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A few enlarged chloroplasts are less efficient in photosynthesis than a large population of small chloroplasts in Arabidopsis thaliana.

ABSTRACT: The photosynthetic, biochemical, and anatomical traits of accumulation and replication of chloroplasts (arc) mutants of Arabidopsis thaliana were investigated to study the effects of chloroplast size and number on photosynthesis. Chloroplasts were found to be significantly larger, and the chloroplast surface area exposed to intercellular air spaces (S c) significantly lower in the mutants than in their wild-types. The decreased S c and increase cytoplasm thickness in the mutants resulted in a lower mesophyll conductance (g m) and a consequently lower chloroplast CO2 concentration (C c). There were no significant differences between the mutants and their wild-types in maximal carboxylation rate (V cmax), maximal electron transport (J cmax), and leaf soluble proteins. Leaf nitrogen (N) and Rubisco content were similar in both Wassilewskija (Ws) wild-type (Ws-WT) and the Ws mutant (arc 8), whereas they were slightly higher in Columbia (Col) wild-type (Col-WT) than the Col mutant (arc 12). The photosynthetic rate (A) and photosynthetic N use efficiency (PNUE) were significantly lower in the mutants than their wild-types. The mutants showed similar A/C c responses as their wild-type counterparts, but A at given C c was higher in Col and its mutant than in Ws and its mutant. From these results, we conclude that decreases in g m and C c are crucial to the reduction in A in arc mutants.

SUBMITTER: Xiong D

PROVIDER: S-EPMC5515944 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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A few enlarged chloroplasts are less efficient in photosynthesis than a large population of small chloroplasts in Arabidopsis thaliana.

Xiong Dongliang D Huang Jianliang J Peng Shaobing S Li Yong Y

Scientific reports 20170718 1

The photosynthetic, biochemical, and anatomical traits of accumulation and replication of chloroplasts (arc) mutants of Arabidopsis thaliana were investigated to study the effects of chloroplast size and number on photosynthesis. Chloroplasts were found to be significantly larger, and the chloroplast surface area exposed to intercellular air spaces (S <sub>c</sub>) significantly lower in the mutants than in their wild-types. The decreased S <sub>c</sub> and increase cytoplasm thickness in the mu ...[more]

PMID: 28720786

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Project description:An improvement in photosynthetic rate promotes the growth of crop plants. The sink-regulation of photosynthesis is crucial in optimizing nitrogen fixation and integrating it with carbon balance. Studies on these processes are essential in understanding growth inhibition in plants with ammonium ( NH4+ ) syndrome. Hence, we sought to investigate the effects of using nitrogen sources with different states of reduction (during assimilation of NO3- versus NH4+ ) on the photosynthetic performance of Arabidopsis thaliana. Our results demonstrated that photosynthetic functioning during long-term NH4+ nutrition was not disturbed and that no indication of photoinhibition of PSII was detected, revealing the robustness of the photosynthetic apparatus during stressful conditions. Based on our findings, we propose multiple strategies to sustain photosynthetic activity during limited reductant utilization for NH4+ assimilation. One mechanism to prevent chloroplast electron transport chain overreduction during NH4+ nutrition is for cyclic electron flow together with plastid terminal oxidase activity. Moreover, redox state in chloroplasts was optimized by a dedicated type II NAD(P)H dehydrogenase. In order to reduce the amount of energy that reaches the photosynthetic reaction centers and to facilitate photosynthetic protection during NH4+ nutrition, non-photochemical quenching (NPQ) and ample xanthophyll cycle pigments efficiently dissipate excess excitation. Additionally, high redox load may be dissipated in other metabolic reactions outside of chloroplasts due to the direct export of nucleotides through the malate/oxaloacetate valve. Mitochondrial alternative pathways can downstream support the overreduction of chloroplasts. This mechanism correlated with the improved growth of A. thaliana with the overexpression of the alternative oxidase 1a (AOX1a) during NH4+ nutrition. Most remarkably, our findings demonstrated the capacity of chloroplasts to tolerate NH4+ syndrome instead of providing redox poise to the cells.

Dataset Information

A few enlarged chloroplasts are less efficient in photosynthesis than a large population of small chloroplasts in Arabidopsis thaliana.

Publications

A few enlarged chloroplasts are less efficient in photosynthesis than a large population of small chloroplasts in Arabidopsis thaliana.

Similar Datasets

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