| Pepper?Capsicum annuum L.?is one of the main vegetable species in facilities in China.Due to the abnormal global climate change,haze,and extreme low-temperature weather frequently occurred during the recent years,the off-season production of pepper severely suffered low-temperature and low-light stress.Previous studies have shown that the total carotenoid content is closely related to the low temperature and low light resistance of pepper.To further clarify that which specific carotenoid components play a decisive role,we simulates low temperature and low light conditions in artificial climate chambers(15°C/5°C,100?molm-2 s-1),and studied the changes of physiological and biochemical changes in response to low temperature and light stress,and focused on growth,photosynthetic characteristics,and carotenoid compositions in 12 different genotype pepper seedlings,futher studied the carotenoid components mediate the regulation mechanism of low temperature and low light stress in depth from the transcriptome level,which provide theoretical basis for the cultivation of special pepper varieties for facilities that are resistant to low temperature and low light.1.12 pepper seedlings with different genotypes were dehydrated,curled up,yellowed,browned,and even dried and died after 20 days under 5?and darkness.Some seedling stem cadres appeared different degrees of lodging phenomenon,even from the base of stem lodging.The chilling index from small to large followed by Xiangtela No.2?11#?>Longjiao No.5?2#?>Haifeng No.12?9#?>Hangjiao No.8?6#?>13-3?7#?>Haifeng No.23?10#?>37-94?8#?>Hangjiao No.5?5#?>Longjiao No.2?1#?>Tianshui Line Pepper?12#?>Hangjiao No.2?3#?>Hangjiao No.4?4#?.2.Low temperature and light stress obviously inhibited the growth of plant,which showed the decrease of plant height,the thinner stem rod,the decrease of leaf number,biomass accumulation,chlorophyll a,chlorophyll b,total chlorophyll content and total carotenoid content with the increasing stress time,but the chlorophyll a/b obviously increased.At the same time,the photosynthesis was inhibited and photosynthetic capacity showed a continuous decrease in transpiration rate,stomatal conductance and net photosynthetic rate,especially at 0-5 days of stress,while the concentration of intercellular CO2 significantly increased.The edge of leaf tip was firstly injured,then the part of injury spread slowly to the blade and down to the blade with the increase of time,while the leaf veins,the leaf base and the leaves near the vein were the lightest.Fv/Fm,YII,qP,qL and Fv/Fo decreased to varying degrees,but NPQ and qN increased.Moreover,the photosynthetic reaction was closed and the actual photochemical efficiency obviously decreased,and the quantum yield used for the non photochemical quenching increased;the pepper seedlings all had photoinhibition,the energy Y II used for photosynthesis decreased obviously,while the partial YNPQ used for heat dissipation and the remaining light energy part YNO obvious increased.3.The contents of 10 major carotenoids in pepper leaves were tested,including neoxanthin,violaxanthin,lutein,zeaxanthin,phytoene,?-carotene,?-carotene,antheraxanthin,lutein epoxide,and lycopene.The first six carotenes were the main elements and the contents were all above 10?g/g,accounting for 91.52%-98.24%in 10 kinds of total carotenoid content,among which lutein was the highest content,accounting for 23.56%-68.82%;the latter 4carotenoid contents took up 1.76%-8.48%of the total carotenoid contents,the content of the smallest is the antheraxanthin,accounting for only 0.02%-1.39%.4.The contents of neoxanthin,violaxanthin,lutein,zeaxanthin,phytoene,?-carotene and?-carotene in the leaves of pepper leaves after 15 days'treatment of low temperature and light were negatively correlated with the plant chilling index,but,there was no significant correlation between the antheraxanthin,lutein epoxide,and lycopene and the chilling index.All of them have significant positive correlation with chlorophyll a,total carotenoid,Pn,Fv/Fm,Y II,qP,qL and Fv/Fo,and a significant negative correlation with YNPQ,NPQ and qN,and the comprehensive membership function values of 12 kinds of pepper varieties with low temperature and weak light resistance are calculated by the index which has a significant relationship with the cold damage index,and 12 kinds of resistance to low temperature and light are calculated:11#?0.791?>9#?0.712?>2#?0.695?>6#?0.618?>7#?0.587?>5#?0.523?>8#?0.515?>10#?0.466?>12#?0.333?>1#?0.325?>3#?0.237?>4#?0.202?.Correlation analysis showed that neoxanthin,violaxanthin,lutein,zeaxanthin,phytoene,and?-carotene have significant positive correlation with the comprehensive membership function value,but there is no significant correlation between?-carotene and the comprehensive membership function value.5.After 15 days of low temperature and light condition,we used RNA-seq technique to studied the genes changes in the leaves of‘Hangjiao No.2'?H2,sensitive to low temperature and weak light?and‘Xiangtela No.2'?X2,strong tolerance to low temperature and weak light?CK and LL respectively.The threshold value Padj<0.05 was set as the significant differential expression gene.The 8392 differently expressed genes were obtained in H2,including 4018up expression of 4018 genes and 4374 down-regulated genes;8028 differentially expressed genes were obtained in X2,including 4284 differentially expressed genes and 3744 down regulated genes.The results of GO function annotation are mainly concentrated in 27subclasses and 39 subclasses of the 3 major categories of cell origin,molecular function and biological process.These genes are involved in thylakoid,photosynthetic membrane,photosynthetic system,photosystem I,photosystem II,photosynthesis and so on.The difference genes between‘H2'and‘X2'were annotated to 106 metabolic pathways and 107metabolic pathways in KEGG,which significantly co-enriched in photosynthesis and photosynthetic antenna protein pathway.Low temperature and light could induce the up-regulated expression of CA1 in carotenoid biosynthetic pathway,and down regulated expression of CA2,ZDS,NCED3 and LOC107840293.In conclusion,low temperature and light inhibited the growth of plants,postponed their growth period and decreased the photosynthetic capacity.The carotenoid components showed a trend of first rised and then decreased.Neoxanthin,violaxanthin,lutein,zeaxanthin,phytoene,and?-carotene in the plant maintained high contents in the plant could improve plant resistance to low temperature and light stress,which can be used as an important indicator for identifying low temperature and weak light of pepper seedlings.The differential expression genes of carotenoids,ZDS,CA1,CA2,NCED3 and LOC107840293,may be the key genes of carotenoid after low temperature and light stress. |
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