Leaf diffusional capacity largely contributes to the reduced photosynthesis in rice plants under magnesium deficiency.

Numerous studies have clarified the impacts of magnesium (Mg) on leaf photosynthesis from the perspectives of protein synthesis, enzymes activation and carbohydrate partitioning. However, it still remains largely unknown how stomatal and mesophyll conductances (gs and gm, respectively) are regulated by Mg. In the present study, leaf gas exchanges, leaf hydraulic parameters, leaf structural traits and cell wall composition were examined in rice plants grown under high and low Mg treatments to elucidate the impacts of Mg on gs and gm. Our results showed that reduction of leaf photosynthesis under Mg deficiency was mainly caused by the decreased gm, followed by reduced leaf biochemical capacity and gs, and leaf outside-xylem hydraulic conductance (Kox) was the major factor restricting gs under Mg deficiency. Moreover, increased leaf hemicellulose, lignin and pectin contents and decreased cell wall effective porosity were observed in low Mg plants relative to high Mg plants. These results suggest that Kox and cell wall composition play important roles in regulating gs and gm, respectively, in rice plants under Mg shortages.

Increased stomatal conductance and leaf biochemical capacity, not mesophyll conductance, contributing to the enhanced photosynthesis in Oryza plants during domestication.

MAIN CONCLUSION: Leaf biochemical capacity and the ratio of leaf biochemical capacity to stomatal conductance are promising to enhance leaf photosynthetic rate and water use efficiency in rice plants, respectively. Domestication may have great impact on crop photosynthetic rate, which has not been fully understood, especially from the perspective of stomatal conductance, mesophyll conductance, and leaf biochemical capacity simultaneously. In this study, we constructed a database consisting of 141 and 92 sets of data from wild and cultivated rice, respectively, including leaf gas exchange parameters, hydraulic conductance, structural traits, and nitrogen content. We found that, compared to wild rice, enhanced leaf photosynthetic rate in cultivated rice was mainly resulted by the increased stomatal conductance and leaf biochemical capacity, rather than mesophyll conductance. The unchanged mesophyll conductance observed during domestication suggested that it might have been optimized during plant evolution in wild rice. Additionally, the positive relationship between stomatal density and stomatal conductance disappeared in Oryza plants during domestication, suggesting that stomatal conductance in cultivated rice is less restricted by stomatal density, compared to wild rice. Moreover, in both wild and cultivated rice, leaf photosynthetic rate was mainly determined by leaf biochemical capacity, rather than stomatal conductance and mesophyll conductance. This study highlighted the important role of stomatal conductance and leaf biochemical capacity in improvement of leaf photosynthetic rate in rice during domestication. Leaf biochemical capacity and the ratio of leaf biochemical capacity to stomatal conductance should be further investigated to enhance leaf photosynthetic rate and water use efficiency in rice plants, respectively.

Plasticity of mesophyll cell density and cell wall thickness and composition play a pivotal role in regulating plant growth and photosynthesis under shading in rapeseed.

BACKGROUND AND AIMS: Plasticity of leaf growth and photosynthesis is an important strategy of plants to adapt to shading stress; however, their strategy of leaf development to achieve a simultaneous increase in leaf area and photosynthesis under shading remains unknown. METHODS: In the present study, a pot experiment was conducted using three rapeseed genotypes of Huayouza 50 (HYZ50), Zhongshuang 11 (ZS11) and Huayouza 62 (HYZ62), and the responses of plant growth, leaf morphoanatomical traits, cell wall composition and photosynthesis to shading were investigated. KEY RESULTS: Shading significantly increased leaf area per plant (LAplant) in all genotypes, but the increase in HYZ62 was greater than that in HYZ50 and ZS11. The greater increment of LAplant in HYZ62 was related to the larger decrease in leaf mass per area (LMA) and leaf density (LD), which were in turn related to less densely packed mesophyll cells and thinner cell walls (Tcw). Moreover, shading significantly increased photosynthesis in HYZ62 but significantly decreased it in HYZ50. The enhanced photosynthesis in HYZ62 was related to increased mesophyll conductance (gm) due primarily to thinner cell walls. CONCLUSIONS: The data presented indicate that the different plasticity of mesophyll cell density, cell wall thickness and cell wall composition in response to shading can dramatically affect leaf growth and photosynthesis.

Reduction of photosynthesis under P deficiency is mainly caused by the decreased CO2 diffusional capacities in wheat (Triticum aestivum L.).

Phosphorus is one of the most important essential mineral elements for plant growth and development. It has been widely recognized that phosphorus deficiency can lead to the significant declines in leaf photosynthetic rate and leaf area. However, the internal mechanism associated with the leaf anatomical traits has not been well understood. In present study, a hydroponic experiment was conducted to study the effect of phosphorus deficiency on leaf growth and photosynthesis in Jimai 22 (JM22, Triticum aestivum L.) and Suk Landarace 26 (SL26, Triticum aestivum L.). With the decrease in phosphorus concentration, leaf photosynthetic rate and leaf area in SL26 and JM22 all decreased significantly, but the decrease in leaf area occurred earlier than that in leaf photosynthetic rate. The thresholds of phosphorus concentration to maintain a high photosynthesis were 145.5 and 138.7 mg m-2, respectively, in SL26 and JM22; and they were 197.5 and 212.0 mg m-2, respectively, for leaf growth. The decrease in leaf photosynthetic rate under low P conditions was mainly caused by the lowered stomatal conductance and mesophyll conductance, and to a less extent by the decrease in biochemical capacities. The decrease in stomatal conductance was attributed to the smaller vascular bundle area, xylem conduits area and the lower leaf hydraulic conductance. However, the reduction in mesophyll conductance was not related to either the cell wall thickness or the development of chloroplast.

Interspecific variation in the temperature response of mesophyll conductance is related to leaf anatomy.

Although mesophyll conductance (gm ) is known to be sensitive to temperature (T), the mechanisms underlying the temperature response of gm are not fully understood. In particular, it has yet to be established whether interspecific variation in gm -T relationships is associated with mesophyll anatomy and vein traits. In the present study, we measured the short-term response of gm in eight crop species, and leaf water potential (Ψleaf ) in five crop species over a temperature range of 15-35°C. The considered structural parameters are surface areas of mesophyll cells and chloroplasts facing intercellular airspaces per unit leaf area (Sm and Sc ), cell wall thickness (Tcw ), and vein length per area (VLA). We detected large interspecific variations in the temperature responses of gm and Ψleaf . The activation energy for gm (Ea,gm ) was found to be positively correlated with Sc , although it showed no correlation with Tcw . In contrast, VLA was positively correlated with the slope of the linear model of Ψleaf -T (a), whereas Ea,gm was marginally correlated with VLA and a. A two-component model was subsequently used to model gm -T relationships, and the mechanisms underlying the temperature response of gm are discussed. The data presented here indicate that leaf anatomy is a major determinant of the interspecific variation in gm -T relationships.

The structural correlations and the physiological functions of stomatal morphology and leaf structures in C3 annual crops.

MAIN CONCLUSION: This study suggests that stomatal and leaf structures are highly correlated, and mesophyll cell size is an important anatomical trait determining the coordination between stomatal size and mesophyll porosity. A comprehensive study of the correlations between the structural traits and on their relationships with gas exchange parameters may provide some useful information into leaf development and improvement in efficiencies of photosynthetic CO2 fixation and transpirational water loss. In the present study, nine plant materials from eight crop species were pot grown in a growth chamber. Leaf structural traits, gas exchange, and leaf nitrogen content were measured. We found that stomatal size, mesophyll cell size (MCS), and mesophyll porosity were positively correlated and that the surface areas of mesophyll cells and chloroplasts facing intercellular air spaces were positively correlated with both stomatal density and stomatal area per leaf area (SA). These results suggested that the developments of stomata and mesophyll cells are highly correlated among different crop species. Additionally, MCS was positively correlated with leaf thickness and negatively correlated with leaf density and leaf mass per area, which indicated that MCS might play an important role in leaf structural investments and physiological functions among species. In summary, this study illustrates the correlations between stomatal and mesophyll structures, and it highlights the importance of considering the covariations among leaf traits with the intent of improving photosynthesis and iWUE.

Variation of photosynthesis during plant evolution and domestication: implications for improving crop photosynthesis.

Studies investigating the mechanisms underlying the variation of photosynthesis along plant phylogeny and especially during domestication are of great importance, and may provide new insights to further improve crop photosynthesis. In the present study, we compiled a database including 542 sets of data of leaf gas exchange parameters and leaf structural and chemical traits in ferns and fern allies, gymnosperms, non-crop angiosperms, and crops. We found that photosynthesis was dramatically improved from ferns and fern allies to non-crop angiosperms, and further increased in crops. The improvement of photosynthesis during phylogeny and domestication was related to increases in carbon dioxide diffusional capacities and, to a lesser extent, biochemical capacity. Cell wall thickness rather than chloroplast surface area facing intercellular airspaces drives the variation of mesophyll conductance. The variation of the maximum carboxylation rate was not related to leaf nitrogen content. The slope of the relationship between mass-based photosynthesis and nitrogen was lower in crops than in non-crop angiosperms. These findings suggest that the manipulation of cell wall thickness is the most promising approach to further improve crop photosynthesis, and that an increase of leaf nitrogen will be less efficient in improving photosynthesis in crops than in non-crop angiosperms.

Leaf Photosynthesis and Its Temperature Response Are Different between Growth Stages and N Supplies in Rice Plants.

Leaf photosynthesis is highly correlated with CO2-diffusion capacities, which are determined by both leaf anatomical traits and environmental stimuli. In the present study, leaf photosynthetic rate (A), stomatal conductance (gs), mesophyll conductance (gm) and the related leaf anatomical traits were studied on rice plants at two growth stages and with two different N supplies, and the response of photosynthesis to temperature (T) was also studied. We found that gm was significantly higher at mid-tillering stage and at high N treatment. The larger gm was related to a larger chloroplast surface area facing intercellular air spaces and a thinner cell wall in comparison with booting stage and zero N treatment. At mid-tillering stage and at high N treatment, gm showed a stronger temperature response. The modelling of the gm-T relationships suggested that, in comparison with booting stage and zero N treatment, the stronger temperature response of gm was related to the higher activation energy of the membrane at mid-tillering stage and at high N treatment. The findings in the present study can enhance our knowledge on the physiological and environmental determinants of photosynthesis.

Leaf photosynthesis is positively correlated with xylem and phloem areas in leaf veins in rice (Oryza sativa) plants.

BACKGROUND AND AIMS: Leaf structure is an important determinant of leaf photosynthesis; however, the impacts of leaf structural traits on gas exchange parameters are still not fully understood. In the present study, 11 rice genotypes were grown in pots to investigate the influence of leaf structural traits on leaf photosynthesis and hydraulic conductance (Kleaf). METHODS: In this study, leaf photosynthetic rate (A), stomatal conductance (gs), mesophyll conductance and Kleaf were measured. In addition, leaf structural traits including leaf thickness (LT), leaf mass per area and leaf xylem and phloem sizes were also measured to investigate their impacts on rice photosynthesis. KEY RESULTS: We found that the total area of xylem conduits per major vein (Xmajor), leaf phloem area per minor vein (Pminor) and LT were positively correlated with Kleaf, gs and A. The path analysis suggested that, however, only Pminor had a direct impact on A; Xmajor had an indirect impact on A via gs and Pminor, while LT did not show any direct or indirect impact on A. CONCLUSION: This study highlighted the importance of manipulations in Xmajor and Pminor, two previously overlooked leaf traits, to improve leaf photosynthesis in rice plants.

Genotypic variation of plant biomass under nitrogen deficiency is positively correlated with conservative economic traits in wheat.

Plant functional traits, including leaf and root economic traits, are important for understanding the composition and function of ecosystems. However, plant functional traits of crop species and the relationships between them, and their responses to environmental variations are not fully understood. In the present study, the traits in the leaf and root economics spectrum (LES and RES) and plant biomass were investigated in 14 wheat genotypes grown with sufficient or limited nitrogen (N) supply. We found that N had significant impacts on the LES and RES traits and on the relationships among them. Our results generally supported the hypothesized LES, but did not support the RES or plant economics spectrum concept among wheat plants regardless of N treatment. More importantly, we found that more conservative leaf and root economic traits are beneficial for shoot biomass accumulation in wheat plants grown with limited N supply, and for the improvement in the tolerance of wheat to N stress. The data presented suggest that growth conditions should be accounted for when studying trait-to-trait relationships, and that more conservative resource use strategies could be used as promising targets for wheat breeding programs with limited N input.

High leaf mass per area Oryza genotypes invest more leaf mass to cell wall and show a low mesophyll conductance.

The intraspecific variations of leaf structure and anatomy in rice leaves and their impacts on gas diffusion are still unknown. Researches about the tradeoff between structural compositions and intracellular chemical components within rice leaves are still lacking. The objectives of the present study were to investigate the varietal differences in leaf structure and leaf chemical compositions, and the tradeoff between leaf structural tissues and intracellular chemical components in rice leaves. Leaf structure, leaf anatomy, leaf chemical composition concentrations and gas exchange parameters were measured on eight Oryza sativa L. genotypes to investigate the intraspecific variations in leaf structure and leaf anatomy and their impacts on gas exchange parameters, and to study the tradeoff between leaf structural compositions (cell wall compounds) and intracellular chemical components (non-structural carbohydrates, nitrogen, chlorophyll). Leaf thickness increased with leaf mass per area (LMA), while leaf density did not correlate with LMA. Mesophyll cell surface area exposed to intercellular airspace (IAS) per leaf area, the surface area of chloroplasts exposed to IAS and cell wall thickness increased with LMA. Cell wall compounds accounted for 71.5 % of leaf dry mass, while mass-based nitrogen and chlorophyll concentrations decreased with LMA. Mesophyll conductance was negatively correlated with LMA and cell wall thickness. High LMA rice genotypes invest more leaf mass to cell wall and possess a low mesophyll conductance.

Temperature responses of photosynthesis and leaf hydraulic conductance in rice and wheat.

Studies on the temperature (T) responses of photosynthesis and leaf hydraulic conductance (Kleaf ) are important to plant gas exchange. In this study, the temperature responses of photosynthesis and Kleaf were studied in Shanyou 63 (Oryza sativa) and Yannong 19 (Triticum aestivum). Leaf water potential (Ψleaf ) was insensitive to T in Shanyou 63, while it significantly decreased with T in Yannong 19. The differential Ψleaf - T relationship partially accounted for the differing gm -T relationships, where gm was less sensitive to T in Yannong 19 than in Shanyou 63. With different gm -T and Ψleaf -T relationships, the temperature responses of photosynthetic limitations were surprisingly similar between the two lines, and the photosynthetic rate was highly correlated with gm . With the increasing T, Kleaf increased in Shanyou 63 while it decreased in Yannong 19. The different Kleaf -T relationships were related to different Ψleaf -T relationships. When excluding the effects of water viscosity and Ψleaf , Kleaf was insensitive to T in both lines. gm and Kleaf were generally not coordinated across different temperatures. This study highlights the importance of Ψleaf on leaf carbon and water exchanges, and the mechanisms for the gm -T and Kleaf -T relationships were discussed.

The correlation between expression of sip protein in different serotypes of group b streptococcus and diagnosis.

Since the surface immunogenic protein (Sip) of group B streptococcus was identified, it's immunogenicity and its potential as a universal vaccine candidate has been evaluated extensively. We developed recombinant Sip protein and used it for monoclonal antibody generation to develop immunochromatographic test kit for GBS detection. The test of bacteria and culture media revealed the correlation between Sip protein expression and diagnosis discrepancy, which has never been reported. Furthermore, not only the surface accessibility of the Sip protein may vary from strains or serotypes; the secretion level of Sip protein may also vary.

KIAA1429 regulates the migration and invasion of hepatocellular carcinoma by altering m6A modification of ID2 mRNA.

PURPOSE: N6-methyladenosine (m6A), the most abundant mRNA modification in mammals, is involved in various biological processes. KIAA1429 is an important methyltransferase participating in m6A modification. However, the role of KIAA1429 in hepatocellular carcinoma (HCC) is still not well understood. Here, we aimed to investigate the function of KIAA1429 and its corresponding regulation mechanisms in HCC. PATIENTS AND METHODS: HCC-related genes were analyzed by clinical and expression data of HCC patients in The Cancer Genome Atlas (TCGA) database. Expression of KIAA1429 was verified by quantitative reverse-transcription PCR, and interference efficiency was obtained using small interfering RNA (siRNA). Cell proliferation, migration, and invasion were assessed by cell counting kit-8 and transwell assays, and the m6A modification was detected by methylated RNA immunoprecipitation-PCR (MeRIP-PCR). RESULTS: We found a difference in the expression of KIAA1429 between HCC and normal hepatic tissues by analyzing data from the TCGA database. Comparing HCC cell lines (HepG2, Huh-7, HepG2.2.15) with normal hepatic cells (HL-7702), we observed an identically significant difference in KIAA1429 expression. KIAA1429 significantly enhanced proliferation, migration, and invasion of HepG2 cells. Moreover, Kyoto Encyclopedia of Genes and Genomes functional enrichment analysis and correlation analysis revealed a significant negative correlation between KIAA1429 and ID2. In the subsequent MeRIP-PCR assay, downregulation of KIAA1429 inhibited m6A modification of ID2 mRNA. CONCLUSION: KIAA1429 facilitated migration and invasion of HCC by inhibiting ID2 via upregulating m6A modification of ID2 mRNA.

Nitrogen Can Alleviate the Inhibition of Photosynthesis Caused by High Temperature Stress under Both Steady-State and Flecked Irradiance.

Nitrogen is one of the most important elements for plants and is closely related to photosynthesis. High temperature stress significantly inhibits photosynthesis under both steady-state and flecked irradiance. However, it is not known whether nitrogen can affect the decrease in photosynthesis caused by high temperature, especially under flecked irradiance. In the present study, a pot experiment was conducted under two nitrogen (N) supplies with rice plants, and the steady-state and dynamic photosynthesis rates were measured under 28 and 40°C. High temperature significantly increased leaf hydraulic conductance (Kleaf) under high N supply (HN) but not under low N supply (LN). The increased Kleaf maintained a constant leaf water potential (Ψleaf) and steady-state stomatal conductance (gs,sat) under HN, while the Ψleaf and gs,sat significantly decreased under high temperature in LN conditions. This resulted in a more severe decrease in steady-state photosynthesis (Asat) under high temperature in the LN conditions. After shifting from low to high light, high temperature significantly delayed the recovery of photosynthesis, which resulted in more carbon loss under flecked irradiance. These effects were obtained under HN to a lesser extent than under LN supply. Therefore, it is concluded that nitrogen can alleviate the inhibition of photosynthesis caused by high temperature stress under both steady-state and flecked irradiance.

Development of a highly sensitive lateral immunochromatographic assay for rapid detection of Vibrio parahaemolyticus.

Vibrio parahaemolyticus is widely present in brackish water all over the world, causing infections in certain aquatic animals. It is also a foodborne pathogen that causes diarrhea in humans. The aim of this study is to develop an immunochromatographic lateral flow assay (LFA) for rapid detection of V. parahaemolyticus in both aquatic products and human feces of diarrheal patients. Two monoclonal antibody (MAb) pairs, GA1a-IC9 and IC9-KB4c, were developed and proven to be highly specific and sensitive to V. parahaemolyticus. Based on the two MAb pairs, two types of LFA strips were prepared. Their testing limits for V. parahaemolyticus culture were both 1.2×103CFU/ml. The diagnostic sensitivities and specificities were both 100% for the 32 tested microbial species, including 6 Vibrio species. Subsequently, the LFA strips were used to test Whiteleg shrimps and human feces. The type II strip showed a higher diagnostic sensitivity. Its sensitivity and specificity for hepatopancreas and fecal samples from 13 Whiteleg shrimps and fecal samples from 146 human diarrheal patients were all 100%. In conclusion, our homemade type II LFA is a very promising testing device for rapid and convenient detection of V. parahaemolyticus infection not only in aquatic animals, but also in human diarrheal patients. This sensitive immunochromtographic LFA allows rapid detection of V. parahaemolyticus without requirement of culture enrichment.

[Detection system for Xanthomonas axonopodis pv. citri using rolling circle amplification].

Padlock probe was designed based on the sequence of the unique hypothetic protein gene in complete genome of Xanthomonas axonopodis pv. citri (Xac), and amplification primers ware designed according to the universal linking sequence of padlock probe. Detection system of rolling circle amplification (RCA) was established and optimized. Results show that the system could detect Xac and its DNA specifically, while other plant pathogens and bacteria attached on the surface of citrus leaves could not be detected. This indicates that the detection system had its specificity. The detection sensitivity of RCA was 20 cfu/microL for Xac cells and 10(2) copy/microL for cloned DNA fragment, which was slightly higher than the sensitivity of conventional PCR. Leaf samples collected from orange orchards were detected with both RCA and conventional PCR. The result shows that the Xac positive percentage had no remarkable difference between the two methods (P>0.01). Because the universal linking sequence in padlock probe can use same amplification condition, the new technology and detection system can be used to detect diverse plant pathogens simultaneously in plant quarantine and disease pre-symptom diagnosis.