Abstract
Extremes in soil mineral supply alter the metallome of seeds much less than that of their herbage. The underlying mechanisms of mineral homeostasis and the “puzzle of seed filling” are not yet understood. Field crops of wheat, rye, pea, and the mushroom Kuehneromyces mutabilis were established on a set of metalliferous uranium mine soils and alluvial sands. Mineral concentrations in mature plants were determined from roots to seeds (and to fungal basidiospores) by ICP-MS following microwave digestion. The results referred to the concentrations of soil minerals to illustrate regulatory breaks in their flow across the plant sections. Root mineral concentrations fell to a mean of 7.8% in the lower stem of wheat in proportions deviating from those in seeds. Following down- and up-regulations in the flow, the rachis/seed interface configured with cuts in the range of 1.6%–12% (AsPbUZn) and up-regulations in the range of 106%–728% (CuMgMnP) the final grain metallome. Those of pea seeds and basidiospores were controlled accordingly. Soil concentration spans of 9–109× in CuFeMnNiZn shrank thereby to 1.3–2× in seeds to reveal the plateau of the cultivar’s desired target metallome. This was brought about by adaptations of the seed:soil transfer factors which increased proportionally in lower-concentrated soils. The plants thereby distinguished chemically similar elements (As/P; Cd/Zn) and incorporated even non-essential ones actively. It is presumed that high- and low-concentrated soils may impair the mineral concentrations of phloems as the donors of seed minerals. In an analytical and strategic top performance, essential and non-essential phloem constituents are identified and individually transferred to the propagules in precisely delimited quantities.
Highlights
Extreme variations in the natural or anthropogenically influenced trace mineral stock of arable land are a challenge to non-endemic high-productivity seed crops rather than to locally-adapted landraces [1,2]
Root mineral concentrations fell to a mean of 7.8% in the lower stem of wheat in proportions deviating from those in seeds
Soil concentrations ranging 9–109ˆ in CuFeMnNiZn shrank to spans of 1.3–2ˆ in seeds to mark the order of their adopted target mineral load (Table 4; Figure 4) and the stability of their inherent metallome in the presence of soil mineral extremes
Summary
Extreme variations in the natural or anthropogenically influenced trace mineral stock of arable land are a challenge to non-endemic high-productivity seed crops rather than to locally-adapted landraces [1,2]. Grains respond least to oversupply of soil minerals and nitrogen, and they stabilize their metallome inherently in a narrow range [27,28,29] This was reported for the FeZn content of soybean [30], rice [28], and pea [31], the respective concentrations in vegetative tissues rose drastically. Variable regimes of fertilization had little impact on the seed content of fatty acids and cellulose in peanut [32], of amino acids and sugars in pea [33], and of starch and proteins in maize [34] It is neither known how plants coordinate the uptake and shoot translocation of the required metal stock [35,36] nor is the “puzzle of seed filling” understood [37,38]. The mineral distribution within the mature plant, its uptake control, and the ability to distinguish (micro)nutrients from chemically similar non-essential toxicants will be discussed
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