Relationship between salt tolerance and proline accumulation in Australian acacia species

 The effects of salinity on the seedlings of five acacia species, Acacia ampliceps, A. salicina, A. ligulata, A. holosericea, and A. mangium were studied with respect to mortality, growth, and proline accumulation. There was marked variation among the species in their response to salinity. A. ampliceps showed the highest level of salt tolerance among the five acacia species. In contrast, A. holosericea and A. mangium were classified as the least tolerant. The concentration which caused 100% mortality in 2-week-old seedlings during 1 week of treatment was 2.5% (w/v) and 1.5% NaCl for A. ampliceps and A. holosericea, respectively. The dry weights of whole plant of two acacia species decreased markedly under the above salt stress conditions. Proline accumulation was found in leaves and roots after NaCl treatment. The maximum level of proline accumulation in A. holosericea was about twice as great as that in A. ampliceps throughout the stress period. Thus, the level of proline accumulation was not related to the degree of salt tolerance in these acacia species, although a positive correlation between the extent of salt stress and the accumulation of proline was found. Received: July 18, 2002 / Accepted: October 10, 2002 Acknowledgments The author thanks Dr. Kiyoshi Tazaki for his technical advice on the quantitative analysis of proline and Toshiro Sumizono for use of the phytotron. He is also grateful to Dr. Kenji Shinohara for reviewing the language. This work was supported by a grant from the Science and Technology Agency of Japan to the Forestry and Forest Products Research Institute (Encouragement of Basic Biology).