Characterization of Epidermal Bladder Cells in Chenopodium quinoa

Abstract

Chenopodium quinoa (quinoa) is considered a superfood, as it has favourable nutrient composition and is gluten free. Quinoa has high tolerance to several abiotic stresses, i.e. salinity, water deficit (drought) and cold. The tolerance mechanisms are yet to be elucidated. Quinoa has Epidermal Bladder Cells (EBCs) that densely cover the shoot surface, particularly the younger parts of the plant. Here, we report on the EBC’s primary and secondary metabolomes, as well as the lipidome in response to abiotic stresses. EBCs were isolated from plants after cold, heat, high-light, water deficit and salt treatments. We used untargeted Gas Chromatography-Mass Spectrometry (GC-MS) to analyse metabolites and untargeted and targeted Liquid Chromatography-MS (LC-MS) for lipids and secondary metabolite analyses. We identified 64 primary metabolites, including sugars, organic acids and amino acids, 19 secondary metabolites, including phenolic compounds, betanin and saponins and 240 lipids categorized in five groups including glycerolipids and phospholipids. Although we found only few changes in the metabolic composition of bladders in response to abiotic stresses, metabolites related with heat, cold and high-light treatments, but not salt stress, were changed significantly. Na concentrations were low in EBCs with all treatments, and approximately two orders of magnitude lower than K concentrations.

The epidermal bladder cell‐free mutant of the salt‐tolerant quinoa challenges our understanding of halophyte crop salinity tolerance

“…( 2020 ) and Otterbach et al . ( 2021 ). If EBCs were to serve as Na + dumps, they would need to be able to store sizable amounts of Na + to reduce its accumulation in the leaf mesophyll and to protect the rest of the leaf from Na + overload.…”

“…The findings presented here, showing that EBCs have no effect on a plant's salt tolerance under our experimental conditions’, will refocus the research on halophyte salt tolerance mechanisms and redirect breeding efforts addressing future food security. Epidermal bladder cells, with high concentrations of osmolytes, may serve as a pull factor for water, which would allow them to play roles in metabolite storage (Otterbach et al ., 2021 ) and protection of the epidermal layer (LoPresti, 2014 ). For example, oxalic acid, which accumulates in EBCs of both halophytes (Lüttge et al ., 1978 ; Jou et al ., 2007 ; Otterbach et al ., 2021 ) and glycophytes (Steudle et al ., 1983 ; Franceschi & Nakata, 2005 ), is a well‐characterized herbivore deterrent (Franceschi & Nakata, 2005 ).…”

“…Epidermal bladder cells, with high concentrations of osmolytes, may serve as a pull factor for water, which would allow them to play roles in metabolite storage (Otterbach et al ., 2021 ) and protection of the epidermal layer (LoPresti, 2014 ). For example, oxalic acid, which accumulates in EBCs of both halophytes (Lüttge et al ., 1978 ; Jou et al ., 2007 ; Otterbach et al ., 2021 ) and glycophytes (Steudle et al ., 1983 ; Franceschi & Nakata, 2005 ), is a well‐characterized herbivore deterrent (Franceschi & Nakata, 2005 ). Potassium transport into EBCs is a means of driving water transport in the same direction by osmosis.…”

Abscisic Acid Perception and Signaling in Chenopodium quinoa

“…EBCs are pronou young leaves, and can contain up to 1 M of NaCl, serving as Na + dumps [89,90] ver, mechanical removal (by brushing) of EBCs makes quinoa more sensitive to [90]. Controversially, a recent work proposes that EBCs function as a K + reservo ing an important role in salt-stress tolerance independently of Na + accumulation ABA could play a key role maintaining EBCs function under high osmot (Figure 2) [19,92]. Moreover, EBCs could also operate as an ABA source and ex phytohormone to other plant tissues to enhance systemic response to abiotic stres Transcriptomic analysis revealed that the ABA synthesis pathway was upregu EBCs [19,92], in particular the transcript levels of NCEDs and SDR genes (enco rate-limiting enzymes for ABA biosynthesis).…”

“…Controversially, a recent work proposes that EBCs function as a K + reservo ing an important role in salt-stress tolerance independently of Na + accumulation ABA could play a key role maintaining EBCs function under high osmot (Figure 2) [19,92]. Moreover, EBCs could also operate as an ABA source and ex phytohormone to other plant tissues to enhance systemic response to abiotic stres Transcriptomic analysis revealed that the ABA synthesis pathway was upregu EBCs [19,92], in particular the transcript levels of NCEDs and SDR genes (enco rate-limiting enzymes for ABA biosynthesis). Furthermore, it was also showed expression levels of ABA transporters, such as ABCG40 and ABCG25, are higher in respect to other tissues.…”