die Gefäße offenbar ein auch zentraler ist, indem wenigstens bei der Verdünnung 1:100000, erst eine Beschleunigung, dann eine Verlangsamung eintritt. Höhere Acetylcholinkonzentrationen, wie 1:5000, verlangsamen nur, wahrscheinlich auch durch eine periphere Wirkung. Durch Atropin 1:5000000 lassen sich alle Acetylcholin Wirkungen, auch die Beschleunigung, beheben, während die Beschleunigung durch Adrenalin erhalten bleibt.Herrn Professor v. Frisch danke ich für die mir gebotene Arbeitsmöglichkeit und für sein Interesse an der Untersuchung, Herrn Professor Umrath für mancherlei Anregungen und für Besprechungen einschlägiger Fragen.     

The transformation of cytoplasmic microtubules into helices and paracrystals by halothane in the foraminifer Allogromia laticollaris Arnold

After treatment of cells of the foraminifer Allogromia laticollaris Arnold (protozoa, rhizopoda) with the volatile anesthetic halothane in concentrations of more than 1 mM no cytoplasmic microtubules are demonstrable. In place of microtubules, other tubulin polymers that are helices or paracrystalline structures, with the same ultrastructure as seen after treatment with vinca alkaloids, can be identified. Below 1 mM halothane, besides loosely arranged paracrystals, single helices, microtubules and transition stages between microtubules and helices can be seen in close juxtaposition. Reasons for the transformation of microtubules and the involvement of microtubules in narcosis are discussed.     

Interspecific nutrient transfer in a tallgrass prairie plant community

Interplant nutrient transfer may be an important ecological process in grasslands, and may significantly influence plant neighborhood interactions. We investigated the potential for phosphorus transfer between the dominant grass Andropogon gerardii and several neighboring plant species in tallgrass prairie via a field ³²PO₄ labelling experiment. The mean amount of ³²P received from donor shoots differed significantly among neighboring species and decreased with increasing distance from the donor. In general, forbs and cool-season C₃ grasses received more labelled ³²P than warm-season C₄ grasses. Phosphorus transfer occurred over distances up to 0.5 m. The effects of species and distance on movement of phosphorus changed with increasing time after labelling. The relative mass of receiver and donor shoots did not affect amounts of ³²P transfer. A benomyl fungicide treatment, applied to suppress mycorrhizal activity, likely did not affect existing vegetative hyphae and did not affect the amount of ³²P transferred. These studies demonstrate that: (1) phosphorus is transferred among neighboring species in tallgrass prairie plant communities, (2) phosphorus may be transferred over significantly greater distances than reported in other grasslands, and (3) there is differential transfer among co-occurring species. Hypothesized mechanisms accounting for these patterns in tallgrass prairie include mycorrhizal hyphal interconnections and/or extensive and differential root and rhizosphere overlap among neighboring species.