Leaf water relations and anatomy of a tropical rainforest tree species vary with crown position

Summary Leaf water potentials, osmotic properties and structural characteristics were examined in the Australian tropical rainforest tree species, Castanospermum australe. These features were compared for individuals growing in the understorey and canopy of the undisturbed forest and in an open pasture from which the forest had been cleared. Leaf water potentials during the day declined to significantly lower values in the open-grown and canopy trees than in the understorey trees. During most of the day the opengrown tree experienced the lowest water potentials. These differences were paralleled by significant differences in tissue osmotic properties. The tissue osmotic potential at full hydration was lowest in the open-grown tree (-1.80 MPa), intermediate in the canopy trees (-1.38 MPa), and highest in the understorey trees (-0.80 MPa). As a result, the degree to which high and positive turgor pressures were maintained as water potentials declined was highest in the open-grown tree, intermediate in the canopy trees, and lowest in the understorey trees. The differences in tissue osmotic properties between individuals in the three crown positions were paralleled, in turn, by differences in leaf structual characteristics. Relative to leaves of the canopy and open-grown trees, leaves of the understorey trees had significantly larger epidermal cells with thinner cell walls, larger specific leaf areas and turgid weight: dry weight ratios, and a higher proportion of intercellular air space.Abbreviations ₁ Leaf tissue water potential - _min Lowest value of ₁ during the day ( noon) - _{P=0 1} zero turgor - R Relative water content - P Tissue turgor pressure - Tissue osmotic potential - ₀ at full hydration     

Cell-wall tension of the inner tissues of the maize coleoptile and its potential contribution to auxin-mediated organ growth

Plant organs such as maize (Zea mays L.) coleoptiles are characterized by longitudinal tissue tension, i.e. bulk turgor pressure produces unequal amounts of cell-wall tension in the epidermis (essentially the outer epidermal wall) and in the inner tissues. The fractional amount of turgor borne by the epidermal wall of turgid maize coleoptile segments was indirectly estimated by determining the water potential ^* of an external medium which is needed to replace quantitatively the compressive force of the epidermal wall on the inner tissues. The fractional amount of turgor borne by the walls of the inner tissues was estimated from the difference between -^* and the osmotic pressure of the cell sap (_i) which was assumed to represent the turgor of the fully turgid tissue. In segments incubated in water for 1 h, -^* was 6.1–6.5 bar at a _i of 6.7 bar. Both -^* and _i decreased during auxin-induced growth because of water uptake, but did not deviate significantly from each other. It is concluded that the turgor fraction utilized for the elastic extension of the inner tissue walls is less than 1 bar, i.e. less than 15% of bulk turgor, and that more than 85% of bulk turgor is utilized for counteracting the high compressive force of the outer epidermal wall which, in this way, is enabled to mechanically control elongation growth of the organ. This situation is maintained during auxin-induced growth.Abbreviations and Symbols _i osmotic pressure of the tissue - ₀ external water potential - ^* water potential at which segment length does not change - IAA indole-3-acetic acid - ITW longitudinal inner tissue walls - OEW outer epidermal wall - P turgor Supported by Deutsche Forschungsgemeinschaft (SFB 206).     

Effects of water stress on the gas exchange,the activities of some enzymes of carbon and nitrogen metabolism,and on the pool sizes of some organic acids in maize leaves

Water-stressed maize (Zea mays L.) leaves showed a large decrease in leaf conductance during photosynthesis. Net CO₂ uptake and evaporation declined fast at mild stress (=–0.6 to –1.0 MPa) and slower at more severe stress (=–1.0 to -1.2 MPa), whereas the CO₂ concentration in the intercellular spaces (C_i) did not drop to the CO₂ compensation point. The activities of the enzymes of photosynthetic carbon metabolism tested in this study dropped by approx. 30% at =-1.2 MPa. Glutamine synthetase activity was unaffected by water stress, whereas the activity of nitrate reductase was almost completely inhibited. The decline of enzyme activities in relation to was correlated with a concomitant decrease in the content of total soluble protein of the stressed leaves. The total leaf pools of malate, pyruvate and oxaloacetate decreased almost linearly in relation to , thus obviously contradicting the almost constant C_i. In comparison to the controls (=0.6 MPa) the content of citrate and isocitrate increaed markedly at =-0.9 MPa and decreased again at =-1.2 MPa.Abbreviations PCR photosynthetic carbon reduction cycle - PCO photosynthetic carbon oxidation cycle - PEP phosphoenolypyruvate - RuBP ribulose-1,5-bisphosphate     

The mitochondrial membrane potential (deltapsi(m)) in apoptosis; an update

Mitochondrial dysfunction has been shown to participate in the induction of apoptosis and has even been suggested to be central to the apoptotic pathway. Indeed, opening of the mitochondrial permeability transition pore has been demonstrated to induce depolarization of the transmembrane potential (_m), release of apoptogenic factors and loss of oxidative phosphorylation. In some apoptotic systems, loss of _m may be an early event in the apoptotic process. However, there are emerging data suggesting that, depending on the model of apoptosis, the loss of _m may not be an early requirement for apoptosis, but on the contrary may be a consequence of the apoptotic-signaling pathway. Furthermore, to add to these conflicting data, loss of _m has been demonstrated to not be required for cytochrome c release, whereas release of apoptosis inducing factor AIF is dependent upon disruption of _m early in the apoptotic pathway. Together, the existing literature suggests that depending on the cell system under investigation and the apoptotic stimuli used, dissipation of _m may or may not be an early event in the apoptotic pathway. Discrepancies in this area of apoptosis research may be attributed to the fluorochromes used to detect _m. Differential degrees of sensitivity of these fluorochromes exist, and there are also important factors that contribute to their ability to accurately discriminate changes in _m.     

The carotenoids of Flavobacterium strain R1560

The main carotenoid of Flavobacterium strain R1560 has been identified as (3R,3R)-zeaxanthin. Also present were small amounts of 15-cis-phytoene, phytofluene, -carotene (7,8,7,8-tetrahydro-, -carotene plus 7,8,11,12-tetrahydro-, -carotene), neurosporene, lycopene, -zeacarotene, -carotene, -carotene, -cryptoxanthin, rubixanthin, 3-hydroxy--zeacarotene and several apo-carotenals. Zeaxanthin production was inhibited by nicotine (10 mM), and lycopene and rubixanthin accumulated. The biosynthesis of zeaxanthin is discussed in terms of pathways and also of half-molecule reaction sequences. The presence of zeaxanthin may be a characteristic of a group of Flavobacterium species, and may thus be useful in the taxonomic classification of these organisms.     

The relationship between leaf water potential ψ leaf and the levels of abscisic acid and ethylene in excised wheat leaves

The amount of diffusible ethylene from excised wheat leaves (Triticum aestivum L. cv. Eclipse) increased when they were subjected to water stress. The quantity of ethylene produced was related to the severity of the stress, reaching a maximum at a leaf water potential _leaf of approximately-12 bars. Irrespective of the severity of the stress, the maximum rate of ethylene production usually occurred between 135–270 min after applying the stress and then the rate declined. Part of the decline may have been due to an oxygen deficiency in the leaf chambers. In excised water-stressed leaves there was a sigmoid relationship between increasing ethylene and abscisic acid (ABA) levels and decreasing leaf water potential values. The two curves were displaced from each other by approximately 1 bar, with ethylene evolution leading that of ABA accumulation. The maximum rate of increase in ethylene occurred between-8 and-9 bars and for ABA between-9 and-10 bars. A significant increase in the levels of these two plant growth regulators was found when the _leaf decreased outside the normal diurnal _leaf range by 1 bar for ethylene and 2 bars for ABA. Because of the sigmoid nature of the curves there was no distinct threshold _leaf value triggering-off an increase in ethylene or ABA, but with ABA the curve became very steep at a _leaf value of-9.3 bars and this could be looked upon as a kind of threshold value.It seems unlikely that the stress-induced ethylene evolution in excised wheat leaves stimulated the accumulation of ABA, because when the leaves were subjected to a substantial water stress (e.g. _leaf bars) ABA increased immediately and at a faster rate than ethylene.Abbreviations ABA abscisic acid - GLC gas-liquid chromatography - RWC relative water content - TLC thin-layer chromatography - _leaf leaf water potential     

Organization of Methanobacterium thermoautotrophicum bacteriophage psi M1 DNA

Summary M1 is a virulent bacteriophage of Methanobacterium thermoautotrophicum strain Marburg. Restriction enzyme analysis of the linear, 30.4 kb phage DNA led to a circular map of the 27.1 kb M1 genome. M1 is thus circularly permuted and exhibits terminal redundancy of approximately 3 kb. Packaging of M1 DNA from a concatemeric precursor initiates at the pac site which was identified at coordinate 4.6 kb on the circular genome map. It proceeds clockwise for at least five packaging rounds. Headful packaging was also shown for M2, a phage variant with a 0.7 kb deletion at coordinate 23.25 on the map.     

Estimation of Membrane Potential Δψ in Reconstituted Plasma Membrane Vesicles Using a Numerical Model of Oxonol VI Distribution

A model of membrane potential-dependent distribution of oxonol VI to estimate the electrical potential difference across Schizosaccharomyces pombe plasma membrane vesicles (PMV) has been developed. was generated by the H⁺-ATPase reconstituted in the PMV. The model treatment was necessary since the usual calibration of the dye fluorescence changes by diffusion potentials (K⁺ + valinomycin) failed. The model allows for fitting of fluorescence changes at different vesicle and dye concentrations, yielding in ATP-energized PMV of 80 mV. The described model treatment to estimate may be applicable for other reconstituted membrane systems.     

Water potential of standing-dead shoots of an intertidal grass

Summary Dead stems and leaves of smooth cordgrass (Spartina alterniflora Loisel.) undergo substantial fungal decay in the standing position. We conducted a series of experiments to determine the probable range of water availabilities that cordgrass-fungal decomposers experience; we determined the effects of duration of wetting and drying, site on shoots, leaching of osmotica, and stage of decomposition on water potential () of cordgrass shoots. Dried pieces of cordgrass shoots took up water rapidly when submerged, rising from values which were probably less than –150 megapascals (MPa) water potential to about –3.5 (soaked in seawater) or –1.5 (soaked in tapwater) within 5 min. Air-drying resulted in a return to low (<–7.5 MPa) within an hour. Literature reports show that most litter and wood-decomposing fungi which have been tested cannot grow at more negative than –6 MPa. The more lignified stems showed a more negative matric than leaves at water contents greater than 25% fresh weight. As leaves decomposed in the marsh, their increased (from –1.7 to –0.5 MPa, under standard conditions of 30 min freshwater soaking and 30 min air-drying), similar to what other investigators have found for wheat and forest litter. The water content at which cordgrass leaves reached –6 MPa was about 23% fresh weight, within the range (15–32%) found for wheat straw and forest litter.     

The activity of nitrate reductase and the pool sizes of some amino acids and some sugars in water-stressed maize leaves

The activity of nitrate reductase and the pool sizes of some amino acids and some sugars were measured in relation to the leaf water potential () of maize leaves. The activity of nitrate reductase was severely inhibited in water-stressed maize leaves. This was not due to substrate shortage or the presence of an inhibitor at reduced leaf water potential. While the typical proteinogenic amino acids valine, tyrosine, leucine and isoleucine were almost undetectable in the leaves of the control plants, their concentrations markedly increased with declining , thus indicating protein degradation. The concentrations of serine, glycine and glutamate increased upon water stress, their total amount in severely stressed leaves ranging 5- to 6-fold higher than the total amount of valine, tyrosine, leucine and isoleucine at this stage of water deficit. The pool sizes of glucose, fructose and sucrose decreased in relation to decreasing . The total amount of organic solutes remained almost constant at least up to a of approx.—1.0 MPa and then dropped to about 50% when reached –1.25 MPa.Abbreviations PCR photosynthetic carbon reduction cycle - PCO photosynthetic carbon oxidation cycle - PAR photosynthetically active radiation