Showing papers on "Plant physiology published in 2016"

Electrical signals as mechanism of photosynthesis regulation in plants

Abstract: This review summarizes current works concerning the effects of electrical signals (ESs) on photosynthesis, the mechanisms of the effects, and its physiological role in plants. Local irritations of plants induce various photosynthetic responses in intact leaves, including fast and long-term inactivation of photosynthesis, and its activation. Irritation-induced ESs, including action potential, variation potential, and system potential, probably causes the photosynthetic responses in intact leaves. Probable mechanisms of induction of fast inactivation of photosynthesis are associated with Ca2+- and (or) H+-influxes during ESs generation; long-term inactivation of photosynthesis might be caused by Ca2+- and (or) H+-influxes, production of abscisic and jasmonic acids, and inactivation of phloem H+-sucrose symporters. It is probable that subsequent development of inactivation of photosynthesis is mainly associated with decreased CO2 influx and inactivation of the photosynthetic dark reactions, which induces decreased photochemical quantum yields of photosystems I and II and increased non-photochemical quenching of photosystem II fluorescence and cyclic electron flow around photosystem I. However, other pathways of the ESs influence on the photosynthetic light reactions are also possible. One of them might be associated with ES-connected acidification of chloroplast stroma inducing ferredoxin-NADP+ reductase accumulation at the thylakoids in Tic62 and TROL complexes. Mechanisms of ES-induced activation of photosynthesis require further investigation. The probable ultimate effect of ES-induced photosynthetic responses in plant life is the increased photosynthetic machinery resistance to stressors, including high and low temperatures, and enhanced whole-plant resistance to environmental factors at least during 1 h after irritation.

Experiments In Plant Physiology

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Regulation of Plant Physiology and Antioxidant Enzymes for Alleviating Salinity Stress by Potassium-Mobilizing Bacteria

Abstract: Potassium (K) is among the most important essential macronutrients for plant growth. About 98 % of the potassium in the earth’s crust exists in insoluble forms as rocks and silicate minerals, resulting in very low concentrations of soluble potassium in the soil for plant growth and development. Rhizosphere bacteria are a group of metal-mobilizing, plant growth–promoting bacteria having the ability to solubilize potassium from insoluble potassium rocks. KSM (a potassium-solubilizing microorganism) is a metal-mobilizing, plant growth–promoting bacterium living symbiotically in/on the root surface and helps directly or indirectly in promoting plant growth via solubilization of insoluble minerals (K and P), assisting in resource acquisition (macro- and micronutrients), production of phytohormones and secretion of different regulatory chemicals in the purlieu of the rhizosphere of the plant root. KSM such as Bacillus spp. and Pseudomonas spp. are the most dominant plant growth–promoting bacteria (PGPB) of rhizospheric soils. Inoculation of KSM is found to be promising to induce growth of plants under 2.3–3.5 dSm−1 salinity levels and low availability of P and K, protecting the plants from salinity injury by enhancing their growth-related physiology and lipid peroxidation. These KSM help in the decrement of lipid peroxidation and enhance the stability of the plant cell membrane for the survival of the plant under salt stress. Inoculation of plants with such beneficial root-associated bacteria could provide salt tolerance to plants as these isolates also reside within the root, which is the plant part first directly in contact with saline soil. Hence it serves as a useful tool for alleviating salinity stress as well as in uptake of important mineral nutrients. The diversity of potassium-solubilizing microbes (KSM) and ability to mobilize important macronutrients from insoluble to soluble forms through biological conversion make them a good choice for agricultural use. Application of such efficient KSM aims to develop future prospects to provide a sustainable environmental system in different crop fields under both normal and stress conditions.

Overexpression of the Wheat Expansin Gene TaEXPA2 Improved Seed Production and Drought Tolerance in Transgenic Tobacco Plants.

Abstract: Expansins are cell wall proteins that are grouped into two main families, α-expansins and β-expansins, and they are implicated in the control of cell extension via the disruption of hydrogen bonds between cellulose and matrix glucans. TaEXPA2 is an α-expansin gene identified in wheat. Based on putative cis-regulatory elements in the TaEXPA2 promoter sequence and the expression pattern induced when polyethylene glycol (PEG) is used to mimic water stress, we hypothesized that TaEXPA2 is involved in plant drought tolerance and plant development. Through transient expression of 35S::TaEXPA2-GFP in onion epidermal cells, TaEXPA2 was localized to the cell wall. Constitutive expression of TaEXPA2 in tobacco improved seed production by increasing capsule number, not seed size, without having any effect on plant growth patterns. The transgenic tobacco exhibited a significantly greater tolerance to water-deficiency stress than did wild-type (WT) plants. We found that under drought stress, the transgenic plants maintained a better water status. The accumulated content of osmotic adjustment substances, such as proline, in TaEXPA2 transgenic plants was greater than that in WT plants. Transgenic plants also displayed greater antioxidative competence as indicated by their lower malondialdehyde (MDA) content, relative electrical conductivity, and reactive oxygen species (ROS) accumulation than did WT plants. This result suggests that the transgenic plants suffer less damage from ROS under drought conditions. The activities of some antioxidant enzymes as well as expression levels of several genes encoding key antioxidant enzymes were higher in the transgenic plants than in the WT plants under drought stress. Collectively, our results suggest that ectopic expression of the wheat expansin gene TaEXPA2 improves seed production and drought tolerance in transgenic tobacco plants.

The α-subunit of the rice heterotrimeric G protein, RGA1, regulates drought tolerance during the vegetative phase in the dwarf rice mutant d1

Abstract: Essential in the Green Revolution was the development of high-yielding dwarf varieties of rice (Oryza sativa L.), but their selection was not based on responses to water limitation. We studied physiological responses to progressive drought of the dwarf rice mutant, d1, in which the RGA1 gene, which encodes the GTP-binding α-subunit of the heterotrimeric G protein, is non-functional. Wild-type (WT) plants cease net carbon fixation 11 days after water is withheld, while d1 plants maintain net photosynthesis for an additional week. During drought, d1 plants exhibit greater stomatal conductance than the WT, but both genotypes exhibit the same transpirational water loss per unit leaf area. This is explained by a smaller driving force for water loss in d1 owing to its lower leaf temperatures, consistent with its more erect architecture. As drought becomes more severe, WT plants show an accelerated decline in photosynthesis, which may be exacerbated by the higher leaf temperatures in the WT. We thus show how a rice mutant with dwarf and erect leaves has a decreased susceptibility to water stress. Accordingly, it may be useful to incorporate RGA1 mutation in breeding or biotechnological strategies for development of drought-resistant rice.

Leaf photosynthetic rate, growth, and morphology of lettuce under different fractions of red, blue, and green light from light-emitting diodes (LEDs)

Abstract: Current LED-based artificial lights for crop cultivation consist of red and blue lights because these spectra effectively promote leaf photosynthesis. However, the absence of green light could be disadvantageous for crop production, as green light plays an important role in plant development. The objective of this study was to investigate whether adding green light to different proportions of red and blue light would affect the leaf photosynthetic rate, growth, and morphology of lettuce plants. Plants were transplanted and grown hydroponically for 25 days under different combinations of red, blue (0, 10, 20, and 30%), and green (0 and 10%) light at 150 ± 15 μmol•m-2•s-1 of photosynthetic photon flux density (PPFD). The leaf photosynthetic rate was highest under 80% red and 20% blue light and decreased significantly with the addition of green light and the absence of blue light. As the fraction of blue light increased, leaf size and plant growth decreased significantly. However, while the addition of green light considerably reduced the leaf photosynthetic rate, it did not reduce plant growth. In the absence of blue light, the plants showed symptoms of the shade avoidance response, which possibly enhanced their growth by improving their light interception. Therefore, the addition of 10% (15 μmol•m-2•s-1) green light did not have a positive effect on the growth of lettuce. Further study using higher intensities of green light is required to investigate the effects of green light on plant growth.

Leaf colour polymorphisms: a balance between plant defence and photosynthesis

Abstract: Summary Whether plants use leaf colour to deter herbivores remains controversial. The warning signal hypothesis predicts that red pigmentation is adaptive by reducing herbivory; plants with predominantly red foliage should have higher fitness than those with green leaves. Despite many discussions, this prediction has rarely been tested, and alternative, non-exclusive hypotheses cannot be ruled out. We have exploited leaf colour polymorphism in Pseudowintera colorata to test the warning signal hypothesis and to address possible alternative explanations. Consistent with warning signals, redder foliage contained higher concentrations of polygodial, a sesquiterpene dialdehyde with strong antifeedant properties, and incurred less herbivory than green leaves. Redder plants hosted 22% fewer lepidopteran leafroller larvae than neighbouring green plants. However, contrary to the predictions of the hypothesis, there were no differences in fitness parameters between red and green plants. Overall leaf canopy colour was not a significant predictor of the number of seeds per fruit or of mean seed weight. This may be explained by differences in photosynthesis: green P. colorata leaves had 47% higher maximum CO2 assimilation rates than matched red leaves from neighbouring plants. These results indicate that the benefits of deterring insect herbivores by signalling may be balanced by the higher photosynthetic rate of non-signalling plants. A balance between signalling and photosynthesis is a novel mechanism for the maintenance of leaf colour polymorphisms in nature. Synthesis. Anthocyanin pigments may simultaneously serve multiple functions within leaves, and individuals of the same plant species may use different strategies to cope with insect herbivores. Therefore, investigations into the role of these pigments in plant–insect interactions need to consider plant physiology and the diversity of plant defence mechanisms.

Effect of synthetic and biosynthesized silver nanoparticles on growth, physiology and oxidative stress of water hyacinth: Eichhornia crassipes (Mart) Solms

Abstract: Silver (Ag) nanoparticles (NPs) are synthesized by several methods and are being widely used in various fields of science. In recent times, evaluation of their toxicological effects on environment, especially to the plant ecosystems has attained special attention. In this study, effect of synthesized AgNPs [chemically (S-AgNPs) and/or biologically (B-AgNPs)] on the growth and physiology of an aquatic plant water hyacinth—Eichhornia crassipes (Mart) Solms was evaluated. Water hyacinth plants were treated with S-AgNPs and B-AgNPs at different concentrations of 1, 10 and 100 mg L−1and growth was monitored for 5 days. Decreased growth of hyacinth was observed only on fifth day in treatments with S-AgNPs treatment alone but not for B-AgNPs. Further, the atomic absorption spectroscopy results (at 100 mg L−1 concentration) showed a higher accumulation of S-AgNPs over the B-AgNPs in various parts of the treated plants. Biochemical analysis on day five in B-AgNPs treated leaf extracts revealed an increase in carbohydrate and protein levels, and a decrease in phenol and chlorophyll content. In contrary, S-AgNPs treated leaf extracts did not show any significant changes in carbohydrate and protein levels, however, observed a significant increase in phenol and chlorophyll content. Interestingly, S-AgNP treatment increased the activities of antioxidative enzymes, such as catalase, peroxidase and superoxide dismutase. No significant differences were measured in plants treated with B-AgNPs when compared to normal plants which may reveal that these B-AgNPs instead enhanced the plant growth with a fewer minor effects on water hyacinth plants over S-AgNPs.

Inoculation with selenobacteria and arbuscular mycorrhizal fungi to enhance selenium content in lettuce plants and improve tolerance against drought stress

Abstract: This study evaluated the co-inoculation effect of the endophytic selenobacteria Bacillus sp., Klebsiella sp. or Acinetobacter sp. and the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices on lettuce plants grown under drought conditions. Plants inoculated with bothnmicroorganisms were able to enhance the Se content in their shoots (1 to 6 pg plant-1) and promote macro-and micronutrient uptake. Moreover, the inoculated plants showed significantntolerance to drought stress, as determined by their adaptation to physiological parameters(relative water content and stomatal conductance), increase in photosynthetic pigments (chlorophyll and carotenoids) and improvement inantioxidant enzyme levels (catalase, ascorbate peroxidase and glutathione reductase). The selenobacteria increased the Se content in lettuce plants and enhanced the effect of AM fungus in controlling the antioxidant systems that play a role as elicitors of plant drought responses and improving the nutritional quality and physiological and biochemical processes involved in plant drought tolerance.

Acclimation of photosynthesis to supersaturated CO2 in aquatic plant bicarbonate users

Abstract: 1. The photosynthesis of submerged aquatic plants can be limited by carbon dioxide (CO2) because of the low diffusivity of dissolved gas in water. About half of the species are able to use bicarbonate (HCO3-) as an alternative source of dissolved inorganic carbon (DIC). HCO3- is usually available in several-fold higher concentrations than CO2 at pH above seven, but its affinity is lower and the costs are higher than for CO2 use. The effects of changes in CO2 concentrations on the growth and physiology of bicarbonate users remain to be explored comparatively across a wide range of species. 2. We studied, in the laboratory, the plasticity in photosynthetic carbon kinetics and tissue composition of 10 submerged species, all able to use bicarbonate, acclimated to air saturated and 22 times supersaturated CO2 concentrations with the same concentration of DIC (0.85 mM). 3. Growth rate of all was stimulated (1.1-2.5 fold) and plants allocated more biomass in roots under elevated CO2 over the 35 days of the acclimation period. The photosynthetic affinity for HCO3- was higher in species acclimated to air saturated rather than supersaturated CO2. Net photosynthesis was more stimulated (2-6 times) by CO2 supersaturation concentrations after acclimation to supersaturated CO2 concentration due to their reduced HCO3- use capacity. 4. Plants grown under elevated CO2 showed reduced investment in tissue nitrogen, protein and free amino acids. Moreover, the high CO2 treatments yielded overall lower gamma-aminobutyric acid (GABA) pools, an indicator of stress relief or changes in nitrogen metabolism. 5. The analysis of 10 freshwater plants confirms that availability of HCO3-, and CO2 is a key regulator of plant physiology affecting growth. Inorganic carbon availability affects the energy budget of plants thereby influencing an array of ecological processes, and hence the distribution of submerged macrophytes in the wild.

Transcriptome response of cassava leaves under natural shade

Abstract: Cassava is an important staple crop in tropical and sub-tropical areas. As a common farming practice, cassava is usually cultivated intercropping with other crops and subjected to various degrees of shading, which causes reduced productivity. Herein, a comparative transcriptomic analysis was performed on a series of developmental cassava leaves under both full sunlight and natural shade conditions. Gene expression profiles of these two conditions exhibited similar developmental transitions, e.g. genes related to cell wall and basic cellular metabolism were highly expressed in immature leaves, genes involved in lipid metabolism and tetrapyrrole synthesis were highly expressed during the transition stages, and genes related to photosynthesis and carbohydrates metabolism were highly expressed in mature leaves. Compared with the control, shade significantly induced the expression of genes involved in light reaction of photosynthesis, light signaling and DNA synthesis/chromatin structure; however, the genes related to anthocyanins biosynthesis, heat shock, calvin cycle, glycolysis, TCA cycle, mitochondrial electron transport, and starch and sucrose metabolisms were dramatically depressed. Moreover, the shade also influenced the expression of hormone-related genes and transcriptional factors. The findings would improve our understanding of molecular mechanisms of shade response, and shed light on pathways associated with shade-avoidance syndrome for cassava improvement.

Functional analysis of CsCBF3 transcription factor in tea plant ( Camellia sinensis ) under cold stress

Abstract: C-repeat binding factors (CBFs) are involved in multiple pathways of plant growth, development and stress responses. In this study, CsCBF3, a gene encoding a polypeptide of 274 amino acids and containing the structural feature of AP2 domain in CBF protein family, was characterized from tea plant [Camellia sinensis (L.) O. Kuntze]. CsCBF3 was located in cell nucleus and cytoplasm by subcellular localization analysis. Expression analysis revealed that CsCBF3 was induced by low temperature stress, abscisic acid and drought treatment in tea leaves. CsCBF3 overexpressed Arabidopsis displayed higher tolerance to cold stress and improved photosynthesis ability with less damage under cold condition compared to wild type plants. Furthermore, it was observed that the CsCBF3 gene regulates the expressions of downstream genes of cold responsive pathway, such as AtCOR15a and AtCOR78. These results indicate that CsCBF3 plays an important role in responding to cold stress and provide potential applications in molecular breeding to enhance cold tolerance in tea plant.

Tomato Jasmonic Acid-Deficient Mutant spr2 Seedling Response to Cadmium Stress

Abstract: The involvement of jasmonic acid (JA) in the plant response to cadmium (Cd) stress has been addressed in some publications by application experiments or analysis of endogenous contents of JA. In this study, we comparatively investigated the response of tomato wild type (WT) and its JA-deficient mutant spr2 to Cd stress aimed at clarifying the role of JA. One-month-old potted plants were exposed to CdCl2 at final concentrations of 5, 25, and 50 mg kg−1 in soil, respectively, for 15 days. The root and leaf Cd contents were dramatically increased, especially in the spr2 plants, in a CdCl2 dose-effect manner. In the Cd dose-dependent inhibitory effect on plant growth, spr2 plants were more obvious than WT plants. This was also reflected by certain physiological and biochemical metabolisms. We analyzed photosynthesis-related parameters including total chlorophyll, actual efficiency of PS2, ratio of variable to maximum chlorophyll fluorescence, and net photosynthetic rate; relative water content, soluble sugar and proline contents, and starch accumulation; oxidative stress and antioxidative defense including malondialdehyde production, electrolyte leakage, H2O2 levels, activities of superoxide dismutase, peroxidase, and catalase, and their isoform expression profiles. The Cd-induced changes in all these parameters supported the conclusion that endogenous JA deficiency enhanced tomato seedling sensitivity to Cd. This implies that JA positively regulates the tomato plant response to Cd stress.

Towards efficient photosynthesis: overexpression of Zea mays phosphoenolpyruvate carboxylase in Arabidopsis thaliana

Abstract: Plants with C4 photosynthesis are efficient in carbon assimilation and have an advantage over C3 photosynthesis. In C4 photosynthesis, the primary CO2 fixation is catalyzed by phosphoenolpyruvate carboxylase (PEPC). Here, we show that overexpression of Zea mays PEPC cDNA, under the control of 35S promoter, in Arabidopsis thaliana resulted in ~7–10 fold higher protein abundance and ~7–10 fold increase in PEPC activity in the transgenic lines than that in the vector control. We suggest that overexpression of PEPC played an anaplerotic role to increase the supply of 4-carbon carboxylic acids, which provided carbon skeletons for increased amino acid and protein synthesis. Higher protein content must have been responsible for increased metabolic processes including chlorophyll biosynthesis, photosynthesis, and respiration. Consequently, the PEPC-overexpressed transgenic plants had higher chlorophyll content, enhanced electron transport rate (ETR), lower non-photochemical quenching (NPQ) of chlorophyll a fluorescence, and a higher performance index (PI) than the vector control. Consistent with these observations, the rate of CO2 assimilation, the starch content, and the dry weight of PEPC-overexpressed plants increased by 14–18 %, 10–18 %, and 6.5–16 %, respectively. Significantly, transgenics were tolerant to salt stress as they had increased ability to synthesize amino acids, including the osmolyte proline. NaCl (150 mM)-treated transgenic plants had higher variable to maximum Chl a fluorescence (F v/F m) ratio, higher PI, higher ETR, and lower NPQ than the salt-treated vector controls. These results suggest that expression of C4 photosynthesis enzyme(s) in a C3 plant can improve its photosynthetic capacity with enhanced tolerance to salinity stress.

Photosynthesis, antioxidant status and gas-exchange are altered by glyphosate application in peanut leaves

Abstract: Glyphosate herbicide caused oxidative stress and exhibited negative effects on photosynthesis and gas exchange of peanut [Arachis hypogaea L. cv. Giza (G) 5 and 6] leaves. We demonstrated that glyphosate caused various morphological symptoms, such as chlorosis, yellowing, and appearance of curly edges in leaves treated with high doses of herbicide in both cultivars; however, the G5 cultivar was more sensitive and showed severer symptoms. Glyphosate lowered photosynthesis and reduced contents of pigments and proteins as well as free amino acids in both cultivars. The gas-exchange parameters, such as photosynthetic (PN) and transpiration rate (E), were highly altered by the glyphosate application. For example, PN and E were reduced by 65 and 61%, respectively, in G5 treated with high dose of glyphosate compared with control. Antioxidant enzymes, such as peroxidase, catalase, ascorbate peroxidase, and superoxide dismutase were induced by both low and high concentrations in the glyphosate-treated leaves. Moreover, the level of lipid peroxidation, indicated by a malondialdehyde content, as well as the hydrogen peroxide content increased in the glyphosate-treated leaves. However, an increase in total antioxidant activity was detected in leaves and this reflected changes in the antioxidant status and accumulation of antioxidants as a defense mechanism against glyphosate toxicity in peanut.

24-Epibrassinolide ameliorates the effects of boron toxicity on Arabidopsis thaliana (L.) Heynh by activating an antioxidant system and decreasing boron accumulation

Abstract: Brassinosteroids (BRs) play a significant role in alleviating the negative effects of various environmental stresses and in promoting the growth and development of plants. In this study, we investigated the effects of 24-epibrassinolide (EBL) on the growth, boron (B) accumulation and activation of the antioxidant system of Arabidopsis thaliana (L.) Heynh exposed to high concentrations of boric acid (BA). A. thaliana plants were grown in a hydroponic culture, and after 4 weeks, the plants were transferred to media containing either 0.80 or 1.60 mM BA. Following BA treatment, 0.01 and 1 µM EBL was sprayed on the entire foliar region of the seedlings. B toxicity induced oxidative stress and considerably inhibited the growth of the plants. The spraying of EBL on the B-treated plants resulted in increases in growth (both fresh and dry shoot mass, silique number, length and mass) and pigment content (total chlorophyll and carotenoids). Excessive B levels increased the activities of antioxidant enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase, and increased the proline content in leaves of plants. However, treatment of the B-stressed plants with EBL further enhanced the activities of the antioxidant enzymes and increased the content of proline. The high level of lipid peroxidation in plants observed during exposure to a higher level of BA was decreased following EBL treatment. Thus, this study showed that the exogenous application of EBL ameliorates the toxic effects of B in a model plant by improving the plant’s antioxidant system and decreasing B accumulation. To our knowledge, this is the one of the first studies to examine the effect of BR in plants subjected to B toxicity.

Effects of high CO2 levels on dynamic photosynthesis: carbon gain, mechanisms, and environmental interactions.

Abstract: Understanding the photosynthetic responses of terrestrial plants to environments with high levels of CO2 is essential to address the ecological effects of elevated atmospheric CO2. Most photosynthetic models used for global carbon issues are based on steady-state photosynthesis, whereby photosynthesis is measured under constant environmental conditions; however, terrestrial plant photosynthesis under natural conditions is highly dynamic, and photosynthetic rates change in response to rapid changes in environmental factors. To predict future contributions of photosynthesis to the global carbon cycle, it is necessary to understand the dynamic nature of photosynthesis in relation to high CO2 levels. In this review, we summarize the current body of knowledge on the photosynthetic response to changes in light intensity under experimentally elevated CO2 conditions. We found that short-term exposure to high CO2 enhances photosynthetic rate, reduces photosynthetic induction time, and reduces post-illumination CO2 burst, resulting in increased leaf carbon gain during dynamic photosynthesis. However, long-term exposure to high CO2 during plant growth has varying effects on dynamic photosynthesis. High levels of CO2 increase the carbon gain in photosynthetic induction in some species, but have no significant effects in other species. Some studies have shown that high CO2 levels reduce the biochemical limitation on RuBP regeneration and Rubisco activation during photosynthetic induction, whereas the effects of high levels of CO2 on stomatal conductance differ among species. Few studies have examined the influence of environmental factors on effects of high levels of CO2 on dynamic photosynthesis. We identified several knowledge gaps that should be addressed to aid future predictions of photosynthesis in high-CO2 environments.

Mitigation of salt stress in wheat plant (Triticum aestivum) by ACC deaminase bacterium Enterobacter sp. SBP-6 isolated from Sorghum bicolor

Abstract: The plant growth promoting bacteria can ameliorate the abiotic stressors through induced systemic tolerance in associated plants. The present work reports the efficiency of a plant growth promoting rhizobacterium (PGPR) Enterobacter sp. SBP-6 containing ACCD activity to stimulate the growth of the wheat plant under salinity stress conditions. Besides ACCD activity, the isolate was able to show other plant growth promoting (PGP) traits like phosphate solubilization, phytohormone production, nitrogen fixation, etc. The application of isolate SBP-6 to the wheat plants alleviated the inhibitory effects of gradient levels of salinity (150, 175, 200 mM NaCl) on various parameters of plant growth and photosynthetic pigments. Results of pot experiments revealed that inoculation with the test isolate significantly increased the plant biomass by 10–42 % as compared to their respective uninoculated control. An ability of the isolate to alleviate the effect of salt stress was also evident by significant increase of chlorophyll content (33–41 %), reduction in toxic Na+ ionic content (19–41 %), increase in K+ uptake (23–31 %), thereby favoring the K+/Na+ ratio and a significant decrease in leaf proline and malondialdehyde content in bacteria-treated plants exposed to salt stress. These results indicated that the selected isolate SBP-6 can be used for promoting the plant growth under salinity stress.

Improved drought and salt tolerance of Arabidopsis thaliana by ectopic expression of a cotton (Gossypium hirsutum) CBF gene

Abstract: Osmotic stress associated with drought or salinity is a major factor that limits plant growth and productivity. CBF transcription factors play key roles in plant stress signaling transduction pathway. In this work, the data revealed that GhCBF3 identified in cotton (Gossypium hirsutum L.) was remarkably induced by NaCl, mannitol and abscisic acid (ABA). Histochemical assay of GUS activity revealed that GhCBF3 promoter was active in stomata guard cells of the GhCBF3p:GUS transgenic seedlings, and its activity was salt- and osmotic-inducible. Overexpression of GhCBF3 in Arabidopsis resulted in the increased drought- and high salinity-tolerance, but led to an ABA-sensitive phenotype of the transgenic plants. In the presence of NaCl and mannitol, rates of seed germination and cotyledon greening of the GhCBF3 overexpression transgenic plants were higher than those of wild type. Relative water content, proline content and chlorophyll content in the GhCBF3 transgenic seedlings were higher than those in wild type. The GhCBF3 transgenic plants showed greater salt- and drought-tolerance, compared with wild type. In the presence of ABA, stomatal aperture in leaves of the transgenic plants was smaller than that in wild type, and expression levels of AREB1 and AREB2 in the transgenic leaves was remarkably higher than those in wild type. Furthermore, expression of some stress-related genes was altered in the GhCBF3 transgenic plants. These data suggested that GhCBF3 may be involved in regulating stomata closure, thereby enhance plant salt and drought tolerance via ABA signaling pathway.

Genetically engineered anthocyanin pathway for high health-promoting pigment production in eggplant

Abstract: Anthocyanins, natural pigments with high antioxidant activities, are widely distributed in the plant kingdom and play important roles in various physiological processes. Much effort has been committed to enhancing the anthocyanin content of these health-promoting pigments in vegetables and grains, for their eye-catching colors and special nutrients. Previously, we reported that the SmMYB1 gene encoding a R2R3 MYB transcription factor participated in the regulation of anthocyanin biosynthesis in the peel of eggplant. In this work, we introduced SmMYB1 into a non-anthocyanin-accumulating eggplant cultivar (Solanum aethiopicum group Gilo) via Agrobacterium-mediated transformation. Genetically engineered plants exhibited high concentrations of anthocyanin in leaves, petals, stamens, and fruit peels under normal growth conditions, especially in fruit flesh. Furthermore, highly methylated anthocyanins, malvidin 3-(p-coumaroyl)rhamnoside(glucoside)-5-glucoside and malvidin 3-(feruloyl)rhamnoside(glucoside)-5-glucoside, were separated from the purple fruit flesh and identified by HPLC–ESI–MS/MS. qRT-PCR analysis revealed that most anthocyanin structural genes were dramatically up-regulated in the tissues of transgenic lines compared with non-transformed plants. In addition, the transgenic seedlings had greater tolerance to freezing stress and better recovery under rewarming conditions. These results provide a good foundation for the breeding of new eggplant cultivars with more healthy agronomic traits in future studies.

Quantitative proteomics study on Lsi1 in regulation of rice (Oryza sativa L.) cold resistance

Abstract: Low temperature is one of the major abiotic stresses which severely affects the productivity and the geographical distribution of rice (Oryza sativa). Silicon is considered a broad spectrum alleviator to combat stress in rice plant. Rice root absorbs silicon by a silicon transporter, Low silicon gene 1 (Lsi1). To gain a better understanding of cold stress responses triggered by overexpression of Lsi1 in rice (Oryza sativa L.), we carried out physiological and molecular studies between Lsi1-overexpression Dular (Lsi1-D) and its wild type (WD). Two leaf stage rice seedlings of above mentioned both lines were treated at 15 °C/12 °C (day/night) for 7 days. WD seedling leaves were turned comparatively yellow as compared to Lsi1-D seedlings. Microscopic studies showed significantly more deposition of silicon bodies in epidermal cells of Lsi1-D leaf seedlings in comparison with WD leaves. Lsi1-D leaves comparatively, depicted more SOD, POD and CAT activity, chlorophyll a, b contents in consistency with more silicon concentration. Protein extraction was carried out from whole seedling of both lines and further analyzed by tandem mass tag quantitative proteomics approach with double replicates. Among 393 reproducible proteins, 63 were up-regulated and 39 proteins were down-regulated. The total cold responsive differential proteins were involved in several processes, i.e. photosynthesis, signal transduction, redox homeostasis, hormone metabolism, carbohydrate metabolism, cell wall organization, N-assimilation, protein processing and secondary metabolism. We confirmed up-regulation of key proteins involved in cold-responsive pathway at mRNA level through qPCR such as chlorophyll a–b binding protein 1, peroxidase 2, signaling G-proteins RIC1, aquaporin PIP1.2, 1, 4-alpha-glucan branching enzyme, germin-like protein subfamily 2 member 4 and germin-like protein subfamily 8 member 2. In conclusion, our study provides new insights into cold stress responses in rice seedlings triggered by Lsi1-overexpression defense pathway.

The influence of silicon application on growth and photosynthesis response of salt stressed grapevines (Vitis vinifera L.)

Abstract: The influences of silicon (Si) on parameters, such as plant growth, pigment contents, photosynthesis, chlorophyll fluorescence, soluble sugar and starch concentration, and some cell ultra-structures, were investigated in grapevines under salt stress. Compared with the control, the treatment with 100 mM NaCl dramatically inhibited the growth of grapevines and greatly decreased the content of pigments. Silicon treatment in the absence of salt had negative effects in most observed parameters. However, the addition of Si under salt stress improved all growth parameters and increased the pigments and photosynthetic rates compared with the NaCl treatment. Furthermore, investigation of chlorophyll fluorescence, soluble sugars, starch concentration and cell ultra-structure indicated that photosynthesis in the NaCl treatment decreased. The supplement of silicon mitigated the inhibited photosynthesis caused by NaCl, and increased the maximum yield and potential photochemical efficiency of the photochemical reactions in photosystem II. On the other hand, the addition of exogenous Si and NaCl also increased the concentration of soluble sugars and starch, and influenced ultra-structural changes. It is possible that silicon might play an important role in protecting photosynthetic machinery from damage and improving the salt-tolerance of the grape by increasing the concentration of soluble sugars and starch.

Pheophytinase Knockdown Impacts Carbon Metabolism and Nutraceutical Content Under Normal Growth Conditions in Tomato

Abstract: Although chlorophyll (Chl) degradation is an essential biochemical pathway for plant physiology, our knowledge regarding this process still has unfilled gaps. Pheophytinase (PPH) was shown to be essential for Chl breakdown in dark-induced senescent leaves. However, the catalyzing enzymes involved in pigment turnover and fruit ripening-associated degreening are still controversial. Chl metabolism is closely linked to the biosynthesis of other isoprenoid-derived compounds, such as carotenoids and tocopherols, which are also components of the photosynthetic machinery. Chls, carotenoids and tocopherols share a common precursor, geranylgeranyl diphosphate, produced by the plastidial methylerythritol 4-phosphate (MEP) pathway. Additionally, the Chl degradation-derived phytol can be incorporated into tocopherol biosynthesis. In this context, tomato turns out to be an interesting model to address isoprenoid-metabolic cross-talk since fruit ripening combines degreening and an intensely active MEP leading to carotenoid accumulation. Here, we investigate the impact of PPH deficiency beyond senescence by the comprehensive phenotyping of SlPPH-knockdown tomato plants. In leaves, photosynthetic parameters indicate altered energy usage of excited Chl. As a mitigatory effect, photosynthesis-associated carotenoids increased while tocopherol content remained constant. Additionally, starch and soluble sugar profiles revealed a distinct pattern of carbon allocation in leaves that suggests enhanced sucrose exportation. The higher levels of carbohydrates in sink organs down-regulated carotenoid biosynthesis. Additionally, the reduction in Chl-derived phytol recycling resulted in decreased tocopherol content in transgenic ripe fruits. Summing up, tocopherol and carotenoid metabolism, together with the antioxidant capacity of the hydrophilic and hydrophobic fractions, were differentially affected in leaves and fruits of the transgenic plants. Thus, in tomato, PPH plays a role beyond senescence-associated Chl degradation that, when compromised, affects isoprenoid and carbon metabolism which ultimately alters the fruit's nutraceutical content.

White stripe leaf 12 (WSL12), encoding a nucleoside diphosphate kinase 2 (OsNDPK2), regulates chloroplast development and abiotic stress response in rice (Oryza sativa L.).

Abstract: Chloroplast is a crucial organelle for plant photosynthesis and maintaining normal life activities in higher plants. Although some genes related to chloroplast development and pigment synthesis have been identified or cloned in rice, little is known about the relationship between these genes and abiotic stress response. In this study, we identified a novel mutant white stripe leaf 12 (wsl12) affecting pigment synthesis, chloroplast development and abiotic stress response in rice. The mutant phenotype was obvious at seeding and tillering stages and in response to the temperature change. Genetic analysis of reciprocal crosses between wsl12 and wild-type plants showed that wsl12 was a recessive mutant in a single nuclear locus. Map-based cloning revealed that the WSL12 locus encoded OsNDPK2, one of the three nucleoside diphosphate kinases (OsNDPKs). WSL12 expressed in all tested tissues, while it highly expressed in leaves and young tissues. The WSL12 protein localized to the chloroplast. The wsl12 mutant showed higher superoxide anion level and enhanced sensitivity to abscisic acid (ABA) and salinity. The transcription pattern of many genes involved in chlorophyll biosynthesis, ABA synthesis, light signaling pathway, reactive oxygen species-scavenging pathway and the other two OsNDPKs was altered in the wsl12 mutant. These results indicate that the OsNDPK2 encoded by WSL12 plays an important role in chloroplast development and chlorophyll biosynthesis by regulating the expression levels of related genes. In addition, WSL12 also affects the response to abiotic stress, such as ABA and salinity in rice, and is beneficial to molecular breeding of stress tolerance.

Photosynthesis in the seeds of chloroembryophytes

Abstract: Depending on the presence or absence of chlorophylls in the embryo, angiosperms are divided into chloroembryophytes and leucoembryophytes. Synthesis of chlorophylls (Chl) in the chloroembryos starts in the globular stage, rises as the embryo is formed, and stops in the late phase of seed maturation. The seeds also contain carotenoids that participate in photosynthesis and act as ABA precursors. The chloroembryos contain photochemically active chloroplasts that contain all the main photosynthetic complexes at a necessary stoichiometric ratio. Dark reactions of photosynthesis in developing seeds are notable for the fact that the main source of carbon therein is sucrose arriving from the maternal plant. Therefore, function of chloroplasts mainly aims at production of NADPH and ATP that are spent on conversion of sucrose into acetyl-CoA and, subsequently, to fatty acids. The CO2 fixation system involving Rubisco and/or phosphoenolpyruvate carboxylase operates in the chloroembryos. In the course of photosynthesis, oxygen is released, which prevents hypoxia and maintains seed respiration. In late stages of ripening, the seeds enter the state of dormancy, which is associated with dehydration, disintegration of photosynthetic apparatus, Chl breakdown, and transformation of chloroplasts into plastids filled with reserve nutrient substances. At the same time, very often Chl are not destroyed completely and their residues are present in mature seeds of numerous plant species.

Effects of Drought Stress on Photosynthesis Factors in Wheat Genotypes during Anthesis

Abstract: Drought is one of most important environmental factors inhibiting photosynthesis and decreasing growth and productivity of plants. The sensitivity of crop plants such as wheat to soil drought is particularly serious during reproductive phase is extremely sensitive to plant water status. The aim of this work was to study the effects of drought stress on photosynthesis, photosynthetic pigments, soluble proteins, a-tocopherol and abscisic acid content in six wheat genotypes, two tolerant (Daric and 92 Zhong), two moderately tolerant (Sabalan and DH-2049-3) and two sensitive (Shark and Tevee’s’). Total chlorophyll content, relative water content and chlorophyll a/b ratio decreased after long-time drought stress, that decrease in sensitive genotypes was higher than others. Net photosynthesis and stomatal conductance decreased significantly (P < 0.05) in flag leaves of our genotypes under drought stress after pollination, that decrease in sensitive genotypes was higher, too. Abscisic acid content, soluble prote...

miR156 modulates rhizosphere acidification in response to phosphate limitation in Arabidopsis.

Abstract: Rhizosphere acidification is a general response to Pi deficiency, especially in dicotyledonous plants. However, the signaling pathway underlying this process is still unclear. Here, we demonstrate that miR156 is induced in the shoots and roots of wild type Arabidopsis plants during Pi starvation. The rhizosphere acidification capacity was increased in 35S:MIR156 (miR156 overexpression) plants, but was completely inhibited in 35S:MIM156 (target mimicry) plants. Both 35S:MIR156 and 35S:MIM156 plants showed altered proton efflux and H(+)-ATPase activity. In addition, significant up-regulation of H(+)-ATPase activity in 35S:MIR156 roots coupled with increased citric acid and malic acid exudates was observed. qRT-PCR results showed that most H(+)-ATPase and PPCK gene transcript levels were decreased in 35S:MIM156 plants, which may account for the decreased H(+)-ATPase activity in 35S:MIM156 plants. MiR156 also affect the root architecture system. Collectively, our results suggest that miR156 regulates the process of rhizosphere acidification in plants.

Effect of phosphorus starvation on hormone content and growth of barley plants

Abstract: To address the question of the role of phytohormones in the growth responses induced by P availability, we compared the effects of low P on the growth of barley plants, and the contents of auxin, cytokinins and abscisic acid (ABA). Comparative study of the changes in growth and hormones’ levels in response to P-starvation showed that relative activation of root growth may be related to the decline in shoot cytokinin content and ABA accumulation in the roots of P-starved (P − ) barley plants. The decline in shoot cytokinins is likely to result from the inhibition of the transport of these hormones from roots, and in turn, may contribute to increased distribution of auxins in favor of roots. Reduced root branching detected in our experiments, despite maintenance of root auxins, may be related to an elevated level of either cytokinins or ABA in roots of P − barley plants. Thus, interactions between auxins, cytokinins and ABA are likely to be responsible for the changes in root architecture in P − plants.