Salinity Stress Treatments Research Articles

A stress-responsive NAC transcription factor SNAC3 confers heat and drought tolerance through modulation of reactive oxygen species in rice.

Adverse environmental conditions such as high temperature and drought stress greatly limit the growth and production of crops worldwide. Several NAC (NAM, ATAF1/2, and CUC2) proteins have been documented as important regulators in stress responses, but the molecular mechanisms are largely unknown. Here, a stress-responsive NAC gene, SNAC3 (ONAC003, LOC_Os01g09550), conferring drought and heat tolerance in rice is reported. SNAC3 was ubiquitously expressed and its transcript level was induced by drought, high temperature, salinity stress, and abscisic acid (ABA) treatment. Overexpression (OE) of SNAC3 in rice resulted in enhanced tolerance to high temperature, drought, and oxidative stress caused by methyl viologen (MV), whereas suppression of SNAC3 by RNAi resulted in increased sensitivity to these stresses. The SNAC3-OE transgenic plants exhibited significantly lower levels of H2O2, malondiadehyde (MDA), and relative electrolyte leakage than the wild-type control under heat stress conditions, implying that SNAC3 may confer stress tolerance by modulating reactive oxygen species (ROS) homeostasis. Quantitative PCR experiments showed that the expression of a large number of ROS-scavenging genes was dramatically increased in the SNAC3-OE plants, but significantly decreased in the SNAC3-RNAi transgenic plants. Five ROS-associated genes which were up-regulated in SNAC3-OE plants showed co-expression patterns with SNAC3, and three of the co-expressed ROS-associated enzyme genes were verified to be direct target genes of SNAC3. These results suggest that SNAC3 plays important roles in stress responses, and it is likely to be useful for engineering crops with improved tolerance to heat and drought stress.

Salinity and Water Stress Effects on Biomass Production in Different Arundo donax L. Clones

Perennial rhizomatous grasses are regarded as leading energy crops due to their environmental benefits and their suitability to regions with adverse conditions. In this paper, two different experiments were carried out in order to study the salinity (S) and water stress (WS) effects on biomass production in giant reed (Arundo donax L.). In Experiment 1, eight clones of giant reed were subjected to four salinity (S) and water stress (WS) treatments: (1) well watered with non-saline solution, (2) water stress with non-saline solution, (3) well watered with saline solution and 4) water stress with saline solution. In Experiment 2, five clones of giant reed were subjected to increasing S levels in two locations: University of Catania (UNICT-Italy) (1) well watered with non-saline solution and (2) well watered with mild saline solution; and University of Barcelona (UB-Spain) (3) well watered with non-saline solution and (4) well watered with severe saline solution. Photosynthetic and physiological parameters as well as biomass production were measured in these plants. According to our data, giant reed seems to be more tolerant to S than WS. Both stresses mainly affected stomatal closure to prevent dehydration of the plant, eventually decreasing the photosynthetic rate. The differential performance of the giant reed clones was ranked according to their tolerance to S and WS by using the Stress Susceptibility Index. ‘Agrigento’ was the most WS resistant clone and ‘Martinensis’ was the most S resistant. ‘Martinensis’ and ‘Piccoplant’ were found to be the most suitable clones for growing under both stress conditions. Moreover, ‘Fondachello’, ‘Cefalu’ and ‘Licata’ were the most resistant clones to increasing S levels.

The over-expression of a chrysanthemum WRKY transcription factor enhances aphid resistance

Members of the large WRKY transcription factor family are responsible for the regulation of plant growth, development and the stress response. Here, five WRKY members were isolated from chrysanthemum. They each contained a single WRKY domain and a C2H2 zinc finger motif, so were classified into group II. Transient expression experiments demonstrated that all five were expressed in the nucleus, although CmWRKY42 was also expressed in the cytoplasm. When expressed heterologously in yeast, the products of CmWRKY22 and CmWRKY48 exhibited transactivation activity, while those of CmWRKY21, CmWRKY40 and CmWRKY42 did not. The transcription of the five CmWRKY genes was profiled when the plants were challenged with a variety of abiotic and biotic stress agents, as well as being treated with various phytohormones. CmWRKY21 proved to be markedly induced by salinity stress, and suppressed by high temperature exposure; CmWRKY22 was induced by high temperature exposure; CmWRKY40 was highly induced by salinity stress, and treatment with either abscisic acid (ABA) or methyl jasmonate (MeJA); CmWRKY42 was up-regulated by salinity stress, low temperature, ABA and MeJA treatment and aphid infestation; CmWRKY48 was induced by drought stress, ABA and MeJA treatment and aphid infestation. The function of CmWRKY48 was further investigated by over-expressing it transgenically. The constitutive expression of this transcription factor inhibited the aphids' population growth capacity, suggesting that it may represent an important component of the plant's defense machinery against aphids.

Improve the salinity stress by using ascorbic acid on Germination, Growth Parameters, Water Relations, Organic and Inorganic Components of Sweet Pepper (Capsicum annuum, L.) Plant

The relationship between compatible solutes (osmolytes) and antioxidants are the strategies that plants have developed to tolerate salt stress. A greenhouse experiment was carried out to study the response of presoaked Sweet Peppers (Capsicum annuum, L.) seeds in freshly prepared ascorbic acid (25 mML-1 ASC) or distilled water (control) for 12 h at natural environmental conditions, to reduce the effect of salinity stress. Generally, the sweet pepper seeds germination occurred after 4 days, while, the germination rate (%) were more faster after soaking the seeds in ascorbic acid compared with control (soaked in distilled water). NaCl salt-stress treatments caused a reduction in all growth parameters (fresh and dry weights of plant, leaf area and number per plant) compared control, particularly at high NaCl level (250 mM) more reduced. In the mean time, ascorbic acid had reduced the effect NaCl salinity stress on all growth parameters. Photosynthetic pigments (chlorophyll a & b and carotenoids) and chloroplast efficiency were increasing with salinity stress, but the response was more pronounced at 250 mM NaCl whether alone or combined with ascorbic acid. Also, salinity stress treatments tended to increased all of the total available carbohydrates (Monosaccharide, Disaccharides & polysaccharides), nitrogenous components (protein, amino acids & proline), antioxidase, (catalase, peroxidase & superoxide dismutases) enzymes activities and inorganic mineral elements (Na+, K+, N+3, P+3, Ca+2, Mg+2 & Cl-) but after soaked the seeds in ascorbic acid, these components tended to increased more. Application of NaCl salinity-stress on tomato plant induced the synthesis of nitrogenous components (protein, amino acids, proline), whereas, the tomato seeds soaked before planting in ascorbic acid which leads to remarkably increasing more for all nitrogenous components, antioxidase, carbohydrates and inorganic mineral elements content.

Overexpression of CuZnSOD from Arachis hypogaea alleviates salinity and drought stress in tobacco.

Overexpression of CuZnSOD gene from Arachis hypogaea demonstrating its involvement in abiotic stress tolerance. Abiotic stress is accompanied by the formation of reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radicals, causing extensive cellular damage and inhibition of photosynthesis that limit the plant productivity. The level of ROS in cells needs to be tightly regulated and the toxic effects of ROS are countered by enzymatic as well as non-enzymatic antioxidant systems. The superoxide dismutase is the first enzyme involved in the detoxification of ROS and converts superoxide (O2(·-)) radicals to H2O2. A full-length cDNA clone encoding a CuZnSOD, named AhCuZnSOD, was isolated from the salt tolerant cell lines of Arachis hypogaea, stably thriving at 200 mM NaCl. The cell line showed higher transcript accumulation under multiple abiotic stresses, including drought, salinity, cold and oxidative stress treatment. The functional role of AhCuZnSOD in alleviation of abiotic stress was assessed by its overexpression in transgenic tobacco plants. The T1 transgenic plants showed improved tolerance to salinity and dehydration stress as indicated by higher seed germination and better chlorophyll content. The transgenic plants survived under longer periods of water deficiency and salinity stress and displayed improved recovery after rehydration compared to the wild type (WT) plants. The enhanced level of the transgene correlated with higher relative water content, less electrolyte damage, less malondialdehyde, higher antioxidant enzyme activity, H2O2 and O2(·-) accumulation under stress conditions compared to WT plants. Our results substantiate that increased levels of SOD activity brought about by overexpression of AhCuZnSOD gene may play an important role in ameliorating oxidative injury induced by various environmental stresses.

Isolation and characterization of six AP2/ERF transcription factor genes in Chrysanthemum nankingense.

The AP2/ERF family of plant transcription factors (TFs) regulate a variety of developmental and physiological processes. Here, we report the isolation of six AP2/ERF TF family genes from Chrysanthemum nankingense. On the basis of sequence similarity, one of these belonged to the Ethylene Responsive Factor (ERF) subfamily and the other five to the Dehydration Responsive Element Binding protein (DREB) subfamily. A transient expression experiment showed that all six AP2/ERF proteins localized to the nucleus. A yeast-one hybrid assay demonstrated that CnDREB1-1, 1-2 and 1-3 all function as transactivators, while CnERF1, CnDREB3-1 and 3-2 have no transcriptional activation ability. The transcription response of the six TFs in response to wounding, salinity and low temperature stress and treatment with abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA) showed that CnERF1 was up-regulated by wounding and low temperature stress but suppressed by salinity stress. The transcription of CnDREB1-1, 1-2 and 1-3 was down-regulated by ABA and JA to varying degrees. CnDREB3-1 and 3-2 was moderately increased or decreased by wounding and SA treatment, suppressed by salinity stress and JA treatment, and enhanced by low temperature stress and ABA treatment.

Cloning and expression analysis of pepper chlorophyll catabolite reductase gene CaRCCR.

Opening the porphyrin macrocycle of pheophorbide a and forming the primary fluorescent chlorophyll catabolites are key steps in the chlorophyll catabolism pathway. These steps are catalyzed by pheophorbide a oxygenase and red chlorophyll catabolite reductase (RCCR). In this study, a novel RCCR gene, CaRCCR, was isolated from the pepper (Capsicum annuum L.). The full-length CaRCCR complementary DNA is comprised of 1173 bp, contains an open reading frame of 945 bp, and encodes a 314-amino acid protein. This deduced protein belongs to the ferredoxin-dependent bilin reductase family. Amino acid sequence alignment showed that CaRCCR shared a high homology to other higher plant RCCR proteins. CaRCCR expression, as determined by quantitative real-time polymerase chain reaction, was higher in the leaves than the roots, stems, flowers, and immature fruits. CaRCCR expression was almost constant during all phases of leaf development. It was upregulated by abscisic acid, methyl jasmonate, and salicylic acid. Moreover, CaRCCR was induced by high salinity and drought stress treatments; it was also slightly regulated by Phytophthora capsici. Taken together, these results suggest that CaRCCR is involved in defense responses to various stresses.

Antioxidant responses of peanut (Arachis hypogaea L.) seedlings to prolonged salt-induced stress

In this study, the effects of long-term NaCl treatment were investigated in two cultivars of peanut designated as drought-resistant and drought-sensitive. Growth parameters, changes in the concentrations of MDA, H2O2 and proline, and the activities of antioxidant enzymes were determined under salinity stress. Growth parameters indicated the superiority of cv. Florispan to cv. Gazipa?a under milder salinity stress treatment. However, comparative analysis of the two cultivars showed that MDA, H2O2, ion leakage levels and photosystem II activities were not significantly different, except for the proline activity, which increased only in Florispan leaf tissues under 100 mM salt treatment. Among the processes that govern the tolerance in peanut tissues, proline level and the activity of glutathione reductase (GR) appeared to be only components that play an important part in salt stress protection.

Genetic analysis of salt tolerance at seedling and reproductive stages in rice (Oryza sativa)

AbstractSalinity is a major abiotic stress that limits rice production across rice areas as high‐yielding modern rice varieties are generally sensitive to salt stress. The study was conducted to deduce heritability and combining ability estimates of rice for various morphological and physiological traits using a 7 × 7 full‐diallel‐cross analysis at seedling and reproductive stages. The salinity stress treatment was 12 dS m−1 at the seedling stage and 8 dS m−1 at the reproductive stage. Diallel analysis revealed high for salinity tolerance scores and shoot height, moderate for shoot dry weight and root dry weight and low for Na+ and K+ concentrations and K+/Na+ ratio. The low‐to‐moderate narrow‐sense heritability for number of panicles, number of fertile spikelets, grain weight, spikelet fertility and K+/Na+ ratio suggests a large breeding population and delayed selection for tolerance until later generations. Significant maternal effects indicate that selection of the female parent is very important for desired trait development. The results of this study confirmed that salinity tolerance at the seedling and reproductive stages is regulated by a different set of genes that could be pyramided using different donors to enhance the level of tolerance.

High‐throughput deep sequencing shows that microRNAs play important roles in switchgrass responses to drought and salinity stress

MicroRNAs (miRNAs) are an important class of small regulatory RNAs. The goal of this study was to analyse stress-responsive miRNAs in switchgrass (Panicum virgatum), the emerging biofuel crop, to facilitate choosing gene targets for improving biomass and biofuel yield. After sequencing three small RNA libraries constructed from control, salt- and drought-treated switchgrass using Illumina sequencing technology, we identified 670 known miRNA families from a total of more than 50 million short reads. A total of 273 miRNAs were identified with precursors: 126 conserved miRNAs and 147 novel miRNAs. Of them, 265 miRNAs were found to have their opposite sequences (miRNA*) with 2-nt overhang on the 3' end. Of them, 194 were detected in switchgrass transcriptome sequences generated from 31 high-throughput RNA sequencing (RNA-Seq) data sets in NCBI. Many miRNAs were differentially or uniquely expressed during salinity or drought stress treatment. We also discovered 11 miRNA clusters containing 29 miRNAs. These identified miRNAs potentially targeted 28549 genes with a various function, including transcription factors, stress-response proteins and cellulose biosynthesis-related proteins. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the identified miRNAs and their targets were classified to 3779 GO terms including 1534 molecular functions, 1851 biological processes and 394 cellular components and were enriched to 147 KEGG pathways. Interestingly, 195 miRNA families and 450 targets were involved in the biosynthesis pathways of carbon, glucose, starch, fatty acid and lignin and in xylem formation, which could aid in designing next-generation switchgrass for biomass and biofuel.

Isolation and characterization of isochorismate synthase and cinnamate 4-hydroxylase during salinity stress, wounding, and salicylic acid treatment in Carthamus tinctorius

Salicylic acid (SA) is a prominent signaling molecule during biotic and abiotic stresses in plants biosynthesized via cinnamate and isochorismate pathways. Cinnamate 4-hydroxylase (C4H) and isochorismate synthase (ICS) are the main enzymes in phenylpropanoid and isochorismate pathways, respectively. To investigate the actual roles of these genes in resistance mechanism to environmental stresses, here, the coding sequences of these enzymes in safflower (Carthamus tinctorius), as an oilseed industrial medicinal plant, were partially isolated and their expression profiles during salinity stress, wounding, and salicylic acid treatment were monitored. As a result, safflower ICS (CtICS) and C4H (CtC4H) were induced in early time points after wounding (3–6 h). Upon salinity stress, CtICS and CtC4H were highly expressed for the periods of 6–24 h and 3–6 h after treatment, respectively. It seems evident that ICS expression level is SA concentration dependent as if safflower treatment with 1 mM SA could induce ICS much stronger than that with 0.1 mM, while C4H is less likely to be so. Based on phylogenetic analysis, safflower ICS has maximum similarity to its ortholog in Vitis vinifera up to 69%, while C4H shows the highest similarity to its ortholog in Echinacea angustifolia up to 96%. Overall, the isolated genes of CtICS and CtC4H in safflower could be considered in plant breeding programs for salinity tolerance as well as for pathogen resistance.

Homologous HAP5 subunit from Picea wilsonii improved tolerance to salt and decreased sensitivity to ABA in transformed Arabidopsis

HAP is a ubiquitous transcription factor family which consists of three distinct subunits, namely HAP2, HAP3, and HAP5. Among them, HAP2 and HAP3 subunits have been reported to be involved in plant response to abiotic stress. Here, a HAP5 subunit was identified from Picea wilsonii Mast. and transformed to Arabidopsis to investigate its functions in plant stress response. We found that transformed Arabidopsis with over-expressing PwHAP5 exhibited higher seed germination under salinity, osmotic and abscisic acid (ABA) stress treatment compared to Col-0 plants. The seedlings of transformed Arabidopsis also showed improved tolerance to salinity and decreased sensitivity to ABA treatment. Over-expression of PwHAP5 in Arabidopsis athap5 mutant rescued partly tolerance to NaCl, mannitol and ABA treatment. Furthermore, we examined transcription levels of several stress-related genes in transformed seedlings. Among them, mRNA expression levels of COR15a, KIN1, DREB2A, and RD29A genes were substantially higher in transformed Arabidopsis than those in wild-type (Col-0) plants. Therefore, our data revealed that PwHAP5 plays positive roles in response to salinity, osmotic and ABA stress at different developmental stages in plants, respectively, via possibly regulating stress-related genes.

Molecular cloning and characterization of a soybean GmMBY184 induced by abiotic stresses

Abstract Drought and high salinity stresses often imposes adverse effects on crop yield. MYB transcription factors have been shown to be an important regulator in defense responses to these environmental stresses. In this study, we have cloned and characterized a soybean gene GmMYB184 ( Glycine max MYB transcription factor 184). Deduced amino acid sequences of GmMYB184 show highest homology with that from Vitis vinifera legume plant (75%). Different ex-pression patterns of GmMYB184 mRNA were observed subjected to drought, cold, high salinity stress and abscisic acid treatment, suggesting its role in the signaling events in the osmotic stress-related defense response. Subcellular localization studies demonstrated that the GFP- GmMYB184 fusion protein was localized in the nucleus. Using the yeast assay system, the C-terminal region of GmMYB184 was found to be essential for the transactivation activity. These results indicate that the GmMYB184 may play a role in abiotic stress tolerance in plant.

CDNA- AFLP analysis of the response of tetraploid black locust (Robinia pseudoacacia L.) to salt stress

Soil salinity is a major abiotic stress that limits plant growth. In this study, to understand the tolerance mechanism associated with salinity stress in tetraploid black locust ( Robinia pseudoacacia L.), 2-yearold plants were treated by salinity. cDNA amplified fragment length polymorphism (cDNA-AFLP) and quantitative real-time polymerase chain reaction (qRT-PCR) were used to study the gene expression of tetraploid black locust in response to 5, 10 and 15 days after salinity stress (300 mM NaCl) treatment. One hundred and ten (110) transcript derived fragments (TDFs) with up-regulation expression in leaves of tetraploid black locust in response to salinity stress were characterized and classified into seven groups. The putative functions of these TDFs were related to energy metabolism, material metabolism, signal transduction, transcription factor, stress and defense-related proteins and transport facilitation. The expression patterns of six genes having direct or indirect relation with salt stress response were analyzed through qRT-PCR. The possible roles of these genes are discussed. These data may enhance the understanding of the salinity tolerance mechanisms in polyploid plants. Keywords : cDNA-AFLP, salt stress, gene expression, qRT-PCR; tetraploid black locust.

Increased salt and drought tolerance by d-ononitol production in transgenic Arabidopsis thaliana

The methylation of myo-inositol forms O-methyl inositol ( d-ononitol) when plants are under abiotic stress in a reaction catalyzed by myo-inositol methyltransferase (IMT). d-Ononitol can serve as an osmoprotectant that prevents water loss in plants. We isolated the IMT cDNA from Glycine max and found by RT-PCR analysis that GmIMT transcripts are induced by drought and salinity stress treatments in the leaves of soybean seedlings. We confirmed the protein product of GmIMT and its substrate using a recombinant system in E. coli. Transgenic Arabidopsis plants over-expressing GmIMT displayed improved tolerance to dehydration stress treatment and to a lesser extent high salinity stress treatment. These results indicate that GmIMT is functional in heterologous Arabidopsis plants.

Effects of salinity and desalination on seed germination of six annual weed species

The effects of various salinities and desalination on seed germination of six annual glycophytes (Artemisia sieversiana, A. scoparia, Chloris virgata, Eragrostis pilosa, Chenopodium acuminatum and Chenopodium glaucum) were studied in Horqin Sandy Land, Inner Mongolia, China. NaCl solutions of five concentrations (0 mM, as the control, and 50, 100, 200 and 300 mM) were used for saline stress and desalination treatments. Increasing salinity significantly reduced germination percentages of A. sieversiana, A. scoparia, Ch.virgata and Ch. acuminatum, but had no effect on the germination percentages of E. pilosa. Lower salinity levels (50 mM) significantly increased germination percentage of Ch. glaucum. High salinity might be a precondition for germination after desalination for five of the six species, excepting E. pilosa at NaCl concentration of 300 mM in comparison with non-primed seeds. Higher salinity (>200 mM) led to some specific ion toxicity and reduced seed viability of A. sieversiana. No specific ion toxicity but an osmotic effect limited the germination of other five species was observed The final germination percentages (salinity stress and desalination) of the six species showed three variations in comparison with the controls, namely, indiscrimination, stimulation, and reduction. Germination responses to salinity and desalination suggested that the six species were separated into three categories. Three species (A. sieversiana, Ch. virgata and Ch. acuminatum) showed similar germination responses to salinity with those of halophyte, but also showed a lower tolerance limit than most halophytes, although this was not always the case. A. scoparia and Ch. glaucum exhibited some ‘salt stimulation’ in seed germination percentages after desalination, whereas E. pilosa did not show any obvious response to salinity. Therefore, salinity usually induces dormancy of seeds with strong germination capacity in fresh water, but has few, or even positive, effects on seeds with strong innate dormancy.

Quantitative trait loci associated with salinity tolerance in field grown bread wheat

The differential response to field salinity of the parents of the ITMI wheat mapping population (cv. Opata 85 and the synthetic hexaploid W7984) was exploited to perform a QTL analysis of the response to salinity stress of a set of agronomic traits over two seasons. The material was irrigated either with potable water (EC of 1.0 dS m−1) or with diluted seawater (12.0 dS m−1). Grain yield was positively correlated with tiller number, plant height, percentage survival, ear weight, ear length, grain number per ear, grain weight and thousand grain weight, and negatively with time to booting, anthesis and physiological maturity, under both the control and salinity stress treatments. In all, 22 QTL were detected under control conditions, and 36 under salinity stress. Of the latter, 13 were major loci (LOD > 3.0) and eight were reproducible across both seasons. Chromosome 2D harboured 15 salinity stress associated QTL and chromosome 4A six such QTL. The remaining loci were located on chromosomes 2A, 5A, 6A, 7A, 1B, 4B, 3B, 6B, 7B and 6D.

Mannitol-1-phosphate dehydrogenase activity in Ectocarpus siliculosus, a key role for mannitol synthesis in brown algae.

Mannitol represents a major end product of photosynthesis in brown algae (Phaeophyceae), and is, with the β-1,3-glucan laminarin, the main form of carbon storage for these organisms. Despite its importance, little is known about the genes and enzymes responsible for the metabolism of mannitol in these seaweeds. Taking benefit of the sequencing of the Ectocarpus siliculosus genome, we focussed our attention on the first step of the synthesis of mannitol (reduction of the photo-assimilate fructose-6-phosphate), catalysed by the mannitol-1-phosphate dehydrogenase (M1PDH). This activity was measured in algal extracts, and was shown to be regulated by NaCl concentration in the reaction medium. Genomic analysis revealed the presence of three putative M1PDH genes (named EsM1PHD1, EsM1PDH2 and EsM1PDH3). Sequence comparison with orthologs demonstrates the modular architecture of EsM1PHD1 and EsM1PDH2, with an additional N-terminal domain of unknown function. In addition, gene expression experiments carried out on samples harvested through the diurnal cycle, and after several short-term saline and oxidative stress treatments, showed that EsM1PDH1 is the most highly expressed of these genes, whatever the conditions tested. In order to assess the activity of the corresponding protein, this gene was expressed in Escherichia coli. Cell-free extracts prepared from bacteria containing EsM1PDH1 displayed higher M1PDH activity than bacteria transformed with an empty plasmid. Further characterisation of recombinant EsM1PDH1 activity revealed its very narrow substrate specificity, salt regulation, and sensitivity towards an inhibitor of SH-enzymes.

Évaluation de la tolérance à la salinité du myrte (Myrtus communis) aux stades germinatif et plantule

The salinity tolerance and development of diverse myrtle ecotypes were evaluated in relation to salinity, at the germination and plantlet stages. Six myrtle ecotypes (Tébaba, Jbel Abderahmane, Diar Ferjan, Ain Bacouche, Ain Dhebla, and Ouchetata) were used to conduct germination tests, as well as cultivation to the plantlet stage. Disinfected seeds were germinated in a controlled growth chamber (RH, 80%; temperature, 25 °C) using different saline treatments (0, 2, 4, 6, 8, 10, and 12 g·L–1 NaCl. Seedlings were cultivated in a greenhouse, in boxes filled with perlite. The seedlings were given Knop’s nutrient solution, up to the four-leaf stage. Thereafter, the saline stress treatments were applied as increasing concentrations of NaCl added to the Knop solution. The effects of salinity on germination varied with ecotype and concentration of NaCl. A progressive decrease in the rate of germination for myrtle was observed with increasing concentration of NaCl. Moreover, germination was delayed by salinity, especially with susceptible ecotypes. Ecotypes from Ouchetata and Diar Ferjan germinated better in presence of salt than did the Jbel Abderahmane ecotype. The growth of myrtle plantlets cultivated under salt stress was also variable according to ecotype and salt concentrations. Growth of aerial, as well as root parts, was reduced by NaCl concentrations higher than 6 g·L–1. The number of leaves was also affected by salinity; a reduction of five leaves was observed for most ecotypes when increasing NaCl from 0 to 12 g·L–1. It is concluded that development of myrtle under saline stress differs according to the development stage (germination, plantlet), and that the ecotypes tested can germinate and grow in the presence of 12 g·L–1 NaCl. This salt tolerance, observed at early stages, remains to be confirmed for the adult plants. This work was conducted as an essential preliminary step in preparing to cultivate myrtle in saline soils or soils irrigated with salt water, for prospective commercial exploitation of the essential oils of this species.

Seed germination responses of Cereus jamacaru DC. ssp. jamacaru (Cactaceae) to environmental factors

In the present study, we assessed the seed germination responses of Cereus jamacaru DC. ssp. jamacaru (Cactaceae) to environmental factors. The seeds were collected from an area within Caatinga, a semiarid vegetation area located in north-eastern Brazil. We determined the optimal temperature for germination of C. jamacaru seeds and evaluated the effect of temperature, light intensity, light quality, water and saline stress on seed germination. Cereus jamacaru was classified as a positive photoblastic species. Maximum germination (95.8 ± 2.6%) was found under white light, and seed germination was not observed in darkness in any of the temperature, water or saline stress treatments. The optimum temperature for seed germination was 30°C because this temperature favored most of the parameters evaluated. Seed germinability responded positively to a wide range of temperatures, but was affected neither by light intensity nor by light quality. A reduction in water availability and an increase in saline concentration affected germinability and promoted slower, unsynchronized germination. The positive response of C. jamacaru seed germination to the environmental factors investigated may account for the abundant occurrence and wide distribution of the species in the Caatinga area.