Assessing the influence of exogenous ethylene on electron transport and fluorescence quenching in leaves of Glycine max

Abstract We conducted a series of modeling exercises designed to re-evaluate the light-response and CO 2 -response curves of Taylor and Gunderson ( Pl. Physiol. 86, 85–92, 1988) and to examine further their conclusion that ethylene-induced inhibition of electron transport may contribute to reduced CO 2 assimilation in leaves of Glycine max . By partitioning the response of CO 2 assimilation to either electron transport-limited or Rubisco-limited rates of carboxylation, we calculated that the electron transport capacity ( J max ) of ethylene-treated leaves decreased by over 30% following a 4-hr exposure to 10 μl/l ethylene and noted that ethylene-induced reductions in CO 2 assimilation could be explained without a decrease in Rubisco activity ( Vc max ). Measurements of in vivo Chl fluorescence supported these observations and indicated that the efficiency by which excitation energy was captured in PSII (i.e. ( F m − F o / F m ) was reduced from 0.80 to 0.73 after a 4-hr exposure to 10 μl/l ethylene. This reduction was also accompanied by a 12% decrease in steady-state photochemical quenching ( q p ), indicating that a lower proportion of open or oxidized PSII reaction centers were participating in light-dependent processes. Effects of ethylene on Chl fluorescence were amplified at increased irradiance, suggesting that photoinhibition may play a role in the ethylene-induced inhibition of CO 2 assimilation.