Tolerance of Douglas Fir Somatic Plantlets to Aluminum Stress: Biological, Cytological, and Mineral Studies

Aluminum (Al) is well known as a potent inhibitor of plant growth and development. It is notably present in soils in the soluble and bioavailable form Al3+ when the soil pH drops below 5. This situation is frequent, especially in softwood forests when litter decomposition is slow. In the present work, we studied the effects of Al3+ on the growth and development of Douglas fir plantlets. Somatic plantlets, regenerated via somatic embryogenesis, were grown in vitro on media supplemented with different concentrations of aluminum chloride (AlCl3): 0 &micro
M, 200 &micro
M, 500 &micro
M. and 1 mM. We show that a concentration of 500 &micro
M AlCl3 in medium significantly reduced root elongation (&minus
21.8%), as well as stem growth (&minus
14.6%). Also, a 25% reduction in dry mass of the plantlets was observed in presence of a concentration of 200 &micro
M of AlCl3. Histological analysis of root tissues revealed significant damage, especially in conducting vessels. In addition, mineral cation content of plantlets was disturbed under Al exposure. More particularly, the Mg and K contents of needles and the Ca content of stems and needles were significantly reduced in presence of a concentration of 500 &micro
M AlCl3 in the culture medium (&minus
35.6%, &minus
33.5%, &minus
24%, and &minus
34% respectively). However, all these damages appeared at relatively high Al concentrations when compared with other herbaceous species. This study shed light on the ability of Douglas fir in vitro plantlets to cope with the acid-driven toxicity of Al.