含銅殺菌劑與植物銅中毒的原理

對於農業生產來說，波爾多液是一個很不錯的應用幾百年都沒有產生抗藥性的殺菌劑。目前生產上還有很多種含銅殺菌劑廣泛應用於葉面噴施、蘸根處理，甚至土壤處理。有的地方一個生長季衝施上一兩次含銅藥劑。那麼，如此大劑量的把銅使用在農業生態體系中，有沒有對人類的生活和生存有安全風險呢？答案是肯定的。因為，銅是重金屬！

下面的英文內容摘自

For centuries, pesticides have been used in agricultural practice to enhance food production by controlling unwanted pests . Many of these pesticides used extensively worldwide are copper-based formulations, including copper sulfate, copper oxychloride and copper carbonate. Pesticides containing copper have a historical significance in that the fungicidal properties of 「Bordeaux mixture」, named after the Bordeaux region in France, were accidentally discovered. When Bordeaux mixture, a chemically undefined mixture of copper sulfate and hydrated lime, was applied to grapes to discourage local pilfering, it was observed that downy mildew disappeared from the treated plants. It was from this serendipitous event that commercialization of fungicides originated。

幾個世紀以來，農藥已被用於農業實踐，通過控制不需要的有害生物來提高糧食產量。 世界上廣泛使用的這些農藥中有許多是銅基製劑，包括硫酸銅，氯氧化銅和碳酸銅。 以法國波爾多地區命名的「波爾多混合物」的殺菌性能被意外發現，使含銅農藥的重要性發生了歷史性的轉變。 當將波爾多混合物（一種化學上不確定的硫酸銅和熟石灰的混合物）應用於葡萄以阻止局部盜竊時，觀察到霜黴病從被處理的植株上消失了。 這個偶然的事件成為殺真菌劑商業化的起始點。

USEPA (2008) listed copper as a pesticide and copper compounds are extensively used in various agricultural settings. Millions tons of copper are applied annually, predominantly in crop protection . Copper is relatively safe from a handling perspective, but there is some concern regarding its buildup in agricultural soils. After application on plants in the field, residual Cu typically accumulates in the upper 15 cm of soil, bound to the organic matter and fine clay fraction . Most importantly, the ecological risk assessments indicate that copper is relatively non toxic for use as a broad-spectrum fungicide on many food and ornamental crops, and for direct use in water applications as an algicide, aquatic herbicide, bactericide, and molluscicide. Copper compounds also are registered for antimicrobials.

USEPA美國環保局（2008）將銅作為農藥和銅化合物廣泛用於各種農業環境。 每年施用數百萬噸銅，主要用於保護作物。 從處理的角度來看，銅是相對安全的，但是它在農業土壤上的積累有一些令人擔憂。 在田間施用在植物上以後，殘留的銅典型地積累在土壤上部15cm處，與有機質和細粘土部分結合。 最重要的是，生態風險評估表明，銅作為廣譜性殺真菌劑在許多食品和觀賞作物上是相對無毒的，並且還作為直接用於水域的殺藻劑，水生除草劑，殺細菌劑和殺軟體動物劑。 銅化合物也被註冊為抗菌藥物。

Copper-based agrochemicals can affect human health, causing different types of cancer, degenerative diseases, and many immune, hematological, neurological and reproductive disorders。

銅基農用化學品會影響人體健康，造成不同類型的癌症，退化性疾病以及許多免疫，血液學，神經和生殖疾病。

The metal copper is a trace element essential as a micronutrient for cyanobacteria, algae and higher plants at low concentration because it is a reactant in biochemical functions of photosynthetic organisms, but at high concentrations it can be toxic . In the later case, copper is very toxic for algae. It increases permeability of the cell membranes and leakage of the cellular constituents. However, the most important effect of copper on plants and algae is associated with the inhibition of photosynthesis. At high concentrations, it can be toxic by interrupting electron transport through photosystem II (PSII) . The reaction center of PSII composes of a heterodimer of two integral membrane proteins, named D1 and D2 which bind electron transfer prosthetic groups such as P680, pheophytin, and plastoquinon. PSII uses light energy to drive two chemical reactions – oxidation of water and reduction of plastoquinone. The photosystem II complex is composed of more than fifteen polypeptides and at least nine different redox components (chlorophyll, pheophytin, plastoquinone, tyrosine, Mn, Fe, cytochrome b559, carotenoids and histidine) . However, only five of these redox components are known to be involved in electron transport from H2O to plastoquinone pool. There are also water oxidizing manganese cluster (Mn)4, amino acid tyrosine, reaction center chlorophyll (P680), pheophytin, and plastoquinone molecules, QA and QB.

金屬銅是一種微量元素，作為藍藻，藻類和高等植物的低濃度微量營養是必不可少的，因為它是光合生物生化功能的反應物，但在高濃度時它可能是有毒的。在後一種情況下，銅對藻類是非常有毒的。它增加了細胞膜的滲透性和細胞成分的滲漏。然而，銅對植物和藻類的最重要的影響與抑制光合作用有關。在高濃度時，它的毒性在於阻斷通過光系統II（PSII）的電子傳遞。 PSII的反應中心由兩個整合膜蛋白的異源二聚體組成，稱為D1和D2，二者與P680，脫鎂葉綠素和質體醌等電子傳遞輔基化合物相結合。 PSII使用光能來驅動兩種化學反應 - 水的氧化和質體醌的還原。光合系統II複合物由十五種以上的多肽和至少九種不同的氧化還原成分（葉綠素，脫鎂葉綠素，質體醌，酪氨酸，錳，鐵，細胞色素b559，類胡蘿蔔素和組氨酸）組成。然而，已知這些氧化還原組分中僅有五種參與從H 2 O到質體醌池的電子傳遞。還有水氧化錳簇（Mn）4，胺基酸酪氨酸，反應中心葉綠素（P680），脫鎂葉綠素和質體醌分子，QA和QB。

Inhibition of oxygen evolution accompanied by quenching of variable fluorescence is the most apparent effect of the toxic action of copper on PSII.However, the precise location of the copper inhibitory binding site is still unknown. Most authors relate the target of the Cu-inhibition of PSII to its oxidizing side . At higher copper concentrations, primary quinone acceptor QA , pheophytin-QA-Fe region , non-haem iron , and secondary quinone acceptor QB  were identifed as the target sites of Cu inhibitory action on the acceptor side of PSII . Schroder et al. (1995) showed that Cu specifically inhibited the electron donation from Tyrz to P680, either by a modification of this amino acid in D1 protein and/or its microenvironment. Furthermore, it was demonstrated that the central magnesium atom of chlorophyll can be substituted by several metals (e.g., mercury, copper or cadmium), damaging the photosystem .

抑制氧的進化伴隨著可變螢光猝滅，是銅對PSII的毒性作用最明顯的結果，但銅抑制結合位點的確切位置尚不清楚。大多數作者將Cu抑制PSII的目標與其氧化側位聯繫起來。 在較高銅濃度下，初級醌受體QA ，脫鎂葉綠素-QA-Fe區，非血紅素鐵和次級醌受體QB 被鑑定為Cu抑制作用的靶位點 PSII的受體方（圖4）。 施洛德等人 （1995）表明，Cu特異性地抑制了從Tyrz到P680的電子供體，或者通過修飾D1蛋白和/或其微環境中的這種胺基酸。 此外，已經證明，葉綠素的中心鎂原子可以被幾種金屬（例如汞，銅或鎘）所取代，從而損害光系統。

Cytochrome b559 is a heme protein and an essential component of all photosystem II reaction centers. If the membrane lacks cytochrome, a stable PS II reaction center cannot be formed . It was also found that copper ions oxidized directly the low potential form cyt b559 at low concentrations (1-10 µM) and the high potential form at higher concentrations (10-100 µM), probably by deprotonation of this labile cyt b559 form.

細胞色素b559是血紅素蛋白質，是所有光系統II反應中心的重要組成部分。 如果膜缺乏細胞色素，則不能形成穩定的PS II反應中心。 還發現銅離子在低濃度（1-10μM）時直接氧化形成低電位形式的細胞色素b559，而在較高濃度（10-100μM）形成高電位形式，可能是通過使這種不穩定的細胞色素b559形式去質子化。

Copper-induced inhibition of photosynthesis was found to be strongly related to the production of reactive oxygen species (ROS), since a number of studies reported activation of the antioxidant defense system, as well as an increase in the levels of ROS-modified lipids and proteins. Nevertheless, all investigations on the specific Cu inhibitory binding site imply direct interference of the metal ion with the photosynthetic apparatus, resulting in a reduced electron flow.

銅誘導的對光合作用的抑制被發現與活性氧（ROS）的產生密切相關，因為許多研究報導了抗氧化防禦系統的活化，以及活性氧修飾的脂質和蛋白質。 儘管如此，對特定Cu抑制結合位點的所有研究都意味著金屬離子與光合裝置的直接幹擾，導致電子流減少。

Toxiclevels of Cu can occur under natural conditions or due to anthropogenic inputs.Anthropogenic inputs include those from the long-term use of Cu-containingfungicides (e.g, in vineyards), industrial and urban activities (air pollution,urbanwaste and sewage sludge),and the application of pig and poultry slurries. Formost crop species. the critical toxicity level of Cu in the leaves is above 20 to30uug-1 dw (Von Hodenberg and Finck, 1975; Robson and Reuter, 1981).There are, however, marked differences in Cu tolerance between plant species.Among certain cu-tolerant species ('metallophytes'), particularly among theflora of the cu-rich soils in the Democratic Republic of Congo, there have beenfield or herbarium reports that the Cu concentration in leaves can be as high as1,000ugg-1 dw However, while these species may have an elevated requirementfor Cu and are certainly highly tolerant of Cu, Cu 'hyperaccumulation, has notbeen demonstrated under controlled conditions, suggesting that some of theserecords may be due to leaf contamination with dust ( Macnair, 2003; Chipeng etal., 2010).

銅的有毒水平可以發生在自然條件或人為的投入。人為投入包括長期使用含Cu殺菌劑（如在葡萄園中），工業和城市活動（空氣汙染，城市垃圾和汙水汙泥）以及豬和家禽泥漿的應用。對於大多數作物品種。 Cu在葉片中的臨界毒性水平在20至30uug-1 dw以上（Von Hodenberg and Finck，1975; Robson and Reuter，1981）。然而，在植物物種之間的Cu耐性有顯著差異。在某些耐銅物種（金屬植物）中，尤其是在剛果民主共和國富銅土壤的植物群中，已有野外或植物標本報導說，葉中的銅濃度可高達1,000ugg- 1 dw。然而，雖然這些物種可能對Cu的需求提高，並且確實對Cu的高度耐受，但Cu'超積累在控制條件下尚未得到證實，這表明這些記錄中的一些可能是由於葉子被灰塵汙染（Macnair ，2003; Chipeng等，2010）。

Ahigh Cu supply usually inhibits root growth before shoot growth (Lexmond andVorm, 1981). This does not mean that roots are inherently more sensitive tohigh Cu concentrations; rather, they are the sites of preferential Cuaccumulation when the external Cu supply is high, as shown in Table 7.16 fortomato plants. With high supply, the Cu concentration of the roots increasesproportionally to the concentration of Cu in the external medium, whereastransport to the shoot is still highly restricted Critical toxicityconcentrations of Cu in the shoots may therefore not necessarily reflect the Cutolerance of plants. This is an important consideration when genotypes are compared.Even at high supply, up  to 60% of thetotal Cu in roots can be bound to the cell wall fraction and the cell wall-plasmamembrane interface (Iwasaki et al., 1990).

一個高銅供應通常抑制莖生長前的根生長（Lexmond和Vorm，1981）。 這並不意味著根，在本質上對高Cu濃度更敏感; 相反，當外源供應量較高時，根是Cu優先積累的場所，如表7.16所示的番茄植物。 隨著供應量的增加，根部Cu濃度與外部介質中Cu濃度成比例地增加，而向地上部分的運輸仍受到高度限制。因此，Cu在枝條中的臨界毒性濃度可能不一定反映植物的Cu耐受性。 當比較基因型時，這是一個重要的考慮因素。 即使在高供給的情況下，根中總銅的60％以上可以結合到細胞壁部分和細胞壁 - 質膜界面（Iwasaki等，1990）。

Inaddition to immobilization of Cu in the root, or reductions in uptake per sethrough binding by root exudates, cellular mechanisms of Cu tolerance are likely to include: (i) enhanced binding to cell walls, (ⅱ) restrictedinflux through the plasma membrane, (iii) stimulation of efflux from thecytoplasm, including via HMA proteins, (iv) compartmentation of Cu by export tothe vacuole(v)chelation at the cell wall-plasma membrane interface, and (vi)intracellular chelation of Cu by organic acids, glutathione-derivedphytochelatins and cysteine rich metallothioneines in the cytoplasm(Fig. 7. 14,see also Burkhead et al., 2009; Yruela, 2009). In perennials root colonizationwith ectomycorrhiza may play an important role in heavy metal tolerance of thehost plant。

除了將Cu固定在根部，或者通過與根分泌物結合而降低攝取本身之外，Cu耐受的細胞機制可能包括：（i）增強與細胞壁的結合，（ⅱ）通過細胞質膜限制其透入 （iii）刺激其從細胞質流出，包括經由HMA蛋白質，（iv）把Cu區隔到液泡中（v）在細胞壁 - 質膜界面螯合，和（vi）在細胞內與 有機酸、穀胱甘肽衍生的植物螯合素和富含半胱氨酸的金屬硫蛋白螯合在細胞質中（圖7.14，另見Burkhead等，2009; Yruela，2009）。 在多年生植物中，外生菌根的定殖可能在寄主植物的重金屬耐受性中起重要作用。

英文內容摘自：

1、《COPPER AND COPPER-CONTAINING PESTICIDES: METABOLISM, TOXICITY AND OXIDATIVE STRESS  》

2、《Marschners Mineral Nutrition of Hihger Plants》

翻譯水平有限，僅為參考，歡迎交流