Abstract:

Aims Plants have evolved self-defense mechanisms against insects and can produce insecticidal protein and other compounds. The development of proteomics has enabled study of the molecular mechanism of this defense. Oilseed rape (Brassica napus cv. Westar) is an important oil crop in China and suffers from damage caused by insect pests and disturbances such as hail. Our objective is to investigate changes of total soluble protein and induced individual protein in B. napus using mechanical damage to mimic insect feeding.
Methods We took two leaf samples from the same leaf of each plant 4 h apart and treated the first sample as mechanical damage. Total soluble protein (TP) of samples was measured by Bio-rad Protein Assay and separated by two-dimensional (2-D) polyacrylamide gel electrophoresis. Up-regulated proteins and new proteins were discriminated on the gel after staining. Two of eight different protein spots were analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and identified by Mascot in database of Matrix Science.
Important findings TP concentration in leaves increased when measured after wounding. The two proteins discriminated on the 2-D gel were the small subunit (SSU) precursor of ribulose-1,5-bisphosphate carboxylase (rubisco) and a mixture containing fructose-bisphosphate aldolase and coproporphyrinogen Ⅲ oxidase (COP). The sequence of rubisco SSU was first reported in B. napus, and the other two enzymes were reported in Arabidopsis thaliana, a relative of B. napus. All of these proteins have been shown to be involved in plant responses to stress. Thus we assume that these three proteins are important in maintaining plant physiological functions during wound-response in leaves of B. napus. This finding could be useful in understanding the relationship between plants and phytophagous insects at the proteomic level.

Key words: proteomics, total soluble protein, two-dimensional (2-D) polyacrylamide gel electrophoresis, MALDI-TOF-MS, plant-insect interaction