Drought-enduring plants: also known as xerophytes, these evergreen shrubs have extensive root systems along with morphological and physiological adaptations which enable them to maintain growth even in times of extreme drought conditions. Drought-resisting plants: also known as succulent perennials, they have water stored in their leaves and stems for sparing uses. Structural adaptations Many adaptations for dry conditions are structural, including the following: Adaptations of the stomata to reduce water loss, such as reduced numbers, sunken pits, waxy surfaces.... Reduced number of leaves and their surface area. Water storage in succulent above-ground parts or water-filled tubers. Crassulacean acid metabolism (CAM metabolism) allows plants to get carbon dioxide at night and store malic acid during the day, allowing photosynthesis to take place with minimized water loss. Adaptations in the root system to increase water absorption. Trichomes (small hairs) on the leaves to absorb atmospheric water. Importance for agriculture With the frequency and severity of droughts increasing in recent years, damage to crops has become more serious, lowering the crop yield, growth, and production. However, research into the molecular pathways involving stress tolerance have revealed that overexpression of such genes can enhance drought tolerance, leading to projects focused on the development of transgenic crop varieties. Drought-tolerant plants which are developed through biotechnology enable farmers to protect their harvest and reduces losses in times of intense drought by using water more efficiently. Collaborations to improve drought tolerance in crop-variety plants International research projects to improve drought tolerance have been introduced, such as the Consultative Group on International Agricultural Research (CGIAR). One such project from CGIAR involves introducing genes such as DREB1 into lowland rice, upland rice, and wheat to evaluate drought tolerance in fields. This project aims to select at least 10 lines for agricultural use. Another similar project in collaboration with CGIAR, Embrapa, RIKEN, and the University of Tokyo have introduced AREB and DREB stress-tolerant genes into soybeans, finding several transgenic soybean lines with drought tolerance. Both projects have found improved grain yield and will be used to help develop future varieties that can be used commercially. Other examples of collaborations to improve drought tolerance in crop-variety plants include the International Center for Agricultural Research in Dry Areas (ICARDA) in Aleppo, Syria; the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in Andhra Pradesh, India; the International Rice Research Institute (IRRI) in Los Baños, Philippines.; and the Heat and Drought Wheat