銅、鋅、鎘對菸草吸收重金屬之交互影響

Abstract

銅、鋅、鎘為台灣常見之重金屬污染物。在目前研究植生復育的技術中，多半是針對單一重金屬作為研究，但在重金屬污染的環境中是含有多種的重金屬。因此，在多種重金屬的影響下，重金屬彼此是否會產生競爭或協同運輸的情況，尚未完全明瞭。故本試驗的目的即在探討混合的銅、鋅、鎘三種重金屬對於菸草吸收重金屬的交互影響。試驗材料為圓葉菸草 (Nicotiana benthamiana)，種子發芽後一週移植於三吋塑膠盆中，以根基旺3號為栽培介質。菸草種植於自然光照之溫室中，溫度控制在24℃到30℃。幼苗種植六週後，在盆中加入 100 mL 單一的銅、鋅、鎘溶液或是混合的銅與鎘、銅與鋅溶液等處理。分析項目有植物萎凋程度、植物鮮重、植物乾重、葉綠素含量、可溶性蛋白質含量、脯氨酸含量、脂質過氧化程度和植體金屬離子含量。重金屬處理三天後的結果顯示，隨銅處理濃度增加，菸草萎凋程度加劇。鎘僅在濃度為 10 mM 的處理下萎凋程度才與 control 有差異，而鋅處理不會對菸草產生萎凋的現象，表示銅對菸草的毒性最大，依次為鎘與鋅。然而，在混合的重金屬處理中發現，鎘處理可以減緩銅處理所誘導的葉片萎凋。鋅處理則需要在 10 mM 銅濃度處理下，方可以減緩銅處理所誘導的葉片萎凋。分析植體中金屬離子含量發現，鎘處理並未降低菸草葉片的銅含量，反而增加銅含量。鋅處理在 10 mM 銅濃度處理下亦增加菸草葉片的銅含量。據以推測，鎘、鋅處理減緩銅處理所誘導的葉片萎凋，不是競爭銅的吸收所致，而可能是干擾銅對菸草的毒害機制。菸草葉片葉綠素及蛋白質含量與脂質過氧化程度不受重金屬處理影響，推測三天的處理下受損的部位僅及於菸草根部，對地上部的影響不顯著。而脯胺酸的含量與植物萎凋程度成正相關，因此菸草中脯胺酸的累積可能與植物萎凋有關。另外，分析植體中金屬離子含量發現，銅處理會增加菸草莖部及葉片的鋅含量，但僅增加莖部的鎘含量。混合重金屬處理下，菸草內的鉀、鈣、鎂、鐵、錳含量，都有增加的趨勢。

Copper, zinc and cadmium are common heavy metal pollutants in Taiwan. In the resent studies of phytoremediation, most of them were focus on the act of single heavy metal in soil, but in many cases, heavy metal pollution was the combination of multielement. Thus, whether the interaction of multiple heavy metals was an antagonistic effect or a synergistic effect needed to be discussed. The aims of this study assess the interaction of copper, zinc and cadmium to the uptake of heavy metal in tobacco. In this study, Nicotiana benthamiana was the test plant and grew in greenhouse with sunlight, and with temperature controlled between 24 to 30 ℃. After grew in the soilless culture for six weeks, tobacco was treated with heavy metal solution where copper, zinc and cadmium were added singly or in the combination of copper with zinc or cadmium. The growth of tobacco was monitored with plant wilting level, fresh weight and dry weight. The physiological status was expressed with chlorophyll content, protein content, proline content and lipid peroxidation level. The metal ion contents were also analyzed at the end of experiment. The result showed that plant wilting level increased with the increase of copper concentration. Cadmium increased plant wilting level only under 10 mM cadmium treatment and zinc did not affect plant wilting level, that implying copper was more toxic than cadmium and zinc to tobacco. Cadmium could reduce Cu-induced plant wilting level. Zinc also ccould reduce Cu-induced plant wilting level, but only at 10 mM copper treatment. Surprisingly, cadmium or zinc also increased copper content in Cu-treated tobacco leaf and stem, suggesting cadmium and zinc reduce Cu-induce plant wilting level was not due to the competition with Cu absorption, but the interfering on Cu toxicity. Chlorophyll content, protein content and lipid peroxidation level did not change after treated with heavy metal for 3d. It’s seemed that it was not the shoot affected by heavy metal after 3d treatment, but the root. Proline content was highly correlated with plant wilting level, thus the proline accumulation may relate to plant wilting level. Copper increased zinc content in Zn-treated tobacco leaf and stem. Copper also increased cadmium content in Cd-treated tobacco stem, but not in leaf. The combined heavy metals treatments also increased the content of potassium, calcium, magnesium, iron and manganese in tobacco.