Native tolerance of four day old seedlings wheat to drought stress

The present study was undertaken in order to evaluate nativedesiccation tolerance and its mechanism in wheat seedlings of different genotypes. At the first step، drought stress was applied by using different concentrations of poly ethylene glycol (PEG) and mannitol. Since the fact that these compounds (even in high concentrations) were not able to produce sever water stress، the experiment was carried out by stop irrigation method. The results of drought tolerance in different days of growth (3،4 & 7 days) showed that four-day wheat seedling had the most tolerance to serious drought stress and this toleration was similar to that of desiccation tolerant and resurrection plants. Also، it was intuitive، irrespectiveof wheat genotypes. Four-day wheat seedlingswere well ableto tolerate droughtstress up to more than 3weeks and produce new roots 3 days after re-watering. One Iranian cultivar which was sensitive to terminal drought stress، Marvdasht، was used for the further analysis. Prolonged drought stress (10 to 30 days) showed that 4-day seedlings of thisgenotype tolerated desiccation and grew up very well. The results also showed that soluble sugars، e. g. glucose and mannose increased after stress but decreasedafter re-watering. Cessation of the growth of seedlings which were separated from seeds even in nutrient media indicated thatconnection to seeds is an inevitablecondition for expression of drought tolerance by seedlings.