Regulation of the mineral concentrations in pea seeds from uranium mine and reference soils diverging extremely in their heavy metal load

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Growing demands in industrial and food crops do not allow for excluding extremely metalliferous to minerally deficient soils from productive use. Seed crops show a strict indigenous heavy metal (HM) control and should thus be able to generate minerally optimized seeds even on soils of highest and lowest (trace) metal resources. Field cultures of pea (Pisum sativum L.) were therefore, established on five soils of seriously diverging HM concentrations. Soils, seeds, and sections of mature plants were analyzed for 20 elements and several organics. In the light of extremes in the mineral supply it was the goal to reveal plant compensatory responses on the way to a dietarily and physiologically balanced seed composition in essential elements by identifying non-essential and chemically similar metals/metalloids. Normal to elevated resources (mgkg−1 DW) of As, Cd, Cu, Mn, Pb, U, and Zn in four clay-loam soils, and negligible ones in a sandy soil represented concentration spans of 5–109x for essential and non-essential minerals and of 475x in Cd. Seed:soil transfer factors diminishing proportionally on higher-concentrated soils by factors 4.5–109x reduced the respective spans of variation in seeds to 1.3–2.4x and to 15.9x in Cd. Non-essential minerals (As, Cd, Pb) were unambiguously distinguished from chemically similar essential ones and were actively incorporated into the seed metallome. The wide soil-HM variations did not interfere with protein content, its amino-acid composition, and sucrose/phenolics equivalents in seeds (range 1–1.4x) but incited disproportionately elevated/reduced mineral concentrations in tissues from root to pod. The narrow and inherited seed target metallome was then formed within the pod wall/seed interface with incisions in the metal (41–94%) and drastic increases in the N (580%) and P transfer (820%). The mean As, Co, Mn, Ni, and Zn stock of seeds from the four clay-loam soils was surpassed by 49% in seeds from the organic- and mineral-poor sandy soil whose highly water-soluble mineral traces provoked extreme soil:seed transfers. It is concluded that pea seeds from soils of widest mineral spans concur with common food/feed hygiene standards and join cereals in the high stability of their mineral and organic composition and a stable dietary value. Seed crops recommend thus themselves for non-remediable metalliferous and extremely mineral-poor soils. Their HM uptake profile under standard conditions should be certified. Expanded permissible soil HM limits for cropland are discussed.