Leaf respiration during early plastidogenesis in light-grown barley seedlings

Oxygen fluxes of protoplasts from different developmental regions of light‐grown (16 h day/8 h dark) barley (Hordeum vulgare L. cv. Patty) seedlings were studied using oxygen electrodes as well as with a more sensitive technique of oxygen exchange measurement, Cartesian‐diver microrespirometry. A pronounced increase in dark respiration of protoplasts from the region close to the intercalary meristem was observed, especially below the amyloplast region. In the dark this region also displayed the greatest activity of the alternative (cyanide‐insensitive) mitochondrial electron‐flow pathway, possibly due to high intracellular sugar levels and suitable cytosolic energy charge engaging the pathway. Etiolated protoplasts from similar regions of dark‐grown barley seedlings close to the intercalary meristem displayed a reduced dark respiratory rate which suggests that mitochondrial participation prior to normal plastid development is a partially light‐initiated process, probably acting through the agency of phytochrome and a blue light receptor. These results demonstrate that in normal light‐grown seedlings, just as in algal and etiolated greening systems, mitochondrial participation is vital for the very early stages of plastid development and may be controlled at least partly through phytochrome action as well as a blue light receptor. Copyright © 1986, Wiley Blackwell. All rights reserved