Salt tolerance strategies of the ancient Andean crop quinoa

Abstract

This research was conducted under the auspices of the Graduate School of Experimental Plant Sciences (EPS) Chapter 1 P a g e | 10  Switch strategy of carbon assimilation (certain halophytes switch from C3 to CAM (e.g. Portulacaria afra, Mesembryanthemum crystallinum) or C4 to CAM (e.g. Portulaca oleracea)).Considering the complexity and diversity of mechanisms that contribute to salt tolerance, breeding or engineering crops adapted to saline soils has proven to be a challenging task. In addition, investment in salt tolerance mechanisms normally come with trade-offs for crop productivity, which might make salt-tolerant varieties commercially uncompetitive (Gilliham et al. 2017;Wani et al. 2020;Yamaguchi and Blumwald 2005). Several approaches have been considered to develop agriculture in saline areas (Flowers 2004; Alqahtani et al. 2019):  Improve farming practices to prevent secondary salinization  Soil remediation to reduce the salt content in soils  Incorporate new/ alternative salt-tolerant crops  Exploit natural variation and use landraces or wild relatives of existing crops that might have improved salt tolerance to improve the salt tolerance of current cropsThis thesis explores the third option mentioned above to face the challenge of salinity: introducing quinoa (Chenopodium quinoa), a novel, globally emerging salt tolerant crop, as an alternative to grow in areas affected by salinity where other crops are failing. P a g e | 26Quinoa is a nutritious seed crop with a great potential to grow in saline soils. Here, we studied ion concentrations in quinoa tissues throughout the life cycle of the plant, and linked ion dynamics to responses in growth parameters, seed yield and efficiency of photosynthesis under salinity (0-400 mM NaCl). Ion dynamics changed from high ion exclusion (>99 %, root contents lower than root medium and low accumulation of ions in the leaves) before flowering, to a build-up of ions during seed filling. This indicates a change in strategy in maintaining the necessary gradient of water potential from the root medium to the leaves. K⁺ concentrations in leaves also increased by more than 100 % in response to prolonged severe salt stress, which may point to a role of this ion in leaf osmotic adjustment. Accumulation of ions in epidermal bladder cells did not contribute substantially to Na⁺-exclusion as it was less than 6 % of the total Na⁺ taken up in leaves. Growth under salt stress was mostly impaired by anatomical adaptations (reduced SLA), while initial light use efficiency (Fv/Fm) and NAR were not affected. The variety Pasto showed a "survival strategy" to high salinity with higher ion exclusion and a higher reduction in transpiration than the other varieties, at the expense of lower biomass and seed yield.

How Does Quinoa (Chenopodium quinoa Willd.) Respond to Phosphorus Fertilization and Irrigation Water Salinity?

“…The wide variation in ion uptake and ratio across the salinity level and P rates indicated that the quinoa response under salinity varies with P application rate (Table 2). Quinoa plants are able to maintain the uptake of potassium despite high sodium concentrations in the soil after prolonged salt stress (16 weeks after the start of the stress) [3]. When plants are transferred into a medium with a high Na + concentration (salt treatment), the K + concentration on the plant decreases as Na + rises [6].…”

“…Of the total cultivated land, 227 Mha is irrigated, and out of those, 20% is salt-affected [1,2]. In addition, out of the nonirrigated cultivated land, an additional 2.5% also suffers from salinity [3]. Soil salinization is expanding at a rate of 1-2 million ha•year −1 globally, offsetting a significant portion of crop production and making land unsuitable for cultivation.…”

“…The sequestration of Na + and Cl − within the vacuole not only protects the cytoplasm against toxicity but also increases the diffusion potential of the cell by adjusting the cytosolic diffusion potential [15]. Likewise, ionic dynamics is another defense mechanism, where the K + concentration (which plays a role in the osmotic regulation) in leaves increases by more than 100% due to prolonged and severe salinity [3]. Under normal conditions, the ratio Na + /K + concentration in shoots is between 0.5 and 1 [3].…”

“…Likewise, ionic dynamics is another defense mechanism, where the K + concentration (which plays a role in the osmotic regulation) in leaves increases by more than 100% due to prolonged and severe salinity [3]. Under normal conditions, the ratio Na + /K + concentration in shoots is between 0.5 and 1 [3]. The regulation of K + homeostasis is an important aspect of salt tolerance, and an optimal K + /Na + ratio is considered crucial for tolerance or adaptation to salt stress [24].…”