RAPID GERMINATION OF SULFONYLUREA-RESISTANT KOCHIA-SCOPARIA L ACCESSIONS IS ASSOCIATED WITH ELEVATED SEED LEVELS OF BRANCHED-CHAIN AMINO-ACIDS

Field observations indicate that sulfonylurea-resistant kochia may ger minate at lower soil temperatures and/or germinate more rapidly than s usceptible kochia in the absence of herbicide. To investigate this pos sibility, seeds from three resistant and two susceptible kochia access ions were germinated at temperatures ranging from 4.6 to 13.2 C on the rmal gradient plates. At 4.6 and 13.2 C, germination rates of all resi stant accessions were higher than susceptible accessions, while germin ation rates of one resistant accession were higher than susceptible ac cessions at 7.2 and 10.5 C. Percent germination of all resistant acces sions was significantly higher than susceptible accessions after 48 h at 4.6 C. At higher temperatures, percent germination of some resistan t accessions was higher after 12 or 24 h, but germination of all acces sions was similar at later times. HPLC analysis revealed that seeds fr om resistant accessions contained about 2-fold higher free levels of b ranched chain amino acids than seeds from susceptible accessions. The results indicate that mutations conferring resistance to sulfonylurea herbicides in these kochia accessions may concomitantly reduce or abol ish acetolactate synthase sensitivity to normal feedback inhibition pa tterns, resulting in elevated levels of branched chain amino acids ava ilable for cell division and growth during early germination.