Concentration-dependent responses of cucumber plants to cadmium (Cd, 5–15 µM) and/or allantoin (Alla, 10–1000 µM) have been investigated to detect a possible protective role of Alla under Cd excess. After 14 days of exposure, Alla often considerably reversed Cd-induced inhibition of growth and reduction of the content of photosynthetic pigments. Higher Alla doses depleted the Cd amount in shoots, which could be related to citric acid (increase in the shoots but depletion in the roots in Cd+Alla treatments) rather than to phytochelatins (Alla had a negative impact on the phytochelatin accumulation). An increase in the Alla concentration suppressed Cd-induced spatial H₂O₂ appearance, which does not seem to be related to antioxidative enzymes (low impact of Alla on catalase, ascorbate peroxidase, and guaiacol peroxidase). On the contrary, shoot glutathione and mainly ascorbic acid accumulation strongly increased in Cd+Alla treatments, indicating their prominent role in Alla-induced amelioration of Cd-stimulated oxidative stress and growth retardation. Similarly, phenolic metabolites (total soluble phenols and flavonols) were slightly influenced by Alla and their antioxidative action was not expected. We conclude that Alla-mediated attenuation of Cd-induced toxicity relies on enhanced accumulation of glutathione and ascorbate in the shoot tissue mainly, rather than on elevated antioxidative enzyme activities.

已经研究了黄瓜植物对镉（Cd，5–15 µM）和/或尿囊素（Alla，10–1000 µM）的浓度依赖性反应，以检测Cd过量时Alla可能的保护作用。暴露14天后，Alla通常会大大逆转Cd诱导的生长抑制和光合色素含量的降低。较高的Alla剂量会耗尽枝条中的Cd量，这可能与柠檬酸（枝条中的增加，但Cd + Alla处理中根部的枯竭）有关，而不是与植物螯合素有关（Alla对植物螯合素的积累有负面影响）。Alla浓度的增加抑制了Cd诱导的空间H ₂ O ₂外观，似乎与抗氧化酶无关（阿拉对过氧化氢酶，抗坏血酸过氧化物酶和愈创木酚过氧化物酶的影响较小）。相反，在Cd + Alla处理中，茎杆上的谷胱甘肽和主要是抗坏血酸的积累大大增加，表明它们在Alla诱导的Cd刺激的氧化应激和生长迟缓的缓解中起着重要作用。同样，酚代谢物（总可溶性酚和黄酮醇）也受到Alla的轻微影响，并且它们的抗氧化作用没有预期。我们得出的结论是，阿拉介导的Cd诱导毒性的减弱主要依赖于芽组织中谷胱甘肽和抗坏血酸的增强积累，而不是取决于抗氧化酶活性的提高。