Lipids, carbohydrates and amino acids exuded from the axenic roots of rape seedlings exposed to water‐deficit stress

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Abstract
Rape (Brassica napus [L.]) plants were cultivated for 25 d with axenic roots in a growth system with quartz sand and circulating nutrient solution. After a water stress period of 24h. fresh nutrient solution was added and root exudates were collected 3d later. The stress did not cause significant differences in the weights between the stressed and the control plants. The stressed plants tended to exude more soluble organic carbon than the control plants. This was not reflected in the amounts of low molecular weight carbohydrates exuded. A significantly lower proportion of the soluble organic carbon exuded by the stressed plants was made up of amino acids in comparison with the control plants, 7% and 28% respectively. Exuded hydrophobic substances could be recovered from the sand particles. The stressed plants exuded more sterols than the control plants, and an increased number of polar lipid types. The exudates of the stressed and control plants also differed regarding their fatty acid composition.