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Differences on photosynthetic limitations between leaf margins and leaf centers under potassium deficiency for Brassica napus L.

ABSTRACT: Analyzing the proportions of stomatal (SL), mesophyll conductance (MCL) and biochemical limitations (BL) imposed by potassium (K) deficit, and evaluating their relationships to leaf K status will be helpful to understand the mechanism underlying the inhibition of K deficiency on photosynthesis (A). A quantitative limitation analysis of K deficiency on photosynthesis was performed on leaf margins and centers under K deficiency and sufficient K supply treatments of Brassica napus L. Potassium deficiency decreased A, stomatal (gs) and mesophyll conductance (gm) of margins, SL, MCL and BL accounted for 23.9%, 33.0% and 43.1% of the total limitations. While for leaf centers, relatively low limitations occurred. Nonlinear curve fitting analysis indicated that each limiting factor generated at same leaf K status (1.07%). Although MCL was the main component of limitations when A began to fall, BL replaced it at a leaf K concentration below 0.78%. Up-regulated MCL was related to lower surface area of chloroplasts exposed to intercellular airspaces (Sc/S) and larger cytosol diffusion resistance but not the cell wall thickness. Our results highlighted that photosynthetic limitations appear simultaneously under K deficiency and vary with increasing K deficiency intensity.

SUBMITTER: Lu Z

PROVIDER: S-EPMC4763197 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Differences on photosynthetic limitations between leaf margins and leaf centers under potassium deficiency for Brassica napus L.

Lu Zhifeng Z Ren Tao T Pan Yonghui Y Li Xiaokun X Cong Rihuan R Lu Jianwei J

Scientific reports 20160223

Analyzing the proportions of stomatal (SL), mesophyll conductance (MCL) and biochemical limitations (BL) imposed by potassium (K) deficit, and evaluating their relationships to leaf K status will be helpful to understand the mechanism underlying the inhibition of K deficiency on photosynthesis (A). A quantitative limitation analysis of K deficiency on photosynthesis was performed on leaf margins and centers under K deficiency and sufficient K supply treatments of Brassica napus L. Potassium defi ...[more]

PMID: 26902263

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Project description:BackgroundMost studies of photosynthesis in chlorenchymas under potassium (K) deficiency focus exclusively on leaves; however, little information is available on the physiological role of K on reproductive structures, which play a critical role in plant carbon gain. Brassica napus L., a natural organ-succession species, was used to compare the morphological, anatomical and photo-physiological differences between leaves and siliques exposed to K-deficiency.ResultsCompared to leaves, siliques displayed considerably lower CO2 assimilation rates (A) under K-deficient (-K) or sufficient conditions (+K), limited by decreased stomatal conductance (g s), apparent quantum yield (α) and carboxylation efficiency (CE), as well as the ratio of the maximum rate of electron transport (J max) and the maximum rate of ribulose 1,5-bisphosphate (RuBP) carboxylation (V cmax). The estimated J max, V cmax and α of siliques were considerably lower than the theoretical value calculated on the basis of a similar ratio between these parameters and chlorophyll concentration (i.e. J max/Chl, V cmax/Chl and α/Chl) to leaves, of which the gaps between estimated- and theoretical-J max was the largest. In addition, the average ratio of J max to V cmax was 16.1% lower than that of leaves, indicating that the weakened electron transport was insufficient to meet the requirements for carbon assimilation. Siliques contained larger but fewer stoma, tightly packed cross-section with larger cells and fewer intercellular air spaces, fewer and smaller chloroplasts and thin grana lamellae, which might be linked to the reduction in light capture and CO2 diffusion. K-deficiency significantly decreased leaf and silique A under the combination of down-regulated stomatal size and g s, chloroplast number, α, V cmax and J max, while the CO2 diffusion distance between chloroplast and cell wall (D chl-cw) was enhanced. Siliques were more sensitive than leaves to K-starvation, exhibiting smaller reductions in tissue K and parameters such as g s, V cmax, J max and D chl-cw.ConclusionSiliques had substantially smaller A than leaves, which was attributed to less efficient functioning of the photosynthetic apparatus, especially the integrated limitations of biochemical processes (J max and V cmax) and α; however, siliques were slightly less sensitive to K deficiency.

Project description:The aim of this study was to systematically analyze the potential and limitations of using plant functional trait observations from global databases versus in situ data to improve our understanding of vegetation impacts on ecosystem functional properties (EFPs). Using ecosystem photosynthetic capacity as an example, we first provide an objective approach to derive robust EFP estimates from gross primary productivity (GPP) obtained from eddy covariance flux measurements. Second, we investigate the impact of synchronizing EFPs and plant functional traits in time and space to evaluate their relationships, and the extent to which we can benefit from global plant trait databases to explain the variability of ecosystem photosynthetic capacity. Finally, we identify a set of plant functional traits controlling ecosystem photosynthetic capacity at selected sites. Suitable estimates of the ecosystem photosynthetic capacity can be derived from light response curve of GPP responding to radiation (photosynthetically active radiation or absorbed photosynthetically active radiation). Although the effect of climate is minimized in these calculations, the estimates indicate substantial interannual variation of the photosynthetic capacity, even after removing site-years with confounding factors like disturbance such as fire events. The relationships between foliar nitrogen concentration and ecosystem photosynthetic capacity are tighter when both of the measurements are synchronized in space and time. When using multiple plant traits simultaneously as predictors for ecosystem photosynthetic capacity variation, the combination of leaf carbon to nitrogen ratio with leaf phosphorus content explains the variance of ecosystem photosynthetic capacity best (adjusted R2 = 0.55). Overall, this study provides an objective approach to identify links between leaf level traits and canopy level processes and highlights the relevance of the dynamic nature of ecosystems. Synchronizing measurements of eddy covariance fluxes and plant traits in time and space is shown to be highly relevant to better understand the importance of intra- and interspecific trait variation on ecosystem functioning.

Project description:BACKGROUND:Leaf shape development research is important because leaf shapes such as moderate curling can help to improve light energy utilization efficiency. Leaf growth and development includes initiation of the leaf primordia and polar differentiation of the proximal-distal, adaxial-abaxial, and centrolateral axes. Changes in leaf adaxial-abaxial polarity formation, auxin synthesis and signaling pathways, and development of sclerenchyma and cuticle can cause abnormal leaf shapes such as up-curling leaf. Although many genes related to leaf shape development have been reported, the detailed mechanism of leaf development is still unclear. Here, we report an up-curling leaf mutant plant from our Brassica napus germplasm. We studied its inheritance, mapped the up-curling leaf locus BnUC1, built near-isogenic lines for the Bnuc1 mutant, and evaluated the effect of the dominant leaf curl locus on leaf photosynthetic efficiency and agronomic traits. RESULTS:The up-curling trait was controlled by one dominant locus in a progeny population derived from NJAU5734 and Zhongshuang 11 (ZS11). This BnUC1 locus was mapped in an interval of 2732.549?kb on the A05 chromosome of B. napus using Illumina Brassica 60?K Bead Chip Array. To fine map BnUC1, we designed 201 simple sequence repeat (SSR) primers covering the mapping interval. Among them, 16 polymorphic primers that narrowed the mapping interval to 54.8?kb were detected using a BC6F2 family population with 654 individuals. We found six annotated genes in the mapping interval using the B. napus reference genome, including BnaA05g18250D and BnaA05g18290D, which bioinformatics and gene expression analyses predicted may be responsible for leaf up-curling. The up-curling leaf trait had negative effects on the agronomic traits of 30 randomly selected individuals from the BC6F2 population. The near-isogenic line of the up-curling leaf (ZS11-UC1) was constructed to evaluate the effect of BnUC1 on photosynthetic efficiency. The results indicated that the up-curling leaf trait locus was beneficial to improve the photosynthetic efficiency. CONCLUSIONS:An up-curling leaf mutant Bnuc1 was controlled by one dominant locus BnUC1. This locus had positive effects on photosynthetic efficiency, negative effects on some agronomic traits, and may help to increase planting density in B. napus.

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Differences on photosynthetic limitations between leaf margins and leaf centers under potassium deficiency for Brassica napus L.

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Differences on photosynthetic limitations between leaf margins and leaf centers under potassium deficiency for Brassica napus L.

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