THE EFFECT OF LIGHT QUALITY ON ETHYLENE PRODUCTION IN LEAVES OF OAT SEEDLINGS (AVENA-SATIVA L)

The effect of UV, blue, green, red, far-red and white fluorescent ligh ts at a fluence of 1.5-20 mumol m-2 s-1 photon flux density (PFD) on e ndogenous and ACC-dependent ethylene production by etiolated and green apical oat-leaf segments was investigated. It was found that endogeno us ethylene production in light-irradiated green and etiolated oat lea ves depends upon light quality and its fluence. All light of the visib le spectrum (400-700 nm) at PFD 5-20 mumol m-2 s-1 reduced conversion of ACC to ethylene in green oat leaves incubated in 10(-3) M ACC. Blue light was most effective in the inhibition of ACC-dependent ethylene production at 5-10 mumol m-2 s-1 PFD, and endogenous ethylene formatio n at 10 mumol m-2 s-1 PFD. At 20 mumol m-2 s-1 PFD, all visible light wavebands substantially reduced endogenous ethylene production but blu e and red light were most effective. In etiolated leaves UV at 1.5 mum ol m-2 s-1 PFD, enhanced endogenous ethylene production and other ligh ts at 20 mumol m-2 s-1 PFD decreased evolution of ethylene, whereas AC C-dependent ethylene formation was stimulated by UV, red and far-red w avebands. Growth of 10-day old seedlings was reduced by 40% under cont inuous blue light irradiation relative to that obtained with white lig ht. Irradiation of etiolated and green leaf segments for 18 hr with bl ue light reduced ACC oxidase activity when compared to dark-treated on es. The influence of light quality and its fluence rate on the control of ethylene biosynthesis in oat leaves is discussed.