Heat stress changes mineral nutrient concentrations in Chenopodium quinoa seed

Abstract

Quinoa is a popular seed crop, often consumed for its high nutritional quality. We studied how heat stress in the roots or the shoots of quinoa plants affected the concentrations of 20 elements (aluminum, arsenic, boron, calcium, cadmium, cobalt, copper, iron, potassium, magnesium, manganese, molybdenum, sodium, nickel, phosphorous, rubidium, sulfur, selenium, strontium, and zinc) in quinoa seed. Elemental concentrations in quinoa seed were significantly changed after an 11-day heat treatment during anthesis. The type of panicle (main, secondary, and tertiary) sampled and the type of heat treatment (root only, shoot only, or whole plants) significantly affected elemental profiles in quinoa seed. Plants were also divided into five sections from top to bottom to assess the effect of panicle position on seed elemental profiles. Plant section had an effect on the concentrations of arsenic, iron, and sodium under control conditions and on copper with heat treatment. Overall, the time of panicle development in relation to the time of heat exposure had the largest effect on seed elemental concentrations. Interestingly, the quinoa plants were exposed to heat only during anthesis of the main panicle, but the elemental concentrations of seeds produced after heat treatment ended were still significantly changed, indicating that heat stress has long-lasting effects on quinoa plants. These findings demonstrate how the nutritional quality of quinoa seeds can be changed significantly even by relatively short heat spells.

Keywords: elemental profile; heat; ionomics; nutrient composition; quinoa; seed.

FIGURE 1

Main panicle seed elemental concentrations. (a) Distribution of the three panicle types along a quinoa plant: Main panicle is shown in orange, secondary panicles are shown in blue, and tertiary panicles are shown in red. (b–t) Concentration of 19 elements. An asterisk over a box indicates significant difference from roots and shoots held at 22°C (Cont.) (Wilcoxon rank‐sum test p value <.05). HR, heated roots, with roots held at 30°C and shoots held at 22°C; HRS, heated roots and shoots, with roots at held at 30°C and shoots held at 35°C; HS, heated shoots, with shoots held at 35°C and roots held at 22°C. For sample sizes, please see Table S1

FIGURE 2

Secondary panicle seed elemental concentrations. (a–t) Concentration of 20 elements. An asterisk over a box indicates significant difference from roots and shoots held at 22°C (Cont.) (Wilcoxon rank‐sum test p value <.05). HR, heated roots, with roots held at 30°C and shoots held at 22°C; HRS, heated roots and shoots, with roots at held at 30°C and shoots held at 35°C; HS, heated shoots, with shoots held at 35°C and roots held at 22°C. For sample sizes, please see Table S1

FIGURE 3

Tertiary panicle seed elemental concentrations. (a–s) Concentration of 19 elements. An asterisk over a box indicates significant difference from roots and shoots held at 22°C (Cont.) (Wilcoxon rank‐sum test p value <.05). HR, heated roots, with roots held at 30°C and shoots held at 22°C; HRS, heated roots and shoots, with roots at held at 30°C and shoots held at 35°C; HS, heated shoots, with shoots held at 35°C and roots held at 22°C. For sample sizes, please see Table S1

FIGURE 4

Median percent changes in seed elemental concentrations for heated roots, with roots held at 30°C and shoots held at 22°C (HR), heated roots and shoots, with roots at held at 30°C and shoots held at 35°C (HRS), and heated shoots, with shoots held at 35°C and roots held at 22°C (HS), relative to roots and shoots held at 22°C (control), for main, secondary, and tertiary panicles. An asterisk inside a box indicates significant difference from control (Wilcoxon rank‐sum test p value <.05). For sample sizes, please see Table S1

FIGURE 5

Secondary panicle seed elemental concentrations for each plant section. (a) Quinoa plant showing how the five plant sections were divided for this analysis. (b) Cu concentration. (c) As concentration. (d) Fe concentration. (e) Na concentration. An asterisk over a box indicates a significant difference from Section 1 of the same treatment (t test with Tukey adjustment p value <.05). Control, roots and shoots held at 22°C; HR, heated roots, with roots held at 30°C and shoots held at 22°C; HRS, heated roots and shoots, with roots at held at 30°C and shoots held at 35°C; HS, heated shoots, with shoots held at 35°C and roots held at 22°C. For sample sizes, please see Table S2. For exact contrast p values, please see Table S3

FIGURE 6

Contributions to the model variance in seed elemental concentrations explained by the factors analyzed in this work. (a) Contributions to the model variance in seed elemental concentrations by the factors panicle type (PT), interaction between shoot heating and panicle type (SH–PT), shoot heating (SH), the interaction between root heating, shoot heating and panicle type (RH–SH–PT), interaction between root heating and shoot heating (RH–SH), interaction between root heating and panicle type (RH–PT), and root heating (RH). (b) Contributions to the model variance in seed elemental concentrations by the factors shoot heating (SH), interaction between root heating and shoot heating (RH–SH), root heating (RH), interaction between root heating, shoot heating and plant section (RH–SH–PS), plant section (PS), interaction between shoot heating and plant section (SH–PS), and interaction between root heating and plant section (RH–PS). Letters above boxes represent statistical significance at p < .05 from a t test. For exact t‐test p values resulting from pairwise comparisons between these factors, please see Table S5. All sample sizes were n = 20