Abstract:Water deficit is one of the most important environmental factors which limit plant growth, especially in arid and semiarid areas. Influences of water stress may be involved in many aspects on plant growth and development. Therefore, knowledge of these mechanisms in physiology, biochemistry, genetics and drought tolerance may assist in decision making in the future for drought resistance breeding. In this paper, we commented on and discussed some results obtained recently from extensive studies in the field in tree species, including influences on DNA transcription and expression, on PSⅠ and PSⅡ system, on stomata movement, on adaptation and response, on water use efficiency, mechanism of drought resistance, screening of drought tolerance index, and tolerance engineering. We presented our points in these aspects, especially in tolerance engineering. We presented our points in these aspects, especially in tolerance engineering and screening of effective traits by which selection is undertaken.