Genetic differentiation in Plantago major: Ca2+- and Mg2+-stimulated ATPases from roots and their role in phenotypic adaptation

The Mg²⁺- and Ca²⁺-stimulated ATPase activities of the microsomal fractions of the roots of four inbred lines of Plantago major L. were followed at two levels of mineral nutrition. In addition the response of a transfer of plants from one condition to the other was studied. Kinetic properties of the ATPases (K_m and V_max) were calculated and used to differentiate between genetic differences among the inbred lines and the plasticity within each inbred line. The V_max values of the ATPase activity differed significantly between the lines and were directly related to seed number per capsule (low V_max→ 11 seeds per capsule, high V_max→ 33 seeds per capsule). In addition, the V_max values of the ATPase acitivty may be related to ecological strategy. Plasticity of enzyme activity is expressed in differences in the V_max values of the ATPase activity, as a response to nutritional level or changes of the strength of the nutrient solution. Differences in this plasticity in the four selected lines and in rapidity of response to a change in mineral nutrition were directly related to the ecological strategy. These results are discussed in relation to the strategy of the genotypes for survival in the field. The presence of plasticity in line 4 (ssp. pleiospema ) makes this genotype behave like an annual plant, following a ruderal strategy. The absence of plasticity in line 1 (ssp. major ) fits a more competitive strategy.     

The effects of exogenously applied plant growth substances on the physiological plasticity in Plantago major ssp. pleiosperma: Responses of growth, shoot to root ratio and respiration

Growth rates, shoot to root ratios and root respiration were studied in plants of Plantago major L. ssp. pleiosperma (Pilger) at two regimes of mineral nutrition. The responses of plants transferred from one condition to the other were compared with similarly transferred plants supplied with a plant growth substance and also with plants permanently grown at the same nutritional level.
The effect of an addition of benzyladenine (BA) depended on the concentration. Changes in the relative growth rates, shoot to root ratios and root respiration as a response to a lowered mineral supply were strongly retarded by 10−⁸ M BA. These effects of BA were very obvious in the first period of 7 days after the transfer of the plants. During the second period of 7 days the hormonal effects disappeared due to limitation of mineral nutrients. Daily spray with abscisic acid or with indoleacetic acid did not significantly affect the measured characteristics. The results from the experiments with BA addition are discussed in relation to a possible regulatory role of cytokinins in physiological plasticity upon mineral nutrition.     

The effect of aluminum exposure on root respiration in an aluminum-sensitive and an aluminum-tolerant cultivar of Triticum aestivum

The effects of aluminum (Al) exposure on intact root respiration of an Al-sensitive (Scout-66) and an Al-tolerant (Atlas-66) cultivar of Triticum aestivum were investigated. Exposure to a wide range of Al concentrations (0–900 μmol) for 4 days stimulated respiration along the energy-conserving cytochrome pathway in both cultivars and increased the ratio of maintenance respiration to growth respiration. The maximum rate of Scout-66 root respiration occurred after exposure to 100–200 μmol Al. Atlas-66 root respiration peaked after exposure to 300–400 μmol Al. Similarly, calculations of theoretical adenosine 5'-triphosphate (ATP) production indicated that maximum daily rate of ATP production also increased upon exposure to Al in both cultivars, with peak ATP production occurring during peak respiration. Maximum root respiration rates in both cultivars were related to the Al concentration that inhibited root growth. Temporal exposure to 200 μmol Al quickly stopped root growth and stimulated cytochrome pathway respiration in Scout-66 after 4 days. Atlas-66 root growth and respiration were unaffected by 200 μmol Al. These results suggest that Al exposure imposes a demand for additional metabolic energy. A model describing Al effects on root respiration is presented     

Growth Responses of Plantago major L. ssp. pleiosperma (Pilger) to Changes in Mineral Supply : Evidence for Regulation by Cytokinins

Plants of an inbred line of Plantago major ssp. pleiosperma were subjected to an alteration in mineral supply. Observed responses of growth rate and shoot to root ratio are thought to be induced by changes in endogenous cytokinin concentration and not by mineral concentration in plant tissue.     

Growth and competitive ability of a highly plastic and a marginally plastic genotype of Plantago major in a fluctuating environment

The hypothesis was tested that a physiologically highly plastic genotype is better adapted to a fluctuating environment than a marginally plastic genotype. For that purpose, two inbred lines of Plantago major L., which differ in their degree of physiological plasticity, were grown in tubes with quartz sand, either singly or in combination. Four treatments were applied with a different frequency of fluctuations in nutrient level. When grown singly, the relative growth rate of both genotypes reacted in the same way to the different treatments. The genotypes showed similar reactions when grown in monoculture with two plants per tube. In mixed culture (also two plants per tube) the response was different. With increasing frequency of fluctuations in nutrient level, the inbred line with the high plasticity grew faster at the expense of the marginally plastic line, whose growth was reduced.     

Root Respiration and Growth in Plantago major as Affected by Vesicular-Arbuscular Mycorrhizal Infection

Effects of vesicular-arbuscular mycorrhizal (VAM) infection and P on root respiration and dry matter allocation were studied in Plantago major L. ssp. pleiosperma (Pilger). By applying P, the relative growth rate of non-VAM controls and plants colonized by Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe was increased to a similar extent (55-67%). However, leaf area ratio was increased more and net assimilation rate per unit leaf area was increased less by VAM infection than by P addition. The lower net assimilation rate could be related to a 20 to 30% higher root respiration rate per unit leaf area of VAM plants. Root respiration per unit dry matter and specific net uptake rates of N and P were increased more by VAM infection than by P addition. Neither the contribution of the alternative respiratory path nor the relative growth rate could account for the differences in root respiration rate between VAM and non-VAM plants. It was estimated that increased fungal respiration (87%) and ion uptake rate (13%) contributed to the higher respiratory activity of VAM roots of P. major.     

铵态氮和硝态氮营养与大豆幼苗的抗氰呼吸作用

在植物体内,NO云还原成NHI是一个耗能很多的生化过程,每还原一个NO。大约要消耗15个ATP分子（Salsac等1987）。植物直接吸收和利用NHi＋,可以减少能量消耗,所节约的能量可用于植物的生长。因此,从理论上讲,供NHI的植株要比供NOt的植株能够获得更高的生物产量。然而,对于大多数植物,供NOS的植株常具有更大的生长量和产量。对于这种现象,过去人们一直在矿物质和有机物积累的差异（Robin和Salsac1985）、根际的酸化程度（Ruftv等1983,Tolley－Henry和Rapen1986）、NHt有害浓度的积累（Haynes和Goh1978）、对光合作用的…     

Efficiency of Root Respiration in Relation to Growth Rate, Morphology and Soil Composition

Root growth respiration and root maintenance respiration rate of the following species were determined: Hypochaeris radicata L. ssp. radicata L., H. radicata ssp. ericetorum Van Soest, Plantago lanceolata L., P. major L. ssp. major, P. major ssp. pleiosperma Pilgcr, P. maritime L., Senecio viscosus L., S. vulgaris L. and Urtica dioica L. A high root growth respiration (i.e. the amount of oxygen consumed for synthesis of a given weight of root material) implied a high maintenance respiration rate (i.e. the amount of oxygen consumed per unit of time and dry weight, but not connected with growth). High values of both components reflect a low efficiency of root respiratory processes. The efficiency of root respiration, as determined by the values for root growth respiration and root maintenance respiration rate could not be demonstrated to be of advantage in adaptation to soil conditions, as e.g. nitrogen content, moisture content and pH. It is concluded that (he degree of ‘wasteful utilization of sugars’ in roots, i.e. such consumption of sugars as cannot be related to structural growth, storage of carbohydrates or maintenance processes, depends on imbalance of transport of sugars from the shoot to the roots with utilization of sugars for synthesis of root material. The results are discussed in relation to Brouwer's explanation for the equilibrium between the growth of shoots and of roots. Root growth rate in the present species appears limited by a factor produced in the shoot under light conditions, and which factor is distinct from carbohydrates. The evidence presented shows that relatively inefficient root respiration does not imply a low growth rate. In regulation of plant growth the growth rate itself and also the shoot to-root ratio may be more important than the regulation of the efficiency of energy metabolism.     

Short-term effects of two aphid species on plant growth and root respiration of three leguminous species

The short-term effects of cowpea aphids ( Aphis craccivora Koch) and pea aphids ( Acyrthosiphon pisum Harris), both Homoptera: Aphididae, on plant growth and respiration of excised, intact roots of cowpea [ Vigna unguiculata (L.) Walp. cv. Caloona], broadbean ( Vicia faba L. cv. Aquadulce) and garden pea ( Pisum sativum L. cv. Victory Freezer) seedlings were investigated, but not all plant-aphid combinations were used. Plant and root mean relative growth rates were significantly reduced within 10 days in the infested plants. Rates of total root respiration were was also significantly reduced in all infested plants within 10 days, presumably because of the reduced availability of translocate to the roots. The contribution of the cytochrome pathway to root respiration was significantly greater in control than in infested plants. The activity and engagement of the alternative respiratory pathway was also greater in control plants, and was absent in infested plants after 10 days infestation in all cases but one. These data indicate that the roots of aphid-infested plants were more efficient, in terms of energy conversion, than their respective controls.     

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.     

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.     

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.     

The regulation of respiration in cell suspensions of Petunia hybrida, studied by inhibiting mitochondrial protein synthesis with chloramphenicol

When Petunia hybrida L. cv. Rosy Morn Fertile suspension cells were inoculated in fresh medium with chloramphenicol (CAP), the activity of cytochrome C oxidase (EC 1. 9. 3. 1), and the respiration via the cytochrome pathway of isolated mitochondria decreased, while in untreated cells these parameters more than doubled in 2–3 days. However, the in vivo respiratory activity of the cytochrome pathway of CAP-treated cells showed a similar course in time as that of untreated cells, even in the presence of an uncoupler, a large rise during the first 2–3 days followed by a decline. This leads to the conclusion that the respiration via the cytochrome pathway, even when measured in the presence of an uncoupler, is not the capacity of this pathway. Furthermore, the results suggest that, although new-synthesis of proteins occurs directly after in-oculation, a large overcapacity must be present of cytochrome pathway elements (at least of those that are mitochondrial encoded). CAP had little effect on the uninhibited respiration and the cyanide-resistant, alternative pathway of the Petunia cells. However, the engagement of the alternative pathway (in the presence or absence of uncoupler) was increased in CAP-treated cells, especially after day 3 of the batch cycle, possibly as an effect of higher sugar degradation in combination with substrate phosphorylation to compensate the loss of ATP-synthesizing ability of the cytochrome pathway. It will be discussed that in general one should be careful using the term 'capacity' for the respiratory pathways.     

Respiration during seed maturation

The contribution of cytochrome and alternative pathways to respiration during soybean [ Glycine max (L.) Merr. cv. Chippewa 64] seed formation and maturation was measured by oxygen consumption of embryonic axis and cotyledon tissues and of mitochondria isolated from immature seeds. Respiration rates (dry weight basis) declined duing the last month of seed maturation. Cyanide sensitive respiration (cytochrome pathway) accounted for 80 to 90% of total oxygen consumption throughout seed formation and maturation. The proportion of the total respiration resistant to 1 m M cyanide and inhibited by 1 m M salicylhydroxamic acid (alternative pathway) did not exceed 6%. A residual oxygen consumption, accounting for 5 to 15% of total respiration, persisted in the presence of both inhibitors. Likewise, virtually no alternative respiration was found in mitochondria prepared from immature seeds. The alternative respiratory pathway seems absent during soybean seed formation and maturation regardless of whether grown in the greenhouse or field.     

Maintenance of growth rate at low temperature in rice and wheat cultivars with a high degree of respiratory homeostasis is associated with a high efficiency of respiratory ATP production

Some plants have the ability to maintain similar respiratory rates (measured at the growth temperature) when grown at different temperatures. This phenomenon is referred to as respiratory homeostasis. Using wheat and rice cultivars with different degrees of respiratory homeostasis (H), we previously demonstrated that high-H cultivars maintained shoot and root growth at low temperature [Kurimoto et al. (2004) Plant Cell Environ., 27: 853]. Here, we assess the relationship between respiratory homeostasis and the efficiency of respiratory ATP production, by measuring the levels of alternative oxidase (AOX) and uncoupling protein (UCP), which have the potential to decrease respiratory ATP production per unit of oxygen consumed. We also measured SHAM- and CN-resistant respiration of intact roots, and the capacity of the cytochrome pathway (CP) and AOX in isolated mitochondria. Irrespective of H, SHAM-resistant respiration of intact roots and CP capacity of isolated root mitochondria were larger when plants were grown at low temperature, and the maximal activity and relative amounts of cytochrome c oxidase showed a similar trend. In contrast, CN-resistant respiration of intact roots and relative amounts of AOX protein in mitochondria isolated from those roots, were lower in high-H plants grown at low temperature. In the roots of low-H cultivars, relative amounts of AOX protein were higher at low growth temperature. Relative amounts of UCP protein showed similar trends to AOX. We conclude that maintenance of growth rate in high-H plants grown at low temperature is associated with both respiratory homeostasis and a high efficiency of respiratory ATP production.     

LIGHT RESPIRATION IN SIX ESTUARINE PHYTOPLANKTON SPECIES: CONTRASTS UNDER PHOTOAUTOTROPHIC AND MIXOTROPHIC GROWTH CONDITIONS1

The photoresponse of respiration was examined in six estuarine phytoplankton species grown at a limiting irradiance in the presence or absence of glucose. Cellular respiration rates in the dark, at the growth irradiance, and at saturating light levels were higher in glucose-grown cultures than in photoautotrophic cultures. Glucose uptake also affected the relationship between incident irradiance and gross respiration rate, and the specific respiratory pathways that contributed to the respiration versus irradiance (R vs. I) response. The energy-conseming Mehler reaction contributed largely to light-stimulated respiration in photoautotrophic (energy-limited) cultures. However, the energy-dissipating alternative pathway was the predominant form of respiration measured in mixotrophic (energy-sufficient) cultures. Based on these and previous observations, a model of phytoplankton R us. I response is presented, in which the relative contributions of different light respiratory processes (cytochrome pathway respiration, alternative pathway respiration, chlororespiration, Mehler reaction) are dependent on the incident irradiance and cellular energy content.     

Energy metabolism of Plantago lanceolata as dependent on the supply of mineral nutrients

Plantago lanceolata L., a grassland species from a relatively nutrient-poor habitat, was grown in nutrient-rich and in nutrient-poor culture solutions. Half of the plants were trensferred from high to low or from low to high nutrient conditions. Shoot growth was immediately reduced upon transfer to low nutrient conditions, whilst it reacted more slowly upon transfer of plants to high nutrient conditions. Root growth was less dependent on the supply of nutrients, but it was slightly reduced upon transfer of plants to high nutrient conditions.
Photosynthesis was largely independent of the nutrient supply, apart from an initial increase upon transfer of plants to low nutrient conditions. Photosynthesis decreased with age in all treatments, and this decrease was not due to mutual shading. The decrease of photosynthetic rate was not accompanied by a decreased relative growth rate: it was compensated by a more efficient root respiration, since the activity of the alternative nonphosphorylating pathway continuously decreased in plants grown in a high nutrient environment.
It is concluded that the alternative pathway was of significance in removal of carbohydrates, which could not be utilized for growth, energy production, etc. , due to a temporary or structural imbalance between assimilate production and requirement. The alternative pathway also appeared to allow P. lanceolata plants to adapt to a changed environment as regards mineral nutrition.
The experimental value for root growth respiration of P. lanceolata grown under high nutrient conditions was compared with a theoretical value, calculated from the biochemical composition of plant dry matter and the known energy costings for biosynthetic and transport processes. A good correlation between the experimental and theoretical value of root growth respiration was found if it was assumed that ion uptake required c . 1.0 molecule of ATP per ion per membrane passage.     

Salinity, growth and root respiration in the grey mangrove, Avicennia marina

Relationships between growth parameters and root respiration under various conditions of salinity were investigated in seedlings of the grey mangrove Avicennia marina (Forsk.) Vierh. Growth, root/shoot ratios, leaf succulence and osmotic potential of leaves were measured for seedlings grown for 6–8 weeks in 100, 50, 25 and 0% seawater. Oxygen uptake of root segments, from distal to proximal ends of roots, was measured for all treatments. Total growth was maximal in 25% seawater, highest leaf succulence was obtained in 50% seawater, and highest leaf osmotic potential in 100% seawater. Oxygen uptake in distal root segments, as measured both by Clark oxygen electrode and Warburg manometry, showed a stimulation in the presence of salt that closely paralleled growth stimulation. The rates of respiration were highest in 25% seawater. The oxygen uptake was not stimulated by salt per se, since concentrations higher than 25% were associated with a decline in rate of oxygen uptake from the maximum. Values for the respiratory quotient approximated to one in all treatments. Avicennia marina has been reported to exclude from its roots about 90% of the salt in the surrounding medium. It might have been expected that increased concentrations of salt in the growth medium would be associated with a standard salt respiration response in the roots; however, this was not obtained.     

Genetic variation in the response of the weed Ruellia nudiflora (Acanthaceae) to arbuscular mycorrhizal fungi

The main goal of this work was to test for plant genetic variation in the phenotypic plasticity response of the weed Ruellia nudiflora to arbuscular mycorrhizal (AM) fungi inoculation. We collected plants in the field, kept them under homogeneous conditions inside a nursery, and then collected seeds from these parent plants to generate five inbred lines (i.e., genetic families). Half of the plants of each inbred line were inoculated with AM fungi while the other half were not (controls); a fully crossed experimental design was then used to test for the effects of treatment (with or without AM fungi inoculation) and inbred line (genetic family). For each plant, we recorded the number of leaves produced and the number of days it survived during a 2-month period. Results showed a strong positive treatment effect (plastic response to AM fungi inoculation) for leaf production and survival. Moreover, in terms of survival, the treatment effect differed between genetic families (significant genetic family by treatment interaction). These findings indicate that the positive effect of AM fungi on plant survival (and potentially also growth) differs across plant genotypes and that such condition may contribute to R. nudiflora’s capacity to colonize new environments.     

Changes in respiratory mitochondrial machinery and cytochrome and alternative pathway activities in response to energy demand underlie the acclimation of respiration to elevated CO2 in the invasive Opuntia ficus-indica

Studies on long-term effects of plants grown at elevated CO(2) are scarce and mechanisms of such responses are largely unknown. To gain mechanistic understanding on respiratory acclimation to elevated CO(2), the Crassulacean acid metabolism Mediterranean invasive Opuntia ficus-indica Miller was grown at various CO(2) concentrations. Respiration rates, maximum activity of cytochrome c oxidase, and active mitochondrial number consistently decreased in plants grown at elevated CO(2) during the 9 months of the study when compared to ambient plants. Plant growth at elevated CO(2) also reduced cytochrome pathway activity, but increased the activity of the alternative pathway. Despite all these effects seen in plants grown at high CO(2), the specific oxygen uptake rate per unit of active mitochondria was the same for plants grown at ambient and elevated CO(2). Although decreases in photorespiration activity have been pointed out as a factor contributing to the long-term acclimation of plant respiration to growth at elevated CO(2), the homeostatic maintenance of specific respiratory rate per unit of mitochondria in response to high CO(2) suggests that photorespiratory activity may play a small role on the long-term acclimation of respiration to elevated CO(2). However, despite growth enhancement and as a result of the inhibition in cytochrome pathway activity by elevated CO(2), total mitochondrial ATP production was decreased by plant growth at elevated CO(2) when compared to ambient-grown plants. Because plant growth at elevated CO(2) increased biomass but reduced respiratory machinery, activity, and ATP yields while maintaining O(2) consumption rates per unit of mitochondria, we suggest that acclimation to elevated CO(2) results from physiological adjustment of respiration to tissue ATP demand, which may not be entirely driven by nitrogen metabolism as previously suggested.