Analysis of early response and tolerance mechanism to Al stress in plant.

以铝在细胞中的存在形态为研究对象，探讨了铝在植物体内的解毒机制。八仙花叶片鲜重含铝高达15.7mmol·kg ~<-1>（-1），其中2/3以上的铝存在于细胞液中。使用13 <27>Al-核磁共振（NMR），在完整叶片和提取的细胞汁液中观察到Al的主峰在11至12 ppm的化学位移处，这与1：1 Al-柠檬酸盐络合物的化学位移良好一致。通过分子筛层析（Sephadex G-10）结合离子排斥层析对细胞汁液进行纯化，表明与柠檬酸相同保留时间的组分中的Al有助于在完整叶片中观察到的^<27>Al峰。在粗品和纯化的细胞液中Al与柠檬酸的摩尔比接近1。经纯化后，用质谱和核磁共振氢谱进一步研究了配体的结构，其分子量、化学位移和偶合常数与柠檬酸相同。生物测定结果表明，从细胞液中纯化的铝络合物对玉米根的伸长没有抑制作用。根尖表面细胞活力也不受影响。这些结果表明，铝结合柠檬酸在八仙花叶细胞。因此，形成强铝-柠檬酸络合物（一种无毒的铝形态）是八仙花叶片对铝的一种内在解毒机制。

The internal detoxification mechanism of aluminum was investigated in an Al-accumulating plant, Hydrangea macrophylla, focusing on Al forms present in the cells. The leaves of Hydrangea macrophylla contained as high as 15.7 mmol Al kg ^<-1> in fresh weight, and more than two thirds of the Al was found in the cell sap. Using ^<27> Al-nuclear magnetic resonance (NMR), the dominant peak of Al was observed at a chemical shift of 11 to 12 ppm in both the intact leaves and extracted cell sap, which is in good accordance with the chemical shift for the 1 : 1 Al-citrate complex. Purification of cell sap by molecular sieve chromatography (Sephadex G-10), combined with ion-exclusion chromatography indicated that Al in fractions with the same retention time as citric acid contributed to the observed ^<27>Al peak in the intact leaves. The molar ratio of Al to citric acid in the crude and purified cell sap approximated 1. The structure of the ligand chelated with Al was further examined by mass spectrometry and ^1 H-nuclear magnetic resonance after purification, and the molecular weight, chemical shifts and coupling constants were the same as those of citric acid. Bioassay experiments showed that the purified Al complex from the cell sap did not inhibit root elongation of corn (Zea mays L.) and the viability of cells on the root tip surface was also not affected. These observations indicated that Al is bound to citric acid in the cell of hydrangea leaves. Therefore, formatin of strong Al-citrate complex, a non-toxic species of Al, is an internal detoxification mechanism of Al in hydrangea leaves.