The growth and development of plants are dependent on the interaction between carbon and nitrogen metabolism. Essential information about the metabolic regulation of carbon−nitrogen metabolism is still lacking, such as possible interactions among nitrogen metabolism, photosynthesis, and photorespiration. This study shows that higher photorespiration consumes more CO 2 fixed by photosynthesis, making the high photosynthetic efficiency mutant fail to increase production. In order to clarify the effects of photosynthesis and photorespiration on carbon and nitrogen metabolism in high photosynthetic efficiency mutant, a yellow-green leaf mutant (ygl53) was isolated from rice (Oryza sativa L.). Its chlorophyll (Chl) content decreased, but chloroplast development was not affected. Genetic analysis demonstrated that YGL53 encodes the magnesium chelatase D subunit (ChlD). The ygl53 mutant showed an increased net assimilation rate (An) and electron transport flux efficiency and catalase (CAT) activity, and it also had a higher photorespiration rate (Pr), lower H 2 O 2 , and reduced nitrogen uptake efficiency (NUpE); however, there was no loss in yield. The higher activities of glutamate synthase (GOGAT) and glutamine synthetase (GS) ensure the α-ketoglutaric acid (2-OG) and ammonia (NH 3 ) availabilities, which are produced from photorespiration in the ygl53 mutant. These have an important function for carbon and nitrogen metabolism homeostasis in ygl53. Further analysis indicated that the energy and substances derived from carbon metabolism supplemented nitrogen metabolism in the form of photorespiration to ensure its normal development when the An of photosynthesis was increased in the ygl53 mutant with reduced NUpE.
Rice undergoes leaf senescence accompanied with grain filling when the plants reach the end of their temporal niche, and a delay in leaf senescence ultimately improves the yield and quality of grain. To estimate the decline in photosynthesis during leaf senescence and to find an efficient and useful tool to identify rice genotypes with a longer duration of active photosynthesis, we examined PSII photosynthetic activity in the flag leaves of japonica rice Shennong265 (SN265) and Beigeng3 (BG3) during leaf senescence using chlorophyll a fluorescence kinetics. The results show that inhibition occurred in the electron transport chains, but the energetic connectivity of PSII units was not affected as dramatically during leaf senescence. PSII reaction centres (RCs) were transformed into ‘silent RCs,’ and the chlorophyll content decreased during leaf senescence. However the size of the ‘economic’ antennae increased. Further, the percentage of variation of the specific energy flux parameters can rationally be used to indicate leaf senescence from the perspective of energy balance. Although the performance indices were more sensitive than other functional and structural JIP-test parameters, they still did not serve as an indicator of crop yield.
The stigma exsertion rate (SER) is a complex agronomy phenotype controlled by multiple genes and climate and a key trait affecting the efficiency of hybrid rice seed production. Using a japonica two-line male sterile line (DaS) with a high SER as the donor and a tropical japonica rice (D50) with a low SER as the acceptor to construct a near-isogenic line [NIL (qSE4DaS)]. Populations were segregated into 2,143 individuals of BC3F2 and BC4F2, and the stigma exsertion quantitative trait locus (QTL) qSE4 was determined to be located within 410.4 Kb between markers RM17157 and RM17227 on chromosome 4. Bioinformatic analysis revealed 13 candidate genes in this region. Sequencing and haplotype analysis indicated that the promoter region of LOC_Os04g43910 (ARF10) had a one-base substitution between the two parents. Further Reverse Transcription-Polymerase Chain Reaction (RT-PCR) analysis showed that the expression level of ARF10 in DaS was significantly higher than in D50. After knocking out ARF10 in the DaS background, it was found that the SER of arf10 (the total SER of the arf10-1 and the arf10-2 were 62.54 and 66.68%, respectively) was significantly lower than that of the wild type (the total SER was 80.97%). Transcriptome and hormone assay analysis showed that arf10 had significantly higher auxin synthesis genes and contents than the wild type and the expression of auxin signaling-related genes was significantly different, Similar results were observed for abscisic acid and jasmonic acid. These results indicate that LOC_Os04g43910 is mostly likely the target gene of qSE4, and the study of its gene function is of great significance for understanding the molecular mechanisms of SER and improving the efficiency of hybrid seed production.
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