Showing papers in "Plant Growth Regulation in 2016"

Plant growth promoting bacteria confer salt tolerance in Vigna radiata by up-regulating antioxidant defense and biological soil fertility

Abstract: Salinity, a frequently occurring abiotic stress, is a major constraint for crop productivity worldwide. The present study was conducted to evaluate the ability of plant growth promoting rhizobacteria (PGPR) Bacillus cereus Pb25, isolated from soil irrigated with saline water, to promote Vigna radiate (mungbean) growth in the absence and presence of salt stress (9 dS m−1). Results demonstrated that B. cereus promoted V. radiate plant growth significantly even in the presence of salt. Inoculations with PGPR improved the plant growth, and increased the root, shoot fresh and dry biomass and yield as compared to plants with no bacterial treatment (control). Results showed that both chlorophyll content and plant growth were inhibited by saline stress and the salt-induced oxidative damage (measured by MDA, H2O2) was alleviated by PGPR inoculation. Furthermore, PGPR inoculation significantly increased the antioxidant enzymes (POD, SOD and CAT) activities and enhanced the accumulation of proline, potassium, nitrogen and phosphorus as well as decreased sodium accumulation in saline stressed plants. Regarding the soil biological activity, inoculated PGPR enhanced the activity of dehydrogenase, alkaline phosphatase, microbial biomass carbon, available phosphorus and total organic carbon under saline stress as compared to saline treatment alone. These results suggest that B. cereus can be used in salinized agricultural lands as bio-inoculant to increase crop productivity.

Seed priming in dry direct-seeded rice: consequences for emergence, seedling growth and associated metabolic events under drought stress

Abstract: Drought stress encumbers the seed germination and delays seedling establishment in dry direct-seeded rice. Pot and field studies were carried out to ascertain the role of seed-priming on emergence, seedling growth and associated metabolic events in dry-direct seeded rice system. Seeds of two indica rice cultivars were subjected to different priming agents viz., hydropriming (H2O), potassium nitrate (KNO3; 0.5 %), polyethelene glycol-6000 (PEG; 10 %) and spermidine (Spd; 0.5 mmol L−1). A no-priming treatment was kept as control for comparison. Drought stress was imposed by 15 % PEG solution in a pot experiment; whilst in field trial soil moisture contents were maintained between 15 and 18 %. In pot experiment, drought stress severely hampered the germination rate, seedling growth, and starch metabolism, but increased the antioxidant enzymes activity and lipid peroxidation in both rice cultivars as compared with normal conditions. All the seed priming treatments particularly Spd priming, were effective in alleviating the damaging effects of drought stress under controlled as well as field conditions. In field trial, Spd priming recorded 21, 232, 173, 67 and 78 % higher emergence, shoot length, shoot fresh weight, maximum root length and root fresh weight of dry direct-seeded rice, respectively, compared with control. And such increments were associated with better starch metabolism particularly increased α-amylase activity in primed rice seedlings.

Group II late embryogenesis abundant (LEA) proteins: structural and functional aspects in plant abiotic stress

Abstract: Group II late embryogenesis abundant (LEA) proteins are crucial phytomolecules which accumulate mainly in the late phases of seed development and also in the vegetative tissues in response to exogenous stress. In spite of considerable research, their mechanism of action to generate plant tolerance against abiotic stresses still remains obscure. The present review focuses on the varied structural aspects which ultimately dictate the multifarious functions of the Group II LEA proteins when the plants are exposed to intense desiccation. Currently, several reports have been documented regarding newer in silico approaches in predicting LEA protein structure and the corresponding cis-elements. Coupled to recent transgenic approaches, these reports need to be properly structured to further characterize the physico-chemical and functional importance of LEA proteins in regulating tolerance against multiple abiotic stresses.

γ-Aminobutyric acid (GABA) priming enhances the osmotic stress tolerance in Piper nigrum Linn. plants subjected to PEG-induced stress

Abstract: The pretreatment of two black pepper varieties, Panniyur 1 (drought-sensitive) and Panniyur 5 (drought-tolerant) with GABA (2 mM) influenced various physiological and biochemical parameters positively and the PEG (poly ethylene glycol 6000; 10 % w/v)-induced stress tolerance was increased in both varieties of black pepper. Although both varieties primed with GABA showed positive responses while encountering PEG-stress, Panniyur 5 showed better performance. When compared to non-primed plants induced with PEG-stress, GABA primed black pepper plants showed enhanced rate of leaf RWC and also a faster reduction of cell osmotic potential. Proline and total sugars were found to accumulate earlier in primed plants and the activity of antioxidant enzymes like guaiacol peroxidase and superoxide dismutase also increased significantly, in response to PEG-stress. When compared to non-primed plants, GABA priming resulted in a reduced rate of lipid peroxidation, and comparatively lesser inhibition of photosynthetic and mitochondrial activity (measured in terms of O2 evolution/uptake) in primed plants during osmotic stress. Occurrence of GABA in plants of black pepper varieties was detected by HPTLC technique. In PEG-treated plants GABA content was higher than that of control; and a multifold enhancement of GABA was observed in black pepper plants subjected to PEG-stress, after priming with GABA.

Silicon nutrition and mycorrhizal inoculations improve growth, nutrient status, K+/Na+ ratio and yield of Cicer arietinum L. genotypes under salinity stress

Abstract: Salinity is a major abiotic stress that limits plant growth and productivity. Role of silicon (Si) nutrition and arbuscular mycorrhiza (AM) in mitigating salt stress has gained importance in recent years. Legumes are sensitive to salinity and are considered low Si-accumulators. AM have been reported to increase Si uptake in mycorrhizal plants. However, little is known about the alleviative role of Si and/or AM in mitigating salt stress in Cicer arietinum L. (chickpea). Therefore, the present study was aimed to evaluate the individual and cumulative effect of Si and AM (Funneliformis mosseae) on nutrient status, growth and productivity of salt tolerant HC 3 and salt sensitive CSG 9505 genotypes of chickpea under salinity stress conditions. The genotypes were subjected to 0, 60, 80,100 mM NaCl and 0, 4 mM potassium silicate—K2SiO3 treatments in the presence and absence of AM fungi. The results indicated that the Si and AM treatments improve the endogenous nutrients profile, growth characteristics and yield attributes under salinity stress. AM was found to be more efficient in improving growth and productivity while Si was more beneficial in improving K+/Na+ ratio. Mycorrhization mediated significant improvement in Si uptake and as a result, Si supplementation along with mycorrhization reduced Na+ content significantly, improved growth, yield and nutrient uptake, arrested chlorophyll pigment damage and increased RUBISCO activity. HC 3 was more responsive to mycorrhization and Si nutrition than CSG 9505. The study will contribute to our understanding of Si and/or AM mediated salinity tolerance mechanism for developing chickpea genotypes resistance to salt stress.

Exogenous hydrogen sulfide alleviates salt stress in wheat seedlings by decreasing Na+ content

Abstract: Hydrogen sulfide (H2S) is an important gaseous molecule in a number of plant developmental processes and stress responses. Triticum aestivum L. (LM 15) is a salt-sensitive wheat cultivar that was used here to examine the effect of exogenous H2S on seedling growth, Na+ and K+ concentration, and Na+ transportation under NaCl stress. The results showed that pretreatment with 0.05 mM sodium hydrosulfide (NaHS), a H2S donor, for 12 h significantly alleviated the growth inhibition of wheat seedlings under 100 mM NaCl. In addition, pretreatment with NaHS decreased the Na+ concentration, Na+/K+ ratio, the selective absorption capacity for K+ over Na+ and Na+ efflux ratio, and increased the selective transport capacity for K+ over Na+ under salt stress. Additional experiments with CaCl2 (an inhibitor of nonselective cation channels—NSCCs), TEA+ (an inhibitor of low affinity K+ transporter) or amiloride (an inhibitor of salt overly sensitive 1—SOS1) showed that NSCCs and SOS1 were the major pathways by which H2S reduced Na+ concentration in wheat seedlings. These results showed that exogenous H2S alleviated growth inhibition by maintaining a lower Na+ concentration in wheat seedlings under NaCl stress via the regulation of NSCCs and SOS1 pathways.

Modulation and significance of nitrogen and sulfur metabolism in cadmium challenged plants

Abstract: As a result of rapidly increasing anthropogenic activities, input of varied metal(loids) such as cadmium (Cd) to worldwide agricultural soils and its subsequent accumulation, and obvious toxicity in plants are increasing. The role of mineral nutrients in the mitigation of Cd-accrued consequences in plants has been credibly suggested. In isolated studies, two essential mineral nutrients such as nitrogen (N) and sulfur (S) have been reported to minimize Cd-impacts in plants, and improve overall plant growth, metabolism and productivity under Cd-exposure. However, the information on the significance of N and S metabolism, and also on cross-talks on the coordination therein in Cd-challenged plants is lacking. Given the highlighted lacunae, in the light of recent research outcomes, the present review attempts to: (a) overview Cd in soil, and its major toxicity and mitigation avenues in plants, (b) appraise Cd-mediated modulation of N and S metabolism, (c) summarize the role of exogenously-sourced N and S for the mitigation of Cd toxicity, (d) critically discuss the significance of coordination between N and S metabolism for Cd-impact-mitigation, and finally to (e) highlight the major aspects to explore in the current context. The literature appraised herein suggests that a fine coordination among major pathways of N and S assimilation can enhance defense metabolites and enzymes that in turn can strengthen overall defense system, and efficiently mitigate Cd-impacts in plants. However, efforts are required to get more insights into the mechanism(s) of (co)regulation of sulfate and nitrate assimilation at the molecular level. Additionally, molecular approaches should be narrowed to enhance the production of thiols, and their products in plants through manipulating major enzymes involved in sulfate and nitrate assimilation in plants under Cd-challenged environment.

The biosynthesis of auxin: how many paths truly lead to IAA?

Abstract: The plant auxin indole-3-acetic acid (IAA) plays critical roles in plant growth and development. There are two main strategies proposed for plant synthesis of IAA: the Trp-dependent (TD) and the Trp-independent (TI) pathways. Four TD pathways, namely the indole-3-acetamide pathway, the indole-3-pyruvic acid pathway, the tryptamine pathway and the indole-3-acetaldoxime pathway, have been postulated, identified and extensively studied. On the other hand, neither genes nor mutants involved in the TI pathway have been identified to date. Interestingly, some bacteria have auxin synthesis pathways that are similar to those in plants, indicating conserved biosynthetic mechanisms. Over the past few years, genetic, biochemical and molecular studies have greatly advanced our understanding of auxin biosynthesis. This review both summarizes recent advances in genetic and molecular knowledge and addresses the unsolved questions regarding auxin biosynthesis pathways in plants.

Growth, photosynthesis and adaptive responses of wild and domesticated watermelon genotypes to drought stress and subsequent re-watering

Abstract: The growth and morphophysiological responses of wild watermelon (C. lanatus var. citroide) M20 and Chinese domesticated watermelon (C. lanatus var. lanatus) Y34 to drought stress and subsequent re-watering were compared. Wild watermelon is drought-tolerant, whereas the domesticated watermelon is susceptible. Irrigation was withheld from seedlings for 10 days and the seedlings were then allowed to recover for 1 day. Drought treatment resulted in the wilting and yellowing of leaves in both genotypes, but symptoms occurred earlier and more visibly in Y34. Drought stress inhibited the growth of both genotypes but increased the root/shoot ratio more pronouncedly in M20 than in Y34. Under drought conditions, M20 maintained a higher leaf water status than Y34 due to its denser trichomes and more sensitive stomatal control, which minimized the transpiration rate. Y34 was more vulnerable to drought, resulting in larger decreases in photosystem II efficiency, initial Rubisco activity and chlorophyll concentration. H2O2, O2 −, and MDA contents were significantly increased in both genotypes; however, these increases were smaller in M20, possibly due to a greater enhancement of antioxidant enzyme activities and related-gene expression levels. Moreover, M20 accumulated soluble sugars and proline to greater levels to counter reduced soil moisture. These adaptive mechanisms enabled M20 to recover more rapidly after re-watering. Our findings provide guidance for improving the drought tolerance of Chinese watermelon cultivars.

Poly(γ-glutamic acid) enhanced tolerance to salt stress by promoting proline accumulation in Brassica napus L.

Abstract: Poly(γ-glutamic acid) (γ-PGA) is a new plant growth regulator with extensive application prospects. The effects of γ-PGA on rape seedlings under salt stress and the mechanism of action were investigated via hydroponic experiments. A salinity model was simulated by exposing the roots of rape seedlings to 100 mM NaCl solution for 48, 96 and 144 h. We determined that the growth of rape seedlings treated with NaCl was significantly inhibited. However, after the application of γ-PGA under NaCl stress, the dry weights of the entire plant, the shoot and the root were increased by 37.4, 38.8 and 34.1 %, respectively, at 144 h compared with those of the NaCl group. Moreover, the K+/Na+ ratio, proline content and antioxidant enzyme activity were all evidently enhanced, and the malondialdehyde content was significantly reduced in samples treated with γ-PGA. Proline metabolism regulation genes, including pyrroline-5-carboxylate synthetase genes (BnP5CS1 and BnP5CS2) and proline dehydrogenase gene (BnPDH), were also upregulated and downregulated by γ-PGA, respectively. Results showed that γ-PGA improved resistance to salt stress in rape seedlings by activating the proline synthesis pathway and promoting proline accumulation.

Effects of sunlight on gene expression and chemical composition of light-sensitive albino tea plant

Abstract: Light-sensitive albino tea plant grows yellow shoots under strong sunlight conditions. The yellow albino shoots contain high level of amino acids and medium level of polyphenols, which is beneficial for sensory quality of green tea. The effects of sunlight intensity on the transcriptions of genes involved in biosynthesis of chlorophylls and carotenoids, as well as the ultrastructure of chloroplasts, were investigated using a light-sensitive albino tea cultivar ‘Huangjinya’, and compared with a normal tea cultivar ‘Fudingdabai’. The results showed that strong sunlight induced hypoplasia of chloroplasts by suppressing the development of grana stacking and thylakoids, and down-regulated the expression levels of the 1-deoxy-d-xylulose-5-phosphate synthase gene family, involved in biosynthesis of precursors of carotenoids and chlorophylls, as well as the magnesium chelatase subunit D gene, involved in biosynthesis of chlorophylls, leading to the reduction of chlorophylls. Strong sunlight up-regulated the expression of genes involved in carotenoid pathway, resulting in the accumulation of carotenoids, including violaxanthin and lutein. The shortage of chlorophylls and the accumulation of carotenoids were considered to cause the yellow color of the albino shoots of the light-sensitive albino tea cultivar ‘Huangjinya’.

Ammonium improves tolerance to salinity stress in Sorghum bicolor plants

Abstract: Sorghum bicolor plants were grown in five combinations of NO3 −:NH4 + nutrition (100:0, 75:25, 50:50, 25:75 and 0:100) to test the hypothesis that nitrogen nutrition with ammonium (NH4 +) increases tolerance to salinity. Analyses were performed after 10 days of 75 mM NaCl stress. The K+ contents in the shoots and roots were reduced under salinity stress; however, salt-stressed plants from NO3 −:NH4 + treatments of 100:0 and 0:100 showed higher K+ concentrations in the shoots. Under salinity, Na+ accumulation was severely limited in the presence of NH4 + (0:100), which positively influenced K+/Na+ homeostasis. In parallel, NH4 +-fed plants displayed a substantial accumulation of N-rich amino acids (primarily glutamine and asparagine) in both tissues, which might be fundamental for alleviating NH4 + toxicity. These responses were reflected in favorable gas exchange and growth. Whereas the photosynthetic rate (A) of plants treated with 100:0, 75:25, 50:50 and 25:75 ratios were unaltered or reduced under salinity stress, plants treated with a ratio 0:100 showed increases in A; this phenomenon was strongly correlated with the higher instantaneous carboxylation efficiency of Rubisco (A/Ci) and total N content in the shoots. As a result, although the leaf area and shoot and root dry mass from all nitrogen treatments were severely reduced through stress, the NH4 + supply was effective to alleviate the harmful effects of salinity. The results clearly demonstrate that ammonium nutrition is more advantageous for the growth of S. bicolor under salinity than nitrate nutrition. Our findings suggest that improved plant acclimation induced through NH4 + resulted from increased photosynthesis performance, reduced Na+ toxicity effects and major N-compound content.

Impact of polyhydroxy fullerene (fullerol or fullerenol) on growth and biophysical characteristics of barley seedlings in favourable and stressful conditions

Abstract: Carbon nanoparticles attract attention of plant researchers as a possible means of improving crop yield and its quality. There are grounds to believe that the beneficial influence of polyhydroxy fullerene (PHF) on plants is due to its antioxidant activity, but the mechanism of its action on their growth and development remains unclear. Our study shows that PHF added to the nutrient medium accelerates barley roots elongation owing to the increase of their longitudinal extensibility in the growth zone. The impact of PHF on root growth was much more pronounced under the action of stressors inducing the accumulation of reactive oxygen species, such as UV-B radiation, salt stress and the excess of salicylic acid. Dichlorofluorescein assay showed that PHF prevented oxidative stress development and subapical root swelling after UV-B irradiation of roots. The conclusion is drawn that the important reason of root growth acceleration in the presence of PHF is its ability to serve as a scavenger of free radicals. That’s why it may be especially useful for the improvement of plant growth under environmental stress.

Hormone and growth interactions of scions and size-controlling rootstocks of young apple trees

Abstract: Size-controlling rootstocks are critical to grow small, efficient trees that enable early and high yield in plantings of apple. Improved knowledge of rootstock-related size-control processes is important for breeding and cultural practices. The research objective was to determine hormone profiles within trees grafted on Malling rootstocks. Buds from ‘Gala’, ‘Fuji’, M.7, M.9, M.27, and MM.111 were grafted to rootstocks M.7, M.9, M.27, and MM.111 and then grown in a greenhouse and the field. After 2 years, heights of trees grafted to growth-controlling rootstocks decreased in the order M.9 > M.7 > MM.111 in the greenhouse, the reverse trend that was measured in the field. Although soil resources were not measured, ample availability of resources such as water and mineral nutrients in the greenhouse may have been responsible for the reversal of rootstock effects on tree height in greenhouse and field. Elevated abscisic acid (ABA) and ABA metabolites were associated with ‘Gala’, MM.111 and M.9 scion that were grafted on M.9 rootstocks. Abscisic acid and abscisic acid glucose ester were generally greater in root, rootstock stem below the graft union, scion above the graft, and xylem exudate of rootstock M.9 than MM.111. Reduced gibberellin (GA19) was found in roots and xylem exudate of ‘Gala’ grafted to M.9 than MM.111 rootstocks. These results support the hypothesis that hormone signals from rootstocks control tree growth but it is likely that stage of development, time after planting, and environmental resources will also interact to influence growth effects of size-controlling rootstocks. It is proposed that gene expression associated with hormone metabolism can be developed to further understand the underpinnings of size-controlling rootstocks and assist the selection of rootstocks for size control and, possibly, for other hormone-related characteristics.

Effects of exogenous putrescine on glycolysis and Krebs cycle metabolism in cucumber leaves subjected to salt stress

Abstract: The effects of exogenous putrescine (8 mmol L−1) on the carbohydrate content, glycolytic metabolism, citric acid cycle intermediates, key enzyme activities and their corresponding gene expression in cucumber (cucumis sativus L. cv. Jingyou NO.4) subjected to salt stress (75 mmol L−1 NaCl) in solution culture was studied. Phosphofructokinase (PFK), pyruvate kinase (PK) and phosphoenolpyruvate pyruvate kinase (PEPC) activities were significantly decreased in leaves when exposed to salt stress. NaCl stress caused the PFK and PK gene expression and the content of pyruvate to significantly decrease, while PEPC gene expression increased. Salt stress also significantly reduced isocitrate dehydrogenase, malate dehydrogenase and succinate dehydrogenase and their levels of transcription, causing decreases in the citric acid, succinic acid and malic acid content in leaves. Exogenous putrescine reversed the salt stress and increased gene expression and, in turn, the key enzymes involved in the glycolysis pathway and Krebs cycle, which significantly increased the amounts of organic acids and pyruvate produced, promoting the release of more energy currency (ATP and ADP). These results suggest that Put effectively participate glycolysis pathway and Krebs cycle, reducing the excessive accumulation of carbohydrates in the leaves, and providing more material and energy for the defense salt-induced injury, thus enhances cucumber seedling to salt stress tolerance.

Effects of nitric oxide on alleviating cadmium stress in Typha angustifolia

Abstract: Nitric oxide (NO) is a key signal molecule that is involved in plant response to various abiotic stresses. The present study was conducted to investigate the effects of NO on Typha angustifolia which has been subjected to cadmium stress. Our results showed that sodium nitroprusside (SNP, a NO donor) treatment could significantly mitigate both the Cd (CdCl2·2.5H2O)-induced increase of malondialdehyde content in the root and relative electrolyte leakage in the root and leaf. NO demonstrated a reduced or counteractive effect on the Cd-induced increase in the activities of some typical antioxidant enzymes. The Cd-induced changes on the contents of non-protein thiol and phytochelatins in the root could also be reversed by NO. The protected effect of NO is likely achieved through trapping Cd in the root and decreasing Cd accumulation in the leaf and sheath. Furthermore, NO enhanced the allocation of Cd in the cell wall and reduced the distribution of Cd in the soluble fraction of the root and leaf. Differential biosynthesis of ascorbic acid content in some tissues might also be responsible for the protected effect of NO. This study concludes that NO counteracts Cd toxicity strongly in T. angustifolia via regulating antioxidant metabolism and enhancing Cd accumulation in the cell wall of the root.

Nitric oxide can induce tolerance to oxidative stress of peanut seedlings under cadmium toxicity

Abstract: To study the role of sodium nitroprusside (SNP, a donor of NO) in alleviating cadmium (Cd) toxicity in peanut (Arachis hypogaea L), peanut seedlings exposed to 50, 100, or 200 µM Cd as CdCl2 were treated with 250 µM SNP Cd exposure depressed plant growth, inhibited the photosynthesis, and resulted in oxidative stress In roots, Cd was mostly trapped in the cell wall under low Cd stress, but most Cd was accumulated in the soluble fraction under high Cd concentrations In leaves, a majority of Cd was accumulated in the cell wall regardless of Cd treatment level Addition of SNP at 250 µM significantly alleviated Cd toxicity in peanut seedlings, including improved photosynthesis, up-regulated antioxidant system, and reduced Cd translocation from roots to shoots as evidenced by decreased Cd accumulation in stems and leaves SNP application also changed the subcellular distribution of Cd in leaf and root tissues, by increasing Cd retention in root and leaf cell wall while reducing Cd accumulation in the soluble fractions and cell organelles These results indicate that SNP has great application potential for improving the growth of plants under heavy metal stress such as Cd toxicity

Transcriptomic analyses giving insights into molecular regulation mechanisms involved in cold tolerance by Epichloë endophyte in seed germination of Achnatherum inebrians

Abstract: Plants have developed mutualistic symbiosis with diverse fungal endophytes that increase their fitness by conferring abiotic and biotic stress tolerance. However, the molecular regulation mechanisms involved in stress tolerance remain largely unknown. Drunken horsegrass (Achnatherum inebrians), an important perennial bunchgrass in China, forms a naturally occurring symbiosis with an asexual symbiotic fungus Epichloe gansuensis. The effect of temperature on germination was determined for E. gansuensis-infected (E+) versus non-infected (E−) A. inebrians. Our results indicate that E+ seed have a higher germination rate under low temperature (10 °C) conditions compared with E− seed. To gain insight into the molecular mechanisms involved in the low temperature resistance of E+ drunken horsegrass, Solexa deep-sequencing was used to identify candidate genes showing differential expression. In total, 152 differentially expressed tags were identified, representing 112 up-regulated and 40 down-regulated genes, which were classified into eight functional categories. Many genes were found to be associated with low temperature response, such as genes participating in biosynthesis of alkaloids and unsaturated fatty acids. This study provides the first comprehensive examination of gene expression changes induced by fungal endophyte infection response to low temperature which is essential for understanding the molecular basis of this aspect of endophyte-enhanced plant improvement.

Effect of exogenous 6-benzylaminopurine (6-BA) on branch type, floral induction and initiation, and related gene expression in ‘Fuji’ apple ( Malus domestica Borkh)

Abstract: To investigate the mechanism by which 6-BA promotes flower bud formation, ‘Fuji’ apple trees were sprayed with 300 mg L−1 6-BA before the onset of floral induction. The differential transcription responses of flowering genes (MdFT, AFL1 and MdTFL1) and key cytokinin biosynthesis genes (MdIPT5a and MdIPT3a) in terminal buds were studied during flower development by real-time quantitative PCR. In addition, endogenous cytokinin and auxin levels in buds, shoot growth and flowering rate were surveyed. 6-BA treatment increased flowering rate, constrained shoot growth and changed the shoot components. Most shoots started to stop growing at 32 days after flowering (DAF), which marked the beginning of floral induction. The cytokinin accumulation was elevated at 30 DAF while MdTFL1 expression was down-regulated. Subsequently, there was a large increase in the transcription of AFL1 at 50 DAF. Thus, we propose that 300 mg L−1 6-BA spraying may indirectly break the cytokinin/IAA ratio suppressing MdTFL1 expression, resulting in higher transcription levels of AFL1 at flower initiation and alter shoots component and growth characteristics, which ultimately promoted flower development.

Identification and expression analysis of LEA gene family members in cucumber genome

Abstract: LEA (late embryogenesis abundant) proteins are firstly discovered in seeds and then identified in vegetative tissues of different plant species. They are mainly regulated under abiotic stress conditions. Although genome wide studies of different gene family members have been performed in cucumber, there is no such a study for LEA genes. We have identified 79 LEA genes in the cucumber genome. Based on phylogenetic analysis, CsLEA genes could be classified into seven groups in which structural motifs are relatively conserved. Tandem duplications play an important role in cucumber genome for LEA gene expansion. Orthologous and chromosomal relationships of CsLEA genes were observed based on comparative mapping analysis with other species. The in silico micro-RNA (miRNA) target analyses indicated that 37 CsLEA genes were targeted by different miRNAs, especially mir854 and mir414 are the most abundant identified ones. Public available RNA-seq data were analyzed for expression analysis of CsLEA genes in different tissues of cucumber. According to genome-wide expression analysis, nine CsLEA genes showed higher expression profiles in all tissues. The expression profiles of ten CsLEA genes in the root and leaf tissues of drought-stressed cucumber were examined using qRT-PCR. Among them, CsLEA-54 induced after stress application in leaf and root tissues and might provide adaptation to drought stress for cucumber. CsLEA-09, CsLEA-32 and CsLEA-57 genes responded to drought after 3 h later and might be considered as early response genes to water limitation. This research could help us to improve understanding of contribution of CsLEAs to drought tolerance in cucumber.

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.

Role of 1-MCP in regulating ‘Kensington Pride’ mango fruit softening and ripening

Abstract: Ripening of mango fruit is characterized by softening of flesh which limits its shelf life. 1-MCP is nontoxic gas that delays fruit softening and improves quality of several fruit. Therefore, the role of 1-MCP in regulating fruit softening and quality of ‘Kensington Pride’ mango was investigated. Physiological mature fruits treated with 1-MCP (1 mL L−1), ethylene (10 mL L−1) or 1-MCP + ethylene for 12 h at ambient condition (20 ± 1 °C). Untreated (control) as well as treated fruits were allowed to ripe at ambient temperature (20 ± 1 °C) for 10 days. Ethylene production, respiration rate and other fruit ripening parameters were determined periodically. Climacteric peaks of ethylene production and respiration rate were significantly supressed by 1-MCP application as compared to ethylene-treated and control fruit. Exogenous application of ethylene accelerated the development of fruit colour, fruit softening with increased activities of exo-PG, endo-PG and EGase enzymes in the pulp tissues. Whereas, activities of fruit softening enzymes were significantly delayed and/or suppressed in 1-MCP-treated fruit. 1-MCP-treated fruit showed improved rheological properties (i.e., firmness, springiness and stiffness), decreased level of citric acid, malic acid, succinic acid, total organic acids, total sugars and sucrose than other treatments. 1-MCP inhibited the activities of fruit softening enzymes which consequently delayed the ripening and ripening related changes in ‘Kensington Pride’ mango.

Effects of exogenous salicylic acid on the physiological characteristics of Dendrobium officinale under chilling stress

Abstract: We investigated the effects of exogenous salicylic acid (SA) on a new variety of Dendrobium officinale seedlings named “ZD-1” under chilling stress and recovery growth. Changes in photosynthetic parameters, PSII key component D1 protein, and antioxidant enzyme activities were determined. Our results indicated that a foliar spray of SA alleviated the decline in the chlorophyll content and increased the malondialdehyde content in D. officinale seedling leaves under chilling stress. The change in the ascorbic acid content, while complex, was understandable. The chilling stress resulted in a decrease in the maximal photochemical efficiency; however, the effect could be removed using exogenous SA. We found significant increases in the net photosynthetic rates of the seedling leaves in plants receiving SA treatments during the chilling stress compared with the control. There were no significant differences in the composition of thylakoid membrane proteins among different treatment groups. However, the western blot analysis showed an increase in the D1 protein content as SA concentrations increased. Approximately 1.5 mmol/L SA had the best effect against stress. SA significantly increased the superoxide dismutase activity and reduced the ascorbate peroxidase and catalase activities during recovery growth after chilling stress. During the recovery period, the maximal photochemical efficiency and net photosynthetic rate of plants receiving SA increased significantly in contrast to the control. These results suggested that the application of SA protected the chloroplast membrane and D1 protein, and enhanced the antioxidant capacity of the plants, which may be beneficial to the recovery growth of D. officinale seedlings.

The role of wheat jasmonic acid and ethylene pathways in response to Fusarium graminearum infection

Abstract: To study the roles of jasmonic acid (JA) and ethylene (ET) pathways in mediating defense against wheat Fusarium head blight (FHB), the expression patterns of genes in the Fusarium graminearum-challenged spikes between Wangshuibai and its susceptible mutant NAUH117 at the Fhb1 locus were compared using wheat microarray. The results showed that most of JA-associated genes were induced in Wangshuibai while only a few were induced in NAUH117, and most ET-associated genes were up-regulated in both genotypes. ELISA assay showed that in the F. graminearum-challenged spikes, endogenous JA content was increased in Wangshuibai while not in NAUH117. Pre-treatment with exogenous methyl JA could decrease the wheat disease severity. However, pretreatment by exogenous ethephon had no such effect. A lipid transfer protein gene, which is a representative gene for JA pathway, was selected for function analysis in Arabidopsis system using a T-DNA insertion mutant line for LTP gene. It was found that the mutant showed compromised FHB resistance compared with its wildtype, proving the possible role of LTP in FHB resistance of Arabidopsis. These results demonstrated that JA pathway should play a critical role in FHB resistance.

Role of salicylic acid-seed priming in the regulation of chromium (VI) and UV-B toxicity in maize seedlings

Abstract: Seed priming is a crucial method to induce tolerance capabilities in plants against various abiotic stresses. Seed priming is associated with an induction of number of physiological and biochemical changes in plants by the treatment of natural and/or synthetic compounds to the seeds before their germination. The aim of this study was to investigate whether salicylic acid (SA)-seed priming is involved in the regulation of hexavalent chromium [Cr(VI)] and UV-B toxicity in maize seedlings. For this, the accumulation of dry mass, Cr and SA, chlorophyll fluorescence, oxidative stress markers i.e. reactive oxygen species (ROS; O 2 ·− , ·OH and H2O2) and antioxidants were determined. Treatment of Cr(VI) (50 and 250 µM) declined growth and chlorophyll fluorescence parameters- Fv/Fm, Fv/F0, Fm/F0 and qP which accompanied by an increase in NPQ and the accumulation of Cr, and a decline in level of SA. The UV-B also exerts similar effects on growth, chlorophyll fluorescence and level of SA, and damaging effects become intense when combined with Cr(VI). SA-seed priming reduced Cr(VI) and UV-B toxicity on growth which accompanied by a decline in the accumulation of Cr. Cr(VI) and UV-B enhanced generation of O 2 ·− , ·OH and H2O2 which subsequently cause damage to lipids and proteins and thus, a decrease in membrane stability was noticed. Both stresses enhanced activities of superoxide dismutase and ascorbate peroxidase while activities of catalase and glutathione reductase were inhibited significantly. Furthermore, the results show that Cr(VI) and UV-B declined contents of total ascorbate and glutathione. This study suggests that Cr(VI) and UV-B might alter biosynthesis of SA as indicated by a decreased level of SA. However, SA-seed priming might act as a signal that reduces the accumulation of Cr and ROS and triggers up-regulation of antioxidants, which subsequently counteract Cr(VI) and UV-B toxicity and hence an improved growth was noticed.

Expansion and evolution of thaumatin-like protein (TLP) gene family in six plants

Abstract: Thaumatin-like protein (TLP) is one of pathogenesis-related protein family, which plays an important role in plant defense system. While its origin and expansion is unknown in plants. Here, we investigated the evolution of this gene family by performing a genome-wide identification and comparison in Arabidopsis, Oryza, Populus, Zea, Physcomitrella and Chlamydomonas. We found a birth process of this gene family in evolution. Tandem and segmental duplication played dominant roles for their expansion. In addition, TLPs were under purifying selection, and most members were responding to some biotic or abiotic stresses. Functional network analysis exhibited some resistance genes working together with TLPs. Our findings shed some light on this family gene evolution in plants, which might provide a base for further functional investigation of this family.

Effects of abscisic acid, jasmonic acid and salicylic acid on the content of phytochemicals and their gene expression profiles and biological activity in turnip ( Brassica rapa ssp. rapa )

Abstract: Turnip (Brassica rapa ssp. rapa) is an important vegetable crop and produces valuable health-promoting phytochemicals which have been used for their nutraceutical value. The exogenous effects of abscisic acid (ABA), jasmonic acid (JA) and salicylic acid (SA) on the contents of glucosinolate, individual and total phenolic compound, carotenoid, chlorophyll and anthocyanin content and their gene regulation of metabolic biosynthesis, as well as antioxidant and antimicrobial activities were studied in turnip plants. The JA treatments significantly increased the amount of glucobrassicin, 4-methoxyglucobrassicin, neoglucobrassicin and 4-hydroxyglucobrassicin. Gluconasturtiin content was considerably increased by ABA treatment. Glucoallysin, sinigrin, progoitrin, gluconapin and glucobrassicanapin were highly increased in SA-treated plants. The content of lutein was higher in ABA and SA-treated plants compared with that in control plants. Carotenoid, chlorophyll and anthocyanin contents were significantly increased with ABA, JA and SA treatment. Individual phenolic (flavonols, hydroxycinnamic and hydroxybenzoic acids) and total phenolic, flavonoid content, antioxidant and antimicrobial activity were noticeably increased in ABA, JA and SA-treated plants. Furthermore, ABA, JA and SA-treated plants exhibited significantly increased expression of genes associated with the phytochemical production. Our results proved that ABA, JA and SA did significantly increase the concentration of health-benefiting phytochemicals and also increased biological activity in turnip plants.

Brassinosteroids increase winter survival of winter rye ( Secale cereale L.) by affecting photosynthetic capacity and carbohydrate metabolism during the cold acclimation process

Abstract: The aim of the study was to verify the hypothesis that brassinosteroids would modify the cold acclimation process through the stimulation of photosynthesis and carbohydrate metabolism, and would consequently cause an increase in the plant’s capacity for winter survival. Seedlings of two winter rye cultivars (winter-resistant and moderately winter-resistant types) were sprayed with 24-epibrassinolide (EBR) and then subjected to cold acclimation at 4 °C. The foliar hormone application was studied for its effects on two components of winter resistance: tolerance to frost; and resistance to snow mould. These were examined after medium (3 weeks) and long (6 weeks) terms of cold acclimation. Additionally, as a control group, the level of endogenous brassinosteroids was measured in non-treated plants. The maximum acquired snow mould resistance was observed in the EBR-treated plants after 3 weeks of cold acclimation, while the maximum frost tolerance was recorded after 6 weeks of cold acclimation, as compared with control. In the winter-resistant cultivars, the EBR-induced snow mould resistance coincided with a lower photosynthetic efficiency and a lack of change in their Rubisco activity and level of total soluble carbohydrates. The elevated EBR-induced frost tolerance in the winter-resistant cultivars was associated with a carbohydrate metabolism that promoted a decrease in the monosaccharides of the leaves that stimulate photosynthetic efficiency and Rubisco activity. For both cultivars, the control plants developed frost tolerance between the third and sixth week of cold acclimation. However, the winter-resistant cultivar was characterised by a constant castasterone (CS) level, while the moderately winter-resistant one experienced a sharp increase in its endogenous CS after 3 weeks, and then after 6 weeks of cold acclimation.

Dendrobium nobile Lindl. seed germination in co-cultures with diverse associated bacteria

Abstract: The conservation of orchids is challenging due to their strong biotic relations and tiny seeds, requiring mycorrhiza for germination. This is aggravated when tropical plants are maintained in artificial conditions of greenhouses. We aimed to select the plant growth promoting rhizobacteria (PGPR) for orchid seed germination, to study plant–microbial interactions, and to determine whether there is any specificity between two species of Dendrobium plants in choosing bacterial partners. By the isolation of rhizoplane and endophytic rhizobacteria from Dendrobium moschatum roots, the known PGPR (Azospirillum, Enterobacter, Streptomyces) and less popular (Roseomonas, Agrococcus) strains were tested for the production of biologically active auxin. The bacterization of another orchid, D. noblie, with several newly selected strains and previously isolated ones (Mycobacterium sp., Bacillus pumilus) revealed that the orchids did not express evident specificity in relations with favorable bacteria, but refused to establish associations with Streptomyces and Azospirillum. Endophytic Agrococcus and Sphingomonas strains showed significant promotion of orchid germination. Mycobacterium and B. pumilus were also stable in their positive influence on the acceleration of D. noblie seed development. The active colonization of the seed surface and the inner tissues by associated bacteria was observed under electron microscopy. The analysis of orchid–bacteria relations was made. Altogether, the data shows that selection provides a good strategy for choosing the active strains for orchid seeds’ bacterization, since not all known PGPR are useful and successful in building associative frameworks with orchid seeds. The stable activity of the strains guarantees their long-term and effective application in orchid in vitro biotechnology.

Inhibitory effect of chemical combinations on seed germination and pre-harvest sprouting in hybrid rice

Abstract: Pre-harvest sprouting (PHS) is a primary cause of decreases in quality and economic value in rice seeds. This study examined the inhibitory effects of four combinations of maleic hydrazide, eugenol and uniconazole on rice PHS and seed quality. After the four treatments, delayed grain germination was observed compared with the control, mean germination time was prolonged by 17.5 % and germination index was decreased by an average of 18.2 %. Activity of α-amylase was significantly reduced, by 26.7–83.5 %, during grain germination and early seedling growth. We then used qRT-PCR to further analyze the mRNA expression levels of four genes involved in α-amylase biosynthesis. The expression of OsAMY3B and OsAMY3E was significantly down-regulated by the four combinations of chemicals. In field trials, each of the four combinations resulted in a significantly lower sprouting rate and sprouting index compared with the control. In addition, freshly harvested rice seeds showed no significant differences in the mean germination time or germination index between the four combination treatments and the control. After 1 month of storage, there was still no significant difference between the four combination treatments and the control with regard to the mean germination time and germination index. These results suggest that the selected combinations strongly inhibited the seed germination speed and PHS of rice in the field. However, these combinations had no inhibitory effects on the final germination percentage and showed no negative effect on seed quality after short-term storage. The combinations of inhibitors used in this study can be applied to decrease the PHS damage caused by high temperatures and moist weather during the production of hybrid rice.