Igamberdiev AU, Zhou GQ, Malmberg G, Gardestrom P
Respiration of barley protoplasts before and after illumination
Physiologia Plantarum: 1997 99:15-22
Respiratory O-2 consumption was investigated in dark-adapted barley (Hordeum vulgare L. cv. Gunilla) protoplasts and after illumination for 10 min at high and very low CO2 in the presence of respiratory and photorespiratory inhibitors. In dark-adapted protoplasts no difference was observed between inhibitor treatments in high and very low CO2. The respiratory rate increased somewhat after illumination and a difference in responce to inhibitors was in some cases observed between high and very low CO2. Thus, the operation of the mitochondrial electron transport chain is affected following a period of active photosynthesis. In all situations tested, oligomycin inhibited respiratiory O-2 uptake indicating that respiration of mitochondria in protoplasts is not strictly ADP limited. Antimycin A inhibited respiration more in dark-adapted protoplasts than after illumination whereas SHAM gave the opposite response. Rotenone inhibited respiration both in dark adapted protoplasts (about 30%) and after illumination where the inhibition was much greater in very low CO2 (50%) than in high CO2 (10%). After iilumination in very low CO2, SHAM + rotenone inhibited respiration almost completely (70%). Photorespiratory inhibitors had very small effect on O-2 consumption in darkness. After illumination the effect of aminoacetonitrile (AAN) was also very low whereas a-hydroxypyridine-2-methane sulphonate (HPMS) in photorespiratory conditions inhibited O-2 uptake much stronger (35%). The addition of glyoxylate enhanced respiration in the presence of HPMS up to the control level suggesting that alternative pathways of glyoxylate conversion might be operating. The differences in inhibitor responses may reflect fine mechanisms for the regulation of energetic balance in the plant cell which consists of switching from electron transport coupled to ATP production to non-coupled transport. Photorespiratory flux is also very flexible, and the suppression of glycine decarboxylation can induce bypass reactions of glyoxylate metabolism.
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