Photosynthetic Response Of Non-photochemical Quenching To Environmental Factors In Rice Leaf

Non-photochemical quenching?NPQ?harmlessly quenches the excitation of chlorophyll within the light-harvesting antennae of PSII by converting excitation energy into thermal energy.So NPQ can decrease generation of reactive oxygen species and avoid photoinhibition.It is an important photoprotective mechanism in rice.In this paper,near-isogenic lines: Zhefu802,Chl-8,Fgl,with differing in leaf color were used to research photosynthetic response of NPQ in rice leaf to light intensity,nitrogen concentration,drought stress.And futherly explore induction and regulation of NPQ and complex genetic regulation of photosynthesis via transcriptome sequencing.The main results are as follows:1 The net photosynthetic rate of Chl-8 were significantly higher than that of Zhefu802,although the chlorophyll content of Chl-8 was approximately three times lower than Zhefu802.Higher NPQ and energy quenching,as well as lower photoinhibitory quenching?qI?were observed in Chl-8 compared with Zhefu802 under 600 and 1200 ?mol m-2 s-1 treatments.The malondialdehyde and H₂O₂ content and productive rate of O2-in Chl-8 were significantly lower than Zhefu802.Under 1200 ?mol m-2 s-1,the difference observed between the genotypes was even greater.Photodamage of Zhefu802 was much serious than Chl-8.Additionally,no significant differences in stomatal limitation and CO₂ assimilation were observed between the genotypes.These results indicated that when the light intensity was higher than 600 ?mol m-2 s-1,no matter for Chl-8 with pale green leaf or Zhefu802 with dark green leaf,NPQ in leaf was enhance to alleviated photodamage,and futher improved photosynthesis and light acclimatization of leaf.2 Chlorophyll content significantly increased with nitrogen concentration increasing in nutrition solution.The content of chlorophyll in zhefu802 was significantly higher than Fgl,especial for Zhefu802.There was no significant difference on CO₂ assimilation between high nitrogen and moderate nitrogen treatment.Little difference in NPQ of Zhefu802 between high nitrogen and moderate nitrogen treatment was found.The significantly higher malondialdehyde and H₂O₂ content and q I of Zhefu802 under high nitrogen treatment were observed compared with moderate nitrogen treatment.These results indicated that excessive light energy derived from high chlorophyll content was not efficiently dissipated in the leaf of Zhefu802 under high nitrogen treatment,and serious oxidative stress might exist in Zhefu802.NPQ of two varieties under low nitrogen treatment were significantly enhanced,compared with moderate nitrogen treatment.Higher zeaxanthin content contributed to induction of NPQ.This phenomenon might be the response of rice photosynthesis to deficience in nitrogen.3 ABA application obviously alleviated suppression of dought stress to photosynthesis,and significantly enhanced NPQ in Zhefu802 and Fgl under drought condition.Increase of NPQ might be the reason that ABA enhance drought resistant of rice.Degree of leaf rolled and decrease of photosynthesis resulted from drought in Fgl were significantly lower than Zhefu802,Suggestting Fgl possessed greater drought resistance.The difference in methyl jasmonate,indole-3-acetic acid and less chlorophyll content might be responsible for the drought resistance of Fgl.4 Less and thiner stacking in chloroplast of Chl-8 was not favor to associated with light harvest complexes,which was closely related with pale-green leaf color in Chl-8.Both zeaxanthin content and the expression of PsbS1 were involved in NPQ induction under 600 ?mol m-2 s-1,while only zeaxanthin content involved in the induction of NPQ under 1200 ?mol m-2 s-1.The difference in indole-3-acetic acid,gibberellin,ABA content in leaf might be related with acclimation of rice photosynthesis and NPQ induction under both light treatments.5 Photosynthesis was controlled by complex different expression genes.In addition to different expression genes directly involved in photosynthesis,other pathways,such as the response to oxidative stress,energy metabolism and nitrate metabolism,co-regulated photosynthetic efficiency in rice.Different expression genes in signal transduction supported the regulation.The different expression genes classified to a functional group named chloroplast?GO: 0009507?were genetic basis of difference on chloroplast ultra-structure.In summary,when light intensity is higher than 600 ?mol m-2 s-1,NPQ and less chlorophyll content can decrease excessive light energy in photosystem and superoxide in leaf,further improve photosynthesis and light acclimatization of leaf.Except for high light,another environment factors also impact the balance between light absorption and utilization.Excessive light energy derived from high chlorophyll content is not efficiently dissipated in leaves under high nitrogen treatment,and serious oxidative stress may exist in leaves.Enhance of NPQ is favor to decrease excessive light energy in photosystem,which may be an adaptable response to deficiency in nigtrogen in rice.Under drought stress,increase of NPQ may be the reason that ABA enhance drought resistant of rice.