Sven-Erik Jacobsen

Ionic and osmotic relations in quinoa (Chenopodium quinoa Willd.) plants grown at various salinity levels

Ionic and osmotic relations in quinoa (Chenopodium quinoa Willd.) were studied by exposing plants to six salinity levels (0–500 mM NaCl range) for 70 d. Salt stress was administered either by pre-mixing of the calculated amount of NaCl with the potting mix before seeds were planted or by the gradual increase of NaCl levels in the irrigation water. For both methods, the optimal plant growth and biomass was achieved between 100 mM and 200 mM NaCl, suggesting that quinoa possess a very efficient system to adjust osmotically for abrupt increases in NaCl stress. Up to 95% of osmotic adjustment in old leaves and between 80% and 85% of osmotic adjustment in young leaves was achieved by means of accumulation of inorganic ions (Na+, K+, and Cl–) at these NaCl levels, whilst the contribution of organic osmolytes was very limited. Consistently higher K+ and lower Na+ levels were found in young, as compared with old leaves, for all salinity treatments. The shoot sap K+ progressively increased with increased salinity in old leaves; this is interpreted as evidence for the important role of free K+ in leaf osmotic adjustment under saline conditions. A 5-fold increase in salinity level (from 100 mM to 500 mM) resulted in only a 50% increase in the sap Na+ content, suggesting either a very strict control of xylem Na+ loading or an efficient Na+ removal from leaves. A very strong correlation between NaCl-induced K+ and H+ fluxes was observed in quinoa root, suggesting that a rapid NaCl-induced activation of H+-ATPase is needed to restore otherwise depolarized membrane potential and prevent further K+ leak from the cytosol. Taken together, this work emphasizes the role of inorganic ions for osmotic adjustment in halophytes and calls for more in-depth studies of the mechanisms of vacuolar Na+ sequestration, control of Na+ and K+ xylem loading, and their transport to the shoot.

Oxidative stress protection and stomatal patterning as components of salinity tolerance mechanism in quinoa (Chenopodium quinoa)

Two components of salinity stress are a reduction in water availability to plants and the formation of reactive oxygen species. In this work, we have used quinoa (Chenopodium quinoa), a dicotyledonous C3 halophyte species displaying optimal growth at approximately 150 mM NaCl, to study mechanisms by which halophytes cope with the afore-mentioned components of salt stress. The relative contribution of organic and inorganic osmolytes in leaves of different physiological ages (e.g. positions on the stem) was quantified and linked with the osmoprotective function of organic osmolytes. We show that the extent of the oxidative stress (UV-B irradiation) damage to photosynthetic machinery in young leaves is much less when compared with old leaves, and attribute this difference to the difference in the size of the organic osmolyte pool (1.5-fold difference under control conditions; sixfold difference in plants grown at 400 mM NaCl). Consistent with this, salt-grown plants showed higher Fv/Fm values compared with control plants after UV-B exposure. Exogenous application of physiologically relevant concentrations of glycine betaine substantially mitigated oxidative stress damage to PSII, in a dose-dependent manner. We also show that salt-grown plants showed a significant (approximately 30%) reduction in stomatal density observed in all leaves. It is concluded that accumulation of organic osmolytes plays a dual role providing, in addition to osmotic adjustment, protection of photosynthetic machinery against oxidative stress in developing leaves. It is also suggested that salinity-induced reduction in stomatal density represents a fundamental mechanism by which plants optimize water use efficiency under saline conditions.

Quinoa biodiversity and sustainability for food security under climate change. A review

Climate change is rapidly degrading the conditions of crop production. For instance, increasing salinization and aridity is forecasted to increase in most parts of the world. As a consequence, new stress-tolerant species and genotypes must be identified and used for future agriculture. Stress-tolerant species exist but are actually underutilized and neglected. Many stress-tolerant species are indeed traditional crops that are only cultivated by farmers at a local scale. Those species have a high biodiversity value. Besides, the human population will probably reach nine billion within coming decades. To keep pace with population growth, food production must increase dramatically despite the limited availability of cultivable land and water. Here, we review the benefits of quinoa, Chenopodium quinoa Willd., a seed crop that has endured the harsh bioclimatic conditions of the Andes since ancient times. Although the crop is still mainly produced in Bolivia and Peru, agronomic trials and cultivation are spreading to many other countries. Quinoa maintains productivity on rather poor soils and under conditions of water shortage and high salinity. Moreover, quinoa seeds are an exceptionally nutritious food source, owing to their high protein content with all essential amino acids, lack of gluten, and high content of several minerals, e.g., Ca, Mg, Fe, and health-promoting compounds such as flavonoids. Quinoa has a vast genetic diversity resulting from its fragmented and localized production over the centuries in the Andean region, from Ecuador to southern Chile, and from sea level to the altiplano. Quinoa can be adapted to diverse agroecological conditions worldwide. Year 2013 has therefore been declared the International Year of Quinoa by the United Nations Food and Agriculture Organization. Here, we review the main characteristics of quinoa, its origin and genetic diversity, its exceptional tolerance to drought and salinity, its nutritional properties, the reasons why this crop can offer several ecosystem services, and the role of Andean farmers in preserving its agrobiodiversity. Finally, we propose a schematic model integrating the fundamental factors that should determine the future utilization of quinoa, in terms of food security, biodiversity conservation, and cultural identity.

Feeding the world: genetically modified crops versus agricultural biodiversity

The growing demand for food poses major challenges to humankind. We have to safeguard both biodiversity and arable land for future agricultural food production, and we need to protect genetic diversity to safeguard ecosystem resilience. We must produce more food with less input, while deploying every effort to minimize risk. Agricultural sustainability is no longer optional but mandatory. There is still an on-going debate among researchers and in the media on the best strategy to keep pace with global population growth and increasing food demand. One strategy favors the use of genetically modified (GM) crops, while another strategy focuses on agricultural biodiversity. Here, we discuss two obstacles to sustainable agriculture solutions. The first obstacle is the claim that genetically modified crops are necessary if we are to secure food production within the next decades. This claim has no scientific support, but is rather a reflection of corporate interests. The second obstacle is the resultant shortage of research funds for agrobiodiversity solutions in comparison with funding for research in genetic modification of crops. Favoring biodiversity does not exclude any future biotechnological contributions, but favoring biotechnology threatens future biodiversity resources. An objective review of current knowledge places GM crops far down the list of potential solutions in the coming decades. We conclude that much of the research funding currently available for the development of GM crops would be much better spent in other research areas of plant science, e.g., nutrition, policy research, governance, and solutions close to local market conditions if the goal is to provide sufficient food for the world’s growing population in a sustainable way.

Genotypic difference in salinity tolerance in quinoa is determined by differential control of xylem Na+ loading and stomatal density

Quinoa is regarded as a highly salt tolerant halophyte crop, of great potential for cultivation on saline areas around the world. Fourteen quinoa genotypes of different geographical origin, differing in salinity tolerance, were grown under greenhouse conditions. Salinity treatment started on 10 day old seedlings. Six weeks after the treatment commenced, leaf sap Na and K content and osmolality, stomatal density, chlorophyll fluorescence characteristics, and xylem sap Na and K composition were measured. Responses to salinity differed greatly among the varieties. All cultivars had substantially increased K(+) concentrations in the leaf sap, but the most tolerant cultivars had lower xylem Na(+) content at the time of sampling. Most tolerant cultivars had lowest leaf sap osmolality. All varieties reduced stomata density when grown under saline conditions. All varieties clustered into two groups (includers and excluders) depending on their strategy of handling Na(+) under saline conditions. Under control (non-saline) conditions, a strong positive correlation was observed between salinity tolerance and plants ability to accumulate Na(+) in the shoot. Increased leaf sap K(+), controlled Na(+) loading to the xylem, and reduced stomata density are important physiological traits contributing to genotypic differences in salinity tolerance in quinoa, a halophyte species from Chenopodium family.

Varietal differences of quinoa’s tolerance to saline conditions

AimsThis study aimed to assess varietal differences of quinoa’s tolerance to salinity and to investigate physiological mechanisms conferring these differences.MethodsProduction of biomass in fourteen varieties grown under saline conditions was analysed in a pot experiment. For two contrasting varieties, the Danish variety Titicaca and the Bolivian variety Utusaya gas exchange, chlorophyll content index (CCI), fluorescence and ion relations were studied.ResultsResponses to salinity differed greatly among the varieties; least affected were two varieties from the Bolivian altiplano and a variety from Peru. Titicaca and Utusaya both had substantially increased K+ concentrations in the leaf sap. But, Utusaya was much more efficient in restricting xylem Na+ loading. Xylem Na+ and K+ loading were found to be uncoupled. Utusaya maintained a relatively high stomatal conductance resulting in an only 25% NaCl-induced reduction in net CO2 assimilation compared to a 67% reduction in salt treated Titicaca plants. Maximum photochemical efficiency of PSII was not affected by salinity.ConclusionIn addition to maintaining high gas exchange, tolerant varieties better control xylem Na+ loading. To what extent this control is related to radial root Na+ uptake or to the activity of Na+/H+-exchangers at the xylem parenchyma boundary remains to be studied.

Differential Activity of Plasma and Vacuolar Membrane Transporters Contributes to Genotypic Differences in Salinity Tolerance in a Halophyte Species, Chenopodium quinoa

Halophytes species can be used as a highly convenient model system to reveal key ionic and molecular mechanisms that confer salinity tolerance in plants. Earlier, we reported that quinoa (Chenopodium quinoa Willd.), a facultative C3 halophyte species, can efficiently control the activity of slow (SV) and fast (FV) tonoplast channels to match specific growth conditions by ensuring that most of accumulated Na+ is safely locked in the vacuole (Bonales-Alatorre et al. (2013) Plant Physiology). This work extends these finding by comparing the properties of tonoplast FV and SV channels in two quinoa genotypes contrasting in their salinity tolerance. The work is complemented by studies of the kinetics of net ion fluxes across the plasma membrane of quinoa leaf mesophyll tissue. Our results suggest that multiple mechanisms contribute towards genotypic differences in salinity tolerance in quinoa. These include: (i) a higher rate of Na+ exclusion from leaf mesophyll; (ii) maintenance of low cytosolic Na+ levels; (iii) better K+ retention in the leaf mesophyll; (iv) a high rate of H+ pumping, which increases the ability of mesophyll cells to restore their membrane potential; and (v) the ability to reduce the activity of SV and FV channels under saline conditions. These mechanisms appear to be highly orchestrated, thus enabling the remarkable overall salinity tolerance of quinoa species.

Effect of saline water on seed germination and early seedling growth of the halophyte quinoa

The introduction of new crops with improved salinity stress tolerance could preserve water quality and protect soil resources from further degradation, providing extra sources of food for salinized areas. In this context, we tested the salinity tolerance of a variety of quinoa. Quinoa, a rich source of minerals, proteins and antioxidants, is considered a major alternative crop to meet food shortages in this century. Our study indicated that salinity tolerance of quinoa is largely conferred by a delicate balance between osmotic adjustment and ion accumulation. Salinity reduced productivity in terms of biomass, but increased the levels of antioxidant compounds, which are important health-protecting factors in food, thus providing economic benefit.

Breeding quinoa (Chenopodium quinoa Willd.): potential and perspectives

Quinoa (Chenopodium quinoa Willd.) originated in the Andean region of South America; this species is associated with exceptional grain nutritional quality and is highly valued for its ability to tolerate abiotic stresses. However, its introduction outside the Andes has yet to take off on a large scale. In the Andes, quinoa has until recently been marginally grown by small-scale Andean farmers, leading to minor interest in the crop from urban consumers and the industry. Quinoa breeding programs were not initiated until the 1960s in the Andes, and elsewhere from the 1970s onwards. New molecular tools available for the existing quinoa breeding programs, which are critically examined in this review, will enable us to tackle the limitations of allotetraploidy and genetic specificities. The recent progress, together with the declaration of “The International Year of the Quinoa” by the Food and Agriculture Organization of the United Nations, anticipates a bright future for this ancient species.

Ionic and photosynthetic homeostasis in quinoa challenged by salinity and drought – mechanisms of tolerance

Quinoa (Chenopodium quinoa Willd.) grown under field conditions was exposed to five irrigation water salinities (0, 10, 20, 30 and 40dSm-1; 4:1 NaCl:CaCl2 molar ratio) from flowering, and divided between full irrigation and progressive drought (PD) during seed filling. Quinoa demonstrated homeostatic mechanisms which contributed to quinoas extraordinary tolerance. Salinity increased K+ and Na+ uptake by 60 and 100kgha-1, respectively, resulting in maintenance of cell turgor by osmotic adjustment, and a 50% increase of the leafs fresh weight (FW):dry weight (DW) ratio and non-significant increase in elasticity enhanced crop water-capacitance. Day respiration (Rd) increased 2.7 times at high salinity but decreased 0.6 times during drought compared with control. Mesophyll conductance (gm) tended to be negatively affected by salinity as the increased succulence (FW:DW) possibly decreased intercellular space and increased cell-wall thickness. However, the increased K+ uptake seemed to alleviate biochemical limitations, as maximum Rubisco carboxylation rate (Vcmax) and photosynthetic electron transport (J) tended to increase under salinity. Overall, salinity and PD restricted stomatal conductance (gs) and photosynthesis (An) moderately, leading to decreased leaf internal to ambient [CO2], increase of intrinsic-water-use-efficiency (An/gs). The saturated electrical conductivity (ECe) resulting in 50% yield was estimated to be 25dSm-1, reaching no yield at 51.5dSm-1.