Morpho-physiological variations in response to NaCl stress during vegetative and reproductive development of rice

The complex nature of plant resistance to adverse environmental conditions, such as salinity and drought requires a better understanding of the stress-induced changes that may be involved in tolerance mechanisms. Here we investigate stress-related morpho-physiological effects during vegetative and reproductive growth in two Japonica rice cultivars (Bomba and Bahia) exposed to a range of NaCl concentrations from the seedling stage. The stress-related detrimental effects were observed either earlier or to a higher extent in cv. Bomba than in Bahia. Damages to the photosynthetic apparatus were related to loss of chlorophyll (Chl) and to a decrease of the maximum potential efficiency of PSII (Fv/Fm), affecting negatively net CO2 assimilation rate (PN). Stress-related leaf anatomical alterations were analysed during the vegetative and reproductive stages. The size of bulliform cells as well as dimensions related to the vascular system increased under mild stress but decreased in the longer term or under higher stress level. The pattern of the anatomical alterations observed at the reproductive stage under 20 mM NaCl was reflected in poor panicle development and yield loss, with effects more pronounced in cv. Bomba than in Bahia. In summary, our results show that some physiological and, particularly, leaf anatomical responses induced by NaCl stress are distinctive indicators of sensitivity to salt stress in rice cultivars

Mechanistic understanding of iron toxicity tolerance in contrasting rice varieties from Africa: 1. Morpho-physiological and biochemical responses

Iron (Fe) is a fundamental element involved in various plant metabolic processes. However, when Fe uptake is excessive, it becomes toxic to the plant and disrupts cellular homeostasis. The aim of this study was to determine the physiological and biochemical mechanisms underlying tolerance to Fe toxicity in contrasting rice varieties adapted to African environments. Four varieties (CK801 and Suakoko 8 (tolerant), Supa and IR64 (sensitive)) selected from our previous work were analysed in more detail, and the first part of this study reports morphological, physiological and biochemical responses induced by Fe toxicity in these four varieties. Morphological (shoot length, root length, number of lateral roots), physiological (photosynthesis rate, stomatal conductance, transpiration rate, fluorescence, relative water content and cell membrane stability) and biochemical (tissue Fe, chlorophyll pigments, soluble sugars, protein and starch) traits were measured, as appropriate, on both shoot and root tissues and at different time points during the stress period. Fe toxicity significantly (P ≤ 0.05) reduced growth and metabolism of all the four varieties. Tolerant varieties showed more lateral roots than the sensitive ones, under Fe toxic conditions as well as higher photosynthesis rate, chlorophyll content and cell membrane stability. Strong dilution of Fe concentration in cells was identified, as one of the additional tolerance mechanisms used by CK801, whereas Suakoko 8 mainly used strong mobilisation of carbohydrates at the early stage of the stress period to anticipate metabolite shortage. Traits associated with Fe toxicity tolerance in this study could be specifically targeted in trait-based breeding programs of superior lowland rice varieties tolerant of Fe toxicity

Isolation and expression analysis of novel silicon absorption gene from roots of mangrove (Rhizophora apiculata) via suppression subtractive hybridization

Silicon (Si) is the second most abundant element in soil after oxygen. It is not an essential element for plant growth and formation but plays an important role in increasing plant tolerance towards different kinds of abiotic and biotic stresses. The molecular mechanism of Si absorption and accumulation may differ between plants, such as monocotyledons and dicotyledons. Silicon absorption and accumulation in mangrove plants are affected indirectly by some proteins rich in serine and proline amino acids. The expression level of the genes responsible for Si absorption varies in different parts of plants. In this study, Si is mainly observed in the epidermal roots’ cell walls of mangrove plants compared to other parts. The present work was carried out to discover further information on Si stress responsive genes in Rhizophora apiculata, using the suppression subtractive hybridization technique. To construct the cDNA library, two-month-old seedlings were exposed to 0.5, 1, and 1.5 mM SiO2 for 15 hrs and for 1 to 6 days resulting in a total of 360 high quality ESTs gained. Further examination by RT-PCR and real-time qRT-PCR showed the expression of a candidate gene of serine-rich protein

Genotype variation in rice (Oryza sativa L.) tolerance to Fe toxicity might be linked to root cell wall lignification

Iron (Fe) is an essential element to plants, but can be harmful if accumulated to toxic concentrations. Fe toxicity can be a major nutritional disorder in rice (Oryza sativa) when cultivated under waterlogged conditions, as a result of excessive Fe solubilization of in the soil. However, little is known about the basis of Fe toxicity and tolerance at both physiological and molecular level. To identify mechanisms and potential candidate genes for Fe tolerance in rice, we comparatively analyzed the effects of excess Fe on two cultivars with distinct tolerance to Fe toxicity, EPAGRI 108 (tolerant) and BR-IRGA 409 (susceptible). After excess Fe treatment, BR-IRGA 409 plants showed reduced biomass and photosynthetic parameters, compared to EPAGRI 108. EPAGRI 108 plants accumulated lower amounts of Fe in both shoots and roots compared to BR-IRGA 409. We conducted transcriptomic analyses of roots from susceptible and tolerant plants under control and excess Fe conditions. We found 423 up-regulated and 92 down-regulated genes in the susceptible cultivar, and 42 up-regulated and 305 down-regulated genes in the tolerant one. We observed striking differences in root gene expression profiles following exposure to excess Fe: the two cultivars showed no genes regulated in the same way (up or down in both), and 264 genes were oppositely regulated in both cultivars. Plants from the susceptible cultivar showed down-regulation of known Fe uptake-related genes, indicating that plants are actively decreasing Fe acquisition. On the other hand, plants from the tolerant cultivar showed up-regulation of genes involved in root cell wall biosynthesis and lignification. We confirmed that the tolerant cultivar has increased lignification in the outer layers of the cortex and in the vascular bundle compared to the susceptible cultivar, suggesting that the capacity to avoid excessive Fe uptake could rely in root cell wall remodeling. Moreover, we showed that increased lignin concentrations in roots might be linked to Fe tolerance in other rice cultivars, suggesting that a similar mechanism might operate in multiple genotypes. Our results indicate that changes in root cell wall and Fe permeability might be related to Fe toxicity tolerance in rice natural variation

The role of silicon in plant tissue culture

Growth and morphogenesis of in vitro cultures of plant cells, tissues and organs are greatly influenced by the composition of the culture medium. Mineral nutrients are necessary for the growth and development of plants. Several morpho-physiological disorders such as hooked leaves, hyperhydricity, fasciation and shoot tip necrosis are often associated with the concentration of inorganic nutrient in the tissue culture medium. Silicon (Si) is the most abundant mineral element in the soil. The application of Si has been demonstrated to be beneficial for growth, development and yield of various plants and to alleviate various stresses including nutrient imbalance. Addition of Si to the tissue culture medium improves organogenesis, embryogenesis, growth traits, morphological, anatomical and physiological characteristics of leaves, enhances tolerance to low temperature and salinity, protects cells and against metal toxicity, prevents oxidative phenolic browning and reduces the incidence of hyperhydricity in various plants. Therefore, Si possesses considerable potential for application in a wide range of plant tissue culture studies such as cryopreservation, organogenesis, micropropagation, somatic embryogenesis and secondary metabolites production

Toxidez de alumínio em culturas anuais.

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Comparative physiology of Australian commercial rice cultivars to salinity stress in controlled environment and the field

Salinity intrusion into agricultural lands in rice-producing countries around the world has become a serious threat to food security. Currently, more than 960 million hectares of productive land is adversely affected by salinity and is expected to grow in the future. This problem is exacerbated by the projected increase in world population from the current 7.2 to 9.6 billion by 2050. The cultivated rice (Oryza sativa) tolerates 10 dSm-1. This study used morpho-physiological methods including gas exchange measurement, microelectrode ion flux estimation (MIFE) and agronomic measurements to screen salinity tolerance levels of two Japonica (Koshihikari and Reiziq) rice genotypes and one Indica (Doongara) genotype. In addition, this is the first time that four basic ion fluxes were measured using MIFE in both glasshouse and field conditions to screen rice for salinity tolerance. The effects of salinity stress on photosynthetic activities, ion fluxes and growth parameters of the three rice genotypes under glasshouse conditions and in the field were also examined. Variations in the response of the three cultivars to salinity stress were found, thus providing evidence that morpho-physiological basis of salinity stress tolerance can be applied to improve the salinity stress tolerance of this important crop. This may allow the exploitation of salt affected marginal lands and could positively contribute to global food security

Finger millet RNA-seq reveals differential gene expression associated with tolerance to aluminum toxicity and provides novel genomic resources

Eleusine coracana, finger millet, is a multipurpose crop cultivated in arid and semi-arid regions of Africa and Asia. RNA sequencing (RNA-seq) was used in this study to obtain valuable genomic resources and identify genes differentially expressed between Al-tolerant and Al-susceptible genotypes. Two groups of finger millet genotypes were used: Al-tolerant (215836, 215845, and 229722) and Al-susceptible (212462, 215804 and 238323). The analysis of the RNA-seq data resulted in 198,546 unigenes, 56.5% of which were annotated with significant hits in one or more of the following six databases: NR (48.8%), GO (29.7%), KEGG (45%), PlantTFDB (19.0%), Uniprot (49.2%), and NT (46.2%). It is noteworthy that only 220 unigenes in the NR database had significant hits against finger millet sequences suggesting that finger millet’s genomic resources are scarce. The gene expression analysis revealed that 322 genes were significantly differentially expressed between the Al-tolerant and Alsusceptible genotypes, of which 40.7% were upregulated while 59.3% were downregulated in Al-tolerant genotypes. Among the significant DEGs, 54.7% were annotated in the GO database with the top hits being ATP binding (GO:0005524) and DNA binding (GO:0003677) in the molecular function, DNA integration (GO:0015074) and cell redox homeostasis in the biological process, as well as cellular anatomical entity and intracellular component in the cellular component GO classes. Several of the annotated DEGs were significantly enriched for their corresponding GO terms. The KEGG pathway analysis resulted in 60 DEGs that were annotated with different pathway classes, of which carbohydrate metabolism and signal transduction were the most prominent. The homologs of a number of significant DEGs have been previously reported as being associated with Al or other abiotic stress responses in various crops, including carboxypeptidase SOL1, HMA3, AP2, bZIP, C3H, and WRKY TF genes. A more detailed investigation of these and other DEGs will enable genomic-led breeding for Al tolerance in finger millet RNA-seq data analysis also yielded 119,073 SNP markers, the majority of which had PIC values above 0.3, indicating that they are highly informative. Additionally, 3,553 single-copy SSR markers were identified, of which trinucleotide SSRs were the most prevalent. These genomic resources contribute substantially to the enrichment of genomic databases for finger millet, and facilitate future research on this crop

Response and Bioaccumulation Potential of Boerhavia diffusa L. Towards Different Heavy Metals

Effect of different concentrations of heavy metals such as Cadmium, Chromium, Mercury and Leadwas studied by cultivating rooted propagules of Boerhavia diffusafor a period of twenty days in Hoagland nutrient medium artificially contaminated with known concentration of those heavy metal ions. Concentrations of the metals selected to impart visible symptoms of growth retardation and to permit survival for prolonged period are 30µM cadmium chloride (CdCl2), 400 µM potassium dichromate (K2Cr2O7), 10 µM mercuric chloride (HgCl2), and 600 µM lead acetate (CH3-COO)2Pb. More or less uniform growth performance was shown by the plants irrespective of the differences of concentration of the heavy metals. However, parameters such as root - and stem length, stomatal - and tolerance index varied among the treatments. Significant differences were observed in the heavy metal accumulation potential among metals and between plant parts such as root, stem and leaf and the pattern was dependent on growth period