Characteristics of Aluminum Accumulation and Distribution in Leaves of Different Ages in Camellia oleifera

Oil tea (Camellia oleifera Abel.), an important edible oil tree found in the acidic soil of south China, is tolerant to aluminum (Al); however, the mechanism via which it detoxifies Al remains unclear. The present study investigated the accumulation and distribution of Al and the changes in antioxidant components in C. oleifera leaves at different stages of growth. The analysis revealed that the content of Al in young, mature, and old leaves was 1.53, 7.49, and 12.04 g kg(-1), respectively. In the leaves, Al was mainly accumulated in the cell wall, which accounted for 66.03%, 79.94%, and 86.51% of the total Al accumulation in young, mature, and old leaves, respectively. In the leaf cell wall, the Al content in hemicellulose increased from 54.22% to 81.72% with leaf age. The proportion of Al in the upper epidermis, lower epidermis, palisade, and spongy parenchyma cell walls increased with leaf age. The activity of antioxidant enzymes increased and showed a synergistic effect on Al stress with leaf age. The peroxidase activity was the highest in mature leaves, 2.3 times that in young leaves. Meanwhile, catalase and superoxide dismutase activities and total phenol content were the highest in young leaves. Correlation analysis showed that antioxidant system composed of catalase, superoxide dismutase and total phenol (CAT, SOD, and TP) was negatively correlated with the Al content in C. oleifera leaves. The malondialdehyde (MDA) content was positively correlated with Al content in C. oleifera leaves, indicating that the MDA in the leaves helped resist Al stress in C. oleifera. Thus, our findings suggest that the increase in antioxidant properties and modification of the cell wall contributed to Al detoxification in the Al hyperaccumulator C. oleifera.