Effects Of Low Light Intensity On Photosynthetic Physiology And Gene Expression Of Potato During Tuberization Period In Potato

Potato?Solanum tuberosum L.?is one of the important food crops in the southwest mountainous area of China,and it is also one of the pillar industries in poverty alleviation.It plays an important strategic role in ensuring food security and winning the war of poverty alleviation.Interplanting between potato and corn is the main mode of cultivation in Southwest China.The yield and quality of potato are affected by maize shading during the period of potato production,which hinders the sustainable development of potato industry.It is of great significance to study the response mechanism of weak light to plant physiology,biochemistry and molecular in potato growing stage,and to genetic improvement and cultivation measures of potato tolerance to weak light.In this study,Favorita,which is the widely cultivated variety,was used as the material,the growth conditions?light cycle 12/12h D/h,22/18??and the light intensity(300?mol·m^-2·s^-11 and 100?mol·m^-2·s^-1)were controlled in the artificial climate chamber to study the dynamic changes of photosynthetic physiology,starch sugar metabolism and gene differential expression changes in a photoperiod of potato plants after reducing light intensity.In addition,the dynamic changes of photosynthetic physiology under low light conditions were studied by using the early identified low light resistant variety E Shu 10 and low light sensitive variety Li Shu 6 as materials.The main results are as follows:1.Effects of different Light intensity on photosynthetic Physiology,starch-Sugar Metabolism and Tuber yield and quality of Potato leaves.The contents of chlorophyll a and chlorophyll b in potato leaves increased under low light intensity,and the increase of chlorophyll b was greater than that of chlorophyll a,which led to the decrease of chlorophyll a/b value,which indicated that the plant could improve the ability of capturing weak light and the utilization efficiency of blue-purple light by increasing the relative content of chlorophyll b,which was the adaptive response to the decrease of light intensity.The carotene content increased,which enhanced the antioxidant function of Potato leaves.The changes of these photosynthetic pigments may be an adaptive response to the decrease of light intensity.In addition,reducing the light intensity changes the photosynthesis parameters and chlorophyll fluorescence parameters:The Pn,Tr,and Gs all decreased,and Ci increased;Both F₀ and F_m increased,Y???and qP decreased,F_v/F_m did not change significantly,and NPQ increased.The contents of starch and sucrose in leaves decreased significantly under low light intensity,indicating that the reduction of light intensity reduced the synthesis efficiency of sucrose and starch in leaves.Low light intensity treatment reduced potato tuber yield and starch and sucrose content.These results showed that the decrease of light intensity decreased photosynthetic efficiency and reduced the supply of source,And the library is also reduced.2.Effects of different light intensity on gene activity in potato leaves and tubers.Leaves and tubers were sampled every 4 hours in a photoperiod,and the dynamic changes of genes under two kinds of light intensity were analyzed by RNA-seq.The results showed that the decrease of light intensity only affected the activity of 24 genes in tuber and 2208 genes in leaves.The differentially expressed genes in tubers were not involved in starch-sugar metabolism pathway,suggesting that low light treatment did not affect the sink strength of tubers,indicating that the decrease of tuber yield and starch accumulation may be related to insufficient sources or poor circulation of aboveground parts.The quantitative analysis of differential genes in leaves during photoperiod showed that the number of differential genes at the alternating time of light and dark was the most,and the number of differential genes tended to decrease with the passage of time.These results suggest that the decrease of light intensity will affect the activity of plant gene biorhythm.The results of GO enrichment analysis of differential genes show that,Up regulated genes are significantly enriched in biological processes such as oxidation-reduction process,chitin catabolic process,cell recognition,This indicates that the reduction of light intensity causes the defense response of plant cells to increase;Up regulated genes are significantly enriched in Cellular components such as photosystem II,photosystem I,chloroplast;Up regulated genes are significantly enriched in Molecular function such as catalytic activity,phosphorylase activity;This indicates that low light intensity causes a reduction in photosynthesis by reducing the gene activity of photosynthetic structures such as chloroplasts,which reduces the activity of enzymes,resulting in a weakened metabolic process.In addition,the up-and down-regulated differentially expressed genes were mainly enriched at two time points,0 h and 12 h,indicating that the changes in gene activity were positively correlated with the changes in photoperiod rhythm.The results of KEGG enrichment showed that the main pathways of gene enrichment were plant hormone signal transduction,fatty acid biosynthesis and other metabolic pathways,suggesting that these pathways were related to the adaptability after reducing light intensity.The main enrichment pathways of differential down regulated genes are photosynthesis,carbon fixation in photosynthetic organisms,porphyrin and chlorophyll metabolism,photosynthesis antenna protein,glyoxylate and dicarboxylate metabolism,nitrogen metabolism,carbon metabolism and other metabolic pathways,suggesting that reducing light intensity down regulated the photosynthetic related pathways,nitrogen utilization and carbon utilization and distribution.These changes may reduce the source of the source and change the distribution of the flow,which is the main reason for the decrease of tuber yield and starch accumulation.3.Dynamic changes of photosynthetic physiology of different shade tolerant potatoes under different light intensity.Under the weak light,the Pn,Gs,Tr,Y???and qP of Li Shu 6 and E Shu 10decreased significantly,and the decrease of Li Shu 6 was greater than that of E Shu 10,and the F₀ and F_m of Li Shu 6 and E Shu 10 increased,and the increasing range of Lishu 6 was gradually higher than that of E Shu 10.indicating that low light intensity reduced the photosynthetic capacity of potato,and E Shu 10 Low light intensity is less sensitive than Li Shu 6 and has higher photosynthetic capacity under low light and is more resistant to low light.Conclusion:on the one hand,the reduction of light intensity can down regulate photosynthesis,carbon fixation in photosynthetic organisms,metabolism of porphyrin and chlorophyll,photosynthesis antenna protein and other metabolic pathways,and reduce the deficiency of sources caused by photosynthetic efficiency;on the other hand,it can down regulate metabolism of glyoxylate and dicarboxylate,nitrogen metabolism,carbon metabolism and other pathways,lead to the reduction of nitrogen use and carbon use and distribution,and change the C/N distribution and utilization.The comparison of photosynthetic parameters between the two materials showed,Under low light intensity,the increase of F₀ and F_m of E Shu 10 was lower than that of Li Shu6,while the Pn,Tr,Gs,Y???and qP of E Shu 10 were higher than that of Li Shu 6under low light intensity.It shows that E Shu 10 can make better use of light energy to resist low light stress,the difference of potato genotypes with low light tolerance was the factor to reduce the influence of low light.These results provide a theoretical basis for the genetic improvement of low light tolerance in potatoes.