Physiological responses and tolerance of plant shoot to aluminum toxicity.

Aluminum (Al) toxicity is one of the most deleterious factors for plant growth in acidic soils because over 50% of the world's potentially arable lands are acidic. In recent years, considerable research has been conducted to understand the mechanisms of Al toxicity and tolerance in plants, and some review papers have been published. But most papers addressed mainly the mechanisms of Al toxicity and tolerance in plant root system, because inhibition of root growth is one of the earliest symptoms of Al injury and the most easily recognized symptom in solution culture. This paper reviews the effects of Al on photosynthesis, photoprotective systems, water use efficiency (WUE), water content, carbohydrate content, mineral nutrition, organic acids, and nitrogen metabolism in plant shoot, and also the mechanisms of Al detoxification (chelation of Al with small organic compounds, and isolating Al in the some parts, which are insensitive to Al, such as vacuoles or epidermal cells) by Al accumulators. Genetics and molecular biology of plant Al tolerance, as well as some aspects needed to be further studied are also discussed.