Differential effects of salt stress on osmotic adjustment and solutes allocation on the basis of root and leaf tissue senescence of two silage maize (Zea mays L.) varieties

The comparative effects of salt stress on osmotic adjustment and solutes accumulation in relation to root–leaf tissue senescence of two silage maize varieties were examined. Studies were carried out with seedlings of two forage maize varieties (Aristo and Arper) subjected to 0, 34, 68 and 102 mM NaCl for 6 weeks under glasshouse conditions. Osmotic potential (OP), osmotic adjustment (OA) and solutes accumulation were quantified in primary roots and in three leaf stages (young, mature and senescent leaves). Moreover, in order to assess the distribution of proline and glycine betaine during root development, the two components were analyzed at different position from the primary root apex of both varieties.The total dry matter was significantly dropped with increasing salinity and reduction was greater in Aristo than in Arper. Salt stress impact in terms of ionic status was more pronounced in roots than in leaves and in older leaves than younger ones. In this setting, Aristo displayed a more sensitivity than Arper. A close relationship between the age of root–leaf tissue and proline and glycine betaine allocation, as salinity response, was shown. During the stress treatment, the accumulation of the two components was higher in growing regions of roots and in young leaves. While total free amino acids (FAA) and sugars were accumulated in roots as well as leaves but preferentially in the mature leaves. The capacity of OA was greater in young than in mature and/or senescent leaves and the contribution efficiency of organic solutes to this occurrence tended to be higher in Arper than in Aristo. Moreover, glycine betaine and proline appeared to be the main solutes that contributed ably to OA mainly in growing regions followed by sugars and other FAA. Inorganic solutes (K+ and Ca2+), however, did not seem to play an important role in OA since their amounts were often reduced in response to salt tolerance.