Potential of hydrogen (pH) differentially modulates cadmium stress response in abscisic acid-deficient sitiens tomato mutant

ABSTRACT Uptake of nutrients and cadmium (Cd) are dependent upon many factors, including plant species, ions concentration and pH. Tolerance to Cd-induced oxidative stress can be modulated by phytohormones such as abscisic acid (ABA), which induce the production of reactive oxygen species, activating proteins and enzymes involved in stress response and possibly stress tolerance. The present study aimed to evaluate the biochemical variations induced by Cd in ABA-deficient sitiens tomato mutant (sit) and its wild-type counterpart, Micro-Tom (MT), grown at different pH conditions. The plants were cultivated in nutrient solution (pH 5, 6 and 7; 20-days) and were then further grown over a 48-h period in 0 or 50 ?M CdCl2 at pH 6. Before Cd addition, the concentrations of nitrogen, sulfur, copper, iron and zinc were determined and variations in nutrients concentrations were observed. After Cd addition, sit roots grown at pH 5 and 7 did not exhibit differences in ascorbate peroxidase (APX) activity in 0 or 50 ?M CdCl2, and sit root grown at pH 6 exhibited lower glutathione reductase (GR) activity in the presence of Cd. Moreover, sit shoot grown at pH 5 showed decreased activities of superoxide dismutase (SOD), Mn-SOD II and Cu/Zn-SOD V, in 0 and 50 ?M CdCl2. The results indicated that pH modulates the plant nutrition in a complex way and may involve multiple ABA signaling pathways. Likewise, ABA status seems to be related with the Cd-translocation within the plant, suggesting that Cd, ABA and pH responses cannot be evaluated as isolated systems.

摘要 养分与镉（Cd）的吸收受诸多因素影响，包括植物种类、离子浓度及pH值。植物激素如脱落酸（abscisic acid, ABA）可调控植物对镉诱导氧化胁迫的耐受性，其能诱导活性氧的产生，激活参与胁迫应答及潜在胁迫耐受的蛋白与酶类。本研究旨在评估镉在脱落酸缺陷型番茄sitiens突变体（sit）及其野生型对照Micro-Tom（MT）中诱导的生化变化，供试材料在不同pH条件下培养。将植物种植于营养液（pH分别为5、6、7，培养20天），随后在pH 6的0或50 μM氯化镉（CdCl₂）溶液中继续培养48小时。添加镉前，测定了氮、硫、铜、铁及锌的浓度，并观察到养分浓度存在差异。添加镉后，在pH 5和7条件下培养的sit根系，在0或50 μM CdCl₂处理下其抗坏血酸过氧化物酶（ascorbate peroxidase, APX）活性无显著差异；而在pH 6条件下培养的sit根系，经镉处理后其谷胱甘肽还原酶（glutathione reductase, GR）活性更低。此外，在pH 5条件下培养的sit地上部分，在0和50 μM CdCl₂处理下，其超氧化物歧化酶（superoxide dismutase, SOD）、Mn-SOD II及Cu/Zn-SOD V的活性均有所下降。研究结果表明，pH以复杂方式调控植物营养状况，可能涉及多条脱落酸信号通路。同样，植物的脱落酸状态似乎与植物体内镉的转运相关，这提示镉、脱落酸及pH的应答不能作为独立系统进行研究。