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Title: CYTOKININS AS BIOREGULATORS PROMOTE INSECT RESISTANCE IN PLANTS TRANSFORMED WITH THE IPT GENE

Author
item Smigocki, Anna
item HEU, SUNGGI - CHONGUI KOREA
item BUTA, GEORGE - ARS-RETIRED

Submitted to: Plant Growth Regulation Society of America Quarterly
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: In order to increase yields and reduce the use of chemical pesticides, we need to develop plants that are resistant to predatory insects. Using genetic engineering approaches, we produced plants that carry a foreign gene (trait) that produces elevated levels of a plant hormone (cytokinin). Insects (tobacco hornworm and green peach aphid) did not eat as much of these plants as those that did not have this gene introduced. We wanted to know what new substances were being made in these plants that repelled the insects. We chemically analyzed the substances being produced in these plants and compared them to ones in the unmodified plants. We found substances that killed the insects at low concentrations that were similar to other natural products that kill insects. We speculate that the plant growth hormone gene may increase the production or secretion of these compounds in plants. This information will be used by scientists to increase our knowledge of how plants respond to insect-induced damage and lead to the production of plants that are resistant to insect attack thus reducing the usage of environmentally damaging pesticides.

Technical Abstract: The expression of the bacterial cytokinin biosynthesis gene (PI-II-ipt ) in Nicotiana plumbaginifolia plants has been associated with antifeedent and toxic effects on Manduca sexta and Myzus persicae larvae. To characterize the components responsible for the resistance, leaf extracts prepared from transgenic plants were bioassayed for insecticidal activity. Surface extracts killed l00% of M. sexta second instars at concentrations of 0.05% (w/v). Partial purification by HPLC yielded a fraction that had three major peaks of molecular mass of 354, 374 and 472 daltons as determined by chemical ionization mass spectroscopy (CIMS). This fraction reduced the hatch rate of M. sexta eggs by 30% and killed first, second and third instars within 24, 48 and 72 hours of exposure, respectively. The extract was stable for up to 2 days at ambient temperatures and for longer than 1 year at 4C when stored in the dark. In transgenic N. tabacum plants, similar antifeedent effects were observed but surface extracts were at least 20 times less active than those from transgenic N. plumbaginifolia plants. Partial characterization of the compounds indicates that they are oxygen-containing aliphatic molecules in the molecular weight range of diterpenes.