Evidence Against Amplification of Four Genes in Giant Cells Induced by Meloidogyne incognita

Giant-cell DNA was isolated from pea (Pisum sativum) inoculated with Meloidogyne incognita and used in slot blots to test for selective sequence amplification. Four sequences representing low (ribulose 1,5-bisphosphate carboxylase and actin), mid-level (histone 3), and highly repetitive (large ribosomal repeat) sequence DNA were used as probes. Known amounts of root-tip DNA and giant-cell DNA were blotted onto hybridization membranes and probed. The signal strength on autoradiographs containing equal amounts of root-tip DNA and giant-cell DNA were compared with a scanning densitometer. No difference in signal strength between equal amounts of root-tip DNA and giant-cell DNA was found. Thus, for the probes tested, there is no difference in copy number and, hence, no selective DNA sequence amplification has occurred.