Difference in response to aluminum among Japanese coniferous species

Seedlings of Chamaecyparis obtusa, Cryptomeria japonica D. Don, and Abies firma Sieb. et Zucco were grown hydroponically for 4 weeks in the presence or absence of aluminum (Al) and with or without reduced pH. Under exposure to AI, root and shoot growth of C. obtusa was enhanced. A. firma showed the same tendency as C. obtusa, though not significantly. Only in C. japonica, growth was reduced with Al, especially shoot growth. In all the species, callose production in the root tips was observed in the presence of Al. A positive correlation was observed between the relative root callose content and relative root growth (r = 0.83), and significant root elongation with AI treatment was observed in all the species. Therefore, it is considered that callose deposition in the root tips of these species may not indicate the Al-induced root cell injury causing root growth inhibition. The highest callose content in the root tip and strong callose fluorescence in the epidermis and zones of cell contact were observed in C. obtusa. Since the Al translocation rate from roots to leaves was the lowest in C. obtusa and since significant growth enhancement was observed in the presence of Al, it is possible that the accumulation of callose in the root epidermis and in the zones of cell contact is related to Al-resistance in C. obtusa.