Drought tolerance of transgenic tobacco plants carrying the iaaM and iaaH genes of auxin biosynthesis

Changes in water regime, drought tolerance, and the content of phytohormone s, free amino acids, and amides were examined in leaves of flowering transg enic tobacco plants (Nicotiana silvestris Spegar et Comes). The transgenic plants exhibited a higher water content, water-retaining capacity, and heat tolerance than the wild-type plants. Under normal conditions, transgenic p lants manifested a higher transpiration rate; however, this index decreased under conditions of severe drought almost to the level typical of the wild -type plants. IAA content was seven times and ABA content was four times hi gher in the transformed plants than in the wild-type plants. IAA level decl ined under drought conditions; however, it remained 2-5 times higher than t hat in the wild-type plants. At the sixth day of drought stress, the total content of free amino acids, including proline, tryptophan, and ten other a mino acids and amides increased, the extent of the increase being higher in the transgenic plants. The higher drought tolerance of the transgenic plan ts is related to IAA involvement in plant adaptation, that is, in the hormo ne-induced modification of plant hormonal status and osmoregulation process .