The properties of photosynthetic O2 evolution by mesophyll cell chloroplasts (MCC) and guard cell chloroplasts (GCC) isolated from protoplasts of Vicia faba L. have been studied and effects on O2 evolution of factors known to regulate stomatal movements have been compared. The O2 evolution of GCC was CO2-dependent. The saturating light intensity for O2 evolution was between 150 and 200 μmol m-2s-1 for MCC and was between 400 and 1,000μmol m-2s-1 for GCC. Light quality (red vs. blue) had no significant effect on O2 evolution by either MCC or GCC. The O2 evolution rate of MCC was strongly dependent on external K+ concentration, but GCC did not respond significantly to variations in external K+ concentration between 0 and 250 mM. The optimal external pH for O2 evolution by MCC was approximately 7.5, and either higher or lower external pH significantly inhibited O2 evolution. However, O2 evolution by GCC was only slightly enhanced when external pH was increased from 6.0 to 8.0. Our observation of differential sensitivity of MCC and GCC to light intensity and to variations of cytoplasmic K+ and pH may indicate differential regulation of photosynthesis in MCC and GCC.
|Original language||English (US)|
|Number of pages||8|
|Journal||Plant and Cell Physiology|
|State||Published - Oct 1993|
All Science Journal Classification (ASJC) codes
- Plant Science
- Cell Biology