ABSTRACT
Defensive strategies of plants ƒ There are two adaptive strategies (Paris-Pireyre 1988; Jacoby 1994): Exclusion. Plants of the excluder type restrict as much as possible the penetration of salts into their tissues. More precisely, they expel to the outside the sodium that has penetrated through exchange for K+ or H+. Thus they practise a kind of desalinization. Compartmentalization. Plants of the includer type are the most salinity-resistant. They absorb the salts and transport them to their aerial parts that get rid of them in two ways. They can accumulate them in special cells located in the epidermis of the leaves. These are salt glands (Thomson 1975). Alternatively, they accumulate the salts in large vacuoles that occupy 90 per cent of the volume of the cell. This provokes a call for water by osmosis. These plants are gorged with saline water and are called succulents (e.g., Salicornia fruticosa). This mechanism ensures their turgor in a situation where the osmotic pressure of the external solution could lead to their wilting. Therefore, in a way, they create a pressure equilibrium. In actual fact, the two strategies can coexist in certain species. At conductivity higher than 16 mmhos/cm, we only see specialized plants. For example, on the Mediterranean coast: Arthrocnemum glaucum, Statice limonium, Salicornia fruticosa, Obione portulacoides, Sueda maritima, etc. (Fig. 13.17).
