Biochemical And Molecular Response Of Maize To Elevated CO₂

Climate change,mainly the greenhouse effect,not only worries government representatives and organizations but also attracts the attention of the scientific community in different contexts.The rising concentration of atmospheric CO₂ is known to increase the total aboveground biomass of several C3（C3photosynthesis）crops,whereas C4（C4 photosynthesis）crops are reported to be hardly affected.As a C4plant,maize is a major crop used as food and feed globally,however,insufficient information is available on how atmospheric CO₂ affects the growth and development of maize regarding feeding around the globe.Therefore,it is an immense need to understand the response of maize against future climate change and to observe whether elevated CO₂effect nutritional efficiency.The current study was designed to investigate the genotypic variations for morphological,physiological,agronomic,and biochemical traits in contrasting maize inbred lines and mutant under various CO₂ conditions.Meanwhile,several experimental approaches were conducted to analyze the nutritional and feeding quality of maize in response to future climate scenarios taking into account elevated CO₂ as environmental stress.Additionally,we also studied the possible variations at the transcription level for lignin alterations in maize inbred line and mutant.The main results obtained are summarized as follows:It was observed that 600 ppm CO₂ treatment enhanced the growth characteristics of maize inbred line B73,e.g.,plant height leaf area and aboveground biomass,and primary and secondary metabolites contents,which was,however,decreased upon treatment with 1800 ppm of CO_2.Moreover,the sugar contents in leaves were higher compared to the stem and the starch contents were higher in both the leaf and stem than soluble sugar.In addition,the total nonstructural carbohydrates contents were higher in the leaf compared to the stem.Folate derivates and total folates,soluble protein,chlorophyll,and Malondialdehyde（MDA）contents were significantly decreased at all the treatments from early growth till maturity.it was observed from the results that the lignin contents of leaf and stem at 40 DAS were higher at all the treatments of CO₂and later at 70 and 90 DAS,it was increased at 600 ppm and decreased at 1800 ppm.The guaiacyl（G）and syringyl（S）lignin were significantly decreased at all the growth stages at every respective treatment of elevated CO₂.On the other hand,the plant height of the inbred line C01（wild type）and its mutant（an EMS mutation that could accumulate 5-Methyl tetrahydrofolate）,were significantly affected by the elevated CO₂.However,there was no difference between the plant height of wild type and mutant.At 40 DAS,the biomass of wild type and mutant decreased at 1800 ppm.On the contrary,at 70 and 90 DAS,the biomass of wild and mutant increased at an elevated CO₂.Additionally,the wild type accumulated more biomass than the mutant.The sugar and starch contents were significantly increased at 600 ppm and decreased at1800 ppm in both.Considerable variation exists in the contents of folate at elevated CO₂between the wild type and the mutant.The contents of 5MTHF and total folate in the mutant were significantly increased compared to the wild type;however,both of them decreased at the maturity of plants.Furthermore,alteration in 5MTHF changes the content of S-adenosylmethionine（SAM）in both wild-type and mutant,the methyl group donor involved in the biosynthesis of G and S lignin that affects the downstream lignification.It was observed from the results that in both wild-type and mutant,lignin contents were higher at 600 ppm and decreased at 1800 ppm.The lignin monomers were comparatively higher in the wild type than the mutant at 40 DAS.In wild type and mutant,the G and S lignin were higher at 600 ppm and decreased at 1800 ppm.At 90 DAS,the elevated CO₂ significantly increased the lignin monomers in the wild type and the mutant.Additionally,the transcript abundance of key genes involved in lignin metabolism had an altered response against elevated CO₂.It was concluded that the production of primary metabolites（sugar and starch）in maize seedlings is sensitive to CO₂ enrichment that may influence and regulate the production efficiency of lignin to a certain level.Furthermore,elevated CO₂ may play an important role in folate and C1 metabolism that ultimately affect lignin accumulation in maize leaves and stems.The current study will offer new evidence to understand the future scenario of climate change and its effects on maize metabolism and the regulation mechanism of lignin biosynthesis under elevated CO₂in the future.