Enhanced lipid and biomass production by a newly isolated and identified marine microalga.

BACKGROUND: The increasing demand for microalgae lipids as an alternative to fish has encouraged researchers to explore oleaginous microalgae for food uses. In this context, optimization of growth and lipid production by the marine oleaginous V2-strain-microalgae is of great interest as it contains large amounts of mono-unsaturated (MUFAs) and poly-unsaturated fatty acids (PUFAs). METHODS: In this study, the isolated V2 strain was identified based on 23S rRNA gene. Growth and lipid production conditions were optimized by using the response surface methodology in order to maximize its cell growth and lipid content that was quantified by both flow cytometry and the gravimetric method. The intracellular lipid bodies were detected after staining with Nile red by epifluorescence microscopy. The fatty acid profile of optimal culture conditions was determined by gas chromatography coupled to a flame ionization detector. RESULTS: The phenotypic and phylogenetic analyses showed that the strain V2 was affiliated to Tetraselmis genus. The marine microalga is known as an interesting oleaginous species according to its high lipid production and its fatty acid composition. The optimization process showed that maximum cell abundance was achieved under the following conditions: pH: 7, salinity: 30 and photosynthetic light intensity (PAR): 133 µmol photons.m-2.s-1. In addition, the highest lipid content (49 ± 2.1% dry weight) was obtained at pH: 7, salinity: 37.23 and photosynthetic light intensity (PAR): 188 µmol photons.m-2.s-1. The fatty acid profile revealed the presence of 39.2% and 16.1% of total fatty acids of mono-unsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs), respectively. Omega 3 (ω3), omega 6 (ω6) and omega 9 (ω9) represented 5.28%, 8.12% and 32.8% of total fatty acids, respectively. CONCLUSIONS: This study showed the successful optimization of salinity, light intensity and pH for highest growth, lipid production and a good fatty acid composition, making strain V2 highly suitable for food and nutraceutical applications.

From Soil Amendments to Controlling Autophagy: Supporting Plant Metabolism under Conditions of Water Shortage and Salinity.

Crop resistance to environmental stress is a major issue. The globally increasing land degradation and desertification enhance the demand on management practices to balance both food and environmental objectives, including strategies that tighten nutrient cycles and maintain yields. Agriculture needs to provide, among other things, future additional ecosystem services, such as water quantity and quality, runoff control, soil fertility maintenance, carbon storage, climate regulation, and biodiversity. Numerous research projects have focused on the food-soil-climate nexus, and results were summarized in several reviews during the last decades. Based on this impressive piece of information, we have selected only a few aspects with the intention of studying plant-soil interactions and methods for optimization. In the short term, the use of soil amendments is currently attracting great interest to cover the current demand in agriculture. We will discuss the impact of biochar at water shortage, and plant growth promoting bacteria (PGPB) at improving nutrient supply to plants. In this review, our focus is on the interplay of both soil amendments on primary reactions of photosynthesis, plant growth conditions, and signaling during adaptation to environmental stress. Moreover, we aim at providing a general overview of how dehydration and salinity affect signaling in cells. With the use of the example of abscisic acid (ABA) and ethylene, we discuss the effects that can be observed when biochar and PGPB are used in the presence of stress. The stress response of plants is a multifactorial trait. Nevertheless, we will show that plants follow a general concept to adapt to unfavorable environmental conditions in the short and long term. However, plant species differ in the upper and lower regulatory limits of gene expression. Therefore, the presented data may help in the identification of traits for future breeding of stress-resistant crops. One target for breeding could be the removal and efficient recycling of damaged as well as needless compounds and structures. Furthermore, in this context, we will show that autophagy can be a useful goal of breeding measures, since the recycling of building blocks helps the cells to overcome a period of imbalanced substrate supply during stress adjustment.

Metabolic Pathway of Natural Antioxidants, Antioxidant Enzymes and ROS Providence.

Based on the origin, we can classify different types of stress. Environmental factors, such as high light intensity, adverse temperature, drought, or soil salinity, are summarized as abiotic stresses and discriminated from biotic stresses that are exerted by pathogens and herbivores, for instance. It was an unexpected observation that overproduction of reactive oxygen species (ROS) is a common response to all kinds of stress investigated so far. With respect to applied aspects in agriculture and crop breeding, this observation allows using ROS production as a measure to rank the stress perception of individual plants. ROS are important messengers in cell signaling, but exceeding a concentration threshold causes damage. This requires fine-tuning of ROS production and degradation rates. In general, there are two options to control cellular ROS levels, (I) ROS scavenging at the expense of antioxidant consumption and (II) enzyme-controlled degradation of ROS. As antioxidants are limited in quantity, the first strategy only allows temporarily buffering of a certain cellular ROS level. This way, it prevents spells of eventually damaging ROS concentrations. In this review, we focus on the second strategy. We discuss how enzyme-controlled degradation of ROS integrates into plant metabolism. Enzyme activities can be continuously operative. Cellular homeostasis can be achieved by regulation of respective gene expression and subsequent regulation of the enzyme activities. A better understanding of this interplay allows for identifying traits for stress tolerance breeding of crops. As a side effect, the result also may be used to identify cultivation methods modifying crop metabolism, thus resulting in special crop quality.

Relationship between the photosynthetic activity and the performance of Cakile maritima after long-term salt treatment.

Cakile maritima is a halophyte with potential for ecological, economical and medicinal uses. We address here the impact of salinity on its growth, photosynthesis and seed quality. Whole plant growth rate and shoot development were stimulated at moderate salinity (100-200 mM NaCl) and inhibited at higher salt concentrations. Although diminished in the presence of salt, potassium and calcium uptake per unit of root biomass was maintained at relatively high value, while nutrient-use efficiency (NUE) was improved in salt-treated plants. Chl and carotenoid concentrations decreased at extreme salinities, but anthocyanin concentration continuously grew with salinity. Net photosynthetic rate (A), stomatal conductance, maximum quantum efficiency of PSII and quantum yield were stimulated in the 100-200 mM NaCl range. Higher salinity adversely affected gas exchange and changed PSII functional characteristics, resulting in a reduction of A per leaf area unit. This phenomenon was associated with increased non-photochemical quenching. Harvest index, silique number and seeds per fruit valve were maximal at 100 mM NaCl. Despite the decreasing salt accumulation gradient from the vegetative to the reproductive organs, high salinities were detrimental for the seed viability and increased the proportion of empty siliques. Overall, the salt-induced changes in the plant photosynthetic activity resulted into analogous responses at the vegetative and reproductive stages. The enhancement of NUE, the absence of pigment degradation, the reduction of water loss and the concomitant PSII protection from photodamage through thermal dissipation of excess excitation significantly accounted for Cakile survival capacity at high salinity.

Aster tripolium L. and Sesuvium portulacastrum L.: two halophytes, two strategies to survive in saline habitats.

Aster tripolium L. (Dollart, Germany) and Sesuvium portulacastrum L. (Dakhla, Morocco) are potential halophytic vegetables, fodder plants, and ornamentals for re-vegetating saline land. To compare their strategies involved in salt tolerance both plants were grown with 0%, 1.5%, and 3% (Aster) or 0%, 2.5%, and 5% (Sesuvium) NaCl in the watering solution. The growth rate was reduced in both species with increasing NaCl concentrations. The quotient of Na(+)/K(+) indicates that Aster accumulates more K(+) in comparison to Na(+) while the reverse is true for Sesuvium. Osmolality of the leaf sap increased with increasing NaCl concentration in both Aster and Sesuvium. Transpiration rate was severely reduced in both Aster (3%) and Sesuvium (5%) plants after 10 d of NaCl watering. The CO(2) assimilation rate decreased in Aster (3%) and Sesuvium (5%) NaCl-treated plants from day 5 to day 10. The most important results from chlorophyll fluorescence measurements were derived from the non-photochemical quenching analysis (NPQ). First, both plants had linearly increasing levels of NPQ with increasing NaCl concentrations. Second, Sesuvium had almost half the NPQ value when compared to Aster under increased soil salinity. In Aster P-ATPase activities were decreased in plants treated with 3% NaCl after three days of treatment, F-ATPase activities increased with increasing NaCl concentrations and no clear changes were measured in V-ATPase activities. In Sesuvium any changes could be observed in the three ATPase activities determined. To conclude, Aster and Sesuvium use different strategies in adaptation to soil salinity.

Putting halophytes to work - genetics, biochemistry and physiology.

Halophytes are a small group of plants able to tolerate saline soils whose salt concentrations can reach those found in ocean waters and beyond. Since most plants, including many of our crops, are unable to survive salt concentrations one sixth those in seawater (about 80mM NaCl), the tolerance of halophytes to salt has academic and economic importance. In 2009 the COST Action Putting halophytes to work - from genes to ecosystems was established and it was from contributions to a conference held at the Leibniz University, Hannover, Germany, in 2012 that this Special Issue has been produced. The 17 contributions cover the fundamentals of salt tolerance and aspects of the biochemistry and physiology of tolerance in the context of advancing the development of salt-tolerant crops.

The effect of hyper-osmotic salinity on protein pattern and enzyme activities of halophytes.

Studies of the convergence of the expression of enzymes and the physiology of salt resistance are rare, and give the general impression of a jigsaw puzzle with many missing pieces. To date, only minor responses of plasma membrane and tonoplast proteins of halophytes have been reported. Mostly, subunits of the catalytic portions of ATPases were found to change. In succulent plants such as Salicornia europea the abundance of V-type ATPase subunits has been correlated with growth performance. This stresses the physiological strategy to sequester incoming salt into vacuoles, which may also benefit osmotic regulation and further promote growth. A considerable amount of information is available on the responses of proteins involved in photosynthesis and detoxification of reactive oxygen species (ROS) under saline conditions. Two aspects deserve special attention: (i) salt responsive multiple spot patterns of individual proteins (due to protein modification, phosphorylation, for instance); and (ii) correlations between salt-mediated protein abundance and plant performance. Relevant observations underline that there exists a tightly knit metabolic network underlying physiological observations. Although the exact functioning of control and signalling sequences remains elusive, another aspect becomes very obvious from the publications analysed: stress responses of halophytes are multi-variant and include not only an increase in abundance of enzymes, but also of chaperones and proteins controlling organisation of the cytoplasm.

The influence of genes regulating transmembrane transport of Na+ on the salt resistance of Aeluropus lagopoides.

Plantlets of Aeluropus lagopoides (Linn.) Trin. Ex Thw. were grown at different NaCl concentrations (26, 167, 373 and 747mM) for 3, 7 and 15 days; their growth, osmotic adjustment, gas exchange, ion compartmentalisation and expression of various genes related to Na+ flux was studied. Plantlets showed optimal growth in non-saline (control; 26mM NaCl) solutions, whereas CO2/H2O gas exchange, leaf water concentration and water use efficiency decreased under all salinity treatments, accompanied by increased leaf senescence, root ash, sodium content and leaf osmolality. A decrease in malondialdehyde (MDA) content with time was correlated with Na+ accumulation in the leaf apoplast and a concomitant increase in Na+ secretion rate. A. lagopoides accumulated a higher concentration of Na+ in root than in leaf vacuoles, corresponding with higher expression of V-NHX and lower expression of PM-NHX in root than leaf tissue. It appears that V-ATPase plays a vital role during Na+ transport by producing an electromotive force, driving ion transport. Leaf calcium increased with increasing salinity, with more rapid accumulation at high salinity than at low salinity, indicating a possible involvement of Ca2+ in maintaining K+:Na+ ratio. Our results suggest that A. lagopoides successfully compartmentalised Na+ at salinities up to 373mM NaCl by upregulating the gene expression of membrane linked transport proteins (V-NHX and PM-NHX). At higher salinity (747mM NaCl), a reduction in the expression of V-NHX and PM-NHX in leaves without any change in the rate of salt secretion, is a possible cause of the toxicity of NaCl.

Proteomic and physiological responses of the halophyte Cakile maritima to moderate salinity at the germinative and vegetative stages.

Responses of the halophyte Cakile maritima to moderate salinity were addressed at germination and vegetative stages by bringing together proteomics and eco-physiological approaches. 75 mM NaCl-salinity delayed significantly the germination process and decreased slightly the seed germination percentage compared to salt-free conditions. Monitoring the proteome profile between 0 h and 120 h after seed sowing revealed a delay in the degradation of seed storage proteins when germination took place under salinity, which may explain the slower germination rate observed. Of the sixty-seven proteins identified by mass spectrometry, several proteins involved in glycolysis, amino acid metabolism, photosynthesis, and protein folding showed significantly increased abundance during germination. This pattern was less pronounced under salinity. At the vegetative stage, 100mM NaCl-salinity stimulated significantly the plant growth, which was sustained by enhanced leaf expansion, water content, and photosynthetic activity. Comparative proteome analyses of leaf tissue revealed 44 proteins with different abundance changes, most of which being involved in energy metabolism. A specific set of proteins predominantly involved in photosynthesis and respiration showed significantly higher abundance in salt-treated plants. Altogether, combining proteomics with eco-physiological tools provides valuable information, which contributes to improve our understanding in the salt-response of this halophyte during its life cycle.