Protein expression in accessions of Chinese onion with different allelopathic potentials under monocropping and intercropping systems

Protein expressions of Chinese onion accessions grown under monoculture and intercropped with cucumber were evaluated in pot experiments. Chinese onion accessions used were L04 (with weak allelopathic potential) and L06 (with strong allelopathic potential). Root proteins were separated by two-dimensional electrophoresis and the variable expressed protein spots were identified with MALDI-TOF-TOF mass spectrometer. Forty-seven identified proteins were classified into nine functional categories. Compared monocropping and intercropping, 31 identified variable protein spots were classified into energy metabolism (14 %), phenylpropanoid biosynthesis (28 %), organosulfur compounds biosynthesis (25 %), carbohydrate metabolism (10 %), fatty acid hydrogen peroxide metabolism (9 %), protein translation (3 %), other function (3 %), and no assigned function (9 %). Compared Chinese onion accessions of differing allelopathy potentials, 22 identified variable protein spots were classified into energy metabolism (18 %), phenylpropanoid biosynthesis (27 %), organosulfur compounds biosynthesis (23 %), carbohydrate metabolism (9 %), nucleosome component (4 %), other function (14 %), and no assigned function (5 %). The level of variable-expressed proteins involved in phenylpropanoid and organosulfur compounds biosynthesis significantly upregulated in treatments intercropped with cucumber. These results suggested that putative allelochemicals of Chinese onion were mainly produced by phenylpropanoid biosynthesis and organosulfur compounds biosynthesis pathway.