Effect of cadmium on growth and respiration of barley plants grown under two temperature regimes

We studied cadmium effect on the respiratory pathways ratio in the organs of barley (Hordeum distichum L., cv. Novichok) plants grown in water culture at two temperature regimes. Mineral nutrients were supplied daily in exponentially increasing amounts in order to provide for steady-state growth. CdSO₄ (30, 60, or 100 μmol/l) was added to nutrient solution at a single time in the beginning of the exponential growth period (19 days after germination). In further 6 days, the relative growth rate and biomass accumulation declined stronger with the increase in the cadmium concentration in plants grown at 13/8°C (day/night) than at 21/17°C (day/night). Cadmium suppressed root respiration (down to 60% of control) stronger than leaf respiration, and the roots manifested a higher sensitivity to the inhibitor of alternative oxidase, salicylhydroxamic acid. The respiratory pathways ratio in the roots occurred against the background of activated lipid peroxidation (POL). The highest POL activity and the highest proportion of alternative respiration pathway (AP) (up to 46% of total respiration) were observed in the roots in the presence of the highest cadmium concentration (100 μM) under lower temperature (13/8°C). Thus, high cadmium concentrations affected strongly the total rate of respiration and respiratory pathways ratio. Growth temperature modulated Cd effects on respiration. AP activation is one of the mechanisms for maintenance of root cell homeostasis under cadmium-induced stress.     

Growth temperature influences the underlying components of relative growth rate: an investigation using inherently fast- and slow-growing plant species

We examined the effect of growth temperature on the underlying components of growth in a range of inherently fast‐ and slow‐growing plant species. Plants were grown hydroponically at constant 18, 23 and 28 °C. Growth analysis was conducted on 16 contrasting plant species, with whole plant gas exchange being performed on six of the 16 species. Inter‐specific variations in specific leaf area (SLA) were important in determining variations in relative growth rate (RGR) amongst the species at 23 and 28 °C but were not related to variations in RGR at 18 °C. When grown at 18 °C, net assimilation rate (NAR) became more important than SLA for explaining variations in RGR. Variations in whole shoot photosynthesis and carbon concentration could not explain the importance of NAR in determining RGR at the lower temperatures. Rather, variations in the degree to which whole plant respiration per unit leaf area acclimated to the different growth temperatures were responsible. Plants grown at 28 °C used a greater proportion of their daily fixed carbon in respiration than did the 18 and 23 °C‐grown plants. It is concluded that the relative importance of the underlying components of growth are influenced by growth temperature, and the degree of acclimation of respiration is of central importance to the greater role played by NAR in determining variations in RGR at declining growth temperatures.     

Energy metabolism of Plantago major ssp. major as dependent on the supply of mineral nutrients

Plantago major L. ssp. major , a grassland species from a relatively nutrient-rich habitat, was grown in nutrient-rich and nutrient-poor culture solutions. Half of the plants were transferred from high to low or from low to high nutrient conditions. The rate of dry matter accumulation in both shoots and roots decreased slowly upon transfer of plants to low nutrient conditions and the shoot to root ratio was unaffected. The rate of structural growth of both roots and shoots increased upon transfer from low to high nutrient conditions and the shoot to root ratio, if calculated from non-structural-carbohydrate-free dry weights, increased.
Photosynthesis was largely independent of the nutrient supply. Root respiration, particularly the activity of the alternative oxidative pathway, decreased with increasing age. This decrease was ascribed to a decreased shoot to root ratio, which reduced the relative amount of carbohydrates translocated to the roots and thus the amount available for the alternative pathway. It is calculated that in young as well as in old plants grown in full nutrient solution 48% of the daily produced photosynthates was translocated to the roots.
This is at variance with data on P. lanceolata , where a decreasing proportion of the daily produced photosynthates was translocated to the roots when the plants grew older. It is concluded that shoot growth plus shoot respiration consumed a constant amount of the daily produced photosynthates in P. major and that the rest was left for translocation. It is further calculated that in P. major plants grown in full nutrient solution c . 25% and c . 2% of the daily produced photosynthates in young and old plants, respectively, was respired in a way that is not involved in production of energy that is utilized in growth and maintenance ('inefficient root respiration').
The results are discussed in comparison with those of P. lanceolata , a species from a relatively nutrient-poor habitat.     

Aphid effects on rhizosphere microorganisms and microfauna depend more on barley growth phase than on soil fertilization

This paper gives the first reports on aphid effects on rhizosphere organisms as influenced by soil nutrient status and plant development. Barley plants grown in pots fertilized with N but without P (N), with N and P (NP), or not fertilized (0) were sampled in the early growth phase (day 25), 1 week before and 1 week after spike emergence. Aphids were added 16 days before sampling was carried out. In a separate experiment belowground respiration was measured on N and NP fertilized plant–soil systems with aphid treatments comparable to the first experiment. Aphids reduced numbers of rhizosphere bacteria and fungal feeding nematodes 1 week before spike emergence. Before spike emergence, aphids reduced belowground respiration in NP treatments. These findings strongly indicate that aphids reduced allocation of photoassimilates to roots and deposition of root exudates in the growth phase of the plant. Contrary to this, 1 week after spike emergence numbers of bacteria, fungal feeding nematodes and Protozoa were higher in rhizospheres of plants subjected to aphids probably because aphids enhanced root mortality and root decomposition. Protozoa and bacterial feeding nematodes were stimulated at different experimental conditions with nematodes being the dominant bacterial grazers at N fertilization and Protozoa in the NP treatment before spike emergence.     

Arbuscular mycorrhizal colonization on carbon economy in perennial ryegrass: quantification by 13CO2/12CO2 steady-state labelling and gas exchange

Effects of the arbuscular mycorrhizal fungus (AMF) Glomus hoi on the carbon economy of perennial ryegrass (Lolium perenne) were investigated by comparing nonmycorrhizal and mycorrhizal plants of the same size, morphology and phosphorus status. Plants were grown in the presence of CO2 sources with different C isotope composition (delta13C -1 or -44). Relative respiration and gross photosynthesis rates, and belowground allocation of C assimilated during one light period ('new C'), as well as its contribution to respiration, were quantified by the concerted use of 13CO2/12CO2 steady-state labelling and 13CO2/12CO2 gas-exchange techniques. AMF (G. hoi) enhanced the relative respiration rate of the root + soil system by 16%, inducing an extra C flow amounting to 3% of daily gross photosynthesis. Total C flow into AMF growth and respiration was estimated at < 8% of daily gross photosynthesis. This was associated with a greater amount of new C allocated belowground and respired in mycorrhizal plants. AMF colonization affected the sources supplying belowground respiration, indicating a greater importance of plant C stores in supplying respiration and/or the participation of storage pools within fungal tissues. When ontogenetic and nutritional effects were accounted for, AMF increased belowground C costs, which were not compensated by increased photosynthesis rates. Therefore the instantaneous relative growth rate was lower in mycorrhizal plants.     

CARBOHYDRATE AVAILABILITY,RESPIRATION, AND THE GROWTH OF KENAF (HIBISCUS CANNABINUS) UNDER MODERATE SALT STRESS

Salt stress may impose osmotic and respiratory costs on nonhalophytes that limit the availability of carbohydrates for growth. This was examined in kenaf (Hibiscus cannabinus L.) by the analysis of soluble carbohydrates, starch, and respiration rates in mature and expanding leaves from plants exposed to moderate salt stress. Plants were grown for 35 days in solution culture at 1, 37, and 75 mM NaCl under greenhouse conditions. Total carbohydrates increased in mature and expanding leaves with increasing salinity. The majority of this increase was as starch. Mature leaf respiration also increased under salt stress. The net accumulation of non-osmotically active carbohydrates in expanding leaves suggests that growth was not limited by the generation or availability of carbohydrates but rather by the ability of the plant to effectively utilize this substrate in osmotic adjustment and growth.     

Long-day effects on growth and flower initiation of tomato plants in low light

Young tomato plants (cv. Minibelle) were grown in plant growth cabinets in 575 kJ m^-2 (400–700 nm) daily radiation. Plants grown in an 8 h day were then compared with those in which 10% of the radiation was taken from the main 8 h light period and supplied over the next 8 h period. After 41 days from sowing the 16 h day plants had almost twice the dry weight of those in short days and a 55 % greater leaf area. Net assimilation rate, relative growth rate and relative leaf area growth rates were all greater in long days, although the differences in growth diminished with time. The long-day treatment also increased the proportion of dry weight in the leaves, a function which is usually relatively stable in different environments. The beneficial effect of the long days may arise from a reduction in night respiration, or an increase in rate of photosynthesis through the observed increase in chlorophyll content. The 8 h light period resulted in flower initiation one or two nodes lower than the 16 h period so that the cultivar is a quantitative short-day plant.     

Differences in chemical composition of plants grown at constant relative growth rates with stable mineral nutrition

Summary Leaf chemistry of a willow clone (Salix aquatica Smith) differed significantly when grown at constant relative growth rates depending upon the relative availability of nutrients and light. Concentration of amino acids and nitrate were high in plants grown with a relative surplus of nutrients. Concentrations of starch, tannin, and lignin, on the other hand, were high in plants grown with a relative surplus of carbon. Photosynthetic rates, expressed per unit leaf area, were similar when plants were grown under high light conditions, regardless of nutrient availability. Dark respiration was much higher in plants supplied with abundant nutrients than in those with a more limited supply, reflecting differences in nitrogen concentration of the tissue. The experimental approach allows plants to be grown to a standard size with differing, but highly uniform chemistry. Plants grown in such a manner may provide good experimental material to evaluate interactions between herbivores or pathogens and their hosts.     

Effects of multiple stresses on radish growth and resource allocation

Summary Acclimation of wild radish plants to a simultaneous combination of SO₂ fumigation and decreasing nitrate availability was investigated. Plants were grown for 24 d under continuous daytime (10h) exposure to 0 or 0.4 ppm SO₂ and were grown in a nutrient solution with stable nitrate concentrations of 100 M for the first 15 d, 50 M from day 15 to day 19, and 25 M from day 19 to day 24. Analysis of relative growth rates (RGR) showed that radish plants responded rapidly to changes in nitrate availability and that SO₂ treatment affected those responses. Shoot RGR of plants from both treatments and root RGR of control plants showed rapid declines and subsequent recoveries in response to decreasing nitrate availability. Root RGR of SO₂-treated plants declined rapidly in response to decreased nitrate availability, but did not recover as quickly or completely as root RGR of control plants. Analysis of specific leaf weights and tissue nitrogen concentrations showed that control plants had significantly higher amounts of nitrogen in tissues after nitrate availability was lowered, and had higher rates of nitrate uptake in comparison to SO₂-treated plants; especially when nitrate availability was highest. Furthermore, control plants had temporarily higher rates of root respiration in comparison to SO₂-treated plants, suggesting that control plants temporarily allocated more resources to physiological processes occurring in roots, such as nutrient uptake. Although SO₂-induced changes in growth and resource allocation of plants were relatively small, it was probable that SO₂ treatment of radish plants affected plant nitrogen balance, and subsequently affected the ability of plants to respond to decreased nitrate availibility, by affecting resource partitioning to nitrate uptake and root growth.     

The effect of an elevated atmospheric CO2 concentration on growth, photosynthesis and respiration of Plantago major

The effect of an elevated atmospheric CO₂ concentration on growth, photosynthesis and root respiration of Plantago major L. ssp. major L. was investigated. Plants were grown in a nutrient solution in growth chambers at 350 and 700 μl I⁻¹ CO₂ during 7 weeks. The total dry weight of the Co₂-enriched plants at the end of this period was 50% higher than that of control plants. However, the relative growth rate (RGR) was stimulated only during the first half of the growing period. The transient nature of the stimulation of the RGR was not likely to be due to end-product inhibition of photosynthesis. It is suggested that in P. major , a rosette plant, self-shading causes a decline in photosynthesis and results in an increase in the shoot: root ratio and a decrease in RGR. CO₂-enriched plants grow faster and cosequently suffer more from self-shading. Corrected for this ontogenetic drift, high CO₂ concentrations stimulated the RGR of P. major throughout the entire experiment.     

Effects of boron foliar applications on vegetative and reproductive growth of sunflower

Foliar application may be used to supply boron (B) to a crop when B demands are higher than can be supplied via the soil. While B foliar sprays have been used to correct B deficiency in sunflower (Helianthus annuus L.) in the field, no studies have determined the amount of B taken up by sunflower plant parts via foliar application. A study was conducted in which sunflower plants were grown at constant B concentration in nutrient solution with adequate B (46 micro m) or with limited B supply (0.24, 0.40 and 1.72 micro m) using Amberlite IRA-743 resin to control B supply. At the late vegetative stage of growth (25 and 35 d after transplanting), two foliar sprays were applied of soluble sodium tetraborate (20.8 % B) each at 0, 28, 65, 120 and 1200 mm (each spray equivalent to 0, 0.03, 0.07, 0.13 and 1.3 kg B ha-1 in 100 L water ha-1). The highest rate of B foliar fertilization resulted in leaf burn but had no other evident detrimental effect on plant growth. Under B-deficient conditions, B foliar application increased the vegetative and reproductive dry mass of plants. Foliar application of 28-1200 mm B increased the total dry mass of the most B-deficient plants by more than three-fold and that of plants grown initially with 1.72 micro m B in solution by 37-49 %. In this latter treatment, the dry mass of the capitulum was similar to that achieved under control conditions, but in no instance was total plant dry mass similar to that of the control. All B foliar spray rates increased the B concentration in various parts of the plant tops, including those that developed after the sprays were applied, but the B concentration in the roots was not increased by B foliar application. The B concentration in the capitulum of the plants sprayed at the highest rate was between 37 and 93 % of that in the control plants. This study showed that B foliar application was of benefit to B-deficient sunflower plants, increasing the B status of plant tops, including that of the capitulum which developed after the B sprays were applied.     

Influence of Cd2+ on growth, chlorophyll content, and water relations in young barley plants

Barley (Hordeum vulgare L., cv. Hemus) plants were grown in nutrient solution with or without 54 μM Cd²⁺ for 12 d. A treatment with Cd²⁺ inhibited the growth of young barley plants. The main factor limiting plant growth was net assimilation rate, due to decreased photosynthetic rate and accelerated dark respiration rate. One of the reasons for the reduced photosynthetic rate was the lower chlorophyll and carotenoid content. Cd²⁺ decreased water potential and transpiration rate, but relative water content in leaves of the treated plants was not significantly changed. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of phosphorus and nitrogen deficiency on growth of seedlings of spring barley in dependence on irradiance: Growth analysis

Seedlings of spring barley,Hordeum vulgare L. cv. Mirena, were grown in a controlled environment chamber at high (HI: 122 Wm^?2) and low (LI: 28 Wm^?2) irradiance in the complete Richter’s nutrient solution (R) or in solution lacking either phosphorus (R -P) or nitrogen (R -N). The experiment was terminated 15 days after sowing when plants (R-N) at HI ceased to grow. At that time the dry mass of one plant was 449.8 mg, 145.7 mg and 116.8mg at HI and 203.4 mg, 110.1 mg and 91.0 at LI for R, (R-P) and (R-N), respectively. Deficiency of P and especially N reduced the size of loaf area more under HI than under LI conditions. Specific dry mass of leaves was the highest in R-N plants. The values of relative growth rate and assimilation rate are presented. Interaction of the effects of deficiency of mineral nutrients and irradiance during cultivation should be analyzed in further experiments for determination of optimum conditions for utilization of mineral nutrients.     

Studies on the growth and phosphatase activities inSuaeda fructicosa

Summary Plants ofSuaeda fructicosa were grown in sand culture with various combinations of excess copper, silicon and sodium. Effects of different concentrations of NaCl on the activities of acid phosphatase and PEP-phosphatase were investigated in the above mentioned plants. Plants which were given extra copper without NaCl showed very poor growth compared with control plants given a normal nutrient whereas plants given extra NaCl alone or with copper displayed luxuriant growth. Enzymes extracted from the plants given extra copper with normal nutrient levels showed stimulation in the activities of both the above mentioned enzymes. In plants supplied with extra sodium chloride the activity of acid phosphatase was inhibited and in that of PEP-phosphatase was stimulated. Sodium silicate in the growth medium eliminated both effects of extra sodium chloride.     

Physiological factors limiting growth and yield ofOryza sativa under unflooded conditions

Summary Rice grown under flooded conditions consistently produces better vegetative growth and higher grain yields than when grown in unflooded culture. Physiological and nutritional differences in rice grown under these two conditions were determined. Growth observations showed that plants under unflooded culture made an initial vigorous start, but soon showed poor tillering, depressed leaf growth, delayed flowering, low moisture content, foliar chlorosis, and 52.6 per cent lower yield than flooded plants.Chemical analysis emphasized the higher manganese content of plants grown under unflooded culture with no significant differences in other elements. Plants grown in nutrient cultures and under field conditions gave evidence that nitrate nitrogen nutrition, as exists for plants under unflooded conditions, favored manganese accumulation.Growth responses suggest differences in auxin metabolism. Since auxins could not be estimated directly, some factors affecting auxin degradation were investigated. It was found that plants grown under unflooded conditions had: 1) a low catalase activity, and: 2) a high peroxidase activity, which favor accelerated auxin degradation. It is proposed that high manganese levels in plants grown under unflooded conditions affects the indoleacetic acid oxidase mechanism resulting in retarded growth and depressed grain yields.     

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.     

The effects of CO2 and nutrient enrichment on photosynthesis and growth of Poa annua in two consecutive generations

We studied short- and long-term growth responses of Poa annua L. (Gramineae) at ambient and elevated (ambient +200???mol?mol^?1) atmospheric CO₂. In experiment 1 we compared plant growth during the early, vegetative and final, reproductive growth phases. Plant growth in elevated CO₂ was significantly enhanced during the early phase, but this was reversed in the reproductive phase. Seed mass and percentage germination were significantly reduced in elevated CO₂. Experiment 2 tested for the impact of transgenerational and nutrient effects on the response of Poa annua to elevated CO₂. Plants were grown at ambient and elevated CO₂ for one or two consecutive generations at three soil nutrient levels. Leaf photosynthesis was significantly higher at elevated CO₂, but was also affected by both soil nutrient status and plant generation. Plants grown at elevated CO₂ and under conditions of low nutrient availability showed photosynthetic acclimation after 12?weeks of growth but not after 6?weeks. First-generation growth remained unaffected by elevated CO₂, while second-generation plants produced significantly more tillers and flowers when grown in elevated CO₂ compared to ambient conditions. This effect was strongest at low nutrient availability. Average above- and belowground biomass after 12?weeks of growth was enhanced in elevated CO₂ during both generations, but more so during plant generation 2. This study demonstrates the importance of temporal/maternal effects in plant responses to elevated CO₂.     

A novel method for growing Arabidopsis thaliana plants hydroponically

In this report we describe the development of a simple system for growing individual Arabidopsis plants hydroponically under environmental conditions which are simple to maintain while maximizing growth and development. The system consists of a Life Raft Float Unit with a 14–20 mm sponge inserted into its center; this unit is placed into a Magenta GA7 vessel containing Arabidopsis nutrient solution. Plants grown in this experimental system do not require aeration, 125 μmol m⁻² s⁻¹ supports vigorous plant growth, 1/4 to 1/8 strength Arabidopsis nutrient solution promotes maximal growth while higher or lower levels have adverse effects and temperatures between 18 and 24°C were found to be optimal. Plants grown under these conditions exhibit physiological factors such as time to flowering and overall appearance similar to those grown in potting media. The low maintenance method described in this paper provides an alternative to existing hydroponic methods used to grow Arabidopsis . Adaptation of this system for growing large numbers of plants in 1 container is also discussed.     

The role of free sugars and amino acids in the regulation of biomass partitioning and plant growth

Theoretical plant growth models postulate an important role for growth substrates such as sugars and amino acids. To test this experimentally, spinach plants were grown under controlled conditions and with nitrogen added daily, following different exponential addition schemes. Plants were harvested during exponential growth. Free amino acid levels or free sugar levels were only weakly correlated with growth and biomass partitioning. Factor analysis showed however that the product of free sugar concentration and amino acid concentration yielded a parameter adequately reflecting the plant's nutritional state.It is concluded that growth and biomass partitioning under limiting N conditions cannot be modelled solely based on N substrate levels.