Aluminum-activated oxalate secretion does not associate with internal content among some oxalate accumulators.

Although aluminum (Al)-activated secretion of oxalate has been considered to be an important Al-exclusion mechanism, whether it is a general response in oxalate accumulators and related to oxalate content in roots are still not clear. Here, we examined the oxalate secretion and oxalate content in some oxalate accumulators, and investigated the role of oxalate secretion in Al resistance. When oxalate content in amaranth roots was decreased by about 50% with the increased ratio of NH4(+)-N to NO3(-)-N in nutrient solution, the amount of Al-activated oxalate secretion still remained constant. There was no relationship between the content of the water soluble oxalate in four species of oxalate accumulators and the amount of the Al-activated oxalate secretion in roots. Furthermore, oxalate secretion is poorly associated with Al resistance among these species. Based on the above results, we concluded that although all of the oxalate accumulators tested could secrete oxalate rapidly, the density of anion channels in plasma membrane may play a more important role in Al-activated oxalate secretion.