RELATIONSHIP BETWEEN PHOTOSYNTHETIC OXYGEN CYCLING AND CARBON ASSIMILATION IN SYNECHOCOCCUS WH7803 (CYANOPHYTA)1

Mass spectrometric analysis of oxygen uptake and evolution in the light by marine Synechococcus WH7803 indicated that the respiration rate was near zero at low irradiance levels but increased significantly at high irradiances. The light intensity (I_r) at which oxygen uptake began to increase with increasing light intensity depended on the growth irradiance of the culture. In each case, I_r coincided with the minimum light intensity for saturation of carbon assimilation (I_k). At irradiances >I_r, net oxygen evolution rates paralleled carbon assimilation rates. Oxygen uptake at high light intensities was inhibited by DCMU, indicating that oxygen uptake was due to Mehler reaction activity. The onset of Mehler activity at I_k supports the idea that oxygen becomes an alternative sink for electrons from photosystem I when NADPH turnover is limited by the capacity of the dark reactions to utilize reductant.     

The effect of photoperiod length on respiration in leaves of Saxifraga cernua L., an arctic herb

Abstract Rates of oxygen uptake were measured in leaves of Saxifraga cernua which had been exposed to an 18-h photoperiod. These rates were compared to those in plants which had been exposed to continuous light. Rates of total dark respiration and alternative pathway respiration measured at the end of the photoperiod gradually decreased over the initial 3 d of exposure to an 18-h photoperiod. Thereafter, respiratory rates were constant. Rates of total dark respiration and alternative pathway respiration decreased during the 6h dark period. Rates of normal and alternative pathway respiration are equally affected during the dark period. The respiratory rates had reached a new minimum level 3 d after the initiation of a dark period. These results suggest that respiration rates in arctic plants are high because of the long photoperiod in the arctic. The kinetics of photoperiod induced changes in respiration are slow enough to suggest the involvement of the biological clock in setting respiration rates. Indeed, total dark respiration and alternative pathway respiration show a definite circadian rhythm. Free-running experiments show that normal respiration changes much less (has a smaller amplitude of variation) than alternative pathway respiration and that alternative pathway respiration accounts for most of the rhythmicity of respiration.     

The Alternative Respiration Pathway in Leaves ofRhodiola roseaand Ajuga reptans: Presumable Physiological Role

The effect of growth conditions and plant age on the relationships between respiratory pathways was investigated in Rhodiola roseaand Ajuga reptans.The alternative pathway (AP) contributed 0–50% to the leaf respiration; however, this pathway was absent from the overwintered leaves of A. reptans.In both plant species, AP contributed 15–20% to the respiration of mature leaves, and in the young rapidly expanding leaves the contribution was twice higher. The highest AP contribution (40–50%) was found in the leaves of A. reptansplants grown in an experimental plot in full light. As compared to the plot-grown plants, A. reptansplants grown in their natural habitats were characterized by a lower AP contribution to the respiration of leaves; they contained two times less nonstructural carbohydrates and accumulated less biomass. We conclude that a high AP contribution to the respiration of leaves correlates with their rapid growth and that a high supply of respiratory substrates is one of prerequisite for the AP activation.     

Changes of the CN-resistant Respiration in Callus Cultures of Nicotiana tabacurn during the Period of Differentiation

The callus cultures obtained from unpollinated young ovaries of willow leaf tobacco were transplanted separately on subculture medium (M-l) and differentiation medium (M-2). They were called M-1 callus and M-2 callus respectively. Only meristematic cells and parenchymas could be observed in M-1 callus. The M-2 callus, however, was able to differentiation into vascular systems, embryoids and bud primordia. The respiration of M-1 callus exhibited CN-insensitive. The relative contributions of alternative pathway and eytochrome pathway to the total respiration were 29–38% and 44–51% respectively during the culture period of 25 days. It was obvious that the bulk of the respiratory electron flux was mediated by the eytochrome pathway. The greater part of the respiration in M-2 callus was insensitive to cyanide. The relative contributions of alternative pathway and cytochrome pathway to the total respiration were 41–47% and 29–32% respectively. These results suggested that the increase in the participation of the alternative pathway in total respiration was probablely related to the differentiation of the callus culture.     

Studies on the CN-resistant Respiration in Callus of Nicotiana rustica,Gansu Yellow Flower

In attempting to examine whether CN-resistant respiratory pathway is present in callus culture, we used tobacco callus cultures grown on different media. The M-1 medium contained tbe mineral and organic elements of MS medium and was supple,nented with 6-BA (0.5 mg/l) and 2,4-D (2 mg/l), and M-2 medium with 6-BA (2mg/l) and IAi (1 mg/l). No differentiation was observed in both of them. The respiration of M-1 callus was partly resistant to CN, and was markedly inhlbited by m-CLAM in the presence or absence of CN. Experiments of m-CLAM titration showed that the averages of relative contribution of alternative and cytochrome pathway in M-1 callus were 31% awl 46%of the total respiration respectively during the euliure period of 25 days. A same experiment was made on the M-2 callus. It was found that the pereeutages of relative contributions of the two electron transport pathways to the total respiration were approximately the same as those of the M-1 callus, although the respiratory rate was higher in M-2 callus. The above results showed that the bulk of respiratory electron flux was mediated by the eytoehrome pathway, although the alternative pathway was operative in callus of tobacco. The change of exogenous hormones added in the medium could not produee significant effects on the degree of relative contribution of two electron transport pathways under non-differentiation conditions.     

甘肃黄花烟草愈伤组织抗氰呼吸的研究

根据呼吸抑制剂试验和氧肟酸滴定法测定结果表明,甘肃黄花烟草愈伤组织呼吸中有明显的抗氰交替途径运行,平均占总呼吸的31%;但仍以细胞色素途径为主,平均占总呼吸的46%;还有23%不受 KCN 加 m-CLAM 抑制的未知剩余呼吸。改变培养基的激素成分和浓度,在不引起愈伤组织发生明显分化条件下,愈伤组织的生长和呼吸速率虽有不同,但抗氰交替途径和细胞色素途径对总呼吸的相对贡献程度和二者的变化趋势基本一致。     

Respiration and respiratory electron transport activity in marine phytoplankton: growth rate dependence and light enhancement

Respiratory electron transport system (ETS) activity and actualoxygen consumption rates were measured in batch cultures offour species of marine phytoplankton, in two different growthstages: exponential or log-phase (L) and stationary phase (S).The L cultures showed higher ETS activity and respiration ratesthan the S cultures of the same species. Among the L cultures,the higher respiration and ETS activity corresponded to thosehaving higher growth rates. The carbon-specific ETS activityand the carbon-specific respiration (h^–1) showed a cleardependence on growth rates. Samples subjected to short (10 min)exposures to high, oversaturating irradiances (1000 µEm^–2 s^–1) displayed enhanced ETS activity and respiration.The experiments show that, under the light regime at which thealgal cells grow, the respiratory ETS activity and actual oxygenconsumption in phytoplankton are strongly related to growthrate and that short, high irradiance exposures enhance boththe respiratory enzyme activity and their actual oxygen consumption.     

Leaf respiration in Piper species native to a Mexican rainforest

We measured leaf respiration with a Clark-type oxygen-electrode in 6 species of the genus Piper (Piperaceae) growing naturally in wet evergreen rainforest, in microsites characterized by a broad range of light availabilities. Species normally found in large gaps and clearings ( Piper auritum and P. umbellatum ) had approximately twice the dark respiration per unit of leaf area or dry mass as species found predominantly in shaded understory sites ( P. aequale, P. lapathifolium and P. amalago ). within a species, dark respiration was lower in the individuals growing in low-light sites than in the individuals growing in high-light sites. Over all species, leaf respiration was positively correlated with the average daily photosynthetically active photon flux density (PFD) at each site, and negatively correlated with mean leaf longevity. Respiration was insensitive to leaf age in a shade species. ( P. lapathifolium ) and in a generalist ( P. hispidum ) but decreased with increasing leaf age in a gap specialist ( P. aurtium ).
In experiments on greenhouse-grown plants, we titrated respiration with potassium cyanide (KCN) and/or salicylhydroxamic acid (SHAM) to determine the cytochrome and alternative pathway components to respiration in 4 Piper species. All 4 species, representing gap, generalist and shade species, exhibited alternative pathway respiration. Engagement of the cytochrome pathway (ϱ_cyt) varied from 0.69 in P. auritum to 1.04 in P. lapathifolium and engagement of the alternative pathway (ϱ_alt varied from 0.41 to 1.02. Although the shade species had lower respiration rates than the gap species, the capacities for cytochrome and alternative pathway respiration made up similar or greater fractions of total respiration in shade species.     

Cytochrome and alternative pathway respiration in white spruce (Picea glauca) roots. Effects of growth and measurement temperature

Interactions between growth temperature and measurement temperature were examined for their effects on white spruce [ Picea glauca (Moench) Voss] root respiration. Total dark respiration rates increased with measurement temperature and were unaffected by growth temperature. Partitioning of respiratory electron flow between the cytochrome and alternative pathways was also unaffected by growth temperature. The proportion of respiration mediated by the alternative pathway was constant at measurement temperatures between 4°C and 18°C, but was increased at higher temperatures. Changes in alternative pathway activity were paralleled by changes in capacity, and the alternative pathway was almost fully engaged at all temperatures. Roots grown at low temperature displayed higher carbohydrate levels than roots grown at higher temperatures, but respiration rate was unaffected. Spruce root respiration did not appear to acclimate to growth temperature, and the alternative pathway was not preferentially engaged at low temperature.     

Assessing the relationship between respiratory acclimation to the cold and photosystem II redox poise in Arabidopsis thaliana

We examined the effect of manipulating photosystem II (PSII) redox poise on respiratory flux in leaves of Arabidopsis thaliana. Measurements were made on wild-type (WT) plants and npq4 mutant plants deficient in non-photochemical quenching (NPQ). Two experiments were carried out. In the first experiment, WT and mutant warm-grown plants were exposed to three different irradiance regimes [75, 150 and 300 micromol photosynthetically active radiation (PAR)], and leaf dark respiration was measured in conjunction with PSII redox poise. In the second experiment, WT and mutant warm-grown plants were shifted to 5 degrees C and 75, 150 or 300 micromol PAR, and dark respiration was measured alongside PSII redox poise in cold-treated and cold-developed leaves. Despite significant differences in PSII redox poise between genotypes and irradiance treatments, neither genotype nor growth irradiance had any effect upon the rate of respiration in warm-grown, cold-treated or cold-developed leaves. We conclude that changes in PSII redox poise, at least within the range experienced here, have no direct impacts on rates of leaf dark respiration, and that the respiratory cold acclimation response is unrelated to changes in chloroplast redox poise.     

Energy metabolism of Plantago lanceolata, as affected by change in root temperature

The long and short term metabolic effects of a shift in root temperature was investigated in Plantago lanceolata L. with special reference to the role of the cyanide resistant alternative pathway in root respiration. After a 10-day period of growth at a 13°C root temperature, a decrease in root as well as shoot growth was observed, compared to control plants grown continuously at 21°C. Apart from an increase in shoot soluble and insoluble sugar level, no changes in metabolism were found, neither in root respiration, shoot photosynthesis, nor in root sugar and plant protein level.
Decreasing the root temperature from 21 to 13°C gave several clear short term changes in metabolism. Within one hour a decrease in cytochrome chain activity of the roots was found together with an increase in activity of the alternative chain. After 24 h a recovery to the initial level of both chains was observed. An increase in root temperature from 13 to 21°C gave an immediate increase in activity of both respiratory chains that was still present 24 h after the switch.
It is concluded that the activity of the alternative respiratory pathway in the root is strongly affected by a sudden temperature change in the root environment. This pathway acts in a way which is described by 'the energy overflow model'. The presence of the alternative electron transport pathway should be taken into account in determinations of the respiratory Q₁₀. Moreover, the length of time between the temperature change and respiration measurements is an important factor.     

Effects of light on respiration and oxygen isotope fractionation in soybean cotyledons

Light effects on electron flow through the cyanide-resistant respiratory pathway, oxygen isotope fractionation and total respiration were studied in soybean (Glycine max L.) cotyledons. During the first 12 h of illumination there was an increase in both electron partitioning through the alternative pathway and oxygen isotope fractionation by the alternative oxidase. The latter probably indicates a change in the properties of the alternative oxidase. There was no engagement of the alternative oxidase in darkness and its fractionation was 27‰. In green cotyledons 60% of the respiration flux was through the alternative pathway and the alternative oxidase fractionation was 32‰. Exposing previously illuminated tissue to continuous darkness induced a decrease in the electron partitioning through the alternative pathway. However, this decrease was not directly linked with the low cellular sugar concentration resulting from the lack of light because 5 min of light every 12 h was sufficient to keep the alternative pathway engaged to the same extent as plants grown under control conditions.     

Metabolic regulation of leaf respiration and alternative pathway activity in response to phosphate supply

In this study the question whether the alternative respiratory pathway acts as an electron bypass for the cytochrome pathway under conditions of growth on limited phosphorus in leaves of bean (Phaseolus vulgaris L.), tobacco (Nicotiana tabacum L.) and Gliricidia sepium Walp was investigated. The oxygen isotope fractionation technique was used to assess the in vivo activities of the cytochrome and alternative respiratory pathways in the absence of added inhibitors. The response of respiration to low phosphorus supply varied among species. Growth at low phosphorus reduced cytochrome pathway activity in bean and tobacco. Alternative pathway activity increased only in bean leaves in response to low phosphorus and not in tobacco. In the case of G. sepium, cytochrome pathway activity remained unchanged whereas the alternative pathway activity increased with low nutritional phosphorus. At low phosphorus, alternative oxidase protein levels increased in the leaves of bean and G. sepium but not in tobacco, suggesting a dependence of alternative pathway activity on protein level. Alternative pathway activity was also not correlated with soluble carbohydrate concentration in bean or tobacco at any phosphorus level. These results show that the alternative pathway does not always act as an electron bypass in response to the downstream restriction of the cytochrome pathway imposed by low phosphorus supply. These results suggest that factors in addition to cellular carbohydrate level and adenylate control can act to regulate alternative pathway activity.     

REGULATION OF ALTERNATIVE PATHWAY RESPIRATION IN CHLAMYDOMONAS REINHARDTH (CHLOROPHYCEAE)1

The inhibitor propyl gallate was used to estimate partitioning of respiratory electron flow between the cytochrome amd alternative pathways in Chlamydomonas reinhardtii Dangeard. Nutrient limitation (nitrogen or phosphorus resulted in a large increase in alternative pathway capacity relative to cytochrome pathway activity, without regulating in engagement of the alternative pathway. High rates of respiration, which could be induced in phosphate-starved cells by a combination of phosphate addition and uncoupler, resulted in alternative pathway activity. Osmotic stress resulted in decreased electron flow through the cytochrome pathway and increased flow through the alternative pathway, while high temperature also resulted in alternative pathway engagement. Incubation with exogenous carbon sources could increase the rate of respiratory O₂ consumption; the increase was mediated entirely by the alternative pathway. We suggest that the alternative pathway functions in these cells both to maintain respiration during environmentally induced stress and as on energy overflow.     

Contribution of current photosynthates to root respiration of non-nodulated Medicago sativa: effects of light and nitrogen supply

Abstract: The effects of light (PFD) and nitrogen (N) supply on root respiration of new C (currently assimilated carbon, R _new) and old C ( R _old) were analysed in non-nodulated Medicago sativa . Plants were pre-treated with high/low PFD and high/low N supply with a regular 16/8 h light/dark cycle. Five to eight weeks after planting current photosynthates were labelled with ¹³C and their contribution to root respiration was continuously measured during a 24 h day/night cycle. PFD conditions during labelling were either those of the pre-treatments (control, 25 or 6 mol m^-2 d^-1) or, for high PFD plants, 6 mol m^-2 d^-1 by shortening the photoperiod or reducing irradiance. The fraction of new C in the respiratory CO₂ increased during the light period, but remained constant in the dark period. In control plants, R _new contributed 40 % to the daily root respiration in high PFD/high N conditions. Continuously low PFD increased (50 %) and low N decreased (26 %) the contribution of R _new. Exposing plants from high PFD pre-treatments to a short photoperiod or to low PFD stimulated R _old, indicating mobilisation of reserve C. This stimulation was more pronounced in plants with high N supply than in those with low N supply. Comparison with other legumes suggested that R _new in root respiration was mainly defined by the ratio between the assimilatory capacity of the shoots and the maintenance costs of roots with a short-term capacity of buffering respiratory demand by mobilisation of reserves in situations of fluctuating PFD.     

Light induction of alternative pathway capacity in leaf slices of Belgium endive

The effect of light on the development of the capacity for alternative pathway respiration was investigated in leaf slices of Belgium endive (Cichorum intybus L. cv. deliva). Dark-grown plants possessed little capacity for the cyanide-insensitive alternative pathway. In contrast, plants grown in continuous light had significant alternative pathway capacity. Light-grown plants also had substantially higher concentrations of ethanol-soluble carbohydrates in their leaves than plants grown in complete darkness. Despite these differences in leaf carbohydrate status and alternative pathway capacity of light- and dark-grown leaf tissue, no differences were found in the activity of the alternative pathway, which was negligible in both treatments. Dark-grown plants were adenylate restricted, as indicated by the increase in cytochrome pathway activity following uncoupling. Adenylates did not limit respiration in light-grown leaf tissue. Plants that had been grown for 8d in complete darkness were also transferred to continuous light. Respiration of dark controls steadily declined over 11d following the transfer of plants to the light, due primarily to a decrease in cytochrome pathway activity. No such decline was observed in the plants transferred to continuous light. Transfer to continuous light led to significant increases in alternative pathway capacity relative to the dark controls. Alternative pathway activity remained negligible in both the dark controls and in plants transferred to continuous light. The results of this study suggest then that light per se may be responsible for the induction of alternative pathway capacity in Belgium endive.     

Growth, photosynthesis and respiration in Plantago coronopus as affected by salinity

Plantago coronopus was grown in a non-saline culture solution and in a culture solution containing 50 m M NaCl. The rates of dry matter accumulation in both roots and shoots were not affected by 50 m M NaCl. Photosynthesis, expressed per shoot, was also the same in both environments. Neither the rate of shoot respiration nor that of root respiration was affected by salinity. In both environments the alternative respiratory pathway contributed to the same extent in root respiration. The activity of the alternative pathway decreased with increasing age. Since the respiratory activities were the same in plants grown under both saline and non-saline conditions and since the alternative respiratory pathway was also equally active in roots under both environmental conditions, it is concluded that respiratory costs involved in growth in 50 m M NaCl are negligible in terms of the plant's total energy costings.     

PHYSIOLOGICAL CHARACTERISTICS OF SPIRULINA PLATENSIS (CYANOBACTERIA) CULTURED AT ULTRAHIGH CELL DENSITIES1

Photosynthetic activity and growth physiology of Spirulina platensis (Nordstedt) Geitler cultures maintained at ultrahigh cell densities (i.e. above 100 mg chlorophyll-L^?1) in a newly designed photobioreactor were investigated. Nitrogen (NaNO₃) in standard Zarouk medium was characterized as a major nutrient-limiting factor in such cultures. The effect of ultrahigh cell density on photoinhibition of photosynthesis, as reflected by chlorophyll fluorescence and photosynthetic oxygen evolution, was studied: elevating the population density may arrest photoinhibition induced by high photon flux density, as well as low temperature. The relationship between incident irradiance and oxygen production rate was linear in situ for cultures at the optimal cell density, indicating that light limitation rather than light saturation or photoinhibition is the dominant condition outdoors in cultures of ultrahigh cell densities. In contrast with other reports, the extent of biomass loss at night due mainly to dark respiration was found to be relatively small when cell density was optimal, exerting only a minor effect on overall net productivity. Measurements of oxygen consumption at night revealed low rates of respiration, which may be explained by the low value of the volumetric mass transfer coefficient (K_La) of oxygen. Hence, reduced oxygen tension may play a role in preventing full expression of the respiratory potential in ultrahigh cell density cultures in which photoadaptive strategy may explain cell composition. Ultrahigh cell densities optimized with respect to the intensity of the light source, the length of the light path, and the extent of stirring represent the key for obtaining high output rates of cell mass and some natural products.     

Characterization of the mitochondrial respiratory pathways in Candida albicans

Candida albicans is an opportunistic oral pathogen. The flexibility of this microorganism in response to environmental changes includes the expression of a cyanide-resistant alternative respiratory pathway. In the present study, we characterized both conventional and alternative respiratory pathways and determined their ADP/O ratios, inhibitor sensitivity profiles and the impact of the utilization of either pathway on susceptibility to commonly used antimycotics. Oxygen consumption by isolated mitochondria using NADH or malate/pyruvate as respiratory substrates indicated that C. albicans cells express both cytoplasmic and matrix NADH-ubiquinone oxidoreductase activities. The ADP/O ratio was higher for malate/pyruvate (2.2±0.1), which generate NADH in the matrix, than for externally added NADH (1.4±0.2). In addition, malate/pyruvate respiration was rotenone-sensitive, and an enzyme activity assay further confirmed that C. albicans cells express Complex I activity. Cells grown in the presence of antimycin A expressed the cyanide-insensitive respiratory pathway. Determination of the respiratory control ratio (RCR) and ADP/O ratios of mitochondria from these cells indicated that electron transport from ubiquinone to oxygen via the alternative respiratory pathway was not coupled to ATP production; however, an ADP/O ratio of 0.8 was found for substrates that donate electrons at Complex I. Comparison of antifungal susceptibility of C. albicans cells respiring via the conventional or alternative respiratory pathways showed that respiration via the alternative pathway does not reduce the susceptibility of cells to a series of clinically employed antimycotics (using Fungitest®), or to the naturally occurring human salivary antifungal peptide, histatin 5.     

Does growth irradiance affect temperature dependence and thermal acclimation of leaf respiration? Insights from a Mediterranean tree with long‐lived leaves

Understanding the response of leaf respiration (R) to changes in irradiance and temperature is a prerequisite for predicting the impacts of climate change on plant function and future atmospheric CO2 concentrations. Little is known, however, about the interactive effects of irradiance and temperature on leaf R. We investigated whether growth irradiance affects the temperature response of leaf R in darkness (Rdark) and in light (Rlight) in seedlings of a broad-leaved evergreen species, Quercus ilex. Two hypotheses concerning Rdark were tested: (1) the Q10 (i.e. the proportional increase in R per 10 degrees C rise in temperature) of leaf Rdark is lower in shaded plants than in high-light-grown plants, and (2) shade-grown plants exhibit a lower degree of thermal acclimation of Rdark than plants exposed to higher growth irradiance. We also assessed whether light inhibition of Rlight differs between leaves exposed to contrasting temperatures and growth irradiances, and whether the degree of thermal acclimation of Rlight is dependent on growth irradiance. We showed that while growth irradiance did impact on photosynthesis, it had no effect on the Q10 of leaf Rdark. Growth irradiance had little impact on thermal acclimation when fully expanded, pre-existing leaves were exposed to contrasting temperatures for several weeks. When Rlight was measured at a common irradiance, Rlight/Rdark ratios were higher in shaded plants due to homeostasis of Rlight between growth irradiance treatments and to the lower Rdark in shaded leaves. We also showed that Rlight does not acclimate to the same degree as Rdark, and that Rlight/Rdark decreases with increasing measuring and growth temperatures, irrespective of the growth irradiance. Collectively, we raised the possibility that predictive carbon cycle models can assume that growth irradiance and photosynthesis do not affect the temperature sensitivity of leaf Rdark of long-lived evergreen leaves, thus simplifying incorporation of leaf R into such models.