P. 1997. Respiration of barley protoplasts before and after illumination. -Physiol. Plant. 99: 15-22.Respiratory Oi consumption was investigated in dark-adapted barley {Hordeum vulgare L. cv. Gunilla) protoplasts and after illumination for 10 min at high and very low COi in the presence of respiratory and photorespiratory inhibitors. In dark-adapted protoplasts no difference was observed between inhibitor treatments in high and very low CO,. The respiratory rate increased somewhat after illumination and a difference in responce to inhibitors was in some cases observed between high and very low CO,. Thus, the operation of the mitochondrial electron transport chain is affected following a period of active photosynthesis. In all situations tested, oligomycin inhibited respiratiory Ol 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 CO, (50%) than in high CO2 (10%). After illumination in very low COi, SHAM + rotenone inhibited respiration almost completely (70%). Photorespiratory inhibitors had very small effect on O2 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, uptake much stronger (359f). 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 fme 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.A'ev words -Barley, glycolate pathway. Hordeum vulgare, light-enhanced dark respiration (LEDR), mitochondrial electron transport, protoplasts, respiratory inhibitors.A. U. Igamberdiev (permaneni address:

We investigated the differential expression of AOX1 multi-gene family and the regulation of alternative respiratory pathway during initial greening development in leaves of rice (Oryza sativa L.) seedlings. After exposing the darkgrown rice seedlings to continuous irradiation, total respiration (V t ), capacity of alternative pathway (V alt ), and their ratio (V alt /V t ) increased with the greening of leaves. In this process, AOX1c transcript increased under constant irradiation, while AOX1a and AOX1b transcripts were hardly detected. Thus AOX1c in rice presents a similar expression pattern as AOX2 does in many dicotyledonous species during greening development. Compared with the rapid increase of cyanideresistant respiration in the presence of photon energy, CO 2 fixation was not observed until 8 h after the onset of irradiation. The AOX inhibitor salicylhydroxamic acid (SHAM; 1 mM) inhibited 67.3 % of cyanide-insensitive oxygen uptake in dark-grown leaves and 69.4 % of it in leaves grown under irradiation. Dark-grown plants pre-treated with SHAM were then irradiated for 12 h. SHAM did not obviously modify photosynthetic CO 2 fixation rate on a chlorophyll (Chl) content basis in both leaves and simultaneously isolated chloroplasts. Hence during initial greening steps of the plants, the induction of alternative pathway and AOX1 expression by irradiation is not directly linked with carbon assimilation of photosynthesis. The application of SHAM partially limited Chl production in rapidly greening leaves, indicating that Chl synthesis in the process of greening might be medicated to some extent by alternative respiratory pathway.

Respiratory O2 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 O2 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 illumination in very low CO2. SHAM + rotenone inhibited respiration almost completely (70%). Photorespiratory inhibitors had very small effect on O2 consumption in darkness. After illumination the effect of aminoacetonitrile (AAN) was also very low whereas α‐hydroxypyridine‐2‐methane sulphonate (HPMS) in photorespiratory conditions inhibited O2 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.