Thylakoid Membrane Proteomics In Hybrid Rice Under Drought Stress

This study explored photosynthetic performance of the high-yield hybrid rice Liangyoupeijiu during senescence stage under drought condition,focusing on variation of thylakoid membrane chlorophyll-protein complex in flag leaf chloroplast.We monitored and analyzed the content and activity of key enzyme in light reaction and carbon assimilation.We attempted to discuss the mechanism of the distribution of excitation energy in two photosystems caused by reorganization of thylakoid membrane proteins,including coordination between light energy conversion and carbon assimilationin rice,and to evaluate the intrinsic character of flag leaf senescence.The project evaluates the intrinsic character of light energy conversion and photo damage under drought stress,paying particular attention to light use efficiency and crop yield,which offer a glimpse into the dynamic behavior of photosynthetic machinery in nature.The results showed:(1)In the condition of prolonged drought stress during the reproductive stage,we addressed the photosynthetic performance in flag leaves of the high-yield hybrid rice(Oryza sativa.L)LYPJ.The chlorophyll a fluorescence transient dynamics analysis indicated a timely and constant responsive pattern involving in both PSI and PS?.For PS? functionality,uncoupling of oxygen evolving complex at the donor side and inhibition of electron transport from QA to QB at the accepter side were both accounted for the decrease of quantum yield of primary photochemistry at early stage(before 21d after the onset of drought stress).Likewise,increased size of functional antenna may be primarily responsible for early reaction centers inactivation in drought stressed plants,but transformation to non-QA-reducing centers for the later.The consequent redundant excitation energy was predominantly eliminated by enhanced thermal dissipation but not the electron transport due to inhibition of intersystem electron transport.Advanced accumulation of drought stress(from 21d to 35d)showed preferential impact on the donor side of PSII and significant loss of RC/CS0 was induced during this period.In brief,up-regulation of thermal dissipation and possible cyclic electron transport,as well as down-regulation of activated reaction centers and linear electron transport was crucial for rebalance the energy distribution between the two photosystems from deviant stoichiometry resulting from the uncoupling of oxygen evolving complex.(2)In order to protect the photosynthetic apparatus of excess light energy damageunder drought stress,LYPJ employed the LHCII complex for heat dissipation,and reducing the number of PSII reaction center to relieve the damage of photosynthetic apparatus for excess light energy.Studies have shown that OEC complex terminally sensitive to drought stress which refrained is the PSII electron transfer.In addition,ATP synthase enhanced by the translation level in order to compensated metabolic countermeasures of response to drought stress.PSII core protein D1?D2?CP43 protein phosphorylation appeared in the special band,played an important role in PSII the stability and maintenance of a dimmer structure.Dissociation and phosphorylation of LHCII from the PSII to form PSI-LHCII super complex was observed.We supposed that thylakoid membranes translate the "state 1" to "state 2",processed light energy to the PSI.The formation of PSI-LHCII super complex in two light systems played an important role in energy distribution.(3)In dark reaction enzymes activities analyses,it was observed that a little increment of C4 photosynthetic enzymes activities(PEPC,NADP-ME)under drought stress to part of the dynamic compensation for Rubisco activity decline and degradation of the adverse effects on the photosynthesis in advance,and confirmed by Western-Blot analysis.SOD enzyme activity presented a downward trend,and POD enzyme and CAT enzyme activity increased under drought stress.In addition,total phenol compounds significantly increased under drought condition,played role in the cells of hydrophobic stabilizers and the light of the photosynthetic apparatus protectant,prevented water loss in the mesophyll cytoplasm.The accumulation of H2O2 and O2-·in photosynthetic pathway was increased under drought condition.The proportion of the unsaturated fatty acid was decreased in LYPJ under drought condition.(4)Hybrid rice has the inferiority of foliar early senescence during reproductive stage.Early senescence of leaves induced by drought causes a constraint on crop productivity.Hence,to better understand traits of drought responsive mechanism in hybrid rice leaves during reproductive stage,we conducted 2-D electrophoresis to investigate proteomic profile of rice leaves to the onset of drought stress.Forty-three out of 114 proteins whose abundance showed significant changes in sliver stained gels were identified by MS/MS at flowering stage and 54 out of 115 at milk stage.For flowering stage,obstructed cell wall structure,impaired subcellular function,especially CO2 assimilation and ATP synthesis in chloroplast,and abnormal floral development could be postulated from differentially expressed proteins.Additionally,higher levels of defense relative proteins in drought-stressed leaves suggested active ROS scavenging system for oxidative load.For milk stage,photosynthetic phosphorylation and oxidative phosphorylation were restricted and thus might cause ATP starvation.Suppressed translation machine and disrupted oxidative defense and proteolysis system indicated premature cell death.Hormone brassinosteroid and jasmonate,along with glyoxalase might be candidates for drought tolerance during reproductive stage.In conclusion,drought stress during reproductive stage impacted a lot on biological processes in rice leaves at protein level,leading to abnormal foliar function.