Showing papers on "Plant physiology published in 2008"

Oxidative signaling in seed germination and dormancy

Abstract: Reactive Oxygen Species (ROS) play a key role in various events of seed life. In orthodox seeds, ROS are produced from embryogenesis to germination, i.e. in metabolically active cells, but also in quiescent dry tissues during after ripening and storage, owing various mechanisms depending on the seed moisture content. Although ROS have been up to now widely considered as detrimental to seeds, recent advances in plant physiology signaling pathways has lead to reconsider their role. ROS accumulation can therefore be also beneficial for seed germination and seedling growth by regulating cellular growth, ensuring a protection against pathogens or controlling the cell redox status. ROS probably also act as a positive signal in seed dormancy release. They interact with abscisic acid and gibberellins transduction pathway and are likely to control numerous transcription factors and properties of specific protein through their carbonylation.

Sucrose transporter StSUT4 from potato affects flowering, tuberization, and shade avoidance response

Abstract: Sucrose (Suc) transporters belong to a large gene family. The physiological role of SUT1 proteins has been intensively investigated in higher plants, whereas that of SUT4 proteins is so far unknown. All three known Suc transporters from potato (Solanum tuberosum), SUT1, SUT2, and SUT4, are colocalized and their RNA levels not only follow a diurnal rhythm, but also oscillate in constant light. Here, we examined the physiological effects of transgenic potato plants on RNA interference (RNAi)-inactivated StSUT4 expression. The phenotype of StSUT4-RNAi plants includes early flowering, higher tuber production, and reduced sensitivity toward light enriched in far-red wavelength (i.e. in canopy shade). Inhibition of StSUT4 led to tuber production of the strict photoperiodic potato subsp. andigena even under noninductive long-day conditions. Accumulation of soluble sugars and Suc efflux from leaves of transgenic plants are modified in StSUT4-RNAi plants, leading to modified Suc levels in sink organs. StSUT4 expression of wild-type plants is induced by gibberellins and ethephon, and external supply of gibberellic acid leads to even more pronounced differences between wild-type and StSUT4-RNAi plants regarding tuber yield and internode elongation, indicating a reciprocal regulation of StSUT4 and gibberellins.

Mycorrhizal and non-mycorrhizal Lactuca sativa plants exhibit contrasting responses to exogenous ABA during drought stress and recovery

Abstract: The arbuscular mycorrhizal (AM) symbiosis enhances plant tolerance to water deficit through the alteration of plant physiology and the expression of plant genes. These changes have been postulated to be caused (among others) by different contents of abscisic acid (ABA) between AM and non-AM plants. However, there are no studies dealing with the effects of exogenous ABA on the expression of stress-related genes and on the physiology of AM plants. The aim of the present study was to evaluate the influence of AM symbiosis and exogenous ABA application on plant development, physiology, and expression of several stress-related genes after both drought and a recovery period. Results show that the application of exogenous ABA had contrasting effects on AM and non-AM plants. Only AM plants fed with exogenous ABA maintained shoot biomass production unaltered by drought stress. The addition of exogenous ABA enhanced considerably the ABA content in shoots of non-AM plants, concomitantly with the expression of the stress marker genes Lsp5cs and Lslea and the gene Lsnced. By contrast, the addition of exogenous ABA decreased the content of ABA in shoots of AM plants and did not produce any further enhancement of the expression of these three genes. AM plants always exhibited higher values of root hydraulic conductivity and reduced transpiration rate under drought stress. From plants subjected to drought, only the AM plants recovered their root hydraulic conductivity completely after the 3 d recovery period. As a whole, the results indicate that AM plants regulate their ABA levels better and faster than non-AM plants, allowing a more adequate balance between leaf transpiration and root water movement during drought and recovery.

Screening of visible and UV radiation as a photoprotective mechanism in plants

Abstract: Prolonged exposure of plants to high fluxes of solar radiation as well as to other environmental stressors disturbs the balance between absorbed light energy and capacity of its photochemical utilization resulting in photoinhibition of and eventually in damage to plants. Under such circumstances, the limiting of the light absorption by the photosynthetic apparatus efficiently augments the general photoprotective mechanisms of the plant cell, such as reparation of macromolecules, elimination of reactive oxygen species, and thermal dissipation of the excessive light energy absorbed. Under stressful conditions, plants accumulate, in different cell compartments and tissue structures, pigments capable of attenuation of the radiation in the UV and visible parts of the spectrum. To the date, four principle key groups of photoprotective pigments are known: mycosporine-like amino acids, phenolic compounds (including phenolic acids, flavonols, and anthocyanins), alkaloids (betalains), and carotenoids. The accumulation of UV-absorbing compounds (mycosporine-like amino acids and phenolics in lower and higher plants, respectively) is a ubiquitous mechanism of adaptation to and protection from the damage by high fluxes of solar radiation developed by photoautotrophic organisms at the early stages of their evolution. Extrathylakoid carotenoids, betalains, and anthocyanins play an important role in long-term adaptation to the illumination conditions and in protection of plants against photodamage. A prominent feature of certain plant taxa lacking some classes of photoprotective pigments (such as anthocyanins) is their substitution by other compounds (e.g. keto-carotenoids or betalains) disparate in terms of chemical structure and subcellular localization but possessing close spectral properties.

Cell wall-bound invertase limits sucrose export and is involved in symptom development and inhibition of photosynthesis during compatible interaction between tomato and Xanthomonas campestris pv vesicatoria

Abstract: Cell wall-bound invertase (cw-Inv) plays an important role in carbohydrate partitioning and regulation of sink-source interaction. There is increasing evidence that pathogens interfere with sink-source interaction, and induction of cw-Inv activity has frequently been shown in response to pathogen infection. To investigate the role of cw-Inv, transgenic tomato (Solanum lycopersicum) plants silenced for the major leaf cw-Inv isoforms were generated and analyzed during normal growth and during the compatible interaction with Xanthomonas campestris pv vesicatoria. Under normal growth conditions, activities of sucrolytic enzymes as well as photosynthesis and respiration were unaltered in the transgenic plants compared with wild-type plants. However, starch levels of source leaves were strongly reduced, which was most likely caused by an enhanced sucrose exudation rate. Following X. campestris pv vesicatoria infection, cw-Inv-silenced plants showed an increased sucrose to hexose ratio in the apoplast of leaves. Symptom development, inhibition of photosynthesis, and expression of photosynthetic genes were clearly delayed in transgenic plants compared with wild-type plants. In addition, induction of senescence-associated and pathogenesis-related genes observed in infected wild-type plants was abolished in cw-Inv-silenced tomato lines. These changes were not associated with decreased bacterial growth. In conclusion, cw-Inv restricts carbon export from source leaves and regulates the sucrose to hexose ratio in the apoplast. Furthermore, an increased apoplastic hexose to sucrose ratio can be linked to inhibition of photosynthesis and induction of pathogenesis-related gene expression but does not significantly influence bacterial growth. Indirectly, bacteria may benefit from low invertase activity, since the longevity of host cells is raised and basal defense might be dampened.

Sulfur starvation in rice: the effect on photosynthesis, carbohydrate metabolism, and oxidative stress protective pathways.

Abstract: Sulfur-deficient plants generate a lower yield and have a reduced nutritional value. The process of sulfur acquisition and assimilation play an integral role in plant metabolism, and response to sulfur deficiency involves a large number of plant constituents. Rice (Oryza sativa) is the second most consumed cereal grain, and the effects of sulfur deprivation in rice were analyzed by measuring changes in photosynthesis, carbohydrate metabolism, and antioxidants. The photosynthetic apparatus was severely affected under sulfur deficiency. The Chl content was reduced by 49% because of a general reduction of PSI I and PSI and the associated light-harvesting antenna. The PSI I efficiency was 31% lower at growth light, and the ability of PSI to photoreduce NADP + was decreased by 61%. The Rubisco content was also significantly reduced in the sulfur-deprived plants. The imbalances between PSII and PSI, and between photosynthesis and carbon fixation led to a general over-reduction of the photosynthetic electron carriers (higher 1 - qp). Chromatographic analysis showed that the level of monosaccharides was lower and starch content higher in the sulfur-deprived plants. In contrast, no changes in metabolite levels were found in the tricarboxylic acid or Calvin cycle. The level ofthethiol-containingantioxidant, GSH, was 70% lower and the redox state was significantly more oxidized. These changes in GSH status led to an upregulation of the cytosolic isoforms of GSH reductase and monodehydroascorbate reductase. In addition, alternative antioxidants like flavonoids and anthocyanins were increased in the sulfur-deprived plants.

Comparative Proteomics of Chloroplast Envelopes from C3 and C4 Plants Reveals Specific Adaptations of the Plastid Envelope to C4 Photosynthesis and Candidate Proteins Required for Maintaining C4 Metabolite Fluxes

Abstract: C4 plants have up to 10-fold higher apparent CO2 assimilation rates than the most productive C3 plants. This requires higher fluxes of metabolic intermediates across the chloroplast envelope membranes of C4 plants in comparison with those of C3 plants. In particular, the fluxes of metabolites involved in the biochemical inorganic carbon pump of C4 plants, such as malate, pyruvate, oxaloacetate, and phosphoenolpyruvate, must be considerably higher in C4 plants because they exceed the apparent rate of photosynthetic CO2 assimilation, whereas they represent relatively minor fluxes in C3 plants. While the enzymatic steps involved in the C4 biochemical inorganic carbon pump have been studied in much detail, little is known about the metabolite transporters in the envelope membranes of C4 chloroplasts. In this study, we used comparative proteomics of chloroplast envelope membranes from the C3 plant pea (Pisum sativum) and mesophyll cell chloroplast envelopes from the C4 plant maize (Zea mays) to analyze the adaptation of the mesophyll cell chloroplast envelope proteome to the requirements of C4 photosynthesis. We show that C3- and C4-type chloroplasts have qualitatively similar but quantitatively very different chloroplast envelope membrane proteomes. In particular, translocators involved in the transport of triosephosphate and phosphoenolpyruvate as well as two outer envelope porins are much more abundant in C4 plants. Several putative transport proteins have been identified that are highly abundant in C4 plants but relatively minor in C3 envelopes. These represent prime candidates for the transport of C4 photosynthetic intermediates, such as pyruvate, oxaloacetate, and malate.

Brassinolide alleviated the adverse effect of water deficits on photosynthesis and the antioxidant of soybean (Glycine max L.)

Abstract: Brassinolide (BR) is a relatively new plant growth regulator. To test whether BR could be used to increase tolerance to water deficits in soybean, the effects of BR application on photosynthesis, assimilate distribution, antioxidant enzymes and seed yield were studied. BR at 0.1 mg l−1 was foliar applied at the beginning of bloom. Two levels of soil moisture (80% field capacity for well-watered control and 35% for drought-stressed treatment) were applied at pod initiation. BR treatment increased biomass accumulation and seed yield for both treatments. Drought stress inhibited translocation of assimilated 14C from the labeled leaf, but BR increased the translocation for both treatments. Drought stress depressed chlorophyll content and assimilation rate (A), while chlorophyll content and A of BR-treated plants were greater than that of drought-stressed plants. BR treatment increased maximum quantum yield of PS II, the activity of ribulose-1,5-bisphosphate carboxylase, and the leaf water potential of drought-stressed plants. Treatment with BR also increased the concentration of soluble sugars and proline, and the activities of peroxidase and superoxide dismutase of soybean leaves when drought-stressed. However, it decreased the malondialdehyde concentration and electrical conductivity of leaves under drought stress. This study show that BR can be used as a plant growth regulator to enhance drought tolerance and minimize the yield loss of soybean caused by water deficits.

Expression of the Vicia faba VfPIP1 gene in Arabidopsis thaliana plants improves their drought resistance.

Abstract: Plant aquaporins are believed to facilitate water transport across cell membranes. However, the relationship between aquaporins and drought resistance in plants remains unclear. VfPIP1, a putative aquaporin gene, was isolated from Vicia faba leaf epidermis, and its expression was induced by abscisic acid (ABA). Our results indicated that the VfPIP1 protein was localized in the plasma membrane, and its expression in V. faba was induced by 20% polyethylene glycol 6000. To further understand the function of VfPIP1, we obtained VfPIP1-expressing transgenic Arabidopsis thaliana plants under the control of the CaMV35S promoter. As compared to the wild-type control plants, the transgenic plants exhibited a faster growth rate, a lower transpiration rate, and greater drought tolerance. In addition, the stomata of the transgenic plants closed significantly faster than those of the control plants under ABA or dark treatment. These results suggest that VfPIP1 expression may improve drought resistance of the transgenic plants by promoting stomatal closure under drought stress.

The phytochrome red/far-red photoreceptor superfamily

Abstract: Proteins of the phytochrome superfamily of red/far-red light receptors have a variety of biological roles in plants, algae, bacteria and fungi and demonstrate a diversity of spectral sensitivities and output signaling mechanisms. Over the past few years the first three-dimensional structures of phytochrome light-sensing domains from bacteria have been determined.

Overexpressing SgNCED1 in Tobacco Increases ABA Level, Antioxidant Enzyme Activities, and Stress Tolerance

Abstract: Abscisic acid (ABA) regulates plant adaptive responses to various environmental stresses. 9-cis-epoxycarotenoid dioxygenase (NCED) is the key enzyme of ABA biosynthesis in higher plants. A NCED gene, SgNCED1, was overexpressed in transgenic tobacco plants which resulted in 51–77% more accumulation of ABA in leaves. Transgenic tobacco plants decreased stomatal conductance, transpiration rate, and photosynthetic rate but induced activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate-peroxidase (APX). Hydrogen peroxide (H2O2) and nitric oxide (NO) in leaves were also induced in the transgenic plants. Compared to the wild-type control, the transgenic plants improved growth under 0.1 M mannitol-induced drought stress and 0.1 M NaCl-induced salinity stress. It is suggested that the ABA-induced H2O2 and NO generation upregulates the stomatal closure and antioxidant enzymes, and therefore increases drought and salinity tolerance in the transgenic plants.

Increased protein carbonylation in leaves of Arabidopsis and soybean in response to elevated [CO2].

Abstract: While exposure of C3 plants to elevated [CO2] would be expected to reduce production of reactive oxygen species (ROS) in leaves because of reduced photorespiratory metabolism, results obtained in the present study suggest that exposure of plants to elevated [CO2] can result in increased oxidative stress. First, in Arabidopsis and soybean, leaf protein carbonylation, a marker of oxidative stress, was often increased when plants were exposed to elevated [CO2]. In soybean, increased carbonyl content was often associated with loss of leaf chlorophyll and reduced enhancement of leaf photosynthetic rate (Pn) by elevated [CO2]. Second, two-dimensional (2-DE) difference gel electrophoresis (DIGE) analysis of proteins extracted from leaves of soybean plants grown at elevated [CO2] or [O3] revealed that both treatments altered the abundance of a similar subset of proteins, consistent with the idea that both conditions may involve an oxidative stress. The 2-DE analysis of leaf proteins was facilitated by a novel and simple procedure to remove ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from soluble soybean leaf extracts. Collectively, these findings add a new dimension to our understanding of global change biology and raise the possibility that oxidative signals can be an unexpected component of plant response to elevated [CO2].

Regulation of CONSTANS and FLOWERING LOCUS T Expression in Response to Changing Light Quality

Abstract: In addition to pathways that regulate flowering in response to environmental signals such as photoperiod or cold temperatures (vernalization), flowering time is also regulated by light quality. In many species, far-red (FR) light is known to accelerate flowering. This is environmentally significant because leaves absorb more red light than FR light; thus, plants growing under a canopy experience light that is enriched in FR light. In this article, we have explored the promotion of flowering by FR-enriched light (FREL) in Arabidopsis (Arabidopsis thaliana). Previous work has shown that the floral promoter CONSTANS (CO) plays a critical role in day-length perception and exhibits complex regulation; CO mRNA is regulated by the circadian clock and CO protein is stabilized by light and degraded in darkness. We find that plants grown under FREL contain higher levels of CO mRNA in the early part of the day than plants under white light. Furthermore, transgenic plants expressing CO under the control of a constitutive promoter accumulate higher levels of CO protein under FREL, indicating that FREL can increase CO protein levels independently of transcription. Consistent with the model that FREL promotes flowering through CO, mutants for co or gigantea, which are required for CO transcript accumulation, are relatively insensitive to FREL. Because the red:FR ratios used in these experiments are in the range of what plants would experience under a canopy, these results indicate that the regulation of CO by light quality likely plays a key role in the regulation of flowering time in natural environments.

Effects of root flooding and stage of development on the growth and photosynthesis of field bean ( Vicia faba L. minor )

Abstract: Field bean plants were subjected to flooding stress for 7 days, during two stages of development: at the vegetative phase (4-week-old seedlings) and at the generative phase (8-week-old plants). The height of plants, total area of leaves, the number of undamaged leaves, dry plant matter, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity, the maximum quantum yield of PS2 photochemistry (Fv/Fm ratio), the photosynthesis rate (P N) and stomatal conductance (g s) were determined. A strong reduction in stem elongation and leaf area as well as in dry matter production was observed as a result of flooding. The responses from vegetative plants were greater than in generative plants. Waterlogging decreased chlorophyll a and b in leaves, notably at the vegetative stage, and persisted after cessation of flooding. After flooding, photosynthesis was strongly reduced and positively correlated with decreased stomatal conductance. Damage to the photosynthetic apparatus resulted in a lower Fv/Fm especially in young seedlings. In vegetative plants Fv/Fm quickly returned to the control levels after the soil was drained. The results show that an excess of water in the soil limits growth and injures the photosynthetic apparatus in field beans, but that the extent of the injury is strongly age dependent.

Abnormal Chloroplast Development and Growth Inhibition in Rice Thioredoxin m Knock-Down Plants

Abstract: Plant cells contain several thioredoxin isoforms that are characterized by subcellular localization and substrate specificity. Here, we describe the functional characterization of a rice (Oryza sativa) thioredoxin m isoform (Ostrxm) using a reverse genetics technique. Ostrxm showed green tissue-specific and light-responsive mRNA expression. Ostrxm was localized in chloroplasts of rice mesophyll cells, and the recombinant protein showed dithiothreitol-dependent insulin β-chain reduction activity in vitro. RNA interference (RNAi) of Ostrxm resulted in rice plants with developmental defects, including semidwarfism, pale-green leaves, abnormal chloroplast structure, and reduced carotenoid and chlorophyll content. Ostrxm RNAi plants showed remarkably decreased Fv/Fm values under high irradiance conditions (1,000 μmol m−2 s−1) with delayed recovery. Two-dimensional electrophoresis and matrix-assisted laser-desorption/ionization time-of-flight analysis showed that the levels of several chloroplast proteins critical for photosynthesis and biogenesis were significantly decreased in Ostrxm RNAi plants. Furthermore, 2-Cys peroxiredoxin, a known target of thioredoxin, was present in oxidized forms, and hydrogen peroxide levels were increased in Ostrxm RNAi plants. The pleiotropic effects of Ostrxm RNAi suggest that Ostrxm plays an important role in the redox regulation of chloroplast target proteins involved in diverse physiological functions.

Photosynthetic activity during olive (Olea europaea) leaf development correlates with plastid biogenesis and Rubisco levels.

Abstract: Olive leaves are known to mature slowly, reaching their maximum photosynthetic activity only after full leaf expansion. Poor assimilation rates, typical to young olive leaves, were previously associated with low stomata conductance. Yet, very little is known about chloroplast biogenesis throughout olive leaf development. Here, the photosynthetic activity and plastids development throughout leaf maturation is characterized by biochemical and ultrastructural analyses. Although demonstrated only low photosynthetic activity, the plastids found in young leaves accumulated both photosynthetic pigments and proteins required for photophosphorylation and carbon fixation. However, Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase), which catalyzes the first major step of carbon fixation and one of the most abundant proteins in plants, could not be detected in the young leaves and only slowly accumulated throughout development. In fact, Rubisco levels seemed tightly correlated with the observed photosynthetic activities. Unlike Rubisco, numerous proteins accumulated in the young olive leaves. These included the early light induced proteins, which may be required to reduce the risk of photodamage, because of light absorption by photosynthetic pigments. Also, high levels of ribosomal L11 subunit, transcription factor elF-5A, Histones H2B and H4 were observed in the apical leaves, and in particular a plastidic-like aldolase, which accounted for approximately 30% of the total proteins. These proteins may upregulate in their levels to accommodate the high demand for metabolic energy in the young developing plant tissue, further demonstrating the complex sink-to-source relationship between young and photosynthetically active mature leaves.

Leaf Development in the Single-Cell C4 System in Bienertia sinuspersici: Expression of Genes and Peptide Levels for C4 Metabolism in Relation to Chlorenchyma Structure under Different Light Conditions

Abstract: Bienertia sinuspersici performs C4 photosynthesis in individual chlorenchyma cells by the development of two cytoplasmic domains (peripheral and central) with dimorphic chloroplasts, an arrangement that spatially separates the fixation of atmospheric CO2 into C4 acids and the donation of CO2 from C4 acids to Rubisco in the C3 cycle. In association with the formation of these cytoplasmic domains during leaf maturation, developmental stages were analyzed for the expression of a number of photosynthetic genes, including Rubisco small and large subunits and key enzymes of the C4 cycle. Early in development, Rubisco subunits and Gly decarboxylase and Ser hydroxymethyltransferase of the glycolate pathway accumulated more rapidly than enzymes associated with the C4 cycle. The levels of pyruvate,Pi dikinase and phosphoenolpyruvate carboxylase were especially low until spatial cytoplasmic domains developed and leaves reached maturity, indicating a developmental transition toward C4 photosynthesis. In most cases, there was a correlation between the accumulation of mRNA transcripts and the respective peptides, indicating at least partial control of the development of photosynthesis at the transcriptional level. During growth under moderate light, when branches containing mature leaves were enclosed in darkness for 1 month, spatial domains were maintained and there was high retention of a number of photosynthetic peptides, including Rubisco subunits and pyruvate,Pi dikinase, despite a reduction in transcript levels. When plants were transferred from moderate to low light conditions for 1 month, there was a striking shift of the central cytoplasmic compartment toward the periphery of chlorenchyma cells; the mature leaves showed strong acclimation with a shade-type photosynthetic response to light while retaining C4 features indicative of low photorespiration. These results indicate a progressive development of C4 photosynthesis with differences in the control mechanisms for the expression of photosynthetic genes and peptide synthesis during leaf maturation and in response to light conditions.

Rearrangement of carbon metabolism in Arabidopsis thaliana subjected to oxidative stress condition: an emergency survival strategy

Abstract: Studies of oxidative stress in plants began several years ago, although many aspects of the antioxidant response are still unknown. In this work, we analyze the transcription profile of Arabidopsis thaliana leaves under oxidative and control conditions. Plants were challenged with methyl viologen (MV), a redox cycling herbicide that produces superoxide anion (O 2 •− ) in the light and in the chloroplasts, generating inhibition of photosynthesis. Gas exchange measurements and starch and soluble sugars were assayed to test the status of primary metabolism of Arabidopsis leaves. Within the first 2 h of 50 μM MV treatment, several genes were differentially expressed, among them were proteins implicated in photosynthesis, respiration, and carbon metabolism. Soluble sugars and starch markedly dropped after 3 h MV treatment, while respiration rate showed a steady increase after 4 h oxidative treatment. It was observed that the anabolic pathways were repressed while catabolic pathways were induced after the oxidative treatment. Overall, results suggest a rearrangement of carbon metabolism in the leaves, which could reflect a short-term mechanism of survival of Arabidopsis seedlings subjected to severe oxidative stress conditions.

Proteins responding to drought and high-temperature stress in Populus × euramericana cv. ‘74/76’

Abstract: Proteomic analysis provides a powerful method of studying plant responses to stress at the protein level. In order to study stress-responsive molecular mechanisms for Populus × euramericana cv. ‘74/76’, one of the most important forest plantation tree species in subtropical and temperate regions, we analyzed the response of 2-year-old cuttings of P. × euramericana cv. ‘74/76’ to drought and high temperature using two-dimensional gel electrophoresis. More than 1,000 reproducible leaf proteins were detected in the controls and treatments, and 26 proteins were found to change notably in abundance. We identified 13 proteins affected by drought stress and 11 proteins affected by high temperature. These proteins are mainly involved in photosynthesis such as ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit and putative photosystem I reaction center subunit II precursor, and detoxification (manganese superoxide dismutase and methionine sulfoxide reductase A). Furthermore, the level of the photosynthesis proteins affected greatly by the imposed stress conditions was consistent with the observed noticeable decrease in net photosynthesis rate. These studies provides a fundamental data for future research on responses to drought and high temperature, two major factors limiting the growth of forest trees during summer under recent climatic warming.

Hormonal regulation in green plant lineage families

Abstract: The patterns of phytohormones distribution, their native function and possible origin of hormonal regulation across the green plant lineages (chlorophytes, charophytes, bryophytes and tracheophytes) are discussed. The five classical phytohormones - auxins, cytokinins, gibberellins (GA), abscisic acid (ABA) and ethylene occur ubiquitously in green plants. They are produced as secondary metabolites by microorganisms. Some of the bacterial species use phytohormones to interact with the plant as a part of their colonization strategy. Phytohormone biosynthetic pathways in plants seem to be of microbial origin and furthermore, the origin of high affinity perception mechanism could have preceded the recruitment of a metabolite as a hormone. The bryophytes represent the earliest land plants which respond to the phytohormones with the exception of gibberellins. The regulation by auxin and ABA may have evolved before the separation of green algal lineage. Auxin enhances rhizoid and caulonemal differentiation while cytokinins enhance shoot bud formation in mosses. Ethylene retards cell division but seems to promote cell elongation. The presence of responses specific to cytokinins and ethylene strongly suggest the origin of their regulation in bryophytes. The hormonal role of GAs could have evolved in some of the ferns where antheridiogens (compounds related to GAs) and GAs themselves regulate the formation of antheridia. During migration of life forms to land, the tolerance to desiccation may have evolved and is now observed in some of the microorganisms, animals and plants. Besides plants, sequences coding for late embryogenesis abundant-like proteins occur in the genomes of other anhydrobiotic species of microorganisms and nematodes. ABA acts as a stress signal and increases rapidly upon desiccation or in response to some of the abiotic stresses in green plants. As the salt stress also increases ABA release in the culture medium of cyanobacterium Trichormus variabilis, the recruitment of ABA in the regulation of stress responses could have been derived from prokaryotes and present at the level of common ancestor of green plants. The overall hormonal action mechanisms in mosses are remarkably similar to that of the higher plants. As plants are thought to be monophyletic in origin, the existence of remarkably similar hormonal mechanisms in the mosses and higher plants, suggests that some of the basic elements of regulation cascade could have also evolved at the level of common ancestor of plants. The networking of various steps in a cascade or the crosstalk between different cascades is variable and reflects the dynamic interaction between a species and its specific environment.

Suppression of the source activity affects carbon distribution and frost hardiness of vegetating winter wheat plants

Abstract: Effect of suppression of the source activity on some physiological characteristics of winter wheat (Triticum aestivum L., cv. Mironovskaya 808) was studied on plants grown in water culture. The plants were examined at the mixotrophic stage of growth period, during their transition from vegetative state to relative dormancy in autumn. The average temperature over 10 days of the experiment was 6°C at 9-h photoperiod and illuminance of 8–20 klx. The source strength was suppressed successively with a series of treatments: intact control plants (V1); plants with the seed endosperm removed (V2); plants with photosynthesis inhibited (V3); plants with the seed endosperm removed and photosynthesis inhibited (V4); plants with the seed endosperm removed, photosynthesis inhibited, and the root nutrient medium replaced with distilled water (V5). On the 6th–10th day of the experiment, the relative growth rate (RGR) was determined from dry weight increments. At the same time, the distribution of biomass among organs, the CO2 exchange rates (photosynthesis and dark respiration), the content and proportions of sugars (sucrose, glucose, and fructose), the total content of phenolic compounds and flavonoids, the index of membrane stability (IMS) in leaves, and frost hardiness of plants were measured. Frost hardiness of vegetating plants was shown to be inversely related to RGR (R = −0.906), dark respiration rate (R = −0.789), the percentage of sucrose in total sugar content (R = −0.737), leaf IMS (R = −0.390), and the rate of apparent photosynthesis (R = −0.288); it was directly proportional to the content of flavonoids (R =0.973), total phenols (R = 0.743), and sugars (R = 0.385). The role of modified source-sink relations in frost hardiness of vegetating plants at the stage of their transition to cold hardening is discussed. The differences between plants undergoing this transition and cold-hardened plants are considered, as well as the importance of phenolic compounds for the development of frost hardiness.

Insertion of cyanobacterial desA gene coding for Δ12-acyl-lipid desaturase increases potato plant resistance to oxidative stress induced by hypothermia

Abstract: The role of Δ12-acyl-lipid desaturase in plant resistance to hypothermia-induced oxidative stress was investigated. This study focused on modulation of free-radical processes occurring at low temperature in leaf cells of potato plants (Solanum tuberosum L., cv. Desnitsa) transformed with the gene for Δ12-acyl-lipid desaturase from the cyanobacterium Synechocystis sp. PCC 6803. Nontransformed plants of the same cultivar were used as a control material. The plants were grown in vitro on Murashige and Skoog agarized medium containing 2% sucrose. During hypothermia the rate of superoxide anion generation and hydrogen peroxide concentration decreased significantly. In addition, the content of both primary products (conjugated dienes and trienes) and secondary products (malonic dialdehyde) of lipid peroxidation was lower in the transformed plant leaves than in leaves of wild-type plants. It is supposed that the insertion into the plant genome of Δ12-acyl-lipid desaturase stabilizes the composition and physical properties of biomembranes by promoting polyunsaturation of fatty acids, which averts the accelerated generation of O 2 ·− , — and suppresses lipid peroxidation during hypothermia. These changes improved cold resistance of potato plants, which was evident from the less severe injury of leaf blades in cold-treated transgenic plants, as compared to that in the wild-type line. The activity of superoxide dismutase, a key enzyme of the antioxidant defense system was lower in leaves of transformed plants than in leaves of wild-type plants. A comparatively low activity of superoxide dismutase in transgenic plants implies that these plants experience less severe thermal and oxidative stress upon cooling and can cope with the cold without considerable increase in the enzyme activity. It is concluded that the insertion of the desA gene encoding Δ12-acyl-lipid desaturase into cold-resistant potato plants improves plant resistance to cold-induced oxidative stress by decreasing the rate of intracellular free-radical processes.

Overexpression of DnaK from a halotolerant cyanobacterium Aphanothece halophytica enhances growth rate as well as abiotic stress tolerance of poplar plants

Abstract: The DnaK/Hsp70 family is a molecular chaperone that binds non-native states of other proteins, and concerns to various physiological processes in the bacterial, plant and animal cells. Previously, we showed that overexpression of DnaK from a halotolerant cyanobacterium Aphanothece halophytica (ApDnaK) enhances tolerance to abiotic stresses such as high salinity and high temperature in tobacco plants. Here, we tested the transformation of poplar (Populus alba) with ApDnaK for enhancing the growth of transformed poplar plants. Under control growth conditions, transgenic poplar plants exhibited similar growth rates with the wild-type plants during young seedlings under low light intensity, whereas they showed faster growth, larger plant size, and higher cellulose contents when poplar plants were grown under high light intensity. Transgenic young poplar plants exhibited more rapid recovery from the stresses of high salinity, drought, and low temperature compared with those of the wild type plants when poplar plants were grown under low light intensity. These results suggest that ApDnaK could be useful to enhance the growth rate as well as to increase the stress tolerance.

Activities of antioxidant system components and polyphenol oxidase in ontogeny of lawn grasses under megapolis conditions

Abstract: The activities of antioxidants enzymes (peroxidase (POX) and catalase (CAT)), the contents of non-enzymatic antioxidants (vitamin C, carotenoids), and the activity of polyphenol oxidase (PPO) were studied in vegetative organs of red clover (Trifolium pratense L.) and meadow-fescue (Festuca pratensis Huds.) growing under city conditions. The plants of three ages (virginal (V), generative (G), and subsenyl (SS)) were analyzed. The highest POX and PPO activities were characteristic of G plants, whereas CAT was most active in V plants. The content of low-molecular-weight antioxidants depended on species specificity and developmental stage and also on environment pollution. The content of ascorbate (vitamin C) declined linearly with plant development. Medium pollution also reduced the ascorbate content in tested plant leaves and roots. In contrast, the content of carotenoids increased with the increased activity of anthropogenic factors. The highest content of the pigments was in G plants. At all developmental stages and in all habitats, meadow-fescue (tolerant species) was characterized by the lower content of studied compounds than red clover (sensitive species). Thus, anthropogenic medium pollution resulted in the peroxide group accumulation, POX and PPO activation, carotenoid accumulation, and the ascorbate content decline in the vegetative tissues during the entire ontogeny of tolerant and sensitive lawn plants.

Effect of Jasmonic Acid on Morphogenesis and Photosynthetic Pigment Level in Arabidopsis Seedlings Grown under Green Light

Abstract: The role of jasmonic acid (JA) in plant photomorhogenesis under green light (GL) was studied. The effect of GL of different intensity (8.1 and 18.1 W/m2) with or without 1 µM JA treatment on growth of plants and photosynthetic pigment level was compared for two types of Arabidopsis thaliana (L.) Heynh. Landsberg erecta ecotype plants: Ler, the wild type, and hy4, a mutant. A much more pronounced growth of hypocotyls and cotyledons of Ler plants in GL was observed compared to that of hy4 with suppressed cryptochrome 1 (cry1), a GL photoreceptor. Treatment with JA in GL caused retardation of hypocotyl and cotyledon growth of Ler plants; however, it stimulated their growth in hy4 plants. JA reduced the chlorophyll a and total carotenoids levels in cotyledons of Arabidopsis plants in GL. Blocked GL signal transduction due to the absence of cry1 in hy4, as well as the higher intensity of GL reduced the negative effect of exogenous JA on growth of cotyledons and photosynthetic pigments. The data obtained provide a basis for discussion of interaction between the JA and GL signals in the growth regulation controlled by cry1.