THE TOLERANCE OF ATRIPLEX HALIMUS L. TO ENVIRONMENTAL STRESSES
Atriplex halimus L. (Amaranthaceae) (Mediterranean Saltbush) is a perennial, halophytic shrub that possesses the C4 photosynthetic anatomy and physiology. It grows under semi-arid and arid conditions (annual rainfall < 600 mm) from Macaronesia, through the Mediterranean basin countries and into western Asia, being particularly common on saline and degraded soils. Many studies have shed light on the physiological and biochemical mechanisms that, together with the morphological and anatomical features of this species, contribute to its notable tolerance of important abiotic stresses: salinity, drought, extreme temperatures and soil contamination by trace elements. These will be discussed here, highlighting their shared and distinct features. Certain processes are common to two or more stress responses: for example, vacuolar accumulation of sodium and the cytoplasmic accumulation of compatible osmolytes - part of the process of osmotic adjustment - are vital components of the adaptation to drought, salinity and cold. Others, such as oxalate accumulation upon trace elements exposure, seem to be stress-specific, while leaf surface vesiculated hairs (trichomes) and abscisic acid have distinct functions according to the stress. The relevance of these mechanisms to the use of A. halimus in soil remediation and as livestock forage is discussed.