|Rajasekaran, Kanniah - Rajah|
|De Lucca Ii, Anthony|
|Van Pee, K|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2001
Publication Date: 1/18/2002
Citation: JACKS, T.J., RAJASEKARAN, K., STROMBERG, K.D., DE LUCCA II, A.J., VAN PEE, K.H. PERACID FORMATION IS NOT THE BASIS FOR RESISTANCE TO FUNGAL INFECTION IN PLANTS TRANSFORMED WITH NONHEME HALOPEROXIDASE. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. 2002. V. 50. P. 706-709. Interpretive Summary: Certain fungi cause tremendous losses in agricultural productivity and adversely affect human health by producing toxins in the crops they infect. We found that an oxidative enzyme from certain bacteria has lethal activity against these fungi. Plants were genetically engineered to contain the enzyme and gained greatly enhanced resistance to fungal infection. The mechanism for the resistance was examined. We found that the formation of oxidized acids catalyzed by the enzyme was not the reason for resistance. Further studies are needed to explain the enhanced resistance. Whatever the mechanism, genetic modification of plants with this enzyme has great utility in protecting plants against fungi without using chemical fungicides.
Technical Abstract: Nonheme haloperoxidase (HPO-P) isolated from Pseudomonas pyrrocinia catalyzed the peroxidation of alkyl acids to peracids. Among alkyl acids tested as substrates, acetate was most readily peroxidized. The reaction product, peracetate, possessed potent antifungal activity: 50% killing (LD50) of Aspergillus flavus occurred at 25 muM peracetate. To determine whether HPO-P could enhance antifungal activity in plants transgenically, tobacco was transformed with the HPO-P gene isolated from P. pyrrocinia. Leaf extracts of transgenic tobacco inhibited A. flavus growth by up to 80%. In order to elucidate if peracid formation by HPO-P could be the basis for increased fungal resistance, effects of hydrogen peroxide-HPO-P mixtures on the lethality of acetate were determined. LD50 of A. flavus exposed to acetate in the presence of these enzyme mixtures occurred at 30 mM acetate. Since this value was identical to that obtained without the eenzyme mixtures (also 30 mM acetate) and was too low to account for enhanced antifungal activity in transgenic plants, kinetics of the enzyme reaction were examined for clarification. The concentration of acetate needed for enzyme saturation (Km = 250 mM) was found to be lethal prior to oxidation to peracetate. Thus, peracid generation by HPO-P is not the basis for enhanced antifungal activity in plants transformed with the HPO-P gene.