Showing papers in "Plant Growth Regulation in 2011"

Somaclonal variation in plants: causes and detection methods

Abstract: Plant tissue culture has become one of the fundamental tools of plant science research. It is extensively employed in the production, conservation and improvement of plant resources. The presence of somaclonal variation in populations derived from tissue culture is affecting the use of tissue culture negatively and has remained a major problem. Conversely, it is a source of new desirable clones/variants with better agronomic traits. In this review, we summarize the possible causes, detection methods and desirability of variants. Somaclonal variation is one of the most researched and reviewed topics. Hence, we restricted ourselves to outlining various examples which may be used as important references for researchers who intend to identify and/or characterize somaclonal variants while using tissue culture for research and production. Emphasis is placed on the negative effects of somaclonal variation. However, this review also includes examples of some useful variants generated as a result of somaclonal variation.

Epigenetics in plant tissue culture

Abstract: Plants produced vegetatively in tissue culture may differ from the plants from which they have been derived. Two major classes of off-types occur: genetic ones and epigenetic ones. This review is about epigenetic aberrations. We discuss recent studies that have uncovered epigenetic modifications at the molecular level, viz., changes in DNA methylation and alterations of histone methylation or acetylation. Various studies have been carried out with animals, and with plant cells or tissues that have grown in tissue culture but only little work has been done with shoots generated by axillary branching. We present various molecular methods that are being used to measure epigenetic variation. In micropropagated plants mostly differences in DNA methylation have been examined. Epigenetic changes are thought to underlie various well-known tissue-culture phenomena including rejuvenation, habituation, and morphological changes such as flower abnormalities, bushiness, and tumorous outgrowths in, among others, oil palm, gerbera, Zantedeschia and rhododendron.

Manganese-excess induces oxidative stress, lowers the pool of antioxidants and elevates activities of key antioxidative enzymes in rice seedlings

Abstract: Manganese (Mn) is an essential element for plant growth but in excess, specially in acidic soils, it can become phytotoxic. In order to investigate whether oxidative stress is associated with the expression of Mn toxicity during early seedling establishment of rice plants, we examined the changes in the level of reactive oxygen species (ROS), oxidative stress induced an alteration in the level of non-enzymic antioxidants and activities of antioxidative enzymes in rice seedlings grown in sand cultures containing 3 and 6 mM MnCl2. Mn treatment inhibited growth of rice seedlings, the metal increasingly accumulated in roots and shoots and caused damage to membranes. Mn treated plants showed increased generation of superoxide anion (O2 .−), elevated levels of H2O2 and thiobarbituric acid reactive substances (TBARS) and decline in protein thiol. The level of nonprotein thiol, however, increased due to Mn treatment. A decline in contents of reduced ascorbate (AsA) and glutathione (GSH) as well as decline in ratios of their reduced to oxidize forms was observed in Mn-treated seedlings. The activities of antioxidative enzymes superoxide dismutase (SOD) and its isoforms Mn SOD, Cu/Zn SOD, Fe SOD as well as guaiacol peroxidase (GPX) increased in the seedlings due to Mn treatment however, catalase (CAT) activity increased in 10 days old seedlings but it declined by 20 days under Mn treatment. The enzymes of Halliwell-Asada cycle, ascorbate peroxidase (APX) monodehydoascorbate reductase (MDHAR), dehyroascorbate reductase (DHAR) and glutathione reductase (GR) increased significantly in Mn treated seedlings over controls. Results suggest that in rice seedlings excess Mn induces oxidative stress, imbalances the levels of antioxidants and the antioxidative enzymes SOD, GPX, APX and GR appear to play an important role in scavenging ROS and withstanding oxidative stress induced by Mn.

Exogenous salicylic acid alleviates effects of long term drought stress and delays leaf rolling by inducing antioxidant system

Abstract: Salicylic acid (SA) is one of the important signal molecules modulating plant responses to environmental stress. In this study, the effects of exogenous SA on leaf rolling, one of drought avoidance mechanisms, and antioxidant system were investigated in Ctenanthe setosa during long term drought stress. The plants were subjected to 38-day drought period and they were treated with or without SA (10−6 M) on the 25th, 27th and 29th days of the period. Leaf samples were harvested on the 30th, 34th and 38th days. Some antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase), reactive oxygen species (hydrogen peroxide and superoxide) and lipid peroxidation were determined during the drought period. Treatment with SA prevented water loss and delayed leaf rolling in comparison with control leaves. Exogenous SA induced all antioxidant enzyme activities more than control leaves during the drought. Ascorbate and glutathione, α-tocopherol, carotenoid and endogenous SA level were induced by the SA treatment. Levels of reactive oxygen species were higher in SA treated plants than control ones on the 34th day. Their levels on the 38th day, however, fastly decreased in SA treated plants. SA treatment prevented lipid peroxidation while the peroxidation increased in control plants. The results showed that exogenous SA can alleviate the damaging effect of long term drought stress by decreasing water loss and inducing the antioxidant system in the plant having leaf rolling, alternative protection mechanism to drought.

Exogenous proline induces soluble sugar accumulation and alleviates drought stress effects on photosystem II functioning of Arabidopsis thaliana leaves

Abstract: The effects of exogenous applied proline (Pro), on photosystem II (PSII) photochemistry of drought stressed (DS) 4-week old Arabidopsis thaliana plants, was studied by using chlorophyll (chl) fluorescence imaging. The maximum quantum yield of PSII photochemistry (F v /F m) in DS plants decreased significantly to 77% of that of the control value, suggesting that DS plants could not maintain PSII function, possibly due to accelerated photoinhibition of PSII. Free Pro and total soluble sugars (SS) increased, in response to DS. Exogenous foliar application of Pro by spraying, led to a remarkable increase in the accumulation of Pro and surprisingly also of SS. Both of them served to scavenge reactive oxygen species (ROS), as it was evident by the decreased lipid peroxidation level measured as malondialdehyde (MDA). DS plants sprayed with Pro showed a tolerance to photoinhibition, this indicated by F v/F m being close to values typical of healthy leaves by maintaining more than 98% of PSII function. Also the higher quantum efficiency of PSII photochemistry (Φ PSΙΙ ) and the decreased excitation pressure (1 − q p ) recorded for stressed leaves with Pro, lead us to conclude that Pro appears to be involved in the protection of chloroplast structures by quenching ROS. The enhanced dissipation of excess light energy of PSII, in part accounts for the observed increased resistance to DS in A. thaliana leaves with Pro. Our data pointed out that Pro signalling interacts with SS signaling pathway and provided a new insight in Pro metabolism.

Effects of phenolic compounds on adventitious root formation and oxidative decarboxylation of applied indoleacetic acid in Malus ‘Jork 9’

Abstract: Stem slices (1-mm thick) cut from apple microshoots were cultured on a modified Murashige-Skoog medium with indole-3-acetic acid (IAA) or α-naphthaleneacetic acid (NAA), and increasing concentrations of various phenolic compounds. Both auxins were added at a concentration suboptimal for rooting. Indole-3-acetic acid is metabolized through oxidation and conjugation but NAA through conjugation only; which might have affected the results. With IAA, all tested orthodiphenols, paradiphenols and triphenols promoted adventitious root formation from the stem slices. Ferulic acid (FA, a methylated orthodiphenol) had the largest effect and increased the number of adventitious roots from 0.9 to 5.8. With NAA there was little or no promotion after addition of phenolics. Phloroglucinol (a triphenol) and FA were examined in detail. Their effects on the dose–response curve of IAA and the timing of their action indicated that both acted as antioxidants protecting IAA from decarboxylation and the tissue from oxidative stress. Experiments with carboxyl-labelled IAA showed that IAA was massively decarboxylated by the slices and that decarboxylation was strongly reduced by phenolics. Decarboxylation was to a great extent attributable to the wound response and did not occur to such an extent in non-wounded plant tissues. In shoots, FA promoted little rooting. Slices were cultured on top of the medium and shoots were stuck into the medium. Possibly, the anaerobic conditions in the medium near the basal part of the stem of shoots reduced the wound response and consequently decarboxylation of IAA. The monophenolic compound salicylic acid (SA) promoted IAA decarboxylation. Accordingly, SA reduced rooting when added during the initial days of the rooting process (the period during which auxin enhances rooting), and promoted outgrowth of root primordia later on (the period during which auxin inhibits rooting).

Role of proline and glycinebetaine pretreatments in improving heat tolerance of sprouting sugarcane ( Saccharum sp.) buds

Abstract: High temperature strongly hampers the plant growth particularly at early growth stages In this study, changes in some physiological and anatomical characteristics and possibility of mitigating the adversities of heat stress by soaking sugarcane nodal buds in 20 mM proline and glycinebetaine (GB) solutions have been explored Heat stress reduced the rate of bud sprouting nonetheless soaking the setts in proline followed by GB was beneficial In addition, heat stress reduced the bud fresh and dry weights, generated H2O2, reduced the tissue levels of K+ and Ca2+, while increased the osmolytes synthesis in a time course manner Heat stress also delayed the emergence and expansion of new bud leaves, by restricting the number and area of mesophyll cells It also caused poor and aberrant development and diffused appearance of mesophyll cells and vascular bundles in the bud leaves However, soaking of buds in proline and GB solutions substantially reduced the H2O2 production, improved the accumulation of soluble sugars and protected the developing tissues from heat stress effects; although proline was more effective than GB Correlations of various attributes indicated that soaking in GB and proline restricted the H2O2 generation, improved K+ and Ca2+ contents, and increased the concentrations of free proline, GB and soluble sugars eventually improving the heat tolerance of buds Cost-benefit analysis showed that, considering increase in sprouting of buds, soaking in 20 mM solution of both osmoprotectants is economical

Effects of the exogenous application of auxin and cytokinin on carbohydrate accumulation in grains of rice under salt stress

Abstract: Phytohormones, such as auxin and cytokinin, are known to be involved in the regulation of plant responses to salinity stress and counteract the adverse effect of stress conditions. This work investigated the effects of the exogenous spraying of indole-3-acetic acid (IAA) and kinetin (KIN) during the reproductive phase on grain yield by examining the 1000-grain weight and filled-grain percentage as well as the changes in starch, total soluble sugars, sucrose, glucose and fructose concentrations in the grains of two rice cultivars under salt stress. The results indicated that the applied IAA and KIN led to an increased grain yield, 1000-grain weight and filled-grain percentage for both rice cultivars under salt stress. The storage starch content in the grain of the salt-sensitive cultivar was more than that in the salt-tolerant cultivar under IAA application compared with KIN, whereas a decrease in the total soluble sugar content was observed with both IAA and KIN treatments, in comparison to the non-hormone treatment. Interestingly, this study showed that IAA led to a much higher increase in the sucrose content in grain, as compared to the KIN. Furthermore, this experiment suggests that glucose and fructose may play important roles during salt stress because there were clearly higher concentrations of these sugars in the grain of the stressed cultivars under IAA and KIN application: it appears that their accumulation was the earliest response detected during the grain-filling period in rice. Finally, this work indicated that an increase in the rice grain yield, 1000-grain weight and filled-grain percentage are associated with an increase in the contents of starch, sucrose, glucose and fructose in grain caused by the application of IAA and KIN.

Vermicompost treatment differentially affects seed germination, seedling growth and physiological status of vegetable crop species

Abstract: Vermicompost preparations are increasingly used in agricultural practice. There is a possibility, that crop plants are sensitive to negative effect of vermicompost at early stages of development. The aim of the present study was to test the effects of vermicompost on seed germination and seedling growth of different vegetable crop species. Vermicompost substitution inhibited seed germination and seedling growth with almost linear decrease of growth with increasing concentration of vermicopost in the substrate. However, both leaf chlorophyll content and photochemical activity of photosynthesis increased in all crop species with the exception of pea seedlings. Vermicompost extract as a watering solution showed positive effect on growth of bean and pea seedlings. Germination response of vermicompost extract-imbibed seeds was clearly crop species-dependent. Hypocotyl growth was stimulated by low and moderate vermicompost extract concentrations. Radicle growth was more sensitive to negative effect of vermicompost extract. It is reported that both solid vermicompost and vermicompost extract contain number of active substances of both phenolic and humic nature, each with own dose- and genotype-dependent effect of seed germination and early stages of seedling development. Findings of this study suggests that vermicompost must be used cautiously for practical purposes of plant propagation.

The role of meta -topolins in alleviating micropropagation problems

Abstract: Low shoot multiplication, morphological abnormalities, poor rooting frequency and high cost of production are among the factors challenging the micropropagation of ornamental perennials and garden plants. Most of these problems can be alleviated by using the appropriate type and concentration of plant growth regulator(s) (especially cytokinins) in developing efficient micropropagation protocols. In this study, we investigated the effects of five different aromatic cytokinins (BA, Kin, mT, mTR and MemTR) on adventitious shoot production from shoot-tip explants of B. greenii, a critically endangered plant with horticultural potential. Of all the cytokinin concentrations evaluated, the highest adventitious shoot production (5.88 ± 0.73 shoots/explant) was observed in cultures containing 7 μM MemTR. Low adventitious shoot production, which was not significantly different from that of the control, was observed at all the concentrations of kinetin (Kin), suggesting that it is a weak cytokinin for shoot production in this species. All the treatments with BA alone showed higher adventitious shoot production when compared to the BA treatments supplemented with NAA concentrations. At equimolar concentrations, however, all the BA concentrations had a higher abnormality index than the other cytokinins. It is noteworthy that the abnormality index in all the topolin treatments was much lower than that recorded at the lowest BA concentration. Almost all the abnormality indices recorded with mTR and MemTR concentrations were lower than that of the control. Given that the explants used were from BA-containing cultures, it is likely that the abnormalities recorded using mTR and MemTR were carry-over effects of BA. Culturing under 16 h light/8 h dark conditions resulted in a higher production of adventitious shoots with lengths greater than 10 mm compared to culturing under continuous light. This measure could help reduce the cost of production. Regenerated shoots were successfully rooted and acclimatized with a 65% survival frequency and no observable morphological variation. The developed micropropagation protocol has the potential for producing more than 60,000 transplantable shoots per year from a single shoot-tip explant of this critically endangered species.

Expression of key antioxidant enzymes under combined effect of heat and cadmium toxicity in growing rice seedlings

Abstract: Effect of Cd2+ toxicity and heat stress in sensitive rice cv. DR-92 and tolerant rice cv. Bh-1 grown in North East region of India were studied in sand cultures. Increasing levels of 0–500 μM Cd2+ alone and/or heat stress showed increased activities of superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase and glutathione reductase enzymes which were associated with induced oxidative stress and altered enzyme activities. The values for SOD and POD activities were always more in cv. DR-92 whereas CAT and GR activities were higher in cv. Bh-1 in roots and shoots under Cd2+ or heat stress alone in sensitive cv. DR-92. Upon imposition of a combination of Cd2+ + heat the activities of SOD and POD decreased significantly in root/shoot of both the sensitive and tolerant rice varieties. A nine fold increase in GR activity under combination of heat + 100 μM Cd2+ stress in shoots of cv. Bh-1 at day 15 was noted when compared to controls. The dual stress combination of Cd2+ + heat did not alter catalase activity in vivo in both the rice varieties. Results suggest a time-specific and varietal distribution of the antioxidant enzymes in rice plants subjected to Cd2+ and/or heat stress. Tolerant cv. Bh-1 has better survival to combined stressors like Cd2+ and heat than sensitive rice cv. DR-92 and heat stress when given in combination with Cd2+ toxicity seem to mitigate the effect of Cd2+ stress alone in rice. The study indicates individual Cd2+ toxicity and heat stress and a combination of the two stresses to have separate implications on antioxidative defense mechanism in rice plants. Among enzymes of the defense apparatus ascorbate peroxidase and glutathione reductase appear to serve as an important component for better survival of rice plants under combination of Cd2+ + heat stress.

Enhancement of artemisinin content and biomass in Artemisia annua by exogenous GA3 treatment

Abstract: Artemisinin is a promising and potent antimalarial drug naturally produced by the plant Artemisia annua L. but in very low yield. Its artemisinin content is known to be greatly affected by both genotype and environmental factors. In this study, the production of artemisinin and leaf biomass in Artemisia annua L. was significantly increased by exogenous GA3 treatment. The effect of GA3 application on expression of proposed key enzymes involved in artemisinin yield was examined in both wild type (007) and FPS-overexpression (253-2) lines of A. annua. In the wild type (007) at 6 h post GA3 application there was an abrupt rise in FPS, ADS and CYP71AV1 expression and at 24 h a temporary and significant peak in artemisinin (1.45-fold higher than the control). After GA3 application in line 253-2, there was a dramatic rise in expression of FPS at 3 h, CYP71AV1 at 9 h and ADS at 72 h and accumulation of artemisinin after 7 days, which was a delay when compared with the wild type plant. Thus, increased artemisinin content from exogenous GA3 treatment was associated with increased expression of key enzymes in the artemisinin biosynthesis pathway. Interestingly, exogenous GA3 continuously enhanced artemisinin content from the vegetative stage to flower initiation in both plant lines and gave significantly higher leaf biomass than in control plants. Consequently, the artemisinin yield in GA3-treated plants was much higher than in control plants. Although the maximum artemisinin content was found at the full blooming stage [2.1% dry weight (DW) in 007 and 2.4% DW in 253-2], the highest artemisinin yield in GA3-treated plants was obtained during the flower initiation stage (2.4 mg/plant in 007 and 2.3 mg/plant in 235-2). This was 26.3 and 27.8% higher, respectively, than in non-treated plants 007 and 253-2. This study showed that exogenous GA3 treatment enhanced artemisinin production in pot experiments and should be suitable for field application.

Chilling tolerance in Nicotiana tabacum induced by seed priming with putrescine

Abstract: Chilling stress is one of primary constraints to tobacco production in many parts of the world. The present study was conducted to induce chilling tolerance in tobacco by seed priming with putrescine (Put) in relation to physiological changes, using seeds from two tobacco varieties, MSk326 (chilling sensitive variety) and Honghuadajinyuan (HHDJY, chilling tolerant variety). Seed germination, seedling antioxidant enzyme activities and malondialdehyde (MDA) concentration, as well as polyamine concentration were determined under low temperature. During chilling stress at 11°C, seed priming with 0.01 mM Put for 48 h (Put0.01mM48 h) and seed priming with 0.1 mM Put for 48 h (Put0.1mM48 h) significantly increased germination percentage, germination index, seedling length and dry weight of both varieties compared to the controls without Put treatment. When seedlings of 4-leaf stage suffered a short chilling stress (5°C), Put 0.1 mM 48 h improved the activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), increased endogenous Put, Spd and Spm concentration and decreased the MDA concentration. The results showed that Put priming treatments were available to enhance the chilling tolerance of tobacco seedlings. The optimal treatment of Put was Put0.1 mM48 h.

Genome-wide analysis of the auxin response factor (ARF) gene family in maize (Zea mays)

Abstract: Auxin response factors (ARFs) are an important family involved in auxin-mediated response through specific binding to auxin response elements (AuxREs). A few members of the ARF family have been functionally characterized in Arabidopsis, rice (Oryza sativa), Poplar (Populous trichocarpa). However, little is known about ARF genes in maize (Zea mays). We performed a comprehensive bioinformatics analysis of the maize ARF gene family including analysis of the genome sequence, conserved domains, chromosomal locations, phylogenetic relationships, gene duplication, and expression profiles. 35 ZmARF genes were identified and categorized into four groups (Class I, II, III, and IV). In addition, a segmental ZmARF duplication event was shown to play an important role in maize ARF gene expansion. 7 ZmARF genes had no expression in specific tissues we obtained, but presented in mixed tissues according to the NCBI EST database, respectively. These studies have laid the theoretical foundation for further functional verification of these ZmARF genes.

Trichoderma harzianum strain T-22 induces changes in phytohormone levels in cherry rootstocks (Prunus cerasus × P. canescens)

Abstract: The aim of this research was to explain the direct plant growth-promoting activity of Trichoderma harzianum strain T-22 (T22), hypothesizing the involvement of different classes of plant growth regulators. Seven days after the transfer to root-inducing medium, in vitro-cultured shoots of GiSeLa6® (Prunus cerasus × P. canescens) were inoculated with T22. Root and shoot growth were significantly affected by T22 (+76 and +61%, respectively). Ten days after inoculation, the levels of indole-3-acetic acid (IAA), trans-zeatin riboside (t-ZR), dihydrozeatin riboside (DHZR), gibberellic acid (GA3) and abscisic acid (ABA) were analyzed by high performance liquid chromatography coupled with mass spectrometry. The results showed that after T22-inoculation, IAA and GA3 significantly increased in both leaves (+49 and +71%, respectively) and roots (+40 and +143%, respectively) whereas t-ZR decreased (−51% in leaves and −37% in roots). Changes in DHZR were observed in T22-inoculated roots (−32%) but not in leaves, whereas the levels of ABA did not differ between the two treatments. The extraction method allowed the simultaneous extraction of phytohormones. There is evidence that the change in phytohormone levels is one of the direct mechanism by which T22 promotes rooting and shoot growth, with notable advantages for rootstock production during nursery processes.

An endophytic bacterium isolated from roots of the halophyte Prosopis strombulifera produces ABA, IAA, gibberellins A1 and A3 and jasmonic acid in chemically-defined culture medium

Abstract: This paper informs the characterization by 16SrDNA partial sequence analysis of an endophytic diazotrophic bacterium isolated from roots of the halophyte shrub Prosopis strombulifera. The bacterium produced ABA, IAA, GA1, GA3 and jasmonic acid in chemically-defined culture medium as assessed by GC-EIMS. The results emphasize the role of phytohormones produced by endophytic bacteria in the association host-beneficial microorganisms, especially under conditions of adverse environments.

Inter-nucleosomal DNA fragmentation and loss of RNA integrity during seed ageing

Abstract: The germination of viable seeds is the basis for new plant growth and development. Seeds lose viability during storage, but the biochemical mechanisms of seed death are not fully understood. This study aimed to investigate degradation patterns of nucleic acids during seed ageing and subsequent water uptake. Seeds of Pisum sativum L. were artificially aged at 50°C and 12% seed water content (WC). Nucleic acids degradation was studied during ageing and during imbibition of four seed lots with differential viability from highly viable to dead. As seeds lost viability during ageing, DNA was gradually degraded into internucleosomal fragments, resulting in ‘DNA laddering’, in conjunction with disintegration of 18S and 28S rRNA bands. During imbibition, non-aged controls had high levels of DNA and RNA integrity through to radicle protrusion. In an aged seed lot with 85% total germination (TG) DNA fragmentation decreased upon imbibition probably due to nucleosome degradation, while rRNA integrity did not improve. In an aged seed lot with 44% TG, neither DNA nor rRNA integrity improved upon imbibition. Dead seeds showed DNA degradation as laddering throughout imbibition along with extensive degradation of rRNA. We present a model in which interlinked programmed and non-programmed events contribute to seed ageing, and suggest that protection of nucleic acids during ageing is key to seed longevity.

Differential expression of farnesyl diphosphate synthase gene from Withania somnifera in different chemotypes and in response to elicitors

Abstract: Withania somnifera (L.) Dunal (Family, Solanaceae), commonly known as Ashwagandha is one of the most valuable medicinal plants synthesizing large number of pharmacologically active secondary metabolites known as withanolides. Though the plant has been well characterized in terms of phytochemical profiles as well as pharmaceutical activities, not much is known about the genes responsible for biosynthesis of these compounds. In this study, we have characterized a gene encoding farnesyl diphosphate synthase (FPPS; EC 2.5.1.10), a key enzyme in the pathway of biosynthesis of isoprenoids, from W. somnifera. The full-length cDNA of Withania somnifera FPPS (WsFPPS) of 1,253 bps encodes a polypeptide of 343 amino acids. The amino acid sequence homology and phylogenetic analysis suggest that WsFPPS has close similarity to its counterparts from tomato (SlFPPS) and capsicum (CaaFPPS). Using semi quantitative RT–PCR, the expression pattern of the WsFPPS gene was analyzed in different tissues of Withania chemotypes (NMITLI-101, NMITLI-108, NMITLI-118 and NMITLI-135) as well as in response to elicitors (salicylic acid and methyl jasmonate) and mechanical wounding. The expression analysis suggests that WsFPPS expression varies in different tissues (with maximal expression in flower and young leaf) and chemotypes (with highest level in NMITLI-101) and was significantly elevated in response to salicylic acid, methyl jasmonate and mechanical injury. This is the first report on characterization of an isoprenoid pathway gene involved in withanolide biosynthesis.

Effects of citric acid as an important component of the responses to saline and alkaline stress in the halophyte Leymus chinensis (Trin.)

Abstract: Some plants accumulate some compatible solutes and exude various organic acids when exposed to environmental stress. These compatible solutes including proline have been suggested to be involved in stress tolerance by maintaining sufficient cell turgor for growth, thereby improving plant growth, protecting enzymes, and membranes. However, less evidence exists regarding the protective roles of organic acids under stress conditions. Here, we investigate the effects of citric acid as a component of the response to stress on plant growth and antioxidant enzyme activities in two genotypes of halophyte Leymus chinensis (Trin.) genotypes, LcWT07 and LcJS0107. Data showed that both saline stress (200 mM NaCl) and alkaline stress (100 mM Na2CO3) reduced plant growth on the relative growth rate and CO2 assimilation rate, but increased the citric acid concentrations in 6-week-old plants over the 72 h experimental period. When 50 mg l−1 citric acid was exogenously applied under stress conditions, it significantly improved the plant growth and internal citric acid concentration, and also induced defense mechanisms by increasing the activities of antioxidant enzymes. To compare with the mitigative effects of exogenous citric acid on stress, exogenous application of proline was also performed under same conditions, and similar effects on the improvement of growth were observed. Based on these results, we suggested that citric acid is an important component of the stress response in L. chinensis, and exogenous application of 50 mg l−1 citric acid might play a positive role on stress tolerance.

Alleviation of salinity stress in broccoli using foliar urea or methyl-jasmonate: analysis of growth, gas exchange, and isotope composition

Abstract: We studied the effects of foliar application of urea or methyl-jasmonate (MeJA) on the salinity tolerance of broccoli plants (Brassisca oleracea L. var. italica). Plant dry weight, leaf CO2 assimilation, and root respiration were reduced significantly under moderate saline stress (40 mM NaCl) but application of either urea or MeJA maintained growth, gas exchange parameters, and leaf N–NO3 − concentrations at values similar to those of non-salinized plants. Additionally, when these two foliar treatments were applied leaf Na+ concentration was reduced compared with control plants grown at 40 mM NaCl. However, at a higher salt concentration (120 mM NaCl), no effect of the foliar applications was found on these parameters. Salinity also decreased leaf δ15N but increased δ13C. Our study shows the feasibility of using foliar urea or MeJA to improve tolerance under moderate saline stress.

The role of ethylene and brassinosteroids in the control of sex expression and flower development in Cucurbita pepo

Abstract: In this paper we compare the sensitivity of different squash genotypes to ethylene and brassinosteroids by studying the effects of different ethylene and brassinosteroid treatments on the sexual expression and flower development of different C. pepo genotypes: Bolognese (Bog) and Vegetable Spaghetti (Veg), two contrasting lines for ethylene production and sensitivity, as well as Cora, a standard commercial hybrid. Results have demonstrated that ethylene has a much greater effect on sexual expression and flower development in C. pepo than brassinosteroids. Ethephon increases the number of female flowers per plant and reduces the first male phase of development, while treatments with the ethylene inhibitors AVG and STS reduce the number of female flowers per plant and expand the first male phase of development. The differential response observed between genotypes appears to be related to ethylene production and sensitivity. Bog, which produces more ethylene and is more sensitive to this hormone, responded much better to AVG and STS, reducing the number of female flowers per plant, while Veg, which is characterised by lower production of and sensitivity to ethylene, responded better to ethephon by reducing the first male phase of development and increasing the number of female flowers per plant. The differential abortion of female and male flowers in ethephon, AVG and STS treatments, as well as the occurrence of bisexual flowers in the AVG and STS treated plants of the more ethylene sensitive genotypes, demonstrate that ethylene is also involved in the development of female flowers. Female flower buds require a minimal level of ethylene not only to complete their development and maturation without a premature abortion, but also to arrest the development of stamens in the third whorl and to promote the appropriate growth of the carpels. On the contrary, the role of brassinosteroids in the sexual expression of C. pepo was not so evident. The application of brassinazole, an inhibitor of brassinosteroid biosynthesis slightly changes the production of ethylene in the three analysed genotypes, but those changes have little effect on their sexual phenotypes, and they do not alter the development of the unisexual flowers.

Calcium can moderate changes on membrane structure and lipid composition in cowpea plants under salt stress

Abstract: The effects of supplemental Ca2+ on membrane integrity and lipid composition of cowpea plants submitted to salt stress (75 mM NaCl) were evaluated. The experimental design was factorial (2 × 6 + 1) corresponding to six saline treatments supplemented with CaCl2 and six saline treatments supplemented with CaSO4, both at 0.5, 1.25, 2.5, 5.0, 7.5 and 10.0 mM, plus control treatment (plants grown in half-strength Hoagland’s nutrient solution without supplemental calcium addition). Samples of leaves and root tips were analyzed for total lipid, glycolipid and fatty acid contents and membrane damage symptoms. Salt stress greatly reduced total lipid content in leaves and roots and caused great damage to membrane structures. In leaves, the glycolipid content was differently influenced by calcium treatments. Moreover, salinity increased the saturated/unsaturated fatty acid ratio in leaves and an increase in the concentration of calcium intensified this response. In roots, only saturated fatty acids were detected and their content was strongly influenced by salinity and very little by calcium treatments. Supplemental Ca2+ was unable to ameliorate the negative effects of salinity on the structural integrity and fluidity of plant membranes in cowpea.

Alleviation of chilling-induced oxidative damage by salicylic acid pretreatment and related gene expression in eggplant seedlings

Abstract: The effects of salicylic acid (SA) pretreatment on ascorbate–glutathione (GSH) cycle under chilling stress in eggplant seedlings were investigated. Salicylic acid pretreatment improved chilling resistance of eggplant seedlings with maximum efficiency at a concentration of 0.3%. The chilling injury index was decreased by 36.9% as compared to that of the control after 0.3% SA pretreatment. Under chilling stress, seedlings pretreated with SA displayed lower hydrogen peroxide (H2O2) content and higher ascorbate peroxidase (APX) activity than the untreated seedlings. Pretreatment with SA increased ascorbic acid and GSH content. Salicylic acid (0.3%) pretreatment enhanced the dehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) activity but not glutathione reductase (GR). Pretreatment with SA also enhanced the induced expression of stress-responsive genes under chilling stress. The highest transcript levels of GST1, GST2, GPX1, GPX2, GSH, MDHAR, GR and DHAR upon pretreatment with SA (0.3%) were 6.21, 6.24, 7.76, 5.99, 6.54, 6.44, 2.86 and 2.15 folds, respectively as compared to non-SA-treated seedlings. Taken together, SA pre-treatment could effectively protect eggplant seedlings from oxidative damage of chilling stress through enhancing antioxidant enzymes activities and related gene expression.

Effect of nitrogen deficiency on antioxidant status and Cd toxicity in rice seedlings

Abstract: Effect of nitrogen (N) deficiency on antioxidant status and Cd toxicity in rice seedlings was investigated. N deficiency resulted in a reduction of shoot growth but not root growth. The contents of N-containing compounds such as nitrate, chlorophyll, and protein decreased in leaves of rice seedlings grown under N deficiency. Accumulation of abscisic acid and H2O2 in leaves was induced by N deficiency. The content of ascorbate and the activities of ascorbate peroxidase, glutathione reductase, and catalase in N-deficient leaves were lower than their respective control leaves. However, glutathione content was not affected and superoxide dismutase activity was increased by N deficiency. Cd toxicity in N-deficient seedlings was more pronounced than that in N-sufficient ones. Pretreatment with ascorbate or L-galactono-1,4-lactone, a biosynthetic precursor of ascorbate resulted in a reduction of Cd toxicity enhanced by N deficiency. N deficiency also resulted in an enhancement of Cd uptake in rice seedlings. The possible mechanism of Cd toxicity enhanced by N deficiency is discussed.

Arbuscular mycorrhizal fungi can alter some root characters and physiological status in trifoliate orange ( Poncirus trifoliata L. Raf.) seedlings

Abstract: Citrus plants strongly depend on mycorrhizal symbiosis because of less or no root hairs, but few reports have studied if their root traits and physiological status could be altered by different arbuscular mycorrhizal fungi (AMF). In a pot experiment we evaluated the effects of three AMF species, Glomus mosseae, G. versiforme and Paraglomus occultum on the root traits and physiological variables of the trifoliate orange (Poncirus trifoliata L. Raf.) seedlings. Root mycorrhizal colonization was 58–76% after 180 days of inoculation. AMF association significantly increased plant height, stem diameter, leaf number per plant, shoot and root biomass. Mycorrhizal seedlings also had higher total root length, total root projected area, total root surface area and total root volume but thinner root diameter. Among the three AMFs, greater positive effects on aboveground growth generally ranked as G. mosseae > P. occultum > G. versiforme, whilst on root traits as G. mosseae ≈ P. occultum > G. versiforme. Compared to the non-mycorrhizal seedlings, contents of chlorophyll, leaf glucose and sucrose, root soluble protein were significantly increased in the mycorrhizal seedlings. In contrast, root glucose and sucrose, leaf soluble protein, and activity of peroxidase (POD) in both leaves and roots were significantly decreased in the mycorrhizal seedlings. It suggested that the improvement of root traits could be dependent on AMF species and be related to the AMF-induced alteration of carbohydrates and POD.

Changes in endogenous cytokinin profiles in micropropagated Harpagophytum procumbens in relation to shoot-tip necrosis and cytokinin treatments

Abstract: Changes in cytokinin (CK) profiles and their physiological implications in micropropagated Harpagophytum procumbens [(Burch.) DC. ex Meisn.] tissues in relation to shoot-tip necrosis (STN) and CK treatments were studied. Total CK content was quantified in benzyladenine (BA)-treated necrotic and normal plantlets and in plantlets treated with the CKs BA, meta-topolin (mT) and meta-topolin riboside (mTR) with and without the auxin indole-3-acetic acid (IAA). Generally necrotic shoots yielded more total CK compared to normal shoots. Cytokinin accumulation was higher at the basal section (basal > middle > top). Further analysis of the CKs based on structural and functional forms revealed excessive accumulation of 9-glucosides (deactivation products—toxic metabolites) and limited amounts of O-glucosides (storage forms—re-utilizable) in necrotic and BA-treated shoots compared to normal and topolin-treated cultures. The addition of IAA enhanced the formation of 9-glucosides in BA-treated cultures but reduced it in topolin-treated cultures. The symptom of STN could therefore be attributed to conversion of active cytokinins to other forms such as 9-glucosides which are neither active nor reversibly sequestrated to active forms. Literature shows that metabolites like 9-glucosides of BA have a detrimental effect in plant tissue culture.

Physiological responses of kiwifruit plants to exogenous ABA under drought conditions

Abstract: We studied the physiological responses to abscisic acid (ABA) when 2-year-old potted plants of kiwifruit (Actinidia deliciosa) were grown under moisture stress. Leaves treated with 60 μM exogenous ABA through various means had less severe damage when water was limiting, and sprayed plants showed relatively greater drought resistance. This indicates that ABA improves tolerance in kiwifruit, reducing membrane permeability and enhancing the activities of antioxidant enzymes, e.g., peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). Exposure to ABA led to higher levels of antioxidants, such as ABA and glutathione (GSH), while altering the amounts of endogenous hormones—ABA, indole-3-acetic acid (IAA), and Gibberellin (GA)—and organic oxalate, malate, and citrate in the leaves. Although daily applications of ABA were more effective than a single spray event, the effect of treatment, i.e., avoiding tissue damage and increasing plant resistance, was more apparent on Day 4 than on Day 6. No difference in response was apparent between control plants (regular irrigation) and those sprayed with ABA on Day 4 of the drought period.

Identification of the tomato ABA-deficient mutant sitiens as a member of the ABA-aldehyde oxidase gene family using genetic and genomic analysis

Abstract: The sitiens (sit) wilty mutant of tomato (Solanum lycopersicum L.) is deficient in functional enzyme activity at the final step in abscisic acid (ABA) biosynthesis. The biochemical lesion is believed to be an impaired aldehyde oxidase (AO). Molecular mapping using various interspecies crosses has previously shown sit to co-map with a cluster of unresolved RFLP markers on the short arm of chromosome 1. Here, the utilisation of bridging lines to produce interspecies mapping populations involving a self-compatible S. peruvianum accession (LA2157) allowed the fine mapping of sit within this cluster. Identification of a novel AO gene, within the region now known to contain the sit locus, was confirmed by analysis of the tomato whole genome shotgun sequence assembly. This novel AO protein shares 76-78% identity at the amino acid level with the previously characterised tomato AO proteins. The DNA sequence of this putative sit gene was characterised in wild type and in two allelic sit mutants (sit and sit w): changes in DNA sequence were identified in these mutant alleles that cause a truncation of exon 2 and the deletion of exon 7, respectively. These results establish the identity of the tomato sit gene and are consistent with its proposed function of encoding the ABA aldehyde oxidase apoenzyme.

Regulation of exogenous spermidine on the reactive oxygen species level and polyamine metabolism in Alternanthera philoxeroides (Mart.) Griseb under copper stress

Abstract: Effects of exogenous spermidine (Spd) on the reactive oxygen species level and polyamine metabolism against copper (Cu) stress in Alternanthera philoxeroides (Mart.) Griseb leaves were investigated. Cu treatment induced a marked accumulation of Cu and enhanced contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and the generation rate of O2 ·−. It also significantly increased putrescine (Put) levels but lowered spermidine (Spd) and spermine (Spm) levels. The activities of arginine decarboxylase (ADC), ornithine decarboxylase (ODC) and polyamine oxidase (PAO) were all elevated with the increase of Cu concentration. However, application of exogenous Spd effectively decreased H2O2 content and the generation rate of O2 ·−, prevented Cu-induced lipid peroxidation and reduced Cu accumulation. Moreover, it declined level of endogenous Put and increased levels of Spd and Spm. Activities of ADC, ODC and PAO were all inhibited by exogenous Spd. The results indicated that application of exogenous Spd could enhance the tolerance of A. philoxeroides to Cu stress by reducing the reactive oxygen level and balancing polyamine metabolism.

Effect of N-(n-butyl) thiophosphoric triamide on urea metabolism and the assimilation of ammonium by Triticum aestivum L

Abstract: The use of urea as an N fertilizer has increased to such an extent that it is now the most widely used fertilizer in the world. However, N losses as a result of ammonia volatilization lead to a decrease in its efficiency, therefore different methods have been developed over the years to reduce these losses. One of the most recent involves the use of urea combined with urease inhibitors, such as N-(n-butyl) thiophosphoric triamide (NBPT), in an attempt to delay the hydrolysis of urea in the soil. The aim of this study was to perform an in-depth analysis of the effect that NBPT use has on plant growth and N metabolism. Wheat plants were cultivated in a greenhouse experiment lasting 4 weeks and fertilized with urea and NBPT at different concentrations (0, 0.012, 0.062, 0.125%). Each treatment was replicated six times. A non-fertilized control was also cultivated. Several parameters related with N metabolism were analysed at the end of growth period. NBPT use was found to have visible effects, such as a transitory yellowing of the leaf tips, at the end of the first week of treatment. At a metabolic level, plants treated with the inhibitor were found to have more urea in their tissues and a lower amino acid content, lower glutamine synthetase activity, and lower urease and glutamine synthetase content at the end of the study period, whereas their urease activity seemed to have recovered by this stage.