Comparative transcriptome analysis reveals major genes, transcription factors and biosynthetic pathways associated with leaf senescence in rice under different nitrogen application.

BACKGROUND: Rice (Oryza sativa L.) is one of the most important food crops in the world and the application of nitrogen fertilizer is an effective means of ensuring stable and high rice yields. However, excessive application of nitrogen fertilizer not only causes a decline in the quality of rice, but also leads to a series of environmental costs. Nitrogen reutilization is closely related to leaf senescence, and nitrogen deficiency will lead to early functional leaf senescence, whereas moderate nitrogen application will help to delay leaf senescence and promote the production of photosynthetic assimilation products in leaves to achieve yield increase. Therefore, it is important to explore the mechanism by which nitrogen affects rice senescence, to search for genes that are tolerant to low nitrogen, and to delay the premature senescence of rice functional leaves. RESULTS: The present study was investigated the transcriptional changes in flag leaves between full heading and mature grain stages of rice (O. sativa) sp. japonica 'NanGeng 5718' under varying nitrogen (N) application: 0 kg/ha (no nitrogen; 0N), 240 kg/ha (moderate nitrogen; MN), and 300 kg/ha (high nitrogen; HN). Compared to MN condition, a total of 10427 and 8177 differentially expressed genes (DEGs) were detected in 0N and HN, respectively. We selected DEGs with opposite expression trends under 0N and HN conditions for GO and KEGG analyses to reveal the molecular mechanisms of nitrogen response involving DEGs. We confirmed that different N applications caused reprogramming of plant hormone signal transduction, glycolysis/gluconeogenesis, ascorbate and aldarate metabolism and photosynthesis pathways in regulating leaf senescence. Most DEGs of the jasmonic acid, ethylene, abscisic acid and salicylic acid metabolic pathways were up-regulated under 0N condition, whereas DEGs related to cytokinin and ascorbate metabolic pathways were induced in HN. Major transcription factors include ERF, WRKY, NAC and bZIP TF families have similar expression patterns which were induced under N starvation condition. CONCLUSION: Our results revealed that different nitrogen levels regulate rice leaf senescence mainly by affecting hormone levels and ascorbic acid biosynthesis. Jasmonic acid, ethylene, abscisic acid and salicylic acid promote early leaf senescence under low nitrogen condition, ethylene and ascorbate delay senescence under high nitrogen condition. In addition, ERF, WRKY, NAC and bZIP TF families promote early leaf senescence. The relevant genes can be used as candidate genes for the regulation of senescence. The results will provide gene reference for further genomic studies and new insights into the gene functions, pathways and transcription factors of N level regulates leaf senescence in rice, thereby improving NUE and reducing the adverse effects of over-application of N.

Uncovering C4-like photosynthesis in C3 vascular cells.

In C4 plants, the vascularization of the leaf is extended to include a ring of photosynthetic bundle sheath cells, which have essential and specific functions. In contrast to the substantial knowledge of photosynthesis in C4 plants, relatively little is known about photosynthesis in C3 plant veins, which differs substantially from that in C3 mesophyll cells. In this review we highlight the specific photosynthetic machinery present in C3 vascular cells, which likely evolved prior to the divergence between C3 and C4 plants. The associated primary processes of carbon recapture, nitrogen transport, and antioxidant metabolism are discussed. This review of the basal C4 photosynthesis in C3 plants is significant in the context of promoting the potential for biotechnological development of C4-transgenic rice crops.

Involvement of 14-3-3 protein GRF9 in root growth and response under polyethylene glycol-induced water stress.

Plant 14-3-3 proteins are phosphoserine-binding proteins that regulate a wide array of targets via direct protein-protein interactions. In this study, the role of a 14-3-3 protein, GRF9, in plant response to water stress was investigated. Arabidopsis wild-type, GRF9-deficient mutant (grf9), and GRF9-overexpressing (OE) plants were treated with polyethylene glycol (PEG) to induce mild water stress. OE plant showed better whole-plant growth and root growth than the wild type under normal or water stress conditions while the grf9 mutant showed worse growth. In OE plants, GRF9 favours the allocation of shoot carbon to roots. In addition, GRF9 enhanced proton extrusion, mainly in the root elongation zone and root hair zone, and maintained root growth under mild water stress. Grafting among the wild type, OE, and grf9 plants showed that when OE plants were used as the scion and GRF9 was overexpressed in the shoot, it enhanced sucrose transport into the root, and when OE plants were used as rootstock and GRF9 was overexpressed in the root, it caused more release of protons into the root surface under water stress. Taken together, the results suggest that under PEG-induced water stress, GRF9 is involved in allocating more carbon from the shoot to the root and enhancing proton secretion in the root growing zone, and this process is important for root response to mild water stress.

Perceived Economic Burden, Mortality, and Health Status in Patients With Heart Failure.

Importance: In the face of an emerging heart failure (HF) epidemic, describing the association between perceived economic burden (PEB) and health care outcomes is an important step toward more equitable and achievable care. Objectives: To examine the association between PEB and risk of 1-year clinical outcomes and HF-specific health status in patients with acute decompensated HF. Design, Setting, and Participants: This prospective, multicenter, hospital-based cohort study prospectively enrolled adult patients hospitalized for acute decompensated HF at 52 hospitals in China from August 2016 to May 2018, with 1-year follow-up. Data were analyzed on June 17, 2022. Exposure: Perceived economic burden, categorized as severe (cannot undertake expenses), moderate (can almost undertake expenses), or little (can easily undertake expenses). Main Outcomes and Measures: The clinical outcomes of the study were 1-year all-cause death and rehospitalization for HF. Heart failure-specific health status was assessed by the 12-Item Kansas City Cardiomyopathy Questionnaire (KCCQ-12). Results: Among 3386 patients, median age was 67 years (IQR, 58-75 years) and 2116 (62.5%) were men. Of these patients, 404 (11.9%) had severe PEB; 2021 (59.7%), moderate PEB; and 961 (28.4%), little PEB. Compared with patients with little PEB, those with severe PEB had increased risk of 1-year mortality (hazard ratio [HR], 1.61; 95% CI, 1.21-2.13; P < .001) but not 1-year HF rehospitalization (HR, 1.21; 95% CI, 0.98-1.49; P = .07). The mean (SD) adjusted KCCQ-12 score was lowest in patients with severe PEB and highest in patients with little PEB at baseline (40.0 [1.7] and 50.2 [1.0] points, respectively; P < .001) and at each visit (eg, 12 months: 61.5 [1.6] and 75.5 [0.9] points respectively; P < .001). Patients reporting severe PEB had a clinically significant lower 1-year KCCQ-12 score compared with those reporting little PEB (mean difference, -11.3 points; 95% CI, -14.9 to -7.6 points; P < .001). Conclusions and Relevance: In this cohort study of patients with acute decompensated HF, greater PEB was associated with higher risk of mortality and poorer health status but not with risk of HF rehospitalization. The findings suggest that PEB may serve as a convenient tool for risk estimation and as a potential target for quality-improvement interventions for patients with HF.

Association of Functional Tricuspid Regurgitation and All-Cause Mortality in Ischemic Heart Failure Varies by Left Atrial Size: A Prospective Cohort Study.

This study aimed to evaluate whether the mortality risk of tricuspid regurgitation (TR) varies by left atrial (LA) size in patients with heart failure (HF). In total, 2,234 patients with ischemic HF were included. Participants were categorized as normal LA group and LA enlargement group based on the guideline recommendations, and in each group, patients were further classified as non/mild TR group and moderate/severe TR group according to echocardiographic examination. All-cause mortality was used as the only end point, and comparisons were conducted between the TR degree groups stratified by LA size status. Propensity-matched analyses and restricted cubic splines were performed to verify the robustness of the results. Of 2,234 patients with ischemic HF participants, 1,002 (44.9%) had LA enlargement and 294 (13.2%) had moderate/severe TR. After a median follow-up of 3.02 years (7,140 person-years), 453 patients (20.3%) died. After adjusting for the covariates, the higher mortality risk of moderate/severe TR was only observed in the normal LA diameter group (hazard ratio 1.64, 95% confidence interval 1.02 to 2.65) rather than the LA enlargement group (hazard ratio 0.96, 95% confidence interval 0.69 to 1.34). A significant interaction of TR degree was observed between the normal LA size group and the LA enlargement group. The relation was consistent in the propensity-matching cohort and in the restricted cubic splines analysis. In conclusion, mortality rate and prevalence of moderate/severe TR were high in patients with ischemic HF. Moderate/severe TR is significantly associated with all-cause mortality in those with normal LA diameter. The mechanisms underlying these observations merit further investigation.

Diabetes mellitus status modifies the association between N-terminal B-type natriuretic peptide and all-cause mortality risk in ischemic heart failure: a prospective cohort study.

BACKGROUND: N-terminal B-type natriuretic peptide (NT-proBNP) discriminates mortality risk in diabetes mellitus (DM) and in heart failure (HF) populations. Whether DM status modifies the association between NT-proBNP and all-cause mortality risk in ischemic HF is unknown. METHODS: This was a single-center, prospective cohort study conducted with 2287 ischemic HF patients. Subjects were divided into with DM group and without DM group. Multivariate Cox proportional-hazards models were conducted to calculate the hazard ratios (HRs) and 95% confidence intervals (CIs). The product of DM status and NT-proBNP were used to assess the interaction. Propensity score matching analysis was used to verify the robustness of the results. RESULTS: Of 2287 ischemic HF participants, 1172 (51.2%) had DM. After a median follow-up of 3.19 years (7287 person-years), 479 (20.9%) of the participants died. After adjusting for the covariates, continuous NT-proBNP was more prominently associated with risk of mortality in HF patients with DM (HR: 1.65, 95% CI: 1.43-1.91) than those without (HR: 1.28, 95% CI: 1.09-1.50). A significant interaction of DM status and NT-proBNP was observed (P-interaction = 0.016). The relationships were consistent when NT-proBNP was considered as a categorical variable and in the propensity matching analysis. CONCLUSIONS: DM status modified the association between NT-proBNP and all-cause mortality in ischemic HF patients, suggesting that NT-proBNP was more prominently associated with risk of mortality in patients with DM than those without. Future studies to clarify the mechanisms underlying these observations are needed.

A functional component of the transcriptionally active chromosome complex, Arabidopsis pTAC14, interacts with pTAC12/HEMERA and regulates plastid gene expression.

The SET domain-containing protein, pTAC14, was previously identified as a component of the transcriptionally active chromosome (TAC) complexes. Here, we investigated the function of pTAC14 in the regulation of plastid-encoded bacterial-type RNA polymerase (PEP) activity and chloroplast development. The knockout of pTAC14 led to the blockage of thylakoid formation in Arabidopsis (Arabidopsis thaliana), and ptac14 was seedling lethal. Sequence and transcriptional analysis showed that pTAC14 encodes a specific protein in plants that is located in the chloroplast associated with the thylakoid and that its expression depends on light. In addition, the transcript levels of all investigated PEP-dependent genes were clearly reduced in the ptac14-1 mutants, while the accumulation of nucleus-encoded phage-type RNA polymerase-dependent transcripts was increased, indicating an important role of pTAC14 in maintaining PEP activity. pTAC14 was found to interact with pTAC12/HEMERA, another component of TACs that is involved in phytochrome signaling. The data suggest that pTAC14 is essential for proper chloroplast development, most likely by affecting PEP activity and regulating PEP-dependent plastid gene transcription in Arabidopsis together with pTAC12.

Overexpression of ZmPCK2, a phosphoenolpyruvate carboxykinase gene from maize confers enhanced tolerance to water deficit stress in rice.

Water deficit is one of the major abiotic stresses that limit plant growth and global crop yields. Phosphoenolpyruvate carboxykinase (PCK) plays important roles in regulating plant growth and development, but its role in water-deficit stress remains elusive. In this study, we found that overexpression of ZmPCK2 significantly enhanced the water-deficit tolerance of transgenic rice. The expression level of ZmPCK2 was strongly induced by PEG and ABA treatments. Overexpression of ZmPCK2 in rice increased stomatal closure and water saving by regulating malate metabolism under water-deficit conditions. Moreover, the expression of ZmPCK2 in rice up-regulated ABA biosynthesis and responsive genes under water-deficit stress, and ZmPCK2 transgenic rice showed hypersensitive to exogenous ABA at germination stage, suggesting that ZmPCK2 may be involved in ABA signalling pathway. Under water-deficit stress, the ZmPCK2 transgenic rice showed higher antioxidant enzyme activities and lower accumulation of reactive oxygen species (ROS) compared with non-transgenic (NT) plants, resulting in less oxidative damage. Taken together, we suggest that ZmPCK2 plays multiple roles in response to water-deficit stress by enhancing ABA signalling pathway, regulating malate metabolism, promoting stomatal closure and further activating the ROS-scavenging system.

Pulse pressure and all-cause mortality in ischaemic heart failure patients: a prospective cohort study.

BACKGROUND: Whether the association between pulse pressure (PP) and mortality varies with systolic blood pressure (SBP) in ischaemic heart failure (HF) with left ventricular systolic dysfunction (LVSD) is unknown. OBJECTIVE: To evaluate the association between PP and all-cause mortality in ischaemic HF patients with SBP status at admission. PATIENTS AND METHODS: This prospective cohort study included 1581 ischaemic HF patients with LVSD. A total of 23.3% (n = 368) and 22.2% (n = 351) of the participants had SBP <110 mmHg and SBP >140 mmHg, respectively, with more than 80% of participants being male. Restricted cubic spline was performed to determine whether a nonlinear relationship existed between PP and all-cause mortality risk. A multivariable Cox proportional hazards model was used to assess the association between PP and all-cause mortality. RESULTS: After a median of follow-up of 3.0 years, 257 events (16.4%) were observed in the cohort. There was a J-shaped relationship between PP and all-cause mortality (P value for nonlinearity = 0.020), with a risk nadir of approximately 46-49 mmHg. All-cause mortality risk varied with SBP status. Higher PP was associated with worse prognosis when the SBP was ≥110 mmHg, whereas the relationship did not reach statistical significance when the SBP was <110 mmHg. CONCLUSION: A J-shaped relationship between PP and all-cause mortality was observed in ischaemic HF patients with LVSD, and higher PP was associated with worse prognosis only in those with SBP ≥110 mmHg. Further studies are needed to corroborate these findings.KEY MESSAGESA J-shaped relationship between pulse pressure and all-cause mortality was observed in ischaemic heart failure patients with left ventricular systolic dysfunction, with a risk nadir of approximately 46-49 mmHg.All-cause mortality risk varied with systolic blood pressure status, and higher pulse pressure was associated with worse prognosis when systolic blood pressure was above 110 mmHg.

The Prognostic Significance of Chronic Kidney Disease on the All-Cause Death of Ischemic Heart Failure in the Chinese Population: A Prospective Cohort Study.

OBJECTIVE: Our team tried to explore the impact of chronic kidney disease (CKD) on all-cause death among ischemic heart failure (IHF) patients. METHODS: From December 2015 to June 2019, IHF patients were continuously recruited in the Department of Cardiology, Guangdong Provincial People's Hospital. Participants were tracked through telephone interviews until October 15, 2020, or until the clinical endpoints appeared. The clinical endpoints were defined as all-cause death. The date of death or the last follow-up date minus the discharge date was used to calculate the follow-up time. RESULTS: A total of 1568 IHF patients (mean age 63.5 ± 11.0 years old, 85.8% male) were included in this study. Using the estimated glomerular filtration rate (eGFR) of 60 mL/min/1.73 m2 as the dividing line, IHF patients were divided into non-CKD group (n = 1,134) and CKD group (n = 434). After a median follow-up of 2.1 years, the all-cause death of non-CKD and CKD patients was 6.1/100 person-years and 13.7/100 person-years, respectively, and the incidence rate ratio was 2.24 (95% CI: 1.75-2.88; p value <0.001). The cumulative all-cause death of non-CKD and CKD patients were 19.4% and 40.7%, respectively (p value <0.001). CKD was an independent predictor of all-cause death in IHF patients (HR: 1.35, 95% CI: 1.03-1.76, p value = 0.029). Among IHF patients, in 8 subgroups, the all-cause death of CKD patients was consistently higher than that of non-CKD patients. Among IHF patients, the risk of all-cause death gradually increased when eGFR gradually decreased. CONCLUSION: Among IHF patients, CKD is a significant risk factor for all-cause death.

MicroRNA-375 promotes 3T3-L1 adipocyte differentiation through modulation of extracellular signal-regulated kinase signalling.

1. Adipocyte hypertrophy and hyperplasia are important processes in the development of obesity. To understand obesity and its associated diseases, it is important to elucidate the molecular mechanisms governing adipogenesis. MicroRNA-375 has been shown to inhibit differentiation of neurites, and participate in the regulation of insulin secretion and blood homeostasis. However, it is unknown whether miR-375 plays a role in adipocyte differentiation. 2. To investigate the role of miR-375 in adipocyte differentiation, we compared the miR-375 expression level between 3T3-L1 pre-adipocytes and adipocytes using miRNA microarray and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) analysis. Furthermore, we evaluated the effects of overexpression or inhibition of miR-375 on 3T3-L1 adipocyte differentiation. 3. In the present study, we found that miR-375 expression was increased after induction of adipogenic differentiation. Overexpression of miR-375 enhanced 3T3-L1 adipocyte differentiation, as evidenced by its ability to increase mRNA levels of both CCAAT/enhancer binding protein-α (C/EBPα) and peroxisome proliferator-activated receptor-γ (PPARγ2), and induction of adipocyte fatty acid-binding protein (aP2) and triglyceride (TG) accumulation. Furthermore, we found overexpression of miR-375 suppressed phosphorylation levels of extracellular signal-regulated kinases 1/2 (ERK1/2). In contrast, anti-miR-375 increased ERK1/2 phosphorylation levels and inhibited mRNA expression of C/EBPα, PPARγ2 and aP2 in 3T3-L1 adipocyte, accompanied by decreased adipocyte differentiation. 4. Taken together, these data suggest that miR-375 promotes 3T3-L1 adipocyte differentiation, possibly through modulating the ERK-PPARγ2-aP2 pathway.

Risk Prediction Model for Uncontrolled Hypertension in Chinese Community.

BACKGROUND: Uncontrolled hypertension rate was still high across China. This study develops and validates an index to help quantify the combination of socio-behavioral aspects to screen high-risk patients in uncontrolled hypertension in Chinese primary care. METHODS: A cross-sectional study included 1,039 of patients with hypertension in the Chinese community. We assessed independent risk factors of uncontrolled blood pressure (defined as having a blood pressure ≥140/90 mmHg, even with antihypertensive therapy) and develop a risk prediction model. RESULTS: Among the 1,039 patients (53.9% male, the average age was 61 ± 13 years), 452 (43.5%) were uncontrolled hypertensive. Multivariable analysis showed that worker (odds ratio, OR: 1.98, 95% CI: 1.46-2.69), no health insurance (OR: 3.47, 95% CI: 2.08-5.80), non-marital status (OR: 2.01, 95% CI: 1.35-3.27), and other socio-behavioral aspects were independent risk factors of uncontrolled hypertension, which were included the final prediction model (C-static: 0.781). With internal validation by the bootstrap method, the risk score showed good discriminating ability and predicting ability for the incidence of uncontrolled hypertension (C-static: 0.771). CONCLUSIONS: This study showed that nearly half of the patients suffered from uncontrolled hypertension in the Chinese community. We established a prediction model with good predictability to help quantify the combination of socio-behavioral aspects and screen high-risk patients with uncontrolled hypertension.

Gene coexpression network analysis reveals the role of SRS genes in senescence leaf of maize (Zea mays L.).

Shi-related sequence (SRS) proteins are plant-specific transcription factors that play important roles in developmental processes, including regulating hormone biosynthesis, response or signal transduction. However, systematical analysis of the SRS gene family in maize has not yet been conducted. In this study, 11 SRS genes with 13 transcripts were identified and characterized. The characteristics of the gene family were analysed in terms of phylogenetic relationships, chromosome distribution and gene structure. RNA-sequencing data analysis showed that the expression patterns of SRS genes were quite different from each other in maize, indicating their divergence in function. Interestingly, the GRMZM2G077752 gene is highly expressed in senescent leaves. Using further coexpression network analysis, we determined that the module containing GRMZM2G077752 were over-represented by genes related to abscisic acid (ABA) stimulus and carbohydrate metabolic process. This result indicated that GRMZM2G077752 might perceive ABA signal and cause the activation of carbohydrate remobilization during leaf ageing. This study provides valuable information for understanding the functions of the SRS genes in maize.

CHANGES IN microRNA (miR) profile and effects of miR-320 in insulin-resistant 3T3-L1 adipocytes.

1. MicroRNAs (miRNAs) play essential roles in many biological processes. It is known that aberrant miRNA expression contributes to some pathological conditions. However, it is not known whether miRNAs play any role in the development of insulin resistance in adipocytes, a key pathophysiological link between obesity and diabetes. 2. To investigate the function of miRNAs in the development of insulin resistance, using miRNA microarray analysis we compared miRNA expression profiles between normal insulinsensitive 3T3-L1 adipocytes and 3T3-L1 adipocytes rendered insulin resistant following treatment with high glucose (25mmol/L) and high insulin (1 mol/L). Furthermore, adipocytes were transfected with specific antisense oligonucleotides against miRNA-320 (anti-miR-320 oligo) and the effects on the development of insulin resistance were evaluated. 3. We identified 50 upregulated and 29 downregulated miRNAs in insulin-resistant (IR) adipocytes, including a 50-fold increase in miRNA-320 (miR-320) expression. Using bioinformatic techniques, the p85 subunit of phosphatidylinositol 3-kinase (PI3-K) was found to be a potential target of miR-320. In experiments with anti-miR-320 oligo, insulin sensitivity was increased in IR adipocytes, as evidenced by increases in p85 expression, phosphorylation of Akt and the protein expression of the glucose transporter GLUT-4, as well as insulin-stimulated glucose uptake. These beneficial effects of anti-miR-320 oligo were observed only in IR adipocytes and not in normal adipocytes. 4. In conclusion, the miRNA profile changes in IR adipocytes compared with normal 3T3-L1 adipocytes. Anti-miR-320 oligo was found to regulate insulin resistance in adipocytes by improving insulin­PI3-K signalling pathways. The findings provide information regarding a potentially new therapeutic strategy to control insulin resistance.

[Effect of aminoguanidine on hemodynamics and nitrogen monoxide in hemorrhagic shock in rabbit].

OBJECTIVE: To explore the effect of aminoguanidine (AG) on hemodynamics and nitric oxide (NO) in hemorrhagic shock in rabbit. METHODS: Shock was produced in twenty rabbits by femoral artery blood letting, and they were randomly divided into two groups with treatment with saline (control group) or AG (each n=10). Pclab system and nitric acid reductase methods were performed to detect hemodynamics parameters and NO levels at preshock, postshock (30 minutes and 150 minutes) and 30 minutes and 180 minutes after resuscitation respectively. RESULTS: No significant differences were observed in hemodynamics parameters and NO levels between the two groups before resuscitation. Whereas after resuscitation, hemodynamics parameters such as systolic arterial pressure (SAP), heart rate (HR), mean arterial pressure (MAP), left ventricular systolic pressure (LVSP) and the max and minimum first derivative of left ventricular pressure (+/-dp/dt max) were all improved greatly in the two groups. AG decreased serum NO level significantly, while saline did not have such effect, suggesting that AG had a longer and more efficient effect against hemorrhagic shock (P<0.05 or P<0.01). CONCLUSION: AG can improve hemodynamics parameters and decrease NO level in hemorrhagic shock in rabbit.

DELLA-PIF Modules: Old Dogs Learn New Tricks.

DELLA proteins are central regulators in gibberellin (GA) signaling that interact with PHYTOCHROME-INTERACTING FACTORS (PIFs) and block their DNA-binding capacity, impairing their function in integrating light signals. A recent report demonstrates that DELLAs also negatively control PIF stability, thus providing a new layer of coordination of light and GA signaling.

Photosynthesis performance, antioxidant enzymes, and ultrastructural analyses of rice seedlings under chromium stress.

The present study was conducted to examine the effects of increasing concentrations of chromium (Cr(6+)) (0, 25, 50, 100, and 200 µmol) on rice (Oryza sativa L.) morphological traits, photosynthesis performance, and the activities of antioxidative enzymes. In addition, the ultrastructure of chloroplasts in the leaves of hydroponically cultivated rice (O. sativa L.) seedlings was analyzed. Plant fresh and dry weights, height, root length, and photosynthetic pigments were decreased by Cr-induced toxicity (200 µM), and the growth of rice seedlings was starkly inhibited compared with that of the control. In addition, the decreased maximum quantum yield of primary photochemistry (Fv/Fm) might be ascribed to the decreased the number of active photosystem II reaction centers. These results were confirmed by inhibited photophosphorylation, reduced ATP content and its coupling factor Ca(2+)-ATPase, and decreased Mg(2+)-ATPase activities. Furthermore, overtly increased activities of antioxidative enzymes were observed under Cr(6+) toxicity. Malondialdehyde and the generation rates of superoxide (O2̄) also increased with Cr(6+) concentration, while hydrogen peroxide content first increased at a low Cr(6+) concentration of 25 µM and then decreased. Moreover, transmission electron microscopy showed that Cr(6+) exposure resulted in significant chloroplast damage. Taken together, these findings indicate that high Cr(6+)concentrations stimulate the production of toxic reactive oxygen species and promote lipid peroxidation in plants, causing severe damage to cell membranes, degradation of photosynthetic pigments, and inhibition of photosynthesis.

The existence of C4-bundle-sheath-like photosynthesis in the mid-vein of C3 rice.

BACKGROUND: Recent studies have shown that C4-like photosynthetic pathways partly reside in photosynthetic cells surrounding the vascular system of C3 dicots. However, it is still unclear whether this is the case in C3 monocots, especially at the molecular level. RESULTS: In order to fill this gap, we investigated several characteristics required for C4 photosynthesis, including C4 pathway enzymes, cyclic/non-cyclic photophosphorylation rates, the levels and assembly state of photosynthetic machineries, in the mid-veins of C3 monocots rice with leaf laminae used as controls. The signature of photosystem photochemistry was also recorded via non-invasive chlorophyll a fluorescence and reflectance changes at 820 nm in vivo. Our results showed that rice mid-veins were photosynthetically active with higher levels of three C4 decarboxylases. Meanwhile, the linear electron transport chain was blocked in mid-veins due to the selective loss of dysfunctional photosystem II subunits. However, photosystem I was sufficient to support cyclic electron flow in mid-veins, reminiscent of the bundle sheath in C4 plants. CONCLUSIONS: The photosynthetic attributes required for C4 photosynthesis were identified for the first time in the monocotyledon model crop rice, suggesting that this is likely a general innate characteristic of C3 plants which might be preconditioned for the C4 pathway evolution. Understanding these attributes would provide a base for improved strategies for engineering C4 photosynthetic pathways into rice.

High light acclimation of Oryza sativa L. leaves involves specific photosynthetic-sourced changes of NADPH/NADP⁺ in the midvein.

Previous studies have shown that exposure of Arabidopsis leaves to high light (HL) causes a systemic acquired acclimation (SAA) response in the vasculature. It has been postulated that C4-like photosynthesis in the leaf veins triggers this response via the Mehler reaction. To investigate this proposed connection and extend SAA to other plants, we examined the redox state of NADPH, ascorbate (ASA), and glutathione (GSH) pools; levels and histochemical localization of O2- and H2O2 signals; and activities of antioxidant enzymes in the midvein and leaf lamina of rice, when they were subjected to HL and low light. The results showed that (1) high NADPH/NADP(+) was generated by C4-like photosynthesis under HL in the midvein and (2) SAA was colocally induced by HL, as indicated by the combined signaling network, including the decrease in redox status of ASA and GSH pools, accumulation of H2O2 and O2- signals, and high superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. The high correlations between these occurrences suggest that the enhanced NADPH/NADP(+) in HL-treated midveins might alter redox status of ASA and GSH pools and trigger H2O2 and O2- signals during SAA via the Mehler reaction. These changes in turn upregulate SOD and APX activities in the midvein. In conclusion, SAA may be a common regulatory mechanism for the adaptation of angiosperms to HL. Manipulation of NADPH/NADP(+) levels by C4-like photosynthesis promotes SAA under HL stress in the midvein.