This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions.

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Cell Wall Metabolism in Response to Abiotic Stress.

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route, represented by a metabolic grid for which most of the genes involved have been sequenced in several plants, mainly in the model-plants Arabidopsis thaliana and Populus. Plants are exposed to different stresses, which may change lignin content and composition. In many cases, particularly for plant-microbe interactions, this has been suggested as defence responses of plants to the stress. Thus, understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall. This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1744-7909.2010.00892.x

Abiotic and Biotic Stresses and Changes in the Lignin Content and Composition in Plants

Chromium speciation, bioavailability, uptake, toxicity and detoxification in soil-plant system: A review.

Quinoa, Chenopodium quinoa Willd., is an Amaranthacean, stress-tolerant plant cultivated along the Andes for the last 7000 years, challenging highly different environmental conditions ranging from Bolivia, up to 4.500 m of altitude, to sea level, in Chile. Its grains have higher nutritive value than traditional cereals and it is a promising worldwide cultivar for human consumption and nutrition. The quinoa has been called a pseudo-cereal for botanical reasons but also because of its unusual composition and exceptional balance between oil, protein and fat. The quinoa is an excellent example of ‘functional food’ that aims at lowering the risk of various diseases. Functional properties are given also by minerals, vitamins, fatty acids and antioxidants that can make a strong contribution to human nutrition, particularly to protect cell membranes, with proven good results in brain neuronal functions. Its minerals work as cofactors in antioxidant enzymes, adding higher value to its rich proteins. Quinoa also contains phytohormones, which offer an advantage over other plant foods for human nutrition. c � 2010 Society of Chemical Industry

http://quinoa-chile.cl/padmin_qui/plugin/kcfinder/upload/files/Vega-Galvez_et_al_JSFA_DOI-2010.pdf

Nutrition facts and functional potential of quinoa (Chenopodium quinoa willd.), an ancient Andean grain: a review.

1. High elevation treelines 1.1 The task 1.2 Previous works 2. Definitions and conventions 2.1 The life form 'tree' 2.2 Lines and transitions 2.3 Limitation, stress and disturbance 2.4 Altitude-related and other environmental drivers 2.5 Treeline nomenclature 3. Treeline patterns 3.1 Treeline taxa 3.2 The summit syndrome and other treeline depressions 3.3 Mass elevation effect 3.4 Treeline elevation 3.5 Time matters 3.6 Forest structure near treeline 4. Treeline climate 4.1 Specific aspects of treeline climatology 4.2 Criteria to define temperature regimes at treeline 4.3 Treeline temperatures in different bioclimatic regions 4.4 Seedbed and branch temperatures 4.5 Whole forest temperatures 5. Global mountain statistics based on treeline elevation 5.1 Mountain geostatistics 5.2 Elevational belts 5.3 Global treeline ecotones 6. Structure and stature of treeline trees 6.1 Foliage properties 6.2 Wood properties 6.3 Bark properties 6.4 Root traits 6.5 Tree stature 6.6 Dry matter allocation in treeline trees 7. Growth and development 7.1 Tree growth near treeline 7.2 Xylogenesis at treeline 7.3 Apical growth dynamics 7.4 Root growth 7.5 Phenology at treeline 8. Evolutionary adjustments to life at treeline 8.1 Phylogenetic selection 8.2 Genotypic responses of growth and development 8.3 Genotypic responses of physiological traits 9. Reproduction, early life stages and tree demography 9.1 Amount and quality of seeds at high elevation 9.2 Germination, seedling and sapling stage 9.3 Tree demography at treeline 10. Freezing and other forms of stress 10.1 Stress at treeline in a fitness context 10.2 Mechanisms and principles of freezing resistance 10.3 Freezing resistance in treeline trees 10.4 Other forms of stress at treeline 11. Water, nutrient and carbon relations 11.1 Tree water relations during the growing season 11.2 Nutrient relations 11.3 Carbon relations 12. Treeline formation - currently, in the past and in the future 12.1 Causes of current treelines 12.2 Treelines in the recent past 12.3. Treelines in the distant past (Holocene) 12.4 Future treelines References Taxonomic index Subject index

Alpine treelines : functional ecology of the global high elevation tree limits

Plants are autotrophic and photosynthetic organisms that both produce and consume sugars. Soluble sugars are highly sensitive to environmental stresses, which act on the supply of carbohydrates from source organs to sink ones. Sucrose and hexoses both play dual functions in gene regulation as exemplified by the upregulation of growth-related genes and downregulation of stress-related genes. Although coordinately regulated by sugars, these growth- and stress-related genes are upregulated or downregulated through HXK-dependent and/or HXK-independent pathways. Sucrose-non-fermenting-1- (SNF1-) related protein pathway, analogue to the protein kinase (SNF-) yeast-signalling pathway, seems also involved in sugar sensing and transduction in plants. However, even if plants share with yeast some elements involved in sugar sensing, several aspects of sugar perception are likely to be peculiar to higher plants. In this paper, we have reviewed recent evidences how plants sense and respond to environmental factors through sugar-sensing mechanisms. However, we think that forward and reverse genetic analysis in combination with expression profiling must be continued to uncover many signalling components, and a full biochemical characterization of the signalling complexes will be required to determine specificity and cross-talk in abiotic stress signalling pathways.

https://www.tandfonline.com/doi/pdf/10.4161/psb.4.5.8294

Soluble sugars--metabolism, sensing and abiotic stress: a complex network in the life of plants.

Effect of NaCl on germination, growth, and soluble sugar content in Chenopodium quinoa Willd. seeds

Low-temperature effect on enzyme activities involved in sucrose-starch partitioning in salt-stressed and salt-acclimated cotyledons of quinoa (Chenopodium quinoa Willd.) seedlings.

BACKGROUND: Quinoa is a good source of protein and can be used as a nutritional ingredient in food products. This study analyses how much growing region and/or seasonal climate might affect grain yield and nutritional quality of quinoa seeds.

RESULTS: Seeds of ten quinoa cultivars from the Andean highlands (Bolivia/Argentina site) and Argentinean Northwest (Encalilla site) were analysed for seed yield, protein content and amino acid composition. Grain yields of five cultivars growing at Encalilla were higher, and four were lower, compared with data from the Bolivia/Argentina site. Protein contents ranged from 91.5 to 155.3 and from 96.2 to 154.6 g kg−1 dry mass for Encalilla and Bolivia/Argentina seeds respectively, while essential amino acid concentrations ranged from 179.9 to 357.2 and from 233.7 to 374.5 g kg−1 protein respectively. Significant positive correlations were found between the content of essential amino acids and protein percentage.

CONCLUSION: It appears that there are clear variations in seed yield, total protein content and amino acid composition among cultivars from the two sites. Essential amino acid composition was more affected than grain yield and protein level. The study revealed that both environmental and climatic factors influence the nutritional composition of quinoa cultivars growing in different agroecological regions. Copyright © 2011 Society of Chemical Industry

Interrelationships among seed yield, total protein and amino acid composition of ten quinoa (Chenopodium quinoa) cultivars from two different agroecological regions.

UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodium quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands.

Fernando Eduardo Prado

Papers

Soluble sugars--metabolism, sensing and abiotic stress: a complex network in the life of plants.

Effect of NaCl on germination, growth, and soluble sugar content in Chenopodium quinoa Willd. seeds

Low-temperature effect on enzyme activities involved in sucrose-starch partitioning in salt-stressed and salt-acclimated cotyledons of quinoa (Chenopodium quinoa Willd.) seedlings.

Interrelationships among seed yield, total protein and amino acid composition of ten quinoa (Chenopodium quinoa) cultivars from two different agroecological regions.

Epidermal Lignin Deposition in Quinoa Cotyledons in Response to UV-B Radiation¶