Differential effects of carbon monoxide in regulating NADH supply for nitrate reduction in tall and dwarf cultivars of wheat

The effect of CO treatment of intact leaves of wheat was monitored by measuring nitrite production in the in vivo nitrate reduction assay under aerobic conditions (S.K. Sawhney et al., Nature, 272 (1978) 647). In the tall cultivar Halberd (lacking the dwarfing reduced height trait (Rht) gene), the CO treatment resulted in an appreciable production of nitrite, whereas in the dwarf variety Bindawarra (Rht positive), this did not occur. When the intact Bindawarra leaves, however, were subjected to stress treatments, e.g. cold, salt or moisture deficit, or when they were cut into small discs, they readily responded to CO and nitrite production was enhanced. Similar effects were also observed when these leaves were treated with uncouplers or with 10–20% (v/v) CO in air. It is also shown that the cytochrome oxidase respiratory pathway only is involved in the regulation of NADH supply for nitrate reduction in leaves because the inhibition of the cyanide (and CO) insensitive alternative oxidase by salicylhydroxamic acid (SHAM) did not result in enhancement of the in vivo nitrate reduction under aerobic conditions.     

Carbon monoxide sensitivity of cytochrome oxidase in wheat leaves in relation to dwarfing genes (Rht) in wheat cultivars

Summary Leaves of young seedlings of a number of tall cultivars of wheat, lacking the dwarfing Rht genes, readily responded to a brief 2 min exposure to CO, as assessed by in vivo aerobic assay of nitrate reductase. This test depends on the inhibition of cytochrome c oxidase by CO, which in turn renders cytosolic NADH available for the reduction of nitrate to nitrite in vivo. Semi-dwarf cultivars of wheat (Rht present) did not respond to CO in this way. Since CO forms a complex only with reduced cytochrome a₃, the results indicate differences in the redox state of cytochrome a₃, during in situ respiration of leaves from tall and semi-dwarf plants which are likely to be under genetic control.     

Comparison of endogenous gibberellins and response to applied gibberellin of some dwarf and tall wheat cultivars

Summary A number of dwarf wheat cultivars of the Norin 10 type were compared with several tall forms. Applied gibberellic acid markedly stimulated the growth of seedlings of the tall cultivars but not the growth of dwarf seedlings. Several other gibberellins were also inactive when tested with one dwarf cultivar. De-embryonated grains of all cultivars formed -amylase in response to gibberellic acid. Gibberellic acid caused an increase in soluble carbohydrates in the leaves of the tall cultivars but not in those of the dwarfs.Germinating grains, light-grown seedlings and developing stems of the dwarf cultivars contained more endogenous gibberellin-like activity than those of tall cultivars. It is suggested that the dwarf cultivars have a block to the utilisation of gibberellin in the shoot.     

Differential carbon monoxide sensitivity of cytochrome C oxidase in the leaves of c(3) and c(4) plants

CO sensitivity of cytochrome a₃ in the leaves of a number of C₃ and C₄ plants was monitored by the nitrate reductase assay under differing CO to O₂ ratios. All the C₃ plants were relatively insensitive to CO and required a high CO to O₂ ratio of 40 to promote significant nitrate reductase activity. However, when treated with 2 millimolar 2,4-dinitrophenol, these leaves readily responded to CO even at low CO to O₂ ratios of 10 or less. On the other hand, the leaves of all C₄ plants tested, belonging to the three subgroups, were highly sensitive to CO, even at CO to O₂ ratios of 5 or less. In these leaves, the uncoupler was without any effect, probably because the mitochondria, either from mesophyll or bundle sheath cells or both, lacked tight respiratory control.     

Cytochrome oxidase from Pseudomonas aeruginosa. IV. Reaction with oxygen and carbon monoxide.

The reaction between a cytochrome oxidase from Pseudomonas aeruginosa and oxygen has been studied by a rapid mixing technique. The data indicate that the heme d1 moiety of the ascorbate-reduced enzyme is oxidized faster than the heme c component. The oxidation of heme d1 is accurately second order with respect to oxygen and has a rate constant of 5.7 - 10(4) M-1 - s-1 at 20 degrees C. The oxidation of the heme c has a first order rate constant of about 8 s-1 at infinite concentration of O2. The results indicate that the rate-limiting step is the internal transfer of electrons from heme c to heme d1. These more rapid reactions are followed by more complicated but smaller abcorbance changes whose origin is still not clear. The reaction of ascorbate-reduced oxidase with CO has also been studied and is second order with a rate constant of 1.8 - 10(4) M-1 - s-1. The initial reaction with CO is followed by a slower reaction of significantly less magnitude. The equilibrium constant for the reaction with CO, calculated as a dissociation constant from titrimetric experiments with dithionite-reduced oxidase, is about 2.3 - 10(-6) M. From these data a rate constant of 0.041 s-1 can be calculated for the dissociation of CO from the enzyme.     

Growth and cell wall properties of two wheat cultivars differing in their sensitivity to aluminum stress

The present study was conducted to investigate the cell wall properties in two wheat (Triticum aestivum L.) cultivars differing in their sensitivity to Al stress. Seedlings of Al-resistant, Inia66 and Al-sensitive, Kalyansona cultivars were grown in complete nutrient solutions for 4 days and then subjected to treatment solutions containing Al (0, 50 microM) in a 0.5 mM CaCl(2) solution at pH 4.5 for 24 h. Root elongation was inhibited greatly by the Al treatment in the Al-sensitive cultivar compared to the Al-resistant cultivar. The Al-resistant cultivar accumulated less amount of Al in the root apex than in the Al-sensitive cultivar. The contents of pectin and hemicellulose in roots were increased with Al stress, and this increase was more conspicuous in the Al-sensitive cultivar. The molecular mass of hemicellulosic polysaccharides was increased by the Al treatment in the Al-sensitive cultivar. The increase in the content of hemicellulose was attributed to increase in the contents of glucose, arabinose and xylose in neutral sugars. Aluminum treatment increased the contents of ferulic acid and p-coumaric acid especially in the Al-sensitive cultivar by increasing the activity of phenylalanine ammonia lyase (PAL, EC 4.3.1.5). Aluminum treatment markedly decreased the beta-glucanase activity in the Al-sensitive cultivar, but did not exert any effect in the Al-resistant cultivar. These results suggest that the modulation of the activity of beta-glucanase with Al stress may be involved in part in the alteration of the molecular mass of hemicellulosic polysaccharides in the Al-sensitive cultivar. The increase in the molecular mass of hemicellulosic polysaccharides and ferulic acid synthesis in the Al-sensitive cultivar with Al stress may induce the mechanical rigidity of the cell wall and inhibit the elongation of wheat roots.     

Cytochrome oxidase from Pseudomonas aeruginosa. IV. Reaction with oxygen and carbon monoxide

The reaction between a cytochrome oxidase from Pseudomonas aeruginosa and oxygen has been studied by a rapid mixing technique. The data indicate that the heme d₁ moiety of the ascorbate-reduced enzyme is oxidized faster than the heme c component. The oxidation of heme d₁ is accurately second order with respect to oxygen and has a rate constant of 5.7 · 10⁴ M⁻¹ · s⁻¹ at 20 °C. The oxidation of the heme c has a first-order rate constant of about 8 s⁻¹ at infinite concentration of O₂. The results indicate that the rate-limiting step is the internal transfer of electrons from heme c to heme d₁. These more rapid reactions are followed by more complicated but smaller absorbance changes whose origin is still not clear.

The reaction of ascorbate-reduced oxidase with CO has also been studied and is second order with a rate constant of 1.8 · 10⁴ M⁻¹ · s⁻¹. The initial reaction with CO is followed by a slower reaction of significantly less magnitude. The equilibrium constant for the reaction with CO, calculated as a dissociation constant from titrimetric experiments with dithionite-reduced oxidase, is about 2.3 · 10⁻⁶ M. From these data a rate constant of 0.041 s⁻¹ can be calculated for the dissociation of CO from the enzyme.     

Antifungal diene in leaves of various avocado cultivars

Leaves (both young and mature) of seventeen commercial avocado (Persea americana) cultivars have been analysed monthly throughout the year to measure the concentration and seasonal variation of the antifungal diene (Z,Z)-2-hydroxy-4-oxohenicosa-12,15-dien-1-yl acetate (persin).     

Water potential gradients of tall and short cultivars of winter wheat

Summary Water and osmotic potentials were measured with thermocouple psychrometers, weekly after heading, two times each day at pre-dawn and at noon, in flag leaves and grain of tall and short cultivars of winter wheat grown in the field under rain-fed conditions.Water was held with less tension in the grain than in the leaf for both tall and short cultivars. The tall cultivars had lower leaf water potentials, but higher grain water potentials, than the short cultivars. The grain osmotic potential was lower in the short cultivars compared to the tall ones. Grain yield of short cultivars (1810 kg/ha) was more than that of tall cultivars (1730 kg/ha). Apparently higher leaf water potentials of short cultivars enabled more photosynthates to move into the grain.     

The binding of carbon monoxide to cytochrome c oxidase.

The effect of CO on the optical absorbance spectrum of partially reduced cytochrome c oxidase has been studied. The changes at 432 and 590 nm suggest that the cytochrome alpha2/3+ - CO compound is formed preferentially and that concomitantly a second electron is taken up by the enzyme. From the CO-induced changes at 830 nm it is concluded that in the partially reduced enzyme addition of CO causes reoxidation of the copper component of cytochrome c oxidase. Addition of CO to partially reduced enzyme (2 electrons per 4 metal ions) also brings about a decrease in the intensities of electron paramagnetic resonance signals of high-spin heme iron near g = 6 and of the low-spin heme at g = 2.6. Concomitantly both the low-spin heme a signal at g = 3 and the copper signal at g = 2 increase in intensity. These results demonstrate that formation of the reduced diamagnetic cytochrome a3 - CO compound is accompanied by reoxidation of both the copper component detectable by electron paramagnetic resonance and possibly also by cytochrome a.     

Hardiness dependent accumulation of phospholipids in leaves of wheat cultivars

Phospholipid content and composition in the leaves of thirteen cultivars of wheat differing in frost hardiness, were compared before and after hardening in order to see whether phospholipids play a role in surviving at low temperatures. The content of phospholipids in the leaves at the end of the hardening could be related to the aquired hardiness, and the relationship between the two phenomena could be described by the regression equation y = (0.174 ± 0.0016) x + 1311. Accumulation of phospholipids represents a hardiness dependent augmentation of membranes. Phosphatidylcholine appeared to be preferentially accumulated in hardy cultivars during the hardening process. As there are no significant differences in phospholipid fatty acid compositions investigated earlier, these results suggest the importance of the polar head group composition of membranes in avoiding frost injury.     

Phytolith occluded carbon and silica variability in wheat cultivars

Phytolith Occluded Carbon (PhytOC) has recently been demonstrated to be an important long-term terrestrial carbon fraction. The aim of this study was to examine the rates of silica accumulation and carbon bio-sequestered within the silica phytoliths of the leaf and stem material of wheat (Triticum sp.) cultivars. The phytolith content of 53 wheat cultivars sourced from 25 countries around the world and grown on a single trial site was first isolated and the PhytOC content then determined. The data shows that the phytolith occluded carbon content of the wheat cultivars ranged from 0.06% to 0.60% of dry leaf and stem biomass: a range of 1,000%. The data also demonstrates that it is the efficiency by which carbon is encapsulated within silica rather than the quantity of silica accumulated by the plant that is the most important factor in determining the relative PhytOC yields. The potential phytolith carbon bio-sequestration rates in the leaf and stem components of these wheat cultivars ranged up to 0.246 t-e-CO₂ ha^?1y^?1. These phytolith carbon bio-sequestration rates indicate a substantial potential (~50 million t-e-CO₂ y^?1) exists for increasing the rate of secure carbon bio-sequestration in wheat crops using existing cultivars.     

In vivo binding of carbon monoxide to cytochrome c oxidase in rat brain

The possibility of binding of CO to cytochrome c oxidase (cytochrome a,a3) in brain cortex has been examined in vivo by reflectance spectrophotometry. During ventilation with CO-containing gases, cytochrome a,a3 absorption at 605 nm increased in the parietal cortex of anesthetized rats during carboxyhemoglobin (HbCO) formation. HbCO levels, measured by changes in absorption at 569-586 nm in vivo, correlated positively with arterial HbCO by CO oximetry. Arterial blood pressure and calculated O2 content varied inversely with HbCO. During CO exposure, decreases in blood pressure, O2 content, and cytochrome a,a3 oxidation level could be reversed partly at constant HbCO by compression to 3 atmospheres absolute (ATA). After removing CO from inspired gas at 3 ATA, optical and physiological parameters recovered completely to control values except for minor persistent elevations of HbCO. Difference spectra from parallel experiments at constant HbCO revealed absorption minima at 588-592 nm and 600-605 nm as a result of hyperbaric exposure. Spectral analysis of these components was consistent with partial dissociation of a cytochrome a3-CO complex and cytochrome a reoxidation with increasing dissolved O2 in hyperbaric conditions.     

Photosynthetic characteristics and enzymatic antioxidant capacity of leaves from wheat cultivars exposed to drought

Two durum (Triticum durum L.), Barakatli-95 and Garagylchyg-2; and two bread (Triticum aestivum L.) wheat cultivars, Azamatli-95 and Giymatli-2/17 with different sensitivities to drought were grown in the field on a wide area under normal irrigation and severe water deficit. Drought caused a more pronounced inhibition in photosynthetic parameters in the more sensitive cvs Garagylchyg-2 and Giymatli-2/17 compared with the tolerant cvs Barakatli-95 and Azamatli-95. Upon dehydration, a decline in total chlorophyll and relative water content was evident in all cultivars, especially in later periods of ontogenesis. Potential quantum yield of PS II (F(v)/F(m) ratio) in cv Azamatli-95 was maximal during stalk emergency stage at the beginning of drought. This parameter increased in cv Garagylchyg-2, while in tolerant cultivar Barakatli-95 significant changes were not observed. Contrary to other wheat genotypes in Giymatli-2/17 drought caused a decrease in PS II quantum yield. Drought-tolerant cultivars showed a significant increase in CAT activity as compared to control plants. In durum wheat cultivars maximal activity of CAT was observed at the milk ripeness and in bread wheat cultivars at the end of flowering. APX activity also increased in drought-treated leaves: in tolerant wheat genotypes maximal activity occurred at the end of flowering, in sensitive ones at the end of ear formation. GR activity increased in the tolerant cultivars under drought stress at all stages of ontogenesis. SOD activity significantly decreased in sensitive cultivars and remained at the control level or increased in resistant ones. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Isolation and characterization of variant wheat cultivars for ABA sensitivity

Genetic variants for abscisic acid (ABA) sensitivity are important for investigating the role of ABA sensitivity in conditioning plant response to environmental stress, and especially to those soil conditions that may elicit a root-mediated hormonal signal. This study was performed in order to isolate variation in ABA sensitivity among wheat (Triticum aestivum and T. durum) cultivars, as characterized by two plant responses: (i) shoot growth reduction in response to 5×10^?2mol m^?3 ABA (racemic) in the root medium of hydroponically grown plants, and (ii) changes in transpiration and gas exchange in a bioassay of detached leaves (leaflaminac) infused with 10^?4mol m^?3 ABA. Very significant (P≤0.01) and repeatable differences were found among 36 wheat cultivars and 19 landraces in the growth rate in ABA-containing nutrient solutions, expressed as a percentage of the growth rate in control nutrient solutions (ABA/control ratio). In duplicate experiments, the ABA/control ratio ranged between 60 and 83% for the least sensitive cultivars (V2151-3, Bethlehem, K1056 and Sunstar) and between 9 and 19% for the most sensitive cultivars (Sundor, Comet, Barkaec and V5). In the transpiration bioassay, performed with seven selected cultivars, it was found that the reductions in transpiration of ABA-infused leaves corresponded very well with the reductions in growth in response to ABA in the root media. Measurement of gas exchange in the detached leaves of two cultivars differing in ABA sensitivity (Bethlehem and Sundor) showed that variable ABA sensitivity was expressed very well in the stomatal conductance, carbon exchange rate (CER) and photosynthetic capacity (CER/C_i ratio) of the leaf. These results therefore allowed us to isolate wheat variants for ABA sensitivity and to conclude that, while ABA sensitivity is expressed in the growth of plants challenged by ABA in the root medium, the control of sensitivity resides, at least partly, in the leaf.     

Dehydrogenase conversion to oxidase and lipid peroxidation in brain after carbon monoxide poisoning.

The conversion of xanthine dehydrogenase to xanthine oxidase and lipid peroxidation were measured in brain from carbon monoxide- (CO) poisoned rats. Sulfhydryl-irreversible xanthine oxidase increased from a control level of 15% to a peak of 36% over the 90 min after CO poisoning, while the conjugated diene level doubled. Reversible xanthine oxidase was 3-6% of the total enzyme activity over this span of time but increased to 31% between 90 and 120 min after poisoning. Overall, reversible and irreversible xanthine oxidase represented 66% of total enzyme activity at 120 min after poisoning. Rats depleted of this enzyme by a tungsten diet and those treated with allopurinol before CO poisoning to inhibit enzyme activity exhibited no lipid peroxidation. Treatment immediately after poisoning with superoxide dismutase or deferoxamine inhibited lipid peroxidation but had no effect on irreversible oxidase formation. Biochemical changes only occurred after removal from CO, and changes could be delayed for hours by continuous exposure to 1,000 ppm CO. These results are consistent with the view that CO-mediated brain injury is a type of postischemic reperfusion phenomenon and indicate that xanthine oxidase-derived reactive oxygen species are responsible for lipid peroxidation.     

Luminescent indicators in various parts of wheat leaves in ontogenesis

A comparative study of slow fluorescence induction, fluorescence spectra, thermoluminescence, photosynthetic activity and chlorophyll content in ontogenesis of wheat seedlings (Triticum aestivum L, cv. Yubileinayd) grown in the laboratory conditions was carried out. It was shown that (FM-FT)/FT values of slow fluorescence induction increased with the age of leaf part, reached a maximum (for 2-week-old seedlings), and then decreased. Changes in (FM-FT)/FT positively correlated with the changes in photosynthetic activity per chlorophyll unit (delta O2/(delta t.chlorophyll)); the coefficient of correlation r = 0.84, p > 0.999. The F685/F730 ratio of the intensities of fluorescence spectrum decreased with the increase in chlorophyll content. The relative light sum SA/S(tot) of band A of thermoluminescence changed in the same direction as delta O2/(delta t-chlorophyll), the relative light sum (SC/S(tot) of band C of thermoluminescence decreased during leaf maturation. The regularities revealed in the experiments are discussed in terms of changes in the structural and functional organization of the photosynthetic apparatus known from the literature.     

Gibberellins in the embryonic axes of tall and dwarf beans and their changes with initial growth

Ten gibberellin-like activities were detected in the dry embryonicaxes of tall (cv. Kentucky Wonder) and dwarf (cv. Masterpiece)beans (Phaseolus vulgaris L.) using the lettuce hypocotyl assayof thin-layer chromatograms; 2 in the non-acidic ethyl acetatefraction (NEI, NEII), 3 in the acidic ethyl acetate fraction(AEI, AEII, AEIII), 2 in the non-acidic n-butanol fraction (NBI,NBII) and 3 in the acidic n-butanol fraction (ABI, ABII, ABIII).There was no qualitative difference in these gibberellins betweenthe tall and dwarf axes, but all, particularly AEIII, NBII andABIII as the main gibberellins in the axes, were contained muchmore abundantly in the tall axes. In both axes the gibberellinactivities of most fractions decreased during germination.Theamounts of some gibberellins in tall axes without cotyledonswere greater than those in axes with cotyledons at 48–72hr of germination. Neither AMO-1618 nor CCC caused significantreduction in the levels of the gibberellins. Axis growth inthe early germinating period depended on the gibberellins storedin the axis, itself. (Received November 26, 1974; )