Showing papers on "Plant physiology published in 2004"

Effects of salt stress on basic processes of photosynthesis

Abstract: Salt stress causes decrease in plant growth and productivity by disrupting physiological processes, especially photosynthesis. The accumulation of intracellular sodium ions at salt stress changes the ratio of K : Na, which seems to affect the bioenergetic processes of photosynthesis. Both multiple inhibitory effects of salt stress on photosynthesis and possible salt stress tolerance mechanisms in cyanobacteria and plants are reviewed.

Effects of salt on growth, ion accumulation, photosynthesis and leaf anatomy of the mangrove, Bruguiera parviflora

Abstract: The effects of a range of salinity (0, 100, 200 and 400 mM NaCl) on growth, ion accumulation, photosynthesis and anatomical changes of leaves were studied in the mangrove, Bruguiera parviflora of the family Rhizophoraceae under hydroponically cultured conditions. The growth rates measured in terms of plant height, fresh and dry weight and leaf area were maximal in culture treated with 100 mM NaCl and decreased at higher concentrations. A significant increase of Na+ content of leaves from 46.01 mmol m-2 in the absence of NaCl to 140.55 mmol m-2 in plants treated with 400 mM NaCl was recorded. The corresponding Cl- contents were 26.92 mmol m-2 and 97.89 mmol m-2. There was no significant alteration of the endogenous level of K+ and Fe2+ in leaves. A drop of Ca2+ and Mg2+ content of leaves upon salt accumulation suggests increasing membrane stability and decreased chlorophyll content respectively. Total chlorophyll content decreased from 83.44 μg cm-2 in untreated plants to 46.56 μg cm-2 in plants treated with 400 mM NaCl, suggesting that NaCl has a limiting effect on photochemistry that ultimately affects photosynthesis by inhibiting chlorophyll synthesis (ca. 50% loss in chlorophyll). Light-saturated rates of photosynthesis decreased by 22% in plants treated with 400 mM NaCl compared with untreated plants. Both mesophyll and stomatal conductance by CO2 diffusion decreased linearly in leaves with increasing salt concentration. Stomatal and mesophyll conductance decreased by 49% and 52% respectively after 45 days in 400 mM NaCl compared with conductance in the absence of NaCl. Scanning electron microscope study revealed a decreased stomatal pore area (63%) in plants treated with 400 mM NaCl compared with untreated plants, which might be responsible for decreased stomatal conductance. Epidermal and mesophyll thickness and intercellular spaces decreased significantly in leaves after treatment with 400 mM NaCl compared with untreated leaves. These changes in mesophyll anatomy might have accounted for the decreased mesophyll conductance. We conclude that high salinity reduces photosynthesis in leaves of B. parviflora, primarily by reducing diffusion of CO2 to the chloroplast, both by stomatal closure and by changes in mesophyll structure, which decreased the conductance to CO2 within the leaf, as well as by affecting the photochemistry of the leaves.

Plantago major plants responses to increase content of lead in soil: Growth and photosynthesis

Abstract: Effects of an increased lead (Pb) content in soil on growth, photosynthesis (P N) and anatomical parameters of Plantago major L. plants grown under controlled conditions were studied. The total dry weights of plants at 500 and 2000 mg kg−1 Pb in soil were correspondingly 70% and 54% of those of control plants. A reduced leaf area and changed leaf structure caused a decrease in P N in the whole plant. The specific leaf weight (SLW) increased as compared with that of control plants. An increasing Pb content in soil caused a larger number of chloroplasts and larger sizes of protoplasts, a decrease in the chlorophyll a+b contents and a larger number of stomata per unit leaf area based both in adaxial and abaxial epidermis, as compared with control plants. However their conductance was from 40% to 50% lower than that in control plants. It was noted that the dimensions of conducting bundles decreased mainly because of the reduced xylem area. The lower functional activity and the changes at different structural levels of the photosynthetic apparatus caused a decrease in the growth rate of plants at a high Pb content in soil.

Changes in the concentration of phenolic compounds and exudation induced by phosphate deficiency in bean plants (Phaseolus vulgaris L.)

Abstract: The effect of prolonged phosphate starvation of bean plants (Phaseolus vulgaris L.) on the concentration of phenolics and their exudation by roots was studied. Plants cultured on phosphate-deficient media maintained a steady concentration of total phenolics in the leaves, whereas in the leaves of plants grown on complete nutrient media the phenolic concentration decreased. After 18 days of culture, higher total phenolics and anthocyanin concentrations in phosphate-deficient leaves compared with control leaves were observed. The divergent trends in total phenolic concentrations between phosphate-deficient and control leaves corresponded to the changes in the activity of L-phenylalanine ammonia-lyase. In the roots, the concentration of total phenolics was lower in phosphate-deficient plants compared with control plants. However, after 18 days of culture of bean plants, the amount of exuded phenolics from phosphate-deficient roots was 5-times higher than that from the roots of control plants. The activity of L-phenylalanine ammonia-lyase was twice as high in the roots of phosphate-starved plants. Comparable rates in the exudation of phenolics by bean roots observed after 18 days of culture on nitrogen-deficient or phosphate-deficient medium may suggest a similar system of signal transduction for phenolics release. The results are discussed in relation to the possible functions of phenolics in nutrient uptake and as chemical signals in root-soil microbe interactions to enhance the plant adaptation to particular environmental conditions.

Influence of arbuscular Mycorrhiza on some physiological growth parameters of pepper

Abstract: Arbuscular Mycorrhiza (AM) is a symbiotic association between plant roots and certain soil fungi. Mycorrhiza establishment is known to modify several aspects of plant physiology such as mineral nutrient composition, hormonal balance, and C allocation patterns. In this study, the effect of the Arbuscular Mycorrhizal fungus Glomus intraradices Schenck & Smith on the physiological growth parameters of pepper (Capsicum annuum L. cv Cetinel-150) plants was investigated. To explain the physiological growth of these plants, some physiological growth parameters were determined in the shoots and leaves of mycorrhizal (M) and nonmycorrhizal (NM) plants such as the P and dry matter (d.m.) contents, chlorophyll (chl) concentrations (chl a, chl b and chl a + b), and amounts of some reducing sugars (fructose, a glucose, b glucose), sucrose and total sugar. All parameters increased in M pepper plants by 12%-47% compared with those of the NM plants (P £ 0.01). Furthermore, it was determined that P concentration was positively correlated with all chlorophyll and sugar contents. It is concluded that increased P concentration, because of the mycorrhizal symbioses, positively affects the physiological performance of pepper plants.

Growth enhancement of transgenic poplar plants by overexpression of Arabidopsis thaliana endo-1,4–β-glucanase (cel1)

Abstract: Poplar (Populus tremula) plants which had been transformed with Arabidopsis thaliana cel1 cDNA and successfully over-expressed the gene, exhibited significant phenotypic alterations which included taller plants, larger leaves, increased stem diameter, wood volume index, dry weight and a higher percentage of cellulose and hemicellulose, compared to the wild-type plants. Transgenic A. thaliana plants over-expressing A. thaliana cel1 exhibited similar levels of cel1 mRNA in the elongation zone of the flowering stem and higher levels in mature leaves when compared with wild-type plants. CEL1 protein levels in the elongation zone of the flowering stem of transgenic plants were similar or slightly higher compared to that of the wild-type plants, whereas mature leaves of transgenic plants contained a higher level of CEL1. These data indicate that in elongating zone of Arabidopsis, CEL1 level is tightly regulated. In contrast to transgenic poplar over-expressing the A. thaliana cel1, no phenotypic difference was found between A. thaliana transgenic and wild-type plants.

Changes in the Activity of Antioxidant Enzymes in Wheat Leaves and Roots as a Function of Nitrogen Source and Supply

Abstract: The activity of enzymes participating in the systems of antioxidant protection was assayed in the second leaf and roots of 21-day-old wheat seedlings (Triticum aestivum L.) grown in a medium with nitrate (NO– 3 treatment), ammonium (NH+ 4 treatment), or without nitrogen added (N-deficiency treatment). The activities of superoxide dismutase (SOD), peroxidase, ascorbate peroxidase, glutathione reductase, and catalase in the leaves and roots of the NH+ 4 plants was significantly higher than in the plants grown in the nitrate medium. The activity of SOD decreased and ascorbate peroxidase markedly increased in leaves, whereas the activity of ascorbate peroxidase increased in the roots of N-deficient plants, as compared to the plants grown in nitrate and ammonium. Low-temperature incubation (5°С, 12 h) differentially affected the antioxidant activity of the studied plants. Whereas leaf enzyme activities did not change in the NH+ 4 plants, the activities of SOD, peroxidase, ascorbate peroxidase, and catalase markedly increased in the NO– 3 plants. In leaves of the N-deficient plant, the activity of SOD decreased; however, the activity of other enzymes increased. In response to temperature decrease, catalase activity increased in the roots of NO– 3 and NH+ 4-plants, whereas in the N-deficient plants, the activity of peroxidase increased. Thus, in wheat, both nitrogen form and nitrogen deficiency changed the time-course of antioxidant enzyme activities in response to low temperature.

Evidence for Positive Regulation by Gibberellins and Ethylene of ACC Oxidase Expression and Activity During Transition From Dormancy to Germination in Fagus sylvatica L. Seeds

Abstract: 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase is a key enzyme in the ethylene biosynthesis pathway. In the present report the changes in ACC content, ACC oxidase activity and ethylene production have been examined in Fagus sylvatica L. dormant seeds after stratification and different treatments that maintain or release dormancy. Additionally, a cDNA encoding an ACC oxidase (ACO) from Fagus sylvatica has been isolated and characterized. This clone, named FsACO1, exhibits high homology to ACC oxidases from several plant species and the corresponding enzyme, expressed in Escherichia coli as a fusion protein, is active in converting ACC into ethylene. The transcript levels of FsACO1 are correlated with the ACC content, the ethylene production and the ACC oxidase activity measured in vitro as well as with the germination percentages observed in the seeds under the different treatments used in this study. There is a drastic increase in all these parameters when seeds are treated with GA3 or ethephon (which releases ethylene in solution), hormones previously proven to be efficient in the breaking of dormancy of beech seeds. The stimulatory effect of ethephon is reverted by paclobutrazol, a well known GA biosynthesis inhibitor. These results indicate that ethylene biosynthesis is positively regulated by both gibberellins and ethylene and suggest a cross-talk regulation by these two hormones of the processes involved in the transition from seed dormancy to germination.

Changes in abscisic acid during leaf yellowing of cut stock flowers

Abstract: Leaf pigments, such as chlorophyll and carotenoids, are essential plant molecules They provide carbohydrates and energy during all plant life Leaf pigments are also important parameters of decorative plants, such as floriculture items, cut foliage and flowers Leaf yellowing is a form of senescence caused by an internal hormone imbalance, such as a lack of cytokinins The aim of this study was to investigate the changes in total carotenoids and endogenous ABA in cut flower stock leaves during post-harvest life The effect of pulse treatment with 5 or 10 μM thidiazuron (TDZ), 150 mg l−1 8-hydroxyquinoline sulphate (8-HQS) and combinations of TDZ with 8-HQS on total carotenoids and ABA concentration was also investigated Results showed that total carotenoids drastically decreased from 1548 μg cm−2, until reaching 565 μg cm−2 at the end of vase life Endogenous ABA strongly increased at the same time, going from 167 ng g−1 DW at the beginning of the experiment to 1322 ng g−1 DW at the end of vase life The TDZ inhibited carotenoid degradation, but did not affect the ABA concentration, while the 8-HQS did not prevent carotenoid degradation and the ABA concentration was only slightly affected ABA seems to be a secondary senescence bio-product that may have a synergic effect with other senescence inducers dramatically accelerating leaf senescence

Research advance in nitrogen metabolism of plant and its environmental regulation

Abstract: Nitrogen metabolism is not only one of the basic processes of plant physiology, but also one of the important parts of global chemical cycle. Plant nitrogen assimilation directly takes part in the synthesis and conversion of amino acid through the reduction of nitrate. During this stage, some key enzymes, e.g., nitrate reductase (NR), glutamine synthetase (GS), glutamate dehydrogenase (GDH), glutamine synthase (GOGAT), aspargine synthetase (AS), and asparate aminotransferase (AspAT) participate these processes. The protein is assimilated in plant cell through amino acid, and becomes a part of plant organism through modifying, classifying, transporting and storing processes, etc. The nitrogen metabolism is associated with carbonic metabolism through key enzyme regulations and the conversion of products, which consists of basic life process. Among these amino acids in plant cell, glutamic acid (Glu), glutamine (Gln), aspartic acid (Asp) and asparagines (Asn), etc., play a key role, which regulates their conversion each other and their contents in the plant cell through regulating formation and activity of those key enzymes. Environmental factors also affect the conversion and recycle of the key amino acids through regulating gene expression of the key enzymes and their activities. Nitrate and light intensity positively regulate the gene transcription of NR, but ammonium ions and Glu, Gln do the negative way. Water deficit is a very serious constraint on N2 fixation rate and soybean (Glycine max Merr.) grain yield, in which, ureide accumulation and degradation under water deficit appear to be the key issues of feedback mechanism on nitrogen fixation. Water stress decreases NR activity, but increases proteinase activity, and thus, they regulate plant nitrogen metabolism, although there are some different effects among species and cultivars. Water stress also decreases plant tissue protein content, ratio of protein and amino acid, and reduces the absorption of amino acid by plant. On the contrary, soil flooding decreases the content and accumulation amount of root nitrogen in winter wheat by 11.9% from booting to flowering stages and 39.1% during grain filling stage, and reduces the ratio of carbon and nitrogen by 79.6%. The results misadjust the metabolism between carbon and nitrogen, and result in the end of the root growth. Elevated CO2 level could decrease plant leaf nitrogen content under well-watered condition, but almost maintain stable under water deficit condition. The radiation of UV-B significantly reduces the partitioning coefficient and synthetic rate of Rubisco, which significantly decreases the photosynthetic rate. This paper reviewed the pathway of plant nitrogen assimilation, characteristics of key enzymes and their regulating mechanisms with picturing the regulating mode of NR, and described the signal sensing and conduct of plant nitrogen metabolism and the formation, transportation, storage and degradation of plant cell protein with picturing the schedule of protein transport of membrane system in plant cell. Seven key tasks are emphasized in this paper in terms of the review on the effects and mechanisms of key ecological factors including water stress on plant nitrogen metabolism. They are: 1) the absorption mechanism of plant based on different nitrogen sources and environmental regulations, 2) the localization and compartmentalization of the key enzymes of nitrogen mechanism in plant cell, 3) the gene and environmental regulating model and their relationships in various key enzymes of nitrogen metabolism, 4) the function of main cell organs and their responses to environmental factors in nitrogen metabolism process, 5) physiological and chemical mechanism of nitrogen and the relationship between the mechanism and protein formation during crop grain filling, 6) improving gene structure of special species or cultivars using gene engineering methods to enhance the resistance to environmental factor stress and the efficiency of absorption and transportation of nitrogen, and 7) the mechanism of natural nitrogen cycle and its response to human activity disturbance.

Relationship between quantum efficiency of PSII and cold-induced plant resistance to fungal pathogens

Abstract: The aim of the presented work was to study whether the efficiency of photosynthesis may influence resistance of hardened plants to disease. Seedlings of spring barley, meadow fescue and winter oilseed rape were chilled at 5 °C for 2, 4 or 6 weeks and at these deadlines the changes in cell membrane permeability (expressed as electrolyte leakage), chlorophyll fluorescence (initial fluorescence - F0, maximal fluorescence - Fm, quantum yield of PSII - Fv/Fm) and net photosynthesis rate (FN) were measured. Also, the influence of cold on the degree of plant resistance to economically important pathogens -Bipolaris sorokiniana or Phoma lingam was estimated. Two, four or six week-hardened plants were artificially infected: barley and fescue by B. sorokiniana, and oilseed rape by P. lingam.

Transformation of Lotus corniculatus Plants with Escherichia coli Asparagine Synthetase A: Effect on Nitrogen Assimilation and Plant Development

Abstract: Asparagine and glutamine are major forms of nitrogen in the phloem sap of many higher plants. In vascular plants, glutamine-dependent asparagine synthetase (AS) is the primary source of asparagine. In Escherichia coli, asparagine is synthesized by the action of two distinct enzymes, AS-A which utilizes ammonia as a nitrogen donor, and AS-B which utilizes both glutamine and ammonia as substrates, but with a preference for glutamine. In this study, the possibility to endow plants with ammonia-dependent AS activity was investigated by heterologous expression of E. coli asnA gene with the aim to introduce a new ammonium assimilation pathway in plants. The bacterial gene is placed under the control of light-dependent promoters, and introduced by transformation into Lotus corniculatus plants. Analysis of transgenic plants has revealed a phenomenon of transgene silencing which has prevented asnA expression in several transgenics. The asnA-expressing plants are characterized by premature flowering and reduced growth. A significant reduction of the total free amino acid accumulation in transgenic plants is observed. Surprisingly, the content of asparagine in wild-type plants is about 2.5-fold higher than that of transgenic plants. While glutamine levels in transgenic plants are about 3–4-fold higher than those in wild-type plants, aspartate levels are significantly lower. Transformation with asnA also induced a significant reduction of photosynthesis when measured under saturated light and ambient CO2 conditions.

Photosynthesis and Dark Respiration in Leaves of Different Ages of Partly Flooded Maize Seedlings

Abstract: Maize seedlings were flooded for periods from 1 to 15 days, and the leaves of different ages were then taken to examine photosynthesis, dark respiration, transpiration, chlorophyll content, and some morphometric parameters. The responses of leaves to root submergence essentially depended on the leaf layer and the treatment duration. A short-term flooding (1–24 h) induced primary stress responses in the first leaf. Photosynthesis and respiration in this leaf oscillated around the control levels with amplitudes of ±15–25% and ±40–60%, respectively. After a longer flooding, the CO2 exchange in the second leaf was suppressed, while oxygen uptake was stimulated. In the third leaf, which was formed during submergence, the photosynthetic rate increased and the respiratory activity decreased. The transpiration rate did not change in these leaves for 15 days of flooding. The hypoxic treatment, at its early stages, retarded growth and disturbed the source–sink relations. At later stages the plants adapted to hypoxic environment: the seedling growth was restored, which elevated the demand for assimilates and stimulated photosynthesis. It is concluded that plants overcome negative impact of the root hypoxia at the systemic level.

Heat-Induced Increase in the Tolerance of the Wheat Photosynthetic Apparatus to Combined Action of High Temperature and Visible Light: CO2 Fixation, Photosynthetic Pigments, and Chloroplast Ultrastructure

Abstract: Heating of the leaves of 15-day-old wheat (Triticum aestivum L.) plants at 42°C in the light (370 W/m2 PAR) suppressed their ability to fix CO2 twice stronger than heating in darkness. Heat hardening (3 h at 38–39°C) improved the tolerance of photosynthesis to combined action of high light and temperature but did not affect the tolerance to photoinhibition at 30°C. Hardening did not induce changes in the levels of photosynthetic pigments and their ratios. De-epoxidation of violaxanthin turned out to be more tolerant to photoinhibition at 42°C than CO2 fixation. Protective effect of hardening was not related to the accumulation of zeaxanthin and activation of the xanthophyll cycle. Hardening protected the most sensitive population of chloroplasts against heat-induced photodamage and simultaneously increased the number and length of thylakoids. An increase in the volume of the thylakoid system was also induced by heating at 42°C and exposure to high light at 30°C. The formation of additional thylakoids and grana of shade type was not associated with improved tolerance of photosynthesis to heat and light stresses.

The Pool of Chlorophyllous Pigments in Barley Seedlings of Different Ages under Heat Shock and Water Deficit

Abstract: The effects of a high temperature (3 h, 40°C) and water deficit (45 h on 3% PEG 6000) on the pool of chlorophyllous pigments in the leaves of 4-, 7-, and 11-day-old barley (Hordeum vulgare L.) seedlings were studied. Heating resulted in a decrease in the total content of chlorophylls (Chl) (a + b) in 4-day-old plants but not in the older leaves. Water deficit induced an increase in the pigment content in young seedlings but reduced it in the leaves of 11-day-old plants. In young seedlings, hyperthermia and dehydration affected similarly Chl (a + b) degradation, leading to a marked inhibition of the chlorophyllase (Chlase) activity hydrolyzing Chl to chlorophyllides and phytol. In old leaves, an activation of this enzyme was observed. The stress factors under study affected different stages of pigment biosynthesis. High temperature inhibited the activity of dark and light stages of Chl(a + b) biosynthesis. Dehydration did not change markedly the resynthesis of protochlorophyllide, while the enzymes of the light stage of Chl biosynthesis were activated in young but inhibited in old barley leaves. The results thus obtained allowed us to conclude that heat treatment and dehydration specifically affected the Chl biosynthesis. At the same time, the Chlase response was nonspecific.

Photosynthetic CO 2 Fixation in the Second Leaf of Wheat Seedlings Grown at Different Conditions of Nitrogen Nutrition

Abstract: The rates of photosynthetic СО2 assimilation were determined in fully expanded second leaves of 21-day-old wheat (Triticum aestivum L.) seedlings grown on media supplied with nitrate or ammonia and on a nitrogen-free medium (NO3 –- or NH4 +-treatments and N-deficit treatment, respectively). The maximal quantum efficiency of photosynthesis was independent on conditions of nitrogen nutrition. When leaves were exposed to 0.03% СО2 and high-intensity light, the lowest photosynthetic rate was noted for N-deficit treatment and the highest rate was characteristic of NH4 + treatment. The elevation of the СО2 concentration in the gas phase to 0.1% stimulated photosynthesis at high-intensity light in all treatments. The rate of СО2 uptake by the leaf of N-deficient seedlings increased with СО2 concentration to a larger extent than in other treatments and approached the СО2 uptake rate characteristic of the NO3 – treatment. In plants grown on a nitrogen-free medium, the leaf accumulated lesser amounts of reduced nitrogen and higher amounts of starch, but the content of chloroplast protein corresponded to that of NO3 – treatment. In the leaf of NH4 +-treated seedlings, the rate of СО2 assimilation was higher than in the leaf of NO3 – treated plants, regardless of the composition of the gas mixture. The ammonium-type nutrition, as compared to the nitrate-type nutrition, elevated the amount of reduced nitrogen in the leaf and promoted accumulation of chlorophyll and protein, the chloroplast protein in particular.

Expression of recombinant protoporphyrinogen oxidase influences growth and morphological characteristics in transgenic rice

Abstract: Transgenic rice plants expressing a Bacillus subtilis protoporphyrinogen oxidase (Protox), the last shared enzyme of the porphyrin pathway, in the cytoplasm (C89) or the plastids (P72) were compared with wild-type rice plants in their growth characteristics. Production of tiller buds 18 d after seeding was more profuse in transgenic plants than in wild-type plants, especially in plastid-targeted plants. Transgenic plants had 12-27% increase in tiller number and 17-33% increase in above-ground biomass compared with wild-type plants 4 and 8 weeks after transplanting of 2-week-old rice seedlings, demonstrating that tiller production and above-ground biomass correlate with each other. Cytoplasm-expressed and plastid-targeted transgenic plants also had a distinct phenotypic characteristic of narrower and more horizontal leaves than wild-type plants. Phenotypic and anatomical characteristics of the transgenic plants were clearly different from wild-type plants, indicating that regulation of porphyrin biosynthesis by expression of B. subtilis Protox in rice influences morphological characteristics of plant growth as well as biomass.

Reduction of phytochrome level and light-induced formation of adventitious shoots by introduction of antisense genes for phytochrome A in horseradish hairy roots

Abstract: In 5′; non-coding regions of genes for phytochrome A from horseradish (ArPHYAs) were fused with the 35S promoter of cauliflower mosaic virus in the antisense direction (CaMV35SantiArPHYAs) and introduced into horseradish hairy roots. Phytochrome levels of proximal areas in many hairy roots that had been transformed with CaMV35SantiArPHYAs decreased to levels of about one-half to one-quarter those of control hairy roots. The extent of the light-induced formation of adventitious shoots from hairy roots with less than half of the control level of phytochrome was lower than in the controls and not different between the three ArPHYAs. In contrast, the efficiency of phytochrome on the extent of shoot formation differed in hairy roots transformed with CaMV35SantiArPHYAs when phytochrome levels were more than 0.02 (Δ;(Δ;A) g−1). The efficiency of ArPHYA3 to initiate shoot formation was greatest and that of ArPHYA2 was smallest. Furthermore, previous reports on hairy roots overexpressing ArPHYAs showed a similar efficiency of phytochrome on shoot formation. These results indicate that the ArphyA1 and/or ArphyA3 play major roles in the light-induced formation of adventitious shoots and that ArphyA2 has a minor role.

Circadian Ethylene Synthesis in Sorghum bicolor : Expression and Control of the System at the Whole Plant Level

Abstract: Ethylene production by sorghum is rhythmic and the amplitude of the rhythm is increased both by dim, far-red enriched light and in mutant plants deficient in phytochrome B. The mechanisms involved in controlling ethylene production were examined in detail by measuring the rate of ethylene production among organs and tissues, examining the organ-specific levels of ACC (1-aminocyclopropane-1-carboxylic acid, the ethylene precursor) and investigating the contribution of the roots to shoot ethylene production. The results demonstrate that the expanding leaves were the major source of ethylene under dim, far-red enriched light and in the phytochrome B mutant. Enhanced ethylene production by the expanding leaf appeared to be the result of targeted delivery of ACC to this tissue. Root ACC levels were much higher than those in the shoot but roots converted much less of this endogenous ACC to ethylene. Applying ACC to the roots had only a marginal effect on their ethylene production, but greatly increased that of the shoots. Decapitated shoots continued to produce ethylene in a rhythmic pattern but the amplitude decreased with time compared to intact plants. The results collectively suggest that some, but not all, of the shoot ethylene rhythm depends on the transport of ACC from the roots to the shoots.

Pigments and Gas Exchange Characteristics in Leaves of Chlorophyll Mutants of Pisum sativum

Abstract: Quantitative and qualitative characteristics of pigment composition and gas exchange were studied in chlorophyll mutants of pea, Pisum sativum L.: chlorotica 2004 and 2014. The mutant 2004 had light-green color, whereas the mutant 2014 has yellow-green leaves and stems; they contained about 80 and 50% of chlorophyll, respectively, compared to the initial line. cv. Torsdag. Leaves of the mutant 2004 had significantly lower carotene content and accumulated more lutein and violaxanthin. In the mutant 2014, the contents of chlorophyll and all carotenoids were reduced almost proportionally. The quantum efficiency of photosynthesis was by 29–30% lower in the mutants, and it was 1.5–2 times higher in F1 hybrids, as compared to control plants. Our data allow us to conclude that the impairment of photosynthesis in the mutant 2014 is caused by the changed mesostructure of leaves, whereas in the mutant 2004, it may be caused by an impairment of photosystem reaction centers.

Contribution of Photorespiration to Changes of Carbon Isotope Characteristics in Plants Affected by Stress Factors

Abstract: Experimental data available in literature on changes in the carbon isotopic composition of biochemical fractions and metabolites isolated from plant biomass (Clusia minor) and photosynthesizing algae (Chlorella stigmatophora) under the action of environmental stress factors are reviewed and analyzed. Within the framework of previously suggested mechanism of carbon isotope fractionation in photosynthesis, all studied fractions and metabolites obtained from plants and photosynthesizing algae can be divided into two groups according to their carbon isotope composition. The first group includes the fractions and metabolite pools that contain carbon stored by cell during the carboxylase phase of Rubisco functioning. The second group consists of those formed primarily by the photorespiratory carbon flow, generated during the oxygenase phase of Rubisco functioning. The first group represents the “assimilatory” branch of photosynthesis and is enriched in 12C relative to carbon of biomass, whereas the second group represents the “photorespiratory” branch and is enriched in 13C. Under the action of environmental stress factors, such as incident light intensity, moisture availability, and salinity; the isotope composition of metabolites and fractions changes, which reflects variable contributions of the “assimilatory” and “photorespiratory” flows to the metabolite synthesis. These isotope shifts were used to study biochemical adaptation of plants to stress conditions and to elucidate the role of photorespiration in this adaptation.

Photoregulation of Protochlorophyllide Oxidoreductase and Rubisco Large Subunit Accumulation in Phytochrome A-Deficient Transgenic Tobacco Plants

Abstract: Some morphogenetic responses, induced by far red (FR) light in tobacco plants (Nicotiana tabacum L.), were studied. The inhibitory effect of FR irradiation on chlorophyll synthesis in transgenic plants with reduced phytochrome A content was almost absent. Phytochrome A-mediated repression of the por gene was demonstrated with the use of polyclonal antiserum against protochlorophyllide oxidoreductase. Continuous FR light induced the accumulation of Rubisco large subunits in wild-type but not in transgenic tobacco plants. Our data confirm the suggestion that phytochrome A mediates photoregulation of the synthesis of these proteins.

Aquaporin Content in Cell Membranes of Mesembryanthemum crystallinum as Affected by Plant Transition from C3 to CAM Type of Photosynthesis

Abstract: Western-blot analysis was used to determine the contents of aquaporin isoforms MIP A, MIP B, and MIP C in cell membranes isolated from roots and leaves of Mesembryanthemum crystallinum plants with C3 and Crassulacean acid metabolism (CAM) types of photosynthesis These membrane preparations were also used to assess osmotic water permeability; to this end, the rate of osmotic vesicle shrinking was registered as the light scattering intensity by the method of stopped flow The cell membranes represented by the plasmalemma and the tonoplast-enriched fraction were obtained by separating the microsomes in a two-phase polymer system Plant transition from C3 to CAM-photosynthesis occurred in the course of plant development or was induced by salinization All three isoforms under study were found in the plasma membranes of roots and leaves of the C3 plants, whereas in the CAM plants, independent of the transition-inducing factor, the aquaporin contents notably decreased in the leaf membranes and remained unchanged in the roots In the membranes isolated from roots and leaves of the C3 plants, the values of osmotic water permeability exceeded two–threefold the corresponding indices characteristic of the CAM plants The authors believe that aquaporin isoforms in M crystallinum are under the organ- and tissue-specific control

Production and Analysis of Tobacco Transgenic Plants Expressing the Agrobacterial Gene for Tryptophan Monooxygenase

Abstract: The expression of the agrobacterial iaaM gene for tryptophan monooxygenase, the enzyme catalyzing the first step in the auxin biosynthesis, induced substantial physiological and biochemical changes in transgenic tobacco (Nicotiana tabacum L.) plants. All lines of transgenic plants grown in vitro manifested abnormal phenotypes: enhanced root formation, adventitious roots on stems, and curled leaves. When grown in vivo, plants manifested abnormal, normal, or intermediate phenotype. Under conditions of a greenhouse, the abnormal plants contained the highest amount of auxins in their leaves and manifested an increased number of adventitious roots, poor reproductivity, and the loss in seed germination. Transgenic plants with the normal phenotype did not substantially differ from the wild-type plants in their morphology, and their auxin content was lower than in the abnormal plants. The intermediate-phenotype plants were devoid of some morphological properties characteristic of the abnormal plants. Only the seeds of normal- and intermediate-phenotype transgenic plants germinated at a high rate.