镉在黄瓜幼苗中的化学形态及亚细胞分布

为探究黄瓜幼苗对镉的吸收累积特性,将黄瓜幼苗置于6种镉浓度梯度(0、10、50、100、200、300μmol·L~(-1))营养液中培养17 d,测定黄瓜幼苗地上部和根部的镉含量以及镉在叶片的亚细胞分布和其化学形态分布。结果表明:随镉浓度升高,转移系数逐渐降低,黄瓜由根向地上部对镉的转运能力减弱。时间或浓度处理均会显著增加黄瓜叶片各亚细胞组分镉含量,镉的富集比例趋势表现为可溶性部分细胞壁细胞器,其中可溶性部分镉含量占44.88%～84.94%,远大于细胞器(3.10%～17.05%)与细胞壁(11.20%～39.66%)。相同时间下,随镉处理浓度的增加,镉在细胞壁组分占比先升高后降低,可溶性部分镉的占比先降低后升高。同时随着处理时间延长,细胞壁组分镉占比降低,可溶性部分镉占比升高。黄瓜叶片中NaCl提取态镉占比最高(33.69%～54.23%),但随着镉浓度提高,乙醇提取态、H2O提取态镉占比升高。当镉浓度达到300μmol·L~(-1)时,黄瓜叶片中的镉形态以乙醇提取态、H2O提取态和NaCl提取态占优势。总的来看,在器官水平上,黄瓜通过限制镉由根部向地上部传递的方式,降低镉对黄瓜地上部的毒害;亚细胞水平上,细胞壁对镉的吸持和液泡区室化是黄瓜对镉胁迫下的重要解毒方式,其中以液泡的区室化占主导位置;在化学形态分布上,镉的化学形态转化也是黄瓜应对镉胁迫的重要耐性策略。

Subcellular distribution and chemical forms of cadmium in cucumber seedlings

To investigate the characteristics of cadmium uptake and accumulation in cucumber seedlings, cucumber seedlings were cultured in nutrient solution at different cadmium concentrations (0, 10, 50, 100, 200, 300 mol·L^-1) for 17 d. The cadmium contents in shoot and root of cucumber seedlings and the subcellular and chemical morphological distribution of cadmium in leaves were determined. The results showed that with the increase of cadmium concentration, the transfer coefficient decreased gradually, and the cadmium transport capacity from root to shoot of cucumber decreased. The cadmium contents of different subcellular components in cucumber leaves increased significantly with time or concentration. The trend of cadmium accumulation was in the order of soluble part > cell wall > organelle, and cadmium contents of soluble fraction (44.88%~84.94%) were much higher than those of organelle (3.10%~17.05%) and cell wall (11.20%~39.66%). When cadmium concentration was increased under the same cultivation time, the proportion of cadmium in cell wall increased first and then decreased, and that of soluble cadmium decreased initially and increased afterwards. With the prolongation of cultivation time, the proportion of Cd in cell wall decreased, while the proportion of Cd in soluble fraction increased. The highest proportion of NaCl-extracted cadmium was found in cucumber leaves (33.69%~54.23%), but with the increase of cadmium concentration, the proportion of ethanol-extracted cadmium and hydrogen peroxide-extracted cadmium increased. When cadmium concentration reached 300 mmol·L^-1, the cadmium in cucumber leaves existed mainly in ethanol-extracted, hydrogen peroxide-extracted and NaCl-extracted speciation. At the organ level, cucumber reduces cadmium toxicity to shoots by limiting cadmium transport from root to shoot. At the subcellular level, cell wall binding and vacuolar compartmentalization are very important for the Cd detoxification in cucumber leaves, while the former is dominant. At the chemical morphological distribution, the chemical transformation of cadmium is also an important strategy for cucumber to deal with cadmium stress.