Effects of α‐difluoromethylornithine on photosynthetic oxygen evolution, respiration and polyamine concentrations in detached barley leaves

Abstract

Detached barley leaves were treated with the polyamine biosynthesis inhibitor, a-difluoromethylornithine (DFMO; I mM) for either 30 min or 12 h. Exposure to DFMO for 30 min led to a substantial reduction in photosynthesis, expressed either on a unit leaf-area or unit chlorophyll basis. On the other hand, photosynthesis (expressed on a unit chlorophyll basis) was increased in leaves exposed to DFMO for 12 h, although when expressed on a unit leaf-area basis, photosynthesis remained unchanged at lower photon flux densities (0-300 pmol m-2 s-') and was slightly reduced at higher photon flux densities (30W300 pmol m-* s-'). Respiration was unaltered in leaves exposed to DFMO for 30 min or 12 h. Exposure to DFMO for 30 min resulted in significant increases in chlorophyll concentrations, while carotenoid concentrations remained unaltered. However, chlorophyll concentrations were reduced in leaves treated with DFMO for 12 h, although no change in carotenoid concentration was observed. Polyamine concentrations were not significantly affected by exposure of detached barley leaves to DFMO for 24 h.

Control of plant disease by perturbation of fungal polyamine metabolism

“…Calculations revealed that DFMO was taken up by the powdery mildew fungus at a rate of 9 pmol (g dr)' weight)"' h"', although this was only sufficient to reduce mildew infection by 45% (Walters and Kingham 1990), It is interesting to note that although DFMO application controls fungai infections on plants, it has no deleterious effect on plant growth. Thus, 0,4 mM DFMO had no effect on growth or polyamine levels in broad beans (Walters 1986), and in fact, treatment of french bean with DFMO actually increased concentrations of putrescine and spermidine in the plant, probably as a result of increased ADC activity (Rajam et al, 1986), Further, although DFMO has been shown to reduce photosynthesis in barley leaves following a 30-min exposure to the inhibitor, this effect disappeared upon prolonged exposure (Coghlan and Walters 1992), It was no surprise therefore that in field trials, 5 mM DFMO not only provided good early season control of barley powdery mildew, but it also increased crop growth and grain yield compared to untreated controls (Havis and Walters 1992), Much less work has been done on the effects of the AdoMetDC inhibitor MGBG or the spermidine synthase inhibitor CHA on fungal growth and disease control. Nevertheless, MGBG has been shown to reduce in vitro growth of a number of economically important plant pathogenic fungi (West and Walters 1989) and to reduce intracellular concentrations of spermidine and spermine in the oat leaf stripe pathogen Pyrenophora avenae (Foster and Walters 1990), Both MGBG and CHA have been shown to reduce powdery mildew infection on barley seedlings (West and Walters 1988) and MGBG was equally effective against black stem rust on wheat, with 0,1 mM reducing infection by 91% (Walters 1995), Biondi et al, (1993) observed that exposure of the Dutch Elm disease pathogen Ophiostoma tdmi to a mixture of MGBG -f CHA reduced spermidine concentrations by 60% and totally depleted spermine in the fungus.…”