Regulation of blue-light-induced proton-pumping by Vicia faba L guard-cell protoplasts—energetic contributions by chloroplastic and mitochondrial activities.
by Mawson B. T. (1993b)
Plant Physiology Research Group, Department of Biological SciencesThe University of CalgaryCalgaryCanada
in Planta 1993b; 191:293–301. – doi:10.1007/BF00195685 –
An initial response during signal transduction in guard cells, following absorption of blue light, is the extrusion of protons. Translocation of protons across the guard-cell plasmalemma is an energy-requiring activity.
The present study has investigated the energetic contribution from guard-cell chloroplasts and mitochondria to blue-light-induced proton pumping by Vicia faba guard-cell protoplasts. The addition of 3(3,4-dichlorophenyl)-1,1-dimethylurea to the protoplast suspension had a minimal effect on rates of acidification when oxygen concentrations of the medium were maintained close to near-saturating levels. Under the same conditions, oligomycin reduced both the rates of blue-light-induced acidification and total proton efflux. Lowering the oxygen concentration of the suspending medium to approximately 20 μM resulted in complete inhibition of blue-light-induced acidification activity. Swelling of protoplasts induced by blue light was also inhibited by low oxygen levels.
Levels of ATP from whole-protoplast extracts were reduced by about 64% when exposed to low levels of oxygen. Increasing oxygen levels to near-saturating levels restored both blue-light-induced acidification rates and swelling of the protoplasts within a 60-min recovery period.
Levels of ATP also increased during the recovery period. Addition of 3(3,4-dichlorophenyl)-1,1-dimethylurea or oligomycin to the suspending medium prior to increasing the oxygen concentration caused a reduction in acidification rates after the recovery period by 40 and 80%, respectively.
Levels of ATP in guard-cell protoplasts were also reduced by both inhibitors after a 60-min recovery period.
The results demonstrate that both guard-cell chloroplasts and mitochondria contribute energetically to blue-light-induced proton pumping by guard-cell protoplasts. Furthermore, both energy sources are inhibited by low oxygen concentrations, suggesting coordinated metabolic regulation between photo- and oxidative phosphorylation in guard cells.