Physiological Role of Glycinebetaine in Alleviating the Deleterious Effects of Drought Stress on Canola Plants (Brassica napus L.)

Pot experiments were conducted during two successive seasons (2011/2012 and 2012/2013) at wire house of the National Research Centre, Giza, Egypt to study the effect of soaking canola seeds with glycinebetaine (GB) (10mM, 15mM and 20mM ) on growth, photosynthetic pigments, osomoprotectants, antioxidant enzymes, seed yield quality and quantity, in fever of antioxidant compounds and fatty acids composition in the yielded canola plants which subjected to moderate and severe drought stress (75% FC and 50% FC). Moderate and severe drought stress caused marked decreases in canola plant growth parameters (shoot height, root length, fresh and dry weights of shoot and root/plant) and significant decreases in photosynthetic pigments and IAA accompanied by significant increases in osomoprotectants (proline and total soluble sugars), MDA and H2O2 in tissues of canola leaf relative to control plants. Antioxidant enzymes activities (POX, PPO, SOD, CAT and APX) were significantly increased accompanied by significant decreases in NR due to drought stress. Drought stress at 75% FC and 50% FC decreased seed yield/plant, oil and carbohydrate, total phenolic content, tannins, flavonoids and antioxidant activity accompanied by significant increases in protein content of the yielded seeds. Drought stress increased total saturated fatty acids and decreased unsaturated fatty acids relative to control plants. On the other hand, GB treatments proved to be effective in enhancing growth parameters and photosynthetic pigments of drought stressed plants. Glycinebetaine treatments at different levels caused significant increases in IAA, proline, total soluble sugars and significant decreases in MDA, H2O2, antioxidant enzymes (POX, PPO, SOD, CAT, APX and NR) in canola plants irrigated with different levels of water relative to corresponding controls. All GB treatments caused significant increases in seed yield, oil, carbohydrate, protein, total phenolic content, tannins, and antioxidant activity of the yielded seeds and non-significant increases in flavonoids in the yielded canola seeds either in plants irrigated with 75% FC or 50% FC relative to corresponding controls. The increases in seed yield/plant due to 20 mM GB were 30.80% and 60.28% at 75% FC and 50% FC respectively relative to corresponding controls. The fatty acid profile of canola oils showed different responses to GB treatments either in unstressed plants or drought stressed plants. Oleic and linoleic acids were increased accompanied by decreases in linolenic and erucic acids under the interaction effect of GB treatments and drought stress (75% FC and 50% FC) and these results led to decreases in total saturated fatty acid and increases in unsaturated fatty acid relative to corresponding controls. Generally, 20 mM GB was the most pronounced and effective treatment in alleviating the deleterious effect of moderate or severe drought stress on canola plants.