Analysis of insecticidal activity in transgenic plants carrying the ipt plant growth hormone gene |
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Authors: | Ann Smigocki Sunggi Heu George Buta |
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Institution: | (1) Agricultural Research Service, U.S. Department of Agriculture, Molecular Plant Pathology Laboratory, 20705 Beltsville, MD, USA;(2) Agricultural Research Service, U.S. Department of Agriculture, Horticultural Crops Quality Laboratory, 20705 Beltsville, MD, USA;(3) 10300 Baltimore Ave., Bldg. 006, Rm. 3, USA |
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Abstract: | The expression of a bacterial cytokinin biosynthesis gene (PI-II-ipt) in Nicotiana plumbaginifolia Viviani plants has been correlated with enhanced resistance to Manduca sexta and Myzus persicae. We expressed the PI-II-ipt gene in N. tabacum and Lycopersicon esculentum and observed similar antifeedent effects with the transgenic tobacco but not tomato. A 30 to 50 % reduction in larval weight
gain was observed with some of the tomato plants but these results could not be repeated consistently. Leaf surface extracts
from transgenic N. plumbaginifolia leaves killed 100 % of M. sexta second instars at concentrations of 0.05 % (w/v) whereas the N. tabacum extracts were at least 20 times less active. Extract suspensions were stable for up to 2 days at ambient temperatures below
42 °C and for at least 3 months at 4 °C when stored in the dark. HPLC analysis of the N. plumbaginifolia extracts yielded an active fraction that reduced hatching of M. sexta eggs by 30 % and killed first, second and third instars within 24, 48 and 72 hours of exposure, respectively. The activity
appears to be associated with oxygen-containing aliphatic compounds, possibly diterpenes, as analyzed by TLC, UV absorption
and fragmentation with EIMS. Based on the partial characterization of this activity, the production, secretion or accumulation
of secondary metabolites in leaves of cytokinin producing PI-II-ipt N. plumbagini-folia plants appears to be responsible for the observed insect resistance. |
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Keywords: | cytokinin insect resistance isopentenyl transferase Lycopersicon esculentum Manduca sexta Nicotiana |
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