A method to rapidly identify acetolactate synthase/acetohydroxyacid synthase (ALS/AHAS)-resistant weeds is described based upon the differential accumulation of acetoin in the presence and absence of an ALS/AHAS inhibitor herbicide. Acetoin accumulation is induced by inhibition of ketol-acid reductoisomerase (KARI), the enzyme immediately following ALS/AHAS in the biosynthesis of branched-chain amino acids. Inhibition of ALS/AHAS prevents the build up of acetoin and forms the basis for distinguishing between sensitive and resistant biotypes. A new inhibitor of KARI, 1,1-cyclopropanedicarboxylic acid (CPCA), is described and was found to cause acetoin accumulation in velvetleaf leaf disks over the concentration range of 2 to 100 000 μM. In the presence of CPCA, a number of species important to monitor for ALS/AHAS resistance were found to accumulate acetoin at rates sufficient for resistance diagnosis in 2 to 8 h. In velvetleaf, the youngest apical leaf was found to be the most active in acetoin accumulation. The resistance diagnosis method was validated by clearly distinguishing between imazaquin-sensitive and imazaquin-resistant cocklebur biotypes.

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Acetolactate synthase (ALS) was isolated from a field population of cocklebur (Xanthium strumarium) that developed resistance to the herbicide Scepter following three consecutive years of application. lhe active ingredient of Scepter, imazaquin, gave an inhibitor concentration required to produce 50% inhibition of the enzyme activity that was more than 300 times greater for the resistant enzyme than for the wild-type cocklebur ALS. Tests with flumetsulam and chlorimuron show that the resistant ALS was not crossresistant to these two other classes of ALS inhibitors.

The in vivo transcripts of the tobacco chloroplast gene for the beta subunit of the ATPase (atpB) were examined. In tobacco, like spinach, the atpB gene encodes multiple transcripts. Six tobacco atpB transcripts are present in vivo, with 5' ends at positions "-90", "-255", "-290", "-490", "-500" and "-610" relative to the translation initiation site. The 5' end of the atpB gene ("-610" position) is 20 base pairs from the 5' end of the rbcL gene, coded for on the complementary strand. The "-255", "-490" and "-610" regions are recognized as promoters in vitro by spinach chloroplast and E. coli RNA polymerases.

The effects of exogenous polyamines and growth regulators on plating efficiency of greenhouse-grown sweet potato (Ipomoea batatas Lam.) petiole protoplasts after six days were analyzed using a central composite test design. The medium components screened were 1-naphthaleneacetic acid (NAA), 6-benzylaminopurine (BAP), putrescine (PUT), spermidine (SPD), and spermine (SPM), each at five concentrations. Stepwise multiple regression analysis revealed significant interaction of NAA with BAP, PUT, and SPD as reflected in plating efficiencies. The interactions of NAA with BAP, and with SPD, were positive. The interaction of NAA and PUT appeared complex. A slight negative interaction was detected between PUT and SPM. These results indicated that plating efficiency of sweet potato protoplasts is highly sensitive to the concentrations of the medium components tested and it should be possible to further optimize the plating medium. Among the media formulations tested, the highest plating efficiency (10.8% after 6 days) was observed with NAA at 4.5 uM, BAP at 1.5 uM, PUT at 35.0 uM, SPD at 5.0 uM, and SPM at 2.5 uM.