| Alternative respiratory pathway(cyanide-resistant respiration pathway)is an important electron transfer pathway of plant mitochondria in addition to cytochrome pathway.It is widely present in higher plants,algae and protists.But to date,the function and signaling pathway of alternative respiration pathway's regulation of plant photosynthesis and respiration haven't got clear conclusion despite that it is a collaborative node of the two major metabolic activities,and the theoretical study of cyanide-resistant respiration pathway will be of great significance in understanding plant light growth and development process of photosynthesis and respiration coordination mechanism.We explored the mechanism of the alternative pathway under light development by monitoring the changes of alternative respiratory pathway operation rate and AOX expression level during development of Arabidopsis seedlings under different light conditions.During the process of greening,the synthesis of chlorophyll increased with the increase of light intensities,and light stress prevented chlorophyll's re-synthesis,and different photoperiod significantly affected the accumulation of chlorophyll:the chlorophyll contents of Col?E-14 and AS-12 under normal photoperiod respectively were 0.69 mg/g?0.53 mg/g and 0.64 mg/g,but under continous illumination,the chlorophyll contents of Col?E-14 went up respectively to 2.0 mg/g and 1.2 mg/g;Illumination stimulated the increasing of alternative respiration capacity and the gene expression of aox1a and aox1c.The rising of alternative respiration capacity may play a role in chlorophyll synthesis and chloroplasts proliferation and development.In addition,the photoperiod significantly affected respiration capacity of the plant.These results alltogether suggested that the physiological significance of alternative pathway in plant greening would be auxiliary to chloroplast biogenesis.Under light stress,the inhibition of alternative pathway by SHAM caused a disorder and disintegration of chloroplast structure,suggesting that the operation of alternative pathway contributed to the maintainence of chloroplast structure.After high light stress,the chloroplast structures of AOX overexpression(XX-1 and E-14)were relatively stable,while the AOX deficient AS-12 strains was severely damaged which means that the inhibition of cytochrome pathway and alternative pathway affected the integrity of the chloroplast structure under light stress,and the alternative pathway alleviated,to some extent,the damage of chloroplast structure caused by light stress.Thus,the alternative respiratory pathway plays an important role in plant's resistance to light stress and chloroplast structure protection.Through study photosynthesis and chlorophyll fluorescence of several mutant Arabidopsis strains of different AOX expression level under different light sress,it found that,the maximal quantum yield of PS II(Fv/Fm)?actual photochemical efficiency of PS II in the light(Yield)and photochemical quenching(qP)all decreased under high light stess,while the non-photochemical quenching(qN)increased significantly,indicating that light suppression increased the dissipation of the Ps ? non-radiative energy.Under light stress,the respiration of AOX deficient mutant AS-12 was significantly lower than that of the wild-type and AOX overexpression mutant E-14.With the increase of light intensity,the rate of photosynthesis,the total respiration and alternative respiration were all enhanced to 12 ?mol CO2m-2s-1?0.82 ?mol O2g-1FWmin-1 and 0.13 ?mol O2g-1FWmin-1 respectively;The proportion of cyanide-resistant respiration in total respiration increased along with the increase of photosynthesis rate,from 11%to 15%.These studies showed that alternative pathway probably had physiological significance in stimulating mitochondrial protein synthesis under light stress. |
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