Nitrogen Metabolism, Respiration, and Growth of Cultured Plant Tissue

Critical examination of the amino-acid composition of proteinsin fast-growing and slow-growing tissues reveals only very 8maUdifferences, indicating that some factor other than the amino-acidcomplement is responsible for, or reflects, the great increasein the mass of protein in the fast-growing tissues. Increases in fresh weight and total protein are exactly parallel,indicating that water uptake is an active process associatedwith growth. Respiration, on the other hand, increases far morein the fast-growing over the slow-growing tissues than doestotal protein. A given amount of protein in the fast-growingtissue will support a much greater respiration rate than thesame amount in slow-growing tissue. The incorporation of radioactivity into amino-acids of the proteinin4icates that there are two distinct types: those in whichincorporation is increased in fast-growing tissue much morethan the total protein, and to the same ezte as respiration(notably glutarnic acid, aspartic acid, and threonine); andthose in which the increased incorporation is much nafler, slightlyless than total protein (notably proline and hydroxyproline).It is concluded that there are two n protein fractions: the‘active’ moiety, which is undergoing rapid breakdownd resynthesis, giving rise to much of the CO through oxidationof its residues; a the ‘inactive’ moiety, whichonce synthesized is not reutilized or broken down. It is theformer, or ‘active‘ protein whose synthesis is greatlyincreased in the fast. growing tissues, and it is the pace,rather than the kind, of reactions which differ entiates betweenthe fast- and slow-growing tissues. The entire experimental data are discussed with reference toa number of cur rent theories and investigations. A number ofexperimental observations are noted which admit of interpretationalong the lines here developed.     

Promotion of Plant Cell Division by an Epidermal Growth Factor

In some specified treatments, an epidermal growth factor (EGF)promoted adventitious root formation in epicotyl cuttings ofVigna angularis. The number of the roots induced in cuttingstreated with 0.1 mg liter^-1 EGF during the first 24 h and with210^-4 M IAA during the second 24 h was 15% greater than thatof the roots in cuttings treated without EGF and with IAA. Analysisof the optimum timing of EGF application was performed by dividingthe first 24 h period into three sequential 8 h periods (0–8h, 8–16 h and 16–24 h). The most effective timeperiods in terms of the root formation were 8–16 h and16–24 h. The 0–8 h period was ineffective with respectto the formation. When carrot suspension cells were culturedfor 15 days at a very low cell density (1,000 cells/3 ml Murashigeand Skoog's medium) with more than 0.1 mg liter^-1 EGF, cellnumbers were 72% higher than those cultured without EGF. Theseresults suggest that EGF promotes cell division of plants. (Received October 5, 1992; Accepted May 24, 1993)     

MAPK对高等植物细胞分裂和生长的调节

综述了MAPKs参与植物细胞周期调控的最新进展 ,植物激素与MAPK ,MAPK与植物细胞有丝分裂 ,以及MAPK与植物细胞分裂和生长的调控等三方面 ,阐述MAPK参与调控高等植物细胞分化和有丝分裂的机制。     

Carbon Partitioning and Assimilation as Affected by Nitrogen Deficiency in Cassava

Plants of cassava (Manihot esculenta Crantz) were raised in a sand root medium watered with nutrient solutions, under greenhouse conditions. As the N-supply increased, shoot dry mass was enhanced to a greater extent than root dry mass, thus leading to an increased shoot to root ratio. In leaves, contents of total soluble saccharides, non-reducing saccharides, and inorganic phosphate increased linearly with increasing N-supply. An opposite response was found for reducing saccharides and starch. In general, content of non-reducing saccharides was considerably greater than starch content. Activity of sucrose synthase was not detected, regardless of the N-treatments; by contrast, activity of neutral and acid invertases increased with increasing N-availability. Roots accumulated more total soluble saccharides, but less reducing saccharides and starch, as the N-supply increased. Photosynthetic rates decreased with increasing N-deficiency. Such a decrease was circumstantially associated to reducing saccharide, but not starch, accumulation. Results suggest a limited capacity for carbon export from source leaves under N-limitation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of Tomato Plant Mycorrhization on Nitrogen Metabolism,Growth and Fructification on P-Limited Soil

Journal of Plant Growth Regulation - The application of mycorrhizal fungi in agricultural soils as bio-fertilizers is going to be established as an agronomic practice for enhancing crop nutrients...     

Seaweed Extracts as Biostimulants of Plant Growth and Development

Marine algal seaweed species are often regarded as an underutilized bioresource, many have been used as a source of food, industrial raw materials, and in therapeutic and botanical applications for centuries. Moreover, seaweed and seaweed-derived products have been widely used as amendments in crop production systems due to the presence of a number of plant growth-stimulating compounds. However, the biostimulatory potential of many of these products has not been fully exploited due to the lack of scientific data on growth factors present in seaweeds and their mode of action in affecting plant growth. This article provides a comprehensive review of the effect of various seaweed species and seaweed products on plant growth and development with an emphasis on the use of this renewable bioresource in sustainable agricultural systems.     

Nitrogen Fixation and Carbon Dioxide Assimilation in Rhizobium japonicum

In free-living Rhizobium japonicum cultures, the stimulatory effect of CO₂ on nitrogenase (acetylene reduction) activity was mediated through ribulose bisphosphate carboxylase activity. Two mutant strains (CJ5 and CJ6) of R. japonicum defective in CO₂ fixation were isolated by mitomycin C treatment. No ribulose bisphosphate carboxylase activity could be detected in strain CJ6, but a low level of enzyme activity was present in strain CJ5. Mutant strain CJ5 also exhibited pleiotropic effects on carbon metabolism. The mutant strains possessed reduced levels of hydrogen uptake, formate dehydrogenase, and phosphoribulokinase activities, which indicated a regulatory relationship between these enzymes. The CO₂-dependent stimulation of nitrogenase activity was not observed in the mutant strains. Both mutant strains nodulated soybean plants and fixed nitrogen at rates comparable to that of the wild-type strain.     

Nitrogen Metabolism in Plant Cell Suspension Cultures: II. Role of Organic Acids during Growth on Ammonia

Tobacco cells (Nicotiana tabacum) are capable of growth on ammonia as a sole nitrogen source only when succinate, malate, fumarate, citrate, α-ketoglutarate, glutamate, or pyruvate is added to the growth medium. A ratio between the molar concentrations of ammonia to succinate (as a complementary organic acid) in the growth medium of 1.5 was optimal. Succinate had no effect on the rate of uptake of ammonia from the medium into the cells although it did affect the intracellular concentration of ammonia. However, the changes were not sufficient to explain inhibition of growth as being due to ammonia toxicity. The radioactivity from ¹⁴C-succinate was incorporated into malate, glutamate, and aspartate within 2 minutes.     

Nitrogen, Carbon, and Sulfur Metabolism in Natural Thioploca Samples

Filamentous sulfur bacteria of the genus Thioploca occur as dense mats on the continental shelf off the coast of Chile and Peru. Since little is known about their nitrogen, sulfur, and carbon metabolism, this study was undertaken to investigate their (eco)physiology. Thioploca is able to store internally high concentrations of sulfur globules and nitrate. It has been previously hypothesized that these large vacuolated bacteria can oxidize sulfide by reducing their internally stored nitrate. We examined this nitrate reduction by incubation experiments of washed Thioploca sheaths with trichomes in combination with ¹⁵N compounds and mass spectrometry and found that these Thioploca samples produce ammonium at a rate of 1 nmol min⁻¹ mg of protein⁻¹. Controls showed no significant activity. Sulfate was shown to be the end product of sulfide oxidation and was observed at a rate of 2 to 3 nmol min⁻¹ mg of protein⁻¹. The ammonium and sulfate production rates were not influenced by the addition of sulfide, suggesting that sulfide is first oxidized to elemental sulfur, and in a second independent step elemental sulfur is oxidized to sulfate. The average sulfide oxidation rate measured was 5 nmol min⁻¹ mg of protein⁻¹ and could be increased to 10.7 nmol min⁻¹ mg of protein⁻¹ after the trichomes were starved for 45 h. Incorporation of ¹⁴CO₂ was at a rate of 0.4 to 0.8 nmol min⁻¹ mg of protein⁻¹, which is half the rate calculated from sulfide oxidation. [2-¹⁴C]acetate incorporation was 0.4 nmol min⁻¹ mg of protein⁻¹, which is equal to the CO₂ fixation rate, and no ¹⁴CO₂ production was detected. These results suggest that Thioploca species are facultative chemolithoautotrophs capable of mixotrophic growth. Microautoradiography confirmed that Thioploca cells assimilated the majority of the radiocarbon from [2-¹⁴C]acetate, with only a minor contribution by epibiontic bacteria present in the samples.     

Changes in Growth and Nitrogen Assimilation in Maize Plants Induced by NaCl and Growth Regulators

Experiments were conducted to determine the interactive effects of salinity and certain growth regulators on growth and nitrogen assimilation in maize (Zea mays L. cv. GS-2). 100 mM NaCl inhibited the biomass accumulation, chlorophyll and carotenoid contents in leaves, nitrate content and uptake and nitrate reductase activity. The application of kinetin, ascorbic acid and 10 and 50 μM abscisic acid in the first experiment and 50 and 100 μM abscisic acid in the second experiment induced a substantial increase in the above parameters, the effect was highest with abscisic acid in salinized as well as non-salinized plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Plant Growth Based on Interrelation between Carbon and Nitrogen Translocation from Leaves

In individual leaves, the photon-saturated photosynthetic activity (P _sat, expressed on a dry mass basis) was closely related to the nitrogen content (Nc) as follows: P _sat = Cf Nc + P _sat0, where Cf and P _sat0 are constants. On a whole plant basis, the relative growth rate (RGR) was closely related to Nc in canopy leaf as follows: RGR = DMf Nc + RGR₀, where DMf and RGR₀ are constants. However, the coefficients Cf and DMf were markedly different among plant species. To explain these differences, it is suggested that carbon assimilation (or dry matter production) is controlled by both the Nc in a leaf (or leaves) and by the net N translocation from leaves. This is supported by the finding that P _sat is related to the rate of ³⁵S-methionine translocation from leaves. We propose another estimation method for the net N translocation rate (NFR) from leaves: Nc, after full leafing, is expressed as a function of time: Nc = (Nc₀ – Ncd) exp(–Nft) + Ncd, where Nf is a coefficient, t is the number of days after leaf emergence, Nc₀ is the initial value of Nc, and Ncd is the Nc of the dead leaf. The NFR is then calculated as NFR = Nc/t = –Nf (Nc – Ncd). Thus Nf is the coefficient for the NFR per unit Nc. NFR is a good indicator of net N translocation from leaves because NFR is closely related to the rate of ³⁵S-methionine translocation from leaves. Since P _sat is related to the ¹⁴C-photosynthate translocation rate, Cf (or DMf) corresponds to the coefficient of saccharide translocation rate per unit amount of Nc. Cf (or DMf) is closely related to the Nf of individual leaves (or the Nf of canopy leaf). This indicates that C assimilation and C translocation from leaves are related to Nc and N translocation from leaves (net translocation of N). Cf and Nf are negatively correlated with leaf longevity, which is important because a high or low CO₂ assimilation rate in leaves is accompanied by a correspondingly high or low N translocation in leaf, and the degree of N translocation in leaves decreases or increases leaf longevity. Thus, since a relatively high P _sat (or RGR) is accompanied by a rapid Nc decrease in leaves, it is difficult to maintain a high P _sat (or RGR) for a sustained time period.     

Disk Inoculum-Solid Medium Method To Test Carbon and Nitrogen Assimilation by Yeast Isolates

Carbon and nitrogen assimilation for 50 yeasts isolated from White Riesling fermentation were tested by using a disk inoculum-solid medium method. This method was quicker and gave results comparable to the conventional liquid medium methods. Yeast characteristics (growth response, pigment production, morphology) could also be compared with this method.     

Carbon Assimilation Characteristics of the Aquatic CAM Plant, Isoetes howellii

The relationship between malic acid production and carbon assimilation was examined in the submerged aquatic Crassulacean acid metabolism (CAM) plant, Isoetes howellii Engelmann. Under natural conditions free-CO₂ level in the water was highest at 0600 hours and ¹⁴CO₂ assimilation rates in I. howellii were also highest at this time. After 0900 hours there was a similar pattern in (a) rate of free-CO₂ depletion from the water, (b) reduction of carbon assimilation rates, and (c) rate of deacidification in leaves. Rates of daytime deacidification increased under CO₂-free conditions and as irradiance intensity increased. Nighttime CO₂ uptake was estimated to contribute one-third to one-half of the total daily gross carbon assimilation. CO₂ uptake, however, accounted for only one-third to one-half of the overnight malic acid accumulation. Internal respiratory CO₂ may be a substrate for a large portion of overnight acid accumulation as leaves incubated overnight without CO₂ accumulated substantial levels of malic acid. Loss of CAM occurred in emergent leaf tips even though submerged bases continued CAM. Associated with loss of CAM in aerial leaves was an increase in total chlorophyll, a/b ratio, and carotenoids, and a decrease in leaf succulence. δ¹³C values of I. howellii were not clearly distinguishable from those for associated non-CAM submerged macrophytes.     

Suppression of Plant Growth by Nitrogen Dioxide

Nicotiana glutinosa and pinto bean seedlings (Phaseolus vulgaris) were exposed for short periods (3 days or less) to high concentrations of NO₂ (4.11-20.53 mg/m³ to compare the resulting leaf lesions with ozone damage produced at concentrations of 0.43 to 0.86 mg/m³. Although the same physiological age leaf tissue was damaged by both toxicants, damage caused by NO₂ was unlike that caused by ozone.

Pinto bean (Phaseolus vulgaris) and Pearson improved tomato (Lycopersicon esculentum) seedlings were continuously exposed for 10 to 22 days, to low concentrations of NO₂ (less than 1.03 mg/m³). These exposures caused significant growth suppression, increase in green color (total chlorophyll content), and distortion of leaves.

     

Carbon Metabolism, Nitrogen Assimilation, and Seed Yield of Cowpea (Vigna unquiculata L. Walp.) Grown in an Adverse Temperature Regime

When grown in an environment known not to favour the productionof large seed yields (warm days-cool nights; 33–19 °C),non-nodulated plants of cowpea cv. K 2809 supplied with abundantinorganic nitrogen not only assimilated N more rapidly but alsoproduced larger total dry weights and seed yields than plantsdependent on Rhizobium CB 756. Remobilization of nitrogen fromvegetative organs started sooner in nitrate-dependent than innodulated plants and contributed 69 and 47%, respectively, tothe N content of mature fruits. Plants dependent on nodulesrelied more on current assimilation of nitrogen during the laterstages of fruit growth than those given inorganic N; they alsoutilized a larger proportion of shoot-derived photosynthatesin growth of organs below ground and in the respiratory activitiesof both nodules and supporting roots. Although nitrate-dependentplants developed larger shoot systems than those relying onnodules, the distribution of carbon and nitrogen to leaves decreasedmarkedly as branches extended during early reproductive growth.The respiration of roots on nodulated plants became more efficientduring the later stages of fruit growth whereas the populationof secondary nodules present at this stage of development respiredless efficiently (mg C consumed per mg N assimilated) than theprimary nodules present earlier during development.