The Effect of Cold Pretreatment on Respiration Rates and the Contents of Proline and Photosynthetic Pigments in Soybean Seedlings)Glicine max cv. L17)

Cold stress is one of the environmental stresses that causes certain physiological، morphological and biochemical changes in plant. During temperature stress، active oxygen species (AOS) is produced in organelle which puts plant life in danger. Low temperature is one of the abiotic stresses that are the principal cause of crop failure world wide، dipping average yields for most major crops. Soybean is native to warm habitat and is cultivated in temperate regions like Iran. It exhibits symptoms of injury، when exposed to low non-freezing temperatures. It is now known that exposure of chilling sensitive plants like soybean to temperatures slightly above chilling conditions، reduces chilling injury. This strategy is one way that makes plant to tolerate cold stress. Plants in their vegetative growth phase were exposed to 15ْ C (cold-acclimated) or 25ْ C (nonacclimated) for 24h، under 250 μmol m-2s-1 photosynthetically active radiations (PAR). Then all plants were exposed to 4ْ C (chilling temperature) for 24h and allowed to recover at 25ْ C for 24h. The contents of photosynthetic pigments، respiration rate and proline contents in leaves and roots were analyzed. The results showed that chilling sensitive soybean plants can be made tolerant to cold (4ْ C) by cold acclimation via exposing the plants to nonfreezing low temperatures.