Effects Of Light,Nitrogen And Their Interaction On Chlorophyll Biosynthesis In Rice

Chlorophyll is an essential material basis for photosynthesis in plants,which is widly present in photosynthetic organisms.Light and nitrogen affect the chlorophyll biosynthesis process.Previous studies of our research group found that the interaction of light and nitrogen affects the content of chlorophyll.This study aims to explore the impact of light and nitrogen interaction on the biosynthesis process of chlorophyll as a starting point.A two-factor split zone experimental design was adopted.The main factor is light intensity,which is the full process shading treatment（L1）,full process natural light treatment（L2）,and full process illumination treatment（L3）.The secondary factor nitrogen application rates are 100 kg hm^-2（N1）,150 kg hm^-2（N2）,and 250 kg hm^-2（N3）.The effects of different light intensities,nitrogen application rates,and their interactions on chlorophyll content,precursor substance content of chlorophyll synthesis,key enzyme levels of chlorophyll synthesis pathway,key gene expression of chlorophyll synthesis pathway,net photosynthetic rate（Pn）,aboveground dry matter,and nitrogen content in rice leaves were studied.The main research results are as follows:1.With the increase of light,the chlorophyll content of rice leaves increased first and then decreased.Under low light（L1）,chlorophyll content decreased with the increase of nitrogen application rate.Under natural light（L2）and strong light（L3）,chlorophyll content increased with the increase of nitrogen application.The light-nitrogen interaction regulates the chlorophyll precursor substances PBG,Upg III,Coprogn III,PP IX,Mg-pp IX and Pchlide content regulates the synthesis of chlorophyll.At tillering stage,chlorophyll content decreased with the increase of light.Under L1,chlorophyll content decreased with the increase of nitrogen application rate.Under L2 and L3,chlorophyll content increased with the increase of nitrogen application.Photonitrogen interaction regulates chlorophyll synthesis by regulating the contents of chlorophyll precursor substances ALA,PBG,Coprogn III,PP IX,and Mg-pp IX.At jointing stage,with the enhancement of light,chlorophyll content under low nitrogen level had no significant difference.Under constant nitrogen application,chlorophyll content decreased first and then increased.Under high nitrogen,chlorophyll content decreased.With the increase of nitrogen application rate,the chlorophyll content increased under weak light and natural light,and increased first and then decreased under strong light.The light-nitrogen interaction regulated the chlorophyll synthesis by regulating the contents of ALA,Coprogn III,PP IX and Mg-pp IX in rice leaves.2.Light and nitrogen application significantly interacted with glutamyl-t RNA reductase（Glu TR）level.At seedling stage and tillering stage,nitrogen application under low light was more beneficial to increase Glu TR level.The highest Glu TR enzyme level was observed under L1N3 treatment.At the joining stage,shading or strong light treatment can reduce Glu TR level of rice,L2N3 treatment Glu TR level is the highest.There was no interaction between light and nitrogen application on the level of prochlorophyllin ester oxidoreductase（POR）at seedling stage,and the level of POR increased with the increase of light.The level of POR enzyme increased with the increase of nitrogen application rate.At tillering stage and jointing stage,the interaction effect of light and nitrogen application on POR enzyme level was significant.At tillering stage,the highest POR enzyme level was found in L1N3treatment.At jointing stage,POR enzyme level was the highest in L2N3 treatment.In conclusion,the Glu TR and POR levels of rice leaves can be increased effectively under different light conditions.3.Light and nitrogen application significantly interacted with the expression levels of Os HEMA,Os HEMD,Os CHLD and Os PORA genes in rice leaves at tillering stage and joint stage.In tillering stage,low light significantly up-regulated the expression of each gene,and the expression of each gene was the highest under L1N3treatment.In the jointing stage,the expression of each gene was the highest under natural light and L2N3 treatment.4.In tillering stage and jointing stage,the Pn of rice leaves increased with the increase of light.Under low light treatment,rice leaf Pn decreased with the increase of nitrogen application rate,while under natural light and strong light treatment,rice leaf Pn increased with the increase of nitrogen application rate.5.In tillering stage and jointing stage,with the increase of nitrogen application rate,the biomass of rice stem and leaf increased,the nitrogen content of rice stem increased,and the nitrogen content of rice leaf showed an increasing trend.The increase of nitrogen application increased the nitrogen absorption of rice and promoted the growth of rice stem and leaf.In summary,light,nitrogen,and their interactions regulate the synthesis of rice chlorophyll by affecting the content of chlorophyll precursor substances Coprogen III,PP IX,Mg-pp IX in rice leaves,the level of key enzymes in the chlorophyll synthesis pathway,Glu TR enzyme,and the expression of Os HEMA,Os HEMD,Os CHLD,and Os PORA.Under low light,increasing nitrogen fertilizer inhibited the accumulation of chlorophyll in rice and limited the photosynthetic rate.Under strong light,increased nitrogen fertilizer was conducive to the chlorophyll biosynthesis and the improvement of photosynthetic rate of rice,and thus increased the biomass and nitrogen content of rice stem and leaf.