工業上的大量使用使得重金屬鉻成為嚴重的環境污染因子。鉻是有毒的金屬離子，並且對動物及植物皆會造成極大的毒害。植物受到鉻的污染後會出現萌芽率的下降、根、莖、葉等器官生長的遲緩、並會使植物的生長受抑制。雖然鉻對植物造成的毒害如此嚴重，但其分子機制仍尚未清楚。在本篇研究中，我們發現水稻根部處理鉻之後，其生長明顯受到抑制；並且根部細胞中的 MAPK 及 CDPK 的表現量明顯上升。前處理 CDPK 抑制劑：W7 時，則可發現 MAPK 的表現量明顯下降，顯示 CDPK 確實參與了鉻在水稻根尖細胞中所引起的 MAPK 訊息傳遞路徑，並且 CDPK 應在 MAPK 的上游部份。此外，處理鉻還會增加水稻根部細胞的氧化壓力。
在阿拉伯芥中，鉻同樣會對根部造成毒害而使根部的生長受到抑制，但卻能使阿拉伯芥的根毛數增加。此現象在處理釩時也可看見，但處理其他金屬如鎘、鎳、鉛、砷時並沒有發生，顯示根毛增加為鉻及釩所特有。而阿拉伯芥處理鉻及釩後，根毛增加的時間點並不相同，顯示鉻與釩所誘導的訊息傳遞路徑並不完全一致。處理 NADPH 氧化酶抑制劑：DPI 及在阿拉伯芥突變株 rhd2 的試驗則發現，NADPH 氧化酶參與了鉻與釩誘導阿拉伯芥根毛數增加的訊息傳遞路徑。利用阿拉伯芥 AtMPK6 突變株進行試驗則發現，AtMPK6 此基因應沒有參與鉻及釩誘導阿拉伯芥根毛數增加的訊息傳遞路徑。

Chromium (Cr) is considered an important environmental contaminant released into the atmosphere due to its huge industrial use. Cr is known to be a toxic metal that can cause severe damage to animals and plants. The effects of Cr in plants include a decrease in germination, an inhibition in the growth of roots, stems and leaves, and a reduction in plant biomass production. But mechanisms controlling these responses are not yet established. Here, we demonstrated the root growth was inhibited when treated with Cr in rice (Oryza sativa) seedlings. In addition, the mitogen-activated protein kinase (MAP kinase) and calcium-dependent protein kinase (CDPK) activities were remarkably induced by Cr treatment. Pretreatment of rice roots with W7, a CDPK inhibitor, was able to reduce the activation of MAPK effectively.
In Arabidopsis, Cr treatment could induce root hair formation. To investigate molecular mechanisms controlling Cr-induced root hair formation, we examined the effect of agents that inhibit or promote specific steps in signaling pathway. Genistein and K252a, two protein kinase inhibitors, and cantharidin, a protein ser/thr phosphatase inhibitor, inhibited the induction of root hair formation by Cr. In addition, diphenyleneiodonium chloride (DPI), an NADPH oxidase inhibitor, decreased the extranumerary root hairs induced by Cr. Furthermore, the Cr-induced root hair formation is not detected in NADPH oxidase mutant, rhd2. Our results suggest that MAP kinase, CDPK, and NADPH oxidase may function in the signalling networks of plant response to Cr stress.

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