Effects of Elevated Root-Zone CO2 on Root Morphology and Nitrogen Metabolism Revealed by Physiological and Transcriptome Analysis in Oriental Melon Seedling Roots.

Xinyu Chen,Zepeng Yin,Wanxin Wang,Tianlai Li,Yang Yin,Yiling Liu,Chuanqiang Xu

doi:10.3390/ijms21030803

Abstract

Rhizosphere CO2 is vital for crop growth, development, and productivity. However, the mechanisms of plants’ responses to root-zone CO2 are unclear. Oriental melons are sensitive to root-zone gas, often encountering high root-zone CO2 during cultivation. We investigated root growth and nitrogen metabolism in oriental melons under T1 (0.5%) and T2 (1.0%) root-zone CO2 concentrations using physiology and comparative transcriptome analysis. T1 and T2 increased root vigor and the nitrogen content in the short term. With increased treatment time and CO2 concentration, root inhibition increased, characterized by decreased root absorption, incomplete root cell structure, accelerated starch accumulation and hydrolysis, and cell aging. We identified 1280 and 1042 differentially expressed genes from T1 and T2, respectively, compared with 0.037% CO2-grown plants. Among them, 683 co-expressed genes are involved in stress resistance and nitrogen metabolism (enhanced phenylpropanoid biosynthesis, hormone signal transduction, glutathione metabolism, and starch and sucrose metabolism). Nitrogen metabolism gene expression, enzyme activity, and nitrogen content analyses showed that short-term elevated root-zone CO2 mainly regulated plant nitrogen metabolism post-transcriptionally, and directly inhibited it transcriptionally in the long term. These findings provided a basis for further investigation of nitrogen regulation by candidate genes in oriental melons under elevated root-zone CO2.

Highlights

IntroductionThe CO2 concentration changes continuously with different soil aeration conditions, which has a great impact on the growth, development, and yield of crops
For plants to grow normally, a good rhizosphere gas environment is required
Root morphology analysis (Figure 1; Table 1) showed that plants grown under elevated root-zone CO2 treatment had longer roots, a greater number of total root tips, and a larger root surface area at 3 day of treatment compared with those under ambient CO2 concentrations, the resistance against elevated root-zone CO2 began to decline on the sixth day of treatment

Summary

Introduction

The CO2 concentration changes continuously with different soil aeration conditions, which has a great impact on the growth, development, and yield of crops. The CO2 concentration in the soil close to the plant root system often reaches values up to ten-fold that of the ambient atmosphere [1,2,3]. Root and soil microorganisms produce CO2 through respiration, which accumulates in the root zone at concentrations normally between 0.2% and 0.5%, but can reach 20% under special circumstances [4]. Responses to high CO2 soil environment have received increased attention recently in several crop species [5,6,7,8]. Little information is available regarding the molecular mechanisms of plants in response to elevated root-zone CO2 conditions, especially at the transcriptome level

Methods

Results

Discussion

Conclusion