Some physiological responses of canola (Brassica napus L.) to water deficit stress under laboratory conditions

Drought is considered as one of the most important limiting factors for oil seed canola plant (Brassica napus L.) growth and productivity in Iran. On the basis of root and shoot dry weight as affected by water stress exerted by PEG 6000, out of 9 canola cultivars, a relatively tolerant (cv. Aghaii) and a sensitive cultivar (cv. PO4) were selected. Their responses to low water potential with respect to changes in activity of the antioxidant enzyme ascorbate peroxidase, K+ uptake, and its translocation to the shoots and production of osmoprotectants proline and soluble sugars were analyzed and compared. Although low water potential did not influence ascorbate peroxidase activity, constitutively the enzyme activity was significantly higher in the tolerant cultivar. A significant increase in root proline content was observed with a decrease in external water potential up to -.48 MPa. The increase was 2 to 3 times higher in the tolerant Aghaii cultivar. Although the total soluble sugars tended to increase under low water potential, the amounts accumulated were mostly comparable in both cultivars. K+ uptake by the roots and its translocation to the shoots decreased at low water potential, however the amount taken up and translocated was consistently higher in the tolerant cultivar. Constitutively higher ascorbate peroxidase activity along with the higher rates of proline accumulation and K+ uptake are taken as part of the mechanisms which confer drought tolerance to the Aghaii cultivar.