Douglas A. Campbell

Endogenous ethane and ethylene of Poa pratensis leaf blades and leaf chlorosis in response to biologically active products of Bipolaris sorokiniana.

Infection of Poa pratensis leaf blades and callus tissue by Bipolaris sorokiniana increases the production of ethylene and ethane. The ethylene is responsible for most of the chlorosis that occurs during pathogenesis. The nonselective toxin(s) produced by B. sorokiniana is known to disrupt membranes and to damage chlorophyll, but it is not known whether it can induce an increase in ethylene or ethane. Research was initiated to determine the effect of a biologically-active extract of B. sorokiniana on the endogenous ethylene and ethane of intact P. pratensis leaf blades and on subsequent development of chlorosis. The extract did not increase endogenous ethylene of treated leaves, but it was associated with an increase in endogenous ethane between 24 and 96 h after treatment. Chlorophyll loss occurred 96 h after treatment and persisted for the duration of the study (168 h). The chlorophyll content of treated leaf blades ranged from 72% to 80% of control leaf blades. The observations suggest that the extract of B. sorokiniana can induce chlorophyll loss from treated leaf blades independent of an increase in endogenous ethylene by directly damaging chloroplasts with a concurrent release of ethane. The ethane is believed to be a by-product of pathogenesis.

Gaseous hydrocarbons associated with black layer induced by the interaction of cyanobacteria and Desulfovibrio desulfuricans

Black layer is a condition of high-sand-content golf greens that results in a subsurface blackened layer in the sand produced by sulfate-reducing bacteria. Black layer can be the product of an interaction of cyanobacteria and sulfate-reducing bacteria and may or may not be toxic to the grass growing on the sand. The organic byproducts of the cyanobacteria coat and plug the sand thereby creating an anoxic environment for development of the sulfate- reducing bacteria. The present study was initiated to determine the range of gaseous hydrocarbons evolved from black layered sand produced by the interaction of two genera of cyanobacteria, Nostoc and Oscillatoria, and Desulfovibrio desulfuricans. The gaseous hydrocarbons measured included methane, ethane, ethylene, and propylene. In nonblackened sand, Nostoc evolved the highest levels of these gases, Oscillatoria evolved relatively low levels except for propylene, and D. desulfuricans evolved the smallest quantities of the gases. When the cyanobacteria and D. desulfuricans were combined to develop black layered sand some changes occurred in the evolution of the gases. Evolution of the gases from Nostoc + D. desulfuricans decreased or remained the same relative to Nostoc alone, and increased relative to D. desulfuricans alone. Except for propylene evolution, gases from Oscillatoria + D. desulfuricans increased relative to Oscillatoria or D. desulfuricans alone. Propylene evolution from Oscillatoria + D. desulfuricans remained unchanged relative to Oscillatoria alone, but increased relative to D. desulfuricans alone. The gases measured are discussed relative to the organisms observed and the conditions of the study.

Ethylene and Ethane from Poa pratensis Callus and from Leaf Blades of Regenerated and Seed-Derived Plants Inoculated with Bipolaris sorokiniana*

Summary Ethylene and ethane production from Poa pratensis callus, from intact leaf blades of plants regenerated from callus, and from intact leaf blades of plants from seed inoculated with Bipolaris sorokiniana was determined during pathogenesis. Ethylene increased from callus and leaf blades in response to inoculation. Ethylene increased progressively from 24 to 96 h after inoculation of callus, whereas, ethylene from inoculated leaf blades peaked at 48 h and then declined through 96 h. The magnitude of ethylene production from leaf blades of plants regenerated from callus was greater than that produced from leaf blades of plants from seed. Ethane from inoculated callus increased sharply at 72 and 96 h after inoculation, whereas that from inoculated leaf blades of plants regenerated from callus and from seed declined at 72 and 96 h. The ethane generated from inoculated callus and leaf blades establishes the gas as a product of pathogenesis in this host-pathogen interaction. The decline in ethylene and ethane in leaf blades at 96 h is believed due to a loss of cell and tissue integrity as pathogenesis progressed and symptoms were expressed by the host. Differences in ethylene production between leaf blades of plants from callus and seed, implications of ethane production during pathogenesis, and the potential use of callus culture for pathogenesis research are addressed in the discussion.

Inhibition of Ethylene Biosynthesis and the Endogenous Ethylene and Chlorophyll Content of Poa pratensis Leaves Infected by Bipolaris sorokiniana

Summary The ethylene-biosynthesis-inhibiting substances CAN, AOA, AIB, CCCP, COCL, and PG were applied to roots of intact Poa pratensis to determine their ability to decrease endogenous ethylene production and subsequent chlorophyll (Chl) loss from leaves inoculated with Bipolaris sorokiniana. Endogenous ethylene of leaf blades was measured 24, 48, 72, and 96 h after inoculation, as pathogenesis progressed, and Chl content was determined at 96 h. Endogenous ethylene was significantly decreased at each 24-h sampling period by CAN, AOA, CCCP, and PG. Loss of Chl during pathogenesis was substantially decreased by CAN and AOA, but Chlloss in response to CCCP and PG did not differ from that of the untreated, inoculated control (43% of control). The differential response of Chlloss to the ethylene inhibitors suggests that substances blocking the conversion of AdoMet to ACC are more effective at decreasing the endogenous ethylene surge and preventing Chl loss during pathogenesis than are substances that block the conversion of ACC to ethylene. The ethylene and Chl responses are discussed relative to physiological manipulation of symptom expression.