重金属复合处理对小麦锌铜镍镉积累和分布的影响

为增加粮食可食用部分有益元素的浓度,同时减少有毒重金属元素的含量,需要更好地了解元素在植株和籽粒内的运输和分布。在温室盆栽条件下,以春小麦为供试材料,设置对照（不添加重金属）和重金属复合处理（同时添加铜、锌、镍、镉,以不影响小麦生长为前提）,研究锌（Zn）、铜（Cu）、镍（Ni）、镉（Cd）在成熟植株和籽粒不同部位的分布特点。结果表明,重金属复合处理对小麦成熟期籽粒和秸秆产量、收获指数以及粒重均无显著影响,但使小麦各器官重金属浓度均显著增加,增幅因不同器官和不同元素而异,籽粒中Zn、Cu、Ni和Cd浓度分别增加1.8、0.5、48.1倍和45.3倍。重金属复合处理还显著改变了Zn和Ni在地上部各器官中的分配模式：对照小麦吸收的Zn更易向生殖器官中转运,处理植株则更多地滞留在营养器官中,而Ni呈相反的趋势。激光剥蚀电感耦合等离子体质谱仪（LA-ICP-MS）对籽粒糊粉层和胚乳的定量分析表明,重金属复合处理使糊粉层Zn和Cu浓度仅增加了78%和86%,而糊粉层Ni和Cd浓度分别增加了30倍和121倍。重金属复合处理使胚乳Zn和Cu浓度分别增加了49%和48%,使Ni和Cd浓度均超出小麦标准中Ni和Cd的最大允许浓度（对照籽粒胚乳中没有检验到Ni和Cd）。以上结果表明,在小麦生物强化实践中,在增加有益营养元素（如Cu和Zn）的同时亦存在有毒重金属（如Ni和Cd）超标的巨大风险。

The Accumulation Pattern of Zn, Cu, Ni, Cd in Wheat Grown in Heavy-metal Enriched Substrate

The better understanding of mineral elements accumulation in plants and distribution in grains is the prerequisite for increasing the concentration of beneficial elements and minimizing the content of toxic heavy metals in edible parts of cereal crops. The effect of elevated concentrations of Zn, Cu, Ni and Cd in a peat substrate on wheat yields and the metal contents of the plants were studied in a pot experiment. The distribution and possible co-localization of the beneficial micronutrients and toxic heavy metals in the wheat grain were examined by laser ablation inductively coupled plasma mass spectrometry（LA-ICP-MS）. The metals were added jointly to the peat substrate as sulfates. Combined heavy metals added to peat substrate did not affect grain yield, single grain dry weight, straw dry weight and harvest index of wheat at maturity. However, great changes on metals distribution in plants or grains as affected by heavy metal treatments were observed. Zn, Cu, Ni and Cd concentrations in the grain, chaff, leaf, leaf sheath and stem were significantly enhanced by heavy metal addition but the enhancement varied with different elements or plant organs. Elevated heavy metal supply increased the concentrations of Zn, Cu, Ni and Cd in wheat grains by factors of 1.8, 0.5, 48.1 and 45.3, respectively. The distribution pattern of Cu and Cd in different organs of wheat were not affected by heavy metal treatments, but the distribution pattern of Zn and Ni were significantly changed by heavy metal treatments. High percentages of Zn were translocated in grains at normal Zn supply conditions, but more Zn was retained in vegetative organs by heavy metal treatments. The changes in distribution pattern of Ni showed different trends compared to Zn. LA-ICP-MS analysis of wheat grains revealed that Cu, Zn, Ni, and Cd were distributed in a similar way with the high concentrations in the aleurone layer and low concentrations in the starchy endosperm. Elevated heavy metal supply increased the concentrations of beneficial elements Zn and Cu by 78% and 86%, toxic heavy metals Ni and Cd by 30 and 121 folds in aleurone layer, respectively. Elevated heavy metal supply increased the concentrations of Zn and Cu in starchy endosperm by 49% and 48%, respectively. The concentrations of Ni and Cd in starchy endosperm were not detectable under control conditions, but elevated heavy metal supply increased Ni and Cd concentrations to levels far over the maximum permitted levels set by food standards for heavy metals. These results indicated that heavy metals could accumulate in plants to levels that did not impair plant growth but might be detrimental to human health when the plant was consumed. In addition, the co-localization of beneficial micronutrients Zn, Cu and toxic heavy metals Ni, Cd in the wheat grain might imply a possible risk of the micronutrient bio-fortification strategy.