Showing papers in "Biologia Plantarum in 2015"

Proline: a key player in plant abiotic stress tolerance

Abstract: Dramatic accumulation of proline is a common physiological response in plants exposed to various abiotic stresses. Accumulation of proline could be due to de novo synthesis, decreased degradation, lower utilization, or hydrolysis of proteins. Extensive intercellular proline transport occurs between the cytosol, chloroplasts, and mitochondria due to its compartmentalized metabolism. Although all functions of proline in stress tolerance are still a matter of debate, it is suggested that proline contributes to stabilization of sub-cellular structures, scavenging free radicals, and buffering cellular redox potential. It also chelates heavy metals, modulates cellular functions, and even triggers gene expression. Apparently, proline acts as stress-related signal exhibiting cross tolerance to a range of different stresses. Besides these significant roles, its metabolism is found to be coupled to several key pathways such as pentose phosphate, tricarboxylic acid, or urea cycles and contributes to, i.e., purine synthesis and the phenylpropanoid pathway. Although the molecular basis of regulation of proline metabolism is still largely obscure, the genetic engineering of proline content could lead to new opportunities to achieve plant stress tolerance.

Roles of exogenous glutathione in antioxidant defense system and methylglyoxal detoxification during salt stress in mung bean

Abstract: The protective roles of glutathione (GSH) applied on salt stress-affected mung bean (Vigna radiata L.) seedlings were studied. The salt stress (200 mM NaCl) significantly increased the malondialdehyde (MDA), methylglyoxal (MG), H2O2, and proline (Pro) content, O2 ·− generation rate, and lipoxygenase (LOX) activity and reduced the leaf relative water content (RWC) and chlorophyll (Chl) content. The salt stress also significantly reduced the ascorbate (AsA) content, increased the endogenous GSH and glutathione disulfide (GSSG) content, and reduced the GSH/GSSG ratio. The activities of mono-dehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and catalase (CAT) decreased; and the activities of ascorbate peroxidase (APX), glutathione reductase (GR), superoxide dismutase (SOD), glutathione S-transferase (GST), and glutathione peroxidase (GPX) increased under the salt stress. The activities of glyoxalase I (Gly I) and glyoxalase II (Gly II) decreased under the salt stress (except the Gly II activity at 48 h). Mung bean seedlings which were treated with NaCl together with GSH showed an improved AsA and GSH content, GSH/GSSG ratio, higher activities of APX (only at 24 h), MDHAR, DHAR, GR, SOD (only at 24 h), CAT, GPX (only at 48 h), GST (only at 24 h), Gly I and Gly II under the salt stress compared with those treated with NaCl alone. The improved antioxidant and glyoxalase systems by GSH application decreased the MDA, H2O2, and MG content, O2 ·− generation rate, as well as increased the leaf RWC and Chl content. Thus, exogenous GSH improved the response of the mung bean seedlings to the salt stress.

Effects of lead and nitric oxide on photosynthesis, antioxidative ability, and mineral element content of perennial ryegrass

Abstract: Hydroponics experiments were conducted to study the effects of sodium nitroprusside (SNP, a donor of NO) on lead toxicity in ryegrass (Lolium perenne L.) seedlings. When the ryegrass seedlings were grown in a nutrient solution containing 500 μM Pb2+ for two weeks, the plant biomass as well as net photosynthetic rate, transpiration rate, chlorophyll and carotenoid content of leaves decreased. The Pb stress also induced the production of superoxide anion (O2 ·−) and hydrogen peroxide (H2O2), leading to malondialdehyde (MDA) accumulation. Furthermore, the activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) decreased in the Pb-treated seedlings, but the catalase (CAT) activity increased. Additionally, the content of Cu in shoots and the content of K, Mg, Fe, and Zn in both shoots and roots decreased, but the content of Ca in shoots and roots increased under the Pb stress. Moreover, Pb accumulated mostly in roots, whereas a small quantity was translocated to shoots. However, the addition of 50, 100, and 200 μM SNP into the solution containing Pb increased the chlorophyll content and net photosynthetic rate, reduced Pb-induced oxidative damages, improved antioxidant enzyme activities, and inhibited translocation of Pb from roots to shoots. In particular, 100 μM SNP had the best effect on promoting growth of the ryegrass seedlings under the Pb toxicity. However, the application of 400 μM SNP had no obvious alleviating effect on Pb toxicity in the ryegrass seedlings.

Methyl jasmonate alleviates cadmium toxicity in Solanum nigrum by regulating metal uptake and antioxidative capacity

Abstract: The growth of the Cd-hyperaccumulator Solanum nigrum L. and its physiological responses to a short-term (7 d) Cd stress and to exogenous methyl jasmonate (MeJA) were investigated. Compared with the leaves of S. nigrum, the roots were more liable to Cd and showed a significantly decreased dry mass and increased malondialdehyde content. Cd accumulation in the shoots and roots of S. nigrum were proportional to the Cd concentration in the hydroponic solution. The application of a low concentration of MeJA (0.01 μM) significantly reduced the translocation/accumulation of Cd in both the shoots and roots compared with a 40 mg dm−3 Cd treatment only. Moreover, 40 mg dm−3 Cd significantly decreased the activity of leaf superoxide dismutase, but 0.01 μM MeJA restored it. MeJA also enhanced the activity of catalase in the leaves but showed no significant effect on peroxidase activity. The content of both endogenous jasmonic acid (JA) and MeJA in the leaves of S. nigrum increased with the increase of exogenous MeJA concentration.

Effects of exogenous salicylic acid and nitric oxide on physiological characteristics of two peanut cultivars under cadmium stress

Abstract: The interactive effects of salicylic acid (SA) and nitric oxide (NO) on alleviating cadmium (Cd) toxicity in peanut (Arachis hypogaea L.) were studied. Seedlings of two cultivars (Huayu 22 — a big seed type, and Xiaobaisha — a small seed type) were treated with 200 μM CdCl2 without or with 0.1 mM SA or 0.25 mM sodium nitroprusside (SNP, an NO donor). Results show that the Cd exposure depressed the plant growth of both the cultivars but more of Huayu 22 than of Xiaobaisha. Exogenous SA and NO alleviated Cd toxicity in both the peanut cultivars: they improved growth, chlorophyll content, photosynthesis, and mineral nutrition. Furthermore, exogenous SA or NO decreased oxidative stress by increasing activities of antioxidant enzymes and content of non-enzymatic antioxidants. Besides, in roots and leaves of both the cultivars, exogenous SA and NO increased Cd accumulation in the cell wall and decreased Cd distribution to organelles. In particular, the effect of SA+SNP was most obvious.

Mechanisms of heat tolerance in crop plants

Abstract: Due to possible climate changes, heat stress has obtained a serious concern all over the world. Tolerance to this stress via knowledge of metabolic pathways will help us in engineering heat tolerant plants. A group of proteins called heat shock proteins are synthesized following stress and their synthesis is regulated by transcription factors. Under high temperature (HT), reactive oxygen species (ROS) are often induced and can cause damage to lipids, proteins, and nucleic acids. To scavenge the ROS and maintain cell membrane stability, synthesis of antioxidants, osmolytes, and heat shock proteins is of a vital importance. In view of above mentioned, this review highlights the detailed mechanism of pathways involving crucial steps that change during HT stress.

Expression of DORMANCY-ASSOCIATED MADS-BOX ( DAM )-like genes in apple

Abstract: Apple (Malus × domestica Borkh.) is a perennial woody plant that undergoes a period of dormancy (in cv. Jonathan between late September and mid-December) to survive freezing temperatures of winter. DORMANCY-ASSOCIATED MADS-BOX (DAM) genes play important roles in the regulation of growth cessation and terminal bud formation in peach. To understand the role of DAM orthologs in apple, we isolated and characterized four DAM-like genes (designated as MdDAMa, MdDAMb, MdDAMc, and MdDAMd) and monitored their expression in apical buds throughout the season by real-time quantitative polymerase chain reaction analyses. The transcription of MdDAMa peaked in October and that of MdDAMc was elevated from August to October, whereas MdDAMb and MdDAMd were practically undetectable. The tandemly arranged genes MdDAMa/MdDAMb and MdDAMc/MdDAMd were localized to chromosomes 16 and 8, respectively. Based on these observations, we infer that MdDAMa and MdDAMc acted in a dominant fashion on each locus and were correlated with the period of endodormancy.

Alleviation of salt-induced oxidative stress in rice seedlings by proline and/or glycinebetaine

Abstract: The effects of proline and/or glycine betaine (GB) application on growth, photosynthetic pigments, H2O2 content, and activities of antioxidant enzymes in rice (Oryza sativa L. cv. KDML105) under salt stress were investigated. The H2O2 content and the activities of superoxide dismutase (SOD), glutathione reductase (GR), and ascorbate peroxidase (APX) but not catalase (CAT) increased under salinity. Under 160 mM NaCl, the CAT activity was maintained on the pre-stress level in the presence of proline, whereas in the presence of GB, the GR activity increased more than without GB application. A co-application of 30 mM proline and 1 mM GB did not reduce the increase in H2O2 caused by the NaCl stress more than applying each of the osmoprotectants and no synergistic effect on the antioxidant enzymes was observed. However, the application of both the osmoprotectants was the most effective in alleviating degradation of photosynthetic pigments.

Embracing new-generation ‘omics’ tools to improve drought tolerance in cereal and food-legume crops

Abstract: Drought stress presents a considerable threat to the global crop production. As a dominant source of vegetarian diet, cereals and grain-legumes remain crucial to meeting the growing dietary demands worldwide. Therefore, breeding cultivars of these staple crops with enhanced drought tolerance stands to be one of the most sustainable solutions to enhance food production in changing climate. Given the context, a more focused survey of environment-defined germplasm sets is imperative to comprehend such adaptive traits. In parallel, uncovering the genetic architecture and the molecular networks that collectively contribute towards drought tolerance is urgently required through rationally combining large-scale genomics, proteomics, and metabolomics data. Also, attention needs to be directed to reasonably quantify the epistatic as well as environmental influences, thereby warranting deployment of analyses like metaquantitative trait loci (QTL) that encompass multiple environments and diverse genetic backgrounds. Further, innovative techniques like genomic selection (GS) and genome wide association study (GWAS) would help to capture the quantitative variation underlying drought tolerance. Equally importantly, integration of physiological traits-based techniques with ever-evolving ‘omics’ technologies and the new-generation phenotyping platforms will be of immense importance in advancing our existing knowledge about the genetically-complex and poorly-understood phenomena, such as plant drought response, and a deeper understanding would likely to provide a great impetus to the progress of crop breeding for drought tolerance.

Brassinosteroid enhances cytokinin-induced anthocyanin biosynthesis in Arabidopsis seedlings

Abstract: To investigate whether brassinosteroids (BR) affects cytokinin (CK)-induced anthocyanin biosynthesis, seedlings of the Arabidopsis dwarf4 (dwf4) mutants including partially suppressing coi1 (psc1) and dwf4-102, which are defective in the BR biosynthesis, and the brassinosteroid-insensitive 1–4 (bri1-4) mutant defective in BR signalling were used for the analysis of CK-induced anthocyanin accumulation and the expression of anthocyanin biosynthetic genes and WD-repeat/Myb/bHLH transcription factors. The results show that the CK-induced anthocyanin accumulation was remarkably reduced in dwf4 and bri1-4 mutants, but distinctly increased in the wild type (WT) treated with BR. Moreover, the CK-induced expressions of the late anthocyanin biosynthetic genes including dihydroflavonol reductase, leucoanthocyanidin dioxygenase, and UDP-glucose: flavonoid-3-O-glucosyl transferase were significantly reduced in bri1-4 and dwf4-102 mutants compared to WT. In addition, the expressions of transcription factors production of anthocyanin pigment 1 (PAP1), glabra 3 (GL3), and enhancer of glabra 3 (EGL3) were induced by CK in WT but not in the bri1-4 and dwf4-102 mutants. These results indicate that BR enhanced the CK-induced anthocyanin biosynthesis by up-regulating the late anthocyanin biosynthetic genes and this regulation might be mediated by the transcription factors PAP1, GL3, and EGL3.

The responses of germinating seedlings of green peas to copper oxide nanoparticles

Abstract: The effects of copper oxide nanoparticles (CuONPs) on germinating seedlings of green pea (Pisum sativum L.) were studied. The seedlings were grown in a half-strength Murashige and Skoog semisolid medium containing 0, 50, 100, 200, 400, and 500 mg dm−3 CuONPs for 14 d under controlled growth chamber conditions. Exposures to 100, 200, 400, and 500 mg dm−3 CuONPs significantly reduced plant growth (shoot and root lengths) and increased reactive oxygen species (ROS) generation and lipid peroxidation. Gene expression study using real-time polymerase chain reaction showed no significant change in the expression of genes coding CuZn-superoxide dismutase (CuZnSOD), catalase (CAT), and ascorbate peroxidase (APX) in shoots. However in roots, a significant increase in the expression of the CuZnSOD gene was observed under the exposures to 100, 200, 400, and 500 mg dm−3 CuONPs, in the expression of the CAT gene under 100 and 200 mg dm−3 CuONPs, and in the expression of APX under 200 and 400 mg dm−3 CuONPs.

Osmoregulation as a key factor in drought hardening-induced drought tolerance in Jatropha curcas

Abstract: Jatropha curcas L. is a plant with various commercial uses, and drought is an important limiting factor for its distribution and production. In this study, we investigated the role of drought hardening in an increased drought tolerance in J. curcas, and the involvement of osmoregulation and biochemical pathways in this enhanced tolerance. Results show that a drought hardening treatment with 10 % (m/v) polyethylene glycol 6000 for two days significantly increased a survival rate, decreased the content of malondialdehyde, and alleviated electrolyte leakage in the J. curcas seedlings under the drought stress. Measurements of leaf water potential, osmotic potential, and pressure potential show that this drought hardening treatment can improve the water status of J. curcas seedlings during the early phase of drought stress. In addition, the drought hardening treatment gradually increased the concentrations of compatible solutes proline, glycinebetaine, and soluble sugars during drought hardening and subsequent drought stress. It also clearly raised the activity of betaine aldehyde dehydrogenase, a key enzyme for the glycinebataine biosynhthesis as well as the activity of enzymes Δ1-pyrroline-5-carboxylate synthetase (P5CS), glutamate dehydrogenase, arginase, and ornithine aminotransferase, all key enzymes in the proline biosynthesis. The expression of P5CS gene in the J. curcas seedlings also increased during drought hardening and subsequent drought stress, but the activity of proline dehydrogenase decreased. These results show that the drought hardening treatment can enhance drought tolerance in J. curcas, and osmoregulation is a key factor in this increased drought tolerance.

Silencing AT3 gene reduces the expression of pAmt, BCAT, Kas, and Acl genes involved in capsaicinoid biosynthesis in chili pepper fruits

Abstract: The effects of AT3-gene silencing on the expression of genes involved in capsaicinoid biosynthesis was investigated in chili pepper (Capsicum annuum L.) cv. Tampiqueno 74 fruits. Seeds were germinated and seedlings were grown in a greenhouse until they produced fruits. Capsaicinoids (capsaicin and dihydrocapsaicin) content and AT3 gene expression were determined in placenta tissue from fruits at 10, 20, 30, 40, 50, and 60 days post-anthesis (DPA). Capsaicin was more abundant than dihydrocapsaicin and both exhibited a similar accumulation pattern at different developmental stages starting at 20 DPA, reaching maximum values at 30–40 DPA before decreasing. The AT3 gene expression, as measured by quantitative RT-PCR, was positively correlated with capsaicinoid accumulation; AT3 transcripts were detected at 20 DPA, achieved a maximum at 30–40 DPA and then decreased. The Tampiqueno 74 seedlings were infected with Agrobacterium tumefaciens bearing a pTRV2-AT3 construct to induce virus-mediated silencing. Fruits were harvested at 40 DPA, and capsaicinoid content and AT3 gene expression were carried out in placenta tissue. A reduction of 81.1 % in AT3 expression and also in capsaicin (89.6 %) and dihydrocapsaicin (87.7 %) content was recorded in the AT3-gene silenced chili pepper plants. Furthermore, fruits from the AT3-silenced plants compared to the non-infected control plants showed a statistically significant reduction in the expression of genes involved in capsaicinoid biosynthesis [pAmt (89.4 %), BCAT (68.8 %), Kas (90.4 %) and Acl (58.6 %)]. These data indicate that AT3 silencing had a negative effect on the transcription of genes involved mainly in the branched-chain fatty acid pathway of capsaicinoid biosynthesis.

Glucose application protects chloroplast ultrastructure in heat-stressed cucumber leaves through modifying antioxidant enzyme activity

Abstract: To elucidate a physiological mechanism of heat stress mitigation by exogenous glucose, seedlings of Cucumis sativus cv. Jinchun No. 4 were pretreated with glucose and then exposed to normal (25/18 °C) and elevated (42/38 °C) temperatures. We investigated whether glucose can protect cucumber plantlets and chloroplast ultrastructure from heat and whether this protection is associated with antioxidant enzymes, proline, and soluble sugars. Heat inhibited plant growth, disorganized membranes of 86.33 % of chloroplasts, and elevated the content of malondialdehyde (MDA), superoxide radical (O2 ·−), and hydrogen peroxide (H2O2). An optimum concentration of glucose was 30 mM as it significantly alleviated plant growth inhibition and obviously reduced the content of MDA, O2 ·−, and H2O2 under the heat stress. The pretreatment with 30 mM glucose mitigated heat-induced damage of chloroplast ultrastructure and changes in leaf morphology more than 30 mM mannitol suggesting that glucose did not act only as osmolyte. Moreover, the glucose pretreatment increased activities of some antioxidant enzymes and enhanced the content of proline and soluble sugars under the heat stress, as well as the transcriptions of Cu/Zn-superoxide dismutase, Mn-superoxide dismutase, catalase, and glutathione reductase genes. We conclude that the pretreatment with 30 mM glucose protected chloroplast ultrastructure and enhanced heat tolerance of the seedlings by the increased activites of antioxidants and the content of proline and soluble sugars, and repressed accumulation of reactive oxygen species.

Exogenous sucrose influences antioxidant enzyme activities and reduces lipid peroxidation in water-stressed cucumber leaves

Abstract: To investigate whether exogenous sucrose can protect cucumber from water stress, cucumber (Cucumis sativus L.) seedlings were pretreated with 90 mM sucrose or 90 mM mannitol for 1 d and then were dehydrated with 10 % (m/v) polyethylene glycol (PEG) 6000 for further 1 d. Dehydration inhibited plant growth and decreased osmotic potential and relative water content (RWC) in leaves. The pretreatment with 90 mM sucrose further reduced the osmotic potential but increased the RWC and alleviated the growth inhibition. Compared with the PEG treatment alone, the combination of sucrose + PEG increased the activities of superoxide dismutase, guaiacol peroxidase, glutathione reductase, dehydroascorbate reductase, monodehydroascorbate reductase, ascorbate peroxidase, and glutathione peroxidase, and elevated the content of endogenous sucrose, glucose, and fructose together with the activities of soluble acid invertase and neutral invertase. This was in accordance with the enhanced transcription of genes encoding copper/zinc superoxide dismutase, guaiacol peroxidase, and glutathione reductase. Furthermore, the sucrose pretreatment decreased the content of malondialdehyde and hydrogen peroxide and increased the content of ascorbate, reduced glutathione, and proline under the dehydration. Taken together, the pretreatment with 90 mM sucrose, but much less with mannitol, induced antioxidants, proline, and soluble sugars and thus reduced dehydration-caused damage to the cucumber seedlings.

RNAi-mediated silencing and overexpression of the FaMYB1 gene and its effect on anthocyanin accumulation in strawberry fruit

Abstract: Strawberry (Fragaria × ananassa) contains anthocyanins which are important secondary metabolites and key contributors to the antioxidant capacity and nutritional value of the fruit. Anthocyanin biosynthetic genes have been identified. However, the detailed mechanism responsible for anthocyanin accumulation and regulation of biosynthetic genes during strawberry fruit ripening remain unclear. In the present study, we examined the effect of a Fragaria × ananassa myeloblastosis 1 homolog, FaMYB1, on anthocyanin accumulation in the strawberry fruit receptacle. Expression analysis shows that FaMYB1 transcripts increased in response to irradiance but not to abscisic acid treatments. Down-regulation of FaMYB1 was achieved in planta using Agrobacterium-mediated RNA interference (RNAi). As a result, FaMYB1-RNAi fruits exhibited a significant increase in anthocyanin content. Conversely, overexpression of FaMYB1 resulted in a decrease in anthocyanin content. Overexpression of FaMYB1 also significantly reduced expression of genes encoding anthocyanidin synthase and flavonoid glycosyltransferase, whereas down-regulation of FaMYB1 resulted in a significant decrease in the amount of transcripts of leucoanthocyanidin reductase. These data suggest that FaMYB1 might negatively control anthocyanin biosynthesis in the strawberry fruit at the branching-point of anthocyanin/proanthocyanidin biosynthesis.

Effects of heat shock and salinity on barley growth and stress-related gene transcription

Abstract: The effects of a short (30 min) heat shock (HS) on plants subsequently grown under a salinity stress (SS, 200 mM NaCl) for 10 d were investigated in barley (Hordeum vulgare L.) cv. Tokak 157/37. The maximum temperature for HS allowing plant survival was 45 °C. The root length was significantly decreased by SS, whereas HS alone did not affect root growth. Interestingly, HS stimulated root elongation under SS. An osmotic adjustment was promoted in leaves by SS. On the contrary, HS increased the osmotic potential in leaves in the absence of SS, and partly counteracted the effect of SS in the HS+SS treatment. Cu/Zn-SOD, HvAPX, HvCAT2, HSP17, HSP18, and HSP90 were transcribed in leaves of HS-treated plants, but not in control plants. The HSP70 was constitutively transcribed in both the SS and control plants, but after HS, a shorter amplicon was also observed. The genes coding antioxidants, Cu/Zn-SOD, HvCAT2 and HvAPX, were differentially influenced by SS or HS+SS in the roots and leaves. In the roots, the mRNA content of BAS1, HvDRF1, HvMT2, and HvNHX1 increased after the HS treatment. In a recovery experiment in which plants were grown to maturity after HS and HS+SS stress exposure, the plant height increased and the time to maturity was reduced in comparison with SS. Our results show that HS could stimulate plant growth and reduce some of the negative effects of SS, and that it affected the transcription of several stress-related genes.

Translation initiation in plants: roles and implications beyond protein synthesis

Abstract: Protein synthesis is a ubiquitous and essential process in all organisms, including plants. It is primarily regulated at translation initiation stage which is mediated through a number of translation initiation factors (eIFs). It is now becoming more apparent that in addition to synthesis of proteins, eIFs also regulate various aspects of plant development and their interaction with environment. Translation initiation factors, such as eIF3, eIF4A, eIF4E, eIF4G, and eIF5A affect different processes during vegetative and reproductive growth like embryogenesis, xylogenesis, flowering, sporogenesis, pollen germination, etc. On the contrary, eIF1A, eIF2, eIF4, and eIF5A are associated with interaction of plants with different abiotic stresses, such as high temperature, salinity, oxidative stress, etc. Similarly, eIF4E and eIF4G have roles in interaction with many viruses. Therefore, the translation initiation factors are important candidates for improving plant performance and adaptation. A large number of genes encoding eIFs can functionally be validated and utilized through genetic engineering approaches for better adaptability and performance of plants by inhibiting/minimizing or increasing expression of desired eIF(s).

Overexpression of maize chloride channel gene ZmCLC-d in Arabidopsis thaliana improved its stress resistance

Abstract: In plant cells, anion channels and transporters are essential for key functions. Members of the chloride channel (CLC) family located in intracellular organelles are required for anion accumulation, pH adjustment, and salt tolerance. Here, we cloned a maize (Zea mays L.) CLC gene, named ZmCLC-d, and found that its transcription was up-regulated under cold, drought, salt, and heat stresses, and after hydrogen peroxide (H2O2) and abscisic acid (ABA) treatments. The overexpression of ZmCLC-d in Arabidopsis conferred tolerance to cold, drought, and salt stresses; this tolerance was primarily displayed by an increased germination rate, root length, plant survival rate, antioxidant enzyme (catalase, peroxidase, and superoxide dismutase) activities, and a reduced accumulation of Cl− in transgenic plants as compared with wild type (WT) plants. The accumulation of H2O2 and superoxide anion in leaves of the ZmCLC-d-overexpressing plants is much less than that of the WT plants. The expressions of some stress related genes, such as CBF1, CBF2, CBF3, DREB2A, and RCI2A, increased to a greater extent in the ZmCLC-d-overexpressing plants than in the WT. Our results strongly suggest that ZmCLC-d played an important role in stress tolerance.

Overexpression of the genes coding ascorbate peroxidase from Brassica campestris enhances heat tolerance in transgenic Arabidopsis thaliana

Abstract: Previously, the ascorbate peroxidase (APX1) activity and gene expression in Chinese cabbage (Brassica campestris, Bc) heat-tolerant cv. ASVEG2 were found to be significantly higher than in heat-sensitive cv. RN720 under a heat stress. Furthermore, BcAPX2 and BcAPX3, isoforms of BcAPX1, were cloned in this study. Our objective was to transfer BcAPX cDNA under the control of the ubiquitin promoter to Arabidopsis via Agrobacterium tumefaciens strain GV3101. We found that BcAPX genes were overexpressed in transgenic Arabidopsis, and the expression of APX, and the APX activity in transgenic lines were higher than in non-transgenic (NT) plants under high temperatures. The chlorophyll content and the germination rate were significantly higher, and the malondialdehyde content was lower in BcAPX1-3, 2-1, and 3–5 lines subjected to the heat-stress treatment than those in the NT plants. Compared to the NT plants, a lower heat-induced H2O2 accumulation was detected by diaminobenzidine staining in leaves of the transgenic lines with a high APX activity indicating that the overexpression of BcAPX in Arabidopsis could enhance heat tolerance by eliminating H2O2.

Roles for NO and ROS signalling in pollen germination and pollen-tube elongation in Cupressus arizonica

Abstract: Roles for nitric oxide (NO) and reactive oxygen species (ROS) during pollen-tube growth have been well established in angiosperms, but there remains lack of information regarding their potential signalling roles in pollen tubes in gymnosperms. Here, the pollen-tube elongation of Arizona cypress (Cupressus arizonica Greene) was investigated. Nitric oxide, ROS, and actin were detected using their respective fluorescent probes. Both NO and ROS were observed in the nuclei of generative cells and pollen-tube cells, and in the cytoplasm in the tip region. An intracellular NO content in the pollen cells was lowered using an NO scavenger or an NO-synthase inhibitor. Similarly, an endogenous ROS content in the pollen cells was lowered using an NAD(P)H oxidase inhibitor. These treatments reduced pollen germination and pollen-tube growth, and induced severe morphological abnormalities. Inhibition of NO and ROS accumulation also severely disrupted the actin cytoskeleton in the pollen tubes. These data indicate that NO and ROS had signalling roles in pollen germination and pollen-tube formation in cypress.

The relationship between red fruit colour formation and key genes of capsanthin biosynthesis pathway in Capsicum annuum

Abstract: Pepper (Capsicum annum L.) fruit colours vary from green, ivory, or yellow at the juvenile stage to red, orange, and yellow at the mature stage. Carotenoid accumulation causes fruit colour formation in ripe Capsicum fruits, and capsanthin is a main carotenoid in ripe red pepper fruits. In this study, pepper cultivars with red, yellow, and orange fruits were employed and four key genes named phytoene synthase (Psy), lycopene-β-cyclase (Lcyb), β-carotene hydroxylase (Crtz), and capsanthin/capsorubin synthase (Ccs) in the capsanthin biosynthetic pathway were analyzed. Results show that a clear expression of the Ccs gene in cv. CK7 (yellow) was detected, but the expressions of the Psy and Lcyb genes were low comparing with the other tested cultivars. In addition, the expression of the Ccs gene was not observed in cv. R37-1 (orange). Furthermore, though the four key genes (Psy, Lcyb, Crtz, and Ccs) were detected in red cultivar R15, the expressions of them were low. Sequence analysis further indicated that the Ccs genes in cv. CK7 and cv. R37-1 had a high sequence identity (97.36 %). Interestingly, amino acid sequences coded by the Ccs genes from cv. CK7, cv. R37-1, and cv. R15 were the same. The above results suggest that the genes Psy, Lcyb, Crtz, and Ccs were required for capsanthin synthesis in pepper, and their varied expression patterns resulted in the variety of pepper fruit colours.

Marker-assisted breeding for TaALMT1, a major gene conferring aluminium tolerance to wheat

Abstract: Aluminium toxicity in acid soils is the main limitation to crop production worldwide. In wheat (Triticum aestivum L.), the Al-activated malate transporter (TaALMT1) gene located on chromosome 4DL is associated with malate efflux and Al-tolerance. To introgress Al-tolerance from the breeding line CAR3911 into the high yielding Al-sensitive cultivar Kumpa-INIA, phenotypic and molecular characterizations of gene/QTL underlying Al-tolerance in CAR3911 followed by marker-assisted backcrossing (MAS-BC) were undertaken. Al-tolerant backcross (BC) lines were selected using the functional marker ALMT1-4 designed immediately upstream of the TaALMT1 coding region. Foreground and background selections using ALMT1-4 and microsatellite markers were conducted. Linkage and sequence analyses suggest that the TaALMT1 gene could underly the Al-tolerance in CAR3911, possessing the same promoter type (V) as the Al-tolerant genotypes Carazinho and ET8. The MAS-BC strategy allowed the selection of Al-tolerant lines with the smallest introgressed region (6 cM) on 4D and the highest recurrent parent genome (RPG) (98 %) covering 2 194 cM of the wheat genome. The homozygous BC3F2 line named Kumpa-INIA-TaALMT1 expressed a 3-fold higher Al-tolerance than its isogenic line Kumpa-INIA at 40 μM Al in the hydroponic solution, and similarly to CAR3911 and Carazinho. The MAS-BC strategy was successful for the introgression of the TaALMT1 gene into Kumpa-INIA in only three BC generations, shortening the breeding cycle to 24 months, which promises to increase wheat production and a greater yield stability in the acid soils of Southern Chile.

Effect of copper and zinc on the in vitro regeneration of Rauvolfia serpentina

Abstract: The present study exemplifies morphogenic roles played by copper and zinc during micropropagation of Rauvolfia serpentina, an important medicinal shrub. Incorporation of 20 μM CuSO4 or 25 μM ZnSO4 to a Murashige and Skoog (MS) medium with optimized concentrations of auxins and cytokinins induced a maximum number of shoots per explant (40.67 ± 1.76 and 45.47 ± 0.24, respectively). However, higher concentrations of both the micronutrients negatively affected the morphogenic potential. The pigment content of the regenerants increased up to the optimal concentrations of both metals and thereafter decreased, whereas the maximum proline content was at the highest concentrations used. In vitro rooting of healthy shoots was accomplished using 0.5 μM IBA in a half strength liquid MS medium with 8.20 ± 0.37 roots, and root length of 5.50 ± 0.14 cm per microshoot. The plants survived a hardening procedure and were successfully acclimatized to field conditions with 95 % survival.

Mapping of QTLs associated with abscisic acid and water stress in wheat

Abstract: A segregating F4 population from the cross between drought sensitive (Yecora Rojo) and drought tolerant (Pavon 76) genotypes was made to identify molecular markers linked to a wheat (Triticum aestivum L.) abscisic acid (ABA) content at two water regimes. The parents and 150 F4 lines were evaluated phenotypically for drought tolerance using two irrigation treatments [0.25 and 0.75 m3(H2O) m−2(soil)]. Forty different target region amplification polymorphism (TRAP) primer combinations, 98 different sequence-related amplified polymorphism (SRAP) primer combinations, and 400 simple sequence repeat (SSR) primers were tested for polymorphism among the parental genotypes and the F4 lines. Seven loci in the F4 lines treated with the drought stress were identified. Single quantitative trait loci (QTLs) were located on chromosomes 1B, 2A, 3A, 5D, and 7B and each of them explained from 15 to 31 % of phenotypic variance with a LOD value of 7.2 to 15.7. Five QTLs were located on chromosome 4A and six QTLs on chromosome 5A. In control (well-watered) F4 lines, two QTLs were mapped on chromosome 3B and one QTL on each chromosome 5B and 5D. Statistically the most significant groups of QTLs for the ABA content were identified in the regions of chromosomes 3B, 4A, and 5A mostly near to Barc164, Wmc96, and Trap9 markers. Therefore, these markers linked to QTLs for the drought-induced ABA content can be further used in breeding for drought tolerance in wheat.

Modulation of NaCl induced DNA damage and oxidative stress in mungbean by pretreatment with sublethal dose

Abstract: Salinity is one of the most severe problems in worldwide agricultural production. The effect of salt on dry mass, total glutathione content, its regulatory enzymes, and extent of DNA damage in growing mungbean (Vigna radiata L. Wilczek) seedlings was investigated. The salt stress decreased a dry mass accumulation in the seedlings. A total glutathione (GSH) content and the activities of the enzymes of GSH metabolism were adversely affected by the salt stress. The enhanced accumulation of reactive oxygen species under the NaCl stress caused an increase in DNA damage, measured using a comet assay, in both roots and leaves of the mungbean seedlings. The pretreatment of mungbean seeds with a sublethal dose of NaCl was able to overcome the adverse effects of the salt stress to variable extents by exhibiting significant alterations of all tested parameters, imparting better growth and metabolism of the mungbean seedlings.

A germin-like protein gene of rice increased superoxide dismutase activity in transformed tobacco

Abstract: Germin and germin-like proteins (GLPs) are a broad and diverse family of developmentally regulated proteins widely distributed in plants. Oryza sativa L. harbours a large family of GLPs and serves as a good model for their study. In the present study, a germin-like protein gene (OsRGLP1) of rice origin was characterized by its heterologous expression in tobacco. The real-time PCR established almost a uniform expression of OsRGLP1 in leaves, stem, and roots of T1 Nicotiana tabacum cv. Samsun. Although no morphological difference was apparent between T0 transgenic and wild-type plants, leaves of mature transgenic plants showed necrotic lesions associated with an elevated content of H2O2, which was evidenced by in situ 3,3′-diaminobenzidine staining. A significantly higher activity of heat resistant superoxide dismutase (SOD) was observed in the transgenic plants as compared to the wild-type. The SOD activity in the transgenic plants was insensitive to potassium cyanide and sensitive to H2O2.

Genome-wide identification and characterization of the DREB transcription factor gene family in mulberry

Abstract: The dehydration responsive element binding (DREB) transcription factor (TF) family comprises unique and important proteins involved in abiotic stress responses and tolerance in plants. Although DREB TFs have been well identified and characterized in a few model plants, there is no detailed information available for mulberry. In this study, 110 AP2/ERF family genes were identified based on a genome-wide analysis of the Morus genome database. Among them, 30 Morus notabilis DREB family genes (MnDREBs) were identified. A comparative analysis with DREB gene families from other plants suggests that MnDREBs could be divided into six subgroups (A-1 to A-6) and could have similar functions in response to abiotic stresses since they have similar conserved domains/motifs within each subgroup. The expression patterns of MnDREBs were analyzed using transcriptome data of different organs from M. notabilis and the quantitative real-time polymerase chain reaction. The expression of most MnDREBs was detected in different organs and induced by various abiotic stresses, which suggest their vital roles in abiotic stress tolerance.

Effect of dehydration on spectral reflectance and photosynthetic efficiency in Umbilicaria arctica and U. hyperborea

Abstract: In many polar and alpine ecosystems, lichens of genus Umbilicaria represent dominant species forming community structure. Photosynthetic and spectral properties of the lichens may change rapidly according to an actual hydration status of their thalli. In this study, we investigated responses of photochemical reflectance index (PRI), normalized difference vegetation index (NDVI), effective quantum yield of photosynthetic efficiency of photosystem (PS) II (ΦPSII), and several photosynthetic parameters derived from fast induction kinetics of chlorophyll fluorescence (OJIP) to controlled dehydration. We used U. arctica and U. hyperborea collected close to Nuuk, Greenland. In both the species, PRI showed a curvilinear increase with dehydration, i.e., a decreasing water potential (Ψw). The increase was apparent within Ψw range of 0 to −10 MPa. The PRI increase was less pronounced in U. arctica than in U. hyperborea. NDVI decreased with a progressive thallus dehydration in both the species, however, throughout Ψw range of 0 to −30 MPa, U. hyperborea had lower NDVI values than U. arctica. The relationship between ΦPSII and Ψw resulted in a typical S curve. A critical Ψw at which photosynthetic processes were fully inhibited was −30 MPa in both the species, however, species-specific differences in the S curve shape were found. Analyses of photosynthetic parameters derived from OJIPs revealed that the absorption of radiation energy and a trapping rate increased with dehydration in active reaction centres of PS II, the number of which decreased with a more pronounced lichen thallus dehydration. It is concluded that U. arctica and U. hyperborea possess effective physiological mechanisms to maintain an effective photosynthesis when partly dehydrated (the Ψw range of 0 to −15 MPa). In spite of similar ecological niches that these two lichens occupy in nature, their spectral and photosynthetic properties differred.

Cloning and characterization of four novel SnRK2 genes from Triticum polonicum

Abstract: SnRK2 are plant-specific serine/threonine kinases that are involved in plant responses to abiotic stresses. In this study, four novel genes SnRK2s:TpSnRK2.11, TpSnRK2.2, TpSnRK2.5, and TpSnRK2.10 from dwarf Polish wheat (Triticum polonicum L.) were characterized and classified into three groups. TpSnRK2.5 and TpSnRK2.11 were members of group 1; TpSnRK2.2 was member of group 2; TpSnRK2.10 belonged to group 3. The expression of TpSNRK2.2 was strongly regulated by polyethylene glycol (PEG), NaCl, and cold in roots and leaves, as well as by ABA in leaves. The transcript of TpSnRK2.5 was intensely induced by all the treatments in roots and leaves. The distinct expression patterns of TpSnRK2.10 indicate that this gene was very sensitive to ABA and NaCl, less sensitive to cold and PEG. The transcript of TpSnRK2.11 was activated significantly by PEG, NaCl, and cold, but weakly by ABA. Our results indicate that these four genes were probably involved in wheat responses to different abiotic stresses in different tissues.