Fluctuating light induces a significant photoinhibition of photosystem I in maize.

In nature, light intensity usually fluctuates and a sudden shade-sun transition can induce photodamage to photosystem I (PSI) in many angiosperms. Photosynthetic regulation in fluctuating light (FL) has been studied extensively in C3 plants; however, little is known about how C4 plants cope FL to prevent PSI photoinhibition. We here compared photosynthetic responses to FL between maize (Zea mays, C4) and tomato (Solanum lycopersicum, C3) grown under full sunlight. Maize leaves had significantly higher cyclic electron flow (CEF) activity and lower photorespiration activity than tomato. Upon a sudden shade-sun transition, maize showed a significant stronger transient PSI over-reduction than tomato, resulting in a significant greater PSI photoinhibition in maize after FL treatment. During the first seconds upon shade-sun transition, CEF was stimulated in maize at a much higher extent than tomato, favoring the rapid formation of trans-thylakoid proton gradient (ΔpH), which was helped by a transient down-regulation of chloroplast ATP synthase activity. Therefore, modulation of ΔpH by regulation of CEF and chloroplast ATP synthase adjusted PSI redox state at donor side, which partially compensated for the deficiency of photorespiration. We propose that C4 plants use different photosynthetic strategies for coping with FL as compared with C3 plants.

Nucleic Acid Nanotechnology: Trends, Opportunities and Challenges.

Nucleic acids (DNA and RNA) hold great potential for the advancement of future medicine but suffer from unsatisfactory clinical success due to the challenges accompanied with their delivery. Nucleic acid-mediated nanomaterials have riveted the researchers from the past two decades and exhilarating tasks have prevailed. Nucleic acid nanotechnology offers unique control over the shape, size, time, mechanics and anisotropy. It can transfect numerous types of tissues and cells without any toxic effect, minimize the induced immune response, and penetrate most of the biological barriers and hence it reveals itself as a versatile tool for multidisciplinary research field and for various therapeutic purposes. Nucleic acid combines with other nanoscale objects also by altering the chemical functional groups and reproducing the varied array of nanomaterials. Interestingly, nucleic acidderived nanomaterials are characterized easily at atomic level accuracy. However, this advent of nanoscience has vital issues which must be addressed, such as the high cost of nucleic acids, their self-assembly nature, etc. Hence, the aim of this review is to highlight the systematic advances and methodology of nucleic acid-mediated synthesis of nanomaterials and their therapeutic applications.

Perspectives of herbs and their natural compounds, and herb formulas on treating diverse diseases through regulating complicated JAK/STAT signaling.

JAK/STAT signaling pathways are closely associated with multiple biological processes involved in cell proliferation, apoptosis, inflammation, differentiation, immune response, and epigenetics. Abnormal activation of the STAT pathway can contribute to disease progressions under various conditions. Moreover, tofacitinib and baricitinib as the JAK/STAT inhibitors have been recently approved by the FDA for rheumatology disease treatment. Therefore, influences on the STAT signaling pathway have potential and perspective approaches for diverse diseases. Chinese herbs in traditional Chinese medicine (TCM), which are widespread throughout China, are the gold resources of China and have been extensively used for treating multiple diseases for thousands of years. However, Chinese herbs and herb formulas are characterized by complicated components, resulting in various targets and pathways in treating diseases, which limits their approval and applications. With the development of chemistry and pharmacology, active ingredients of TCM and herbs and underlying mechanisms have been further identified and confirmed by pharmacists and chemists, which improved, to some extent, awkward limitations, approval, and applications regarding TCM and herbs. In this review, we summarized various herbs, herb formulas, natural compounds, and phytochemicals isolated from herbs that have the potential for regulating multiple biological processes via modulation of the JAK/STAT signaling pathway based on the published work. Our study will provide support for revealing TCM, their active compounds that treat diseases, and the underlying mechanism, further improving the rapid spread of TCM to the world.

Exogenous melatonin strongly affects dynamic photosynthesis and enhances water-water cycle in tobacco.

Melatonin (MT), an important phytohormone synthesized naturally, was recently used to improve plant resistance against abiotic and biotic stresses. However, the effects of exogenous melatonin on photosynthetic performances have not yet been well clarified. We found that spraying of exogenous melatonin (100 µM) to leaves slightly affected the steady state values of CO2 assimilation rate (A N ), stomatal conductance (g s ) and mesophyll conductance (g m ) under high light in tobacco leaves. However, this exogenous melatonin strongly delayed the induction kinetics of g s and g m , leading to the slower induction speed of A N . During photosynthetic induction, A N is mainly limited by biochemistry in the absence of exogenous melatonin, but by CO2 diffusion conductance in the presence of exogenous melatonin. Therefore, exogenous melatonin can aggravate photosynthetic carbon loss during photosynthetic induction and should be used with care for crop plants grown under natural fluctuating light. Within the first 10 min after transition from low to high light, photosynthetic electron transport rates (ETR) for A N and photorespiration were suppressed in the presence of exogenous melatonin. Meanwhile, an important alternative electron sink, namely water-water cycle, was enhanced to dissipate excess light energy. These results indicate that exogenous melatonin upregulates water-water cycle to facilitate photoprotection. Taking together, this study is the first to demonstrate that exogenous melatonin inhibits dynamic photosynthesis and improves photoprotection in higher plants.

Neobaicalein Inhibits Th17 Cell Differentiation Resulting in Recovery of Th17/Treg Ratio through Blocking STAT3 Signaling Activation.

Huangqin is the dried root of Scutellaria baicalensis Georgi, which has been widely utilized for heat-clearing (Qingre) and dewetting (Zaoshi), heat-killed (Xiehuo) and detoxifying (Jiedu) in the concept of Traditional Chinese Medicine and is used for treating inflammation and cancer in clinical formulas. Neobaicalein (NEO) is of flavonoid isolated from Huangqin and has been reported to possess prominent anti-inflammatory effects in published work. Th17/Treg balance shift to Th17 cells is an essential reason for autoimmune inflammatory diseases. However, the role NEO plays in Th17 and Treg and the underlying mechanism has not been elucidated yet. Network pharmacology-based study revealed that NEO predominantly regulated IL-17 signaling pathway. Moreover, our result shown that NEO (3-30 µmol/L) down-regulated Th17 differentiation and cellular supernatant and intracellular IL-17A level and tumor necrosis factor α production in a concentration-dependent manner. The further mechanism research revealed that NEO also specifically inhibited phosphorylation of STAT3(Tyr725) and STAT4 (Y693) without influence on activation of STAT5 and STAT6 in splenocytes. Immunofluorescence results illuminated that NEO effectively blocked STAT3 translocated into nucleus. Interestingly, NEO at appreciated dose could only inhibit Th17 cell differentiation and have no effect on Treg differentiation. The present study revealed that NEO effectively inhibited Th17 cell differentiation through specifically blocking the activation of STAT3 signaling without inactivation of STAT5 and STAT6. Additional inhibitory effect on activation of STAT4 by NEO also suggested the potential for antagonism against Th1 differentiation. All work suggested that NEO may be a potential candidate for immunoregulation and treating autoimmune inflammatory diseases through inhibiting immune cell viability and T cell differentiation.

Angucycline and angucyclinone derivatives from the marine-derived Streptomyces sp.

Atramycin C (1), one new angucycline bearing an O-6 rhamnose side chain, along with one new highly hydroxylated angucyclinone emycin G (2), and ten known analogs (3-12) were isolated from the marine-derived Streptomyces sp. strain BHB-032. Their structures were assigned by spectroscopic analysis and comparison with literature data. The absolute configuration of the sugar unit of 1 was assigned as 6-O-α-l-rhamnoside, based on the analysis of the coupling constants and chemical derivatization, whereas the absolute configuration of 2 was determined by X-ray diffraction. Furthermore, the stereochemistry of saccharothrixin A (3) and SNA-8073-A (4) was established unequivocally by X-ray crystallography for the first time. Compounds 1 and 2 exhibited moderate antimicrobial activities with minimum inhibitory concentration (MIC) values ranging from 16 to 64 µg/ml.

Roles of alternative electron flows in response to excess light in Ginkgo biloba.

Ginkgo biloba L., the only surviving species of Ginkgoopsida, is a famous relict gymnosperm, it may provide new insight into the evolution of photosynthetic mechanisms. Flavodiiron proteins (FDPs) are conserved in nonflowering plants, but the role of FDPs in gymnosperms has not yet been clarified. In particular, how gymnosperms integrate FDPs and cyclic electron transport (CET) to better adapt to excess light is poorly understood. To elucidate these questions, we measured the P700 signal, chlorophyll fluorescence and electrochromic shift signal under fluctuating and constant light in G. biloba. Within the first seconds after light increased, G. biloba could not build up a sufficient proton gradient (ΔpH). Concomitantly, photo-reduction of O2 mediated by FDPs contributed to the rapid oxidation of P700 and protected PSI under fluctuating light. Therefore, in G. biloba, FDPs mainly protect PSI under fluctuating light at acceptor side. Under constant high light, the oxidation of PSI and the induction of non-photochemical quenching were attributed to the increase in ΔpH formation, which was mainly caused by the increase in CET rather than linear electron transport. Therefore, under constant light, CET finely regulates the PSI redox state and non-photochemical quenching through ΔpH formation, protecting PSI and PSII against excess light. We conclude that, in G. biloba, FDPs are particularly important under fluctuating light while CET is essential under constant high light. The coordination of FDPs and CET fine-tune photosynthetic apparatus under excess light.

Carbamylated Erythropoietin Alleviates Kidney Damage in Diabetic Rats by Suppressing Oxidative Stress.

The oxidative stress response plays an important role in the occurrence and development of diabetic kidney disease (DKD). It has become a new treatment target for DKD. In the current study, the effects of carbamylated erythropoietin (CEPO) on renal oxidative stress and damage in diabetic rats were examined. Thirty Sprague Dawley rats were intraperitoneally administered with 60 mg/kg streptozotocin to establish the diabetes model. The diabetic rats were randomly allocated into 4 groups (n=6 each): diabetes model group (DM group), DM + CEPO treatment group (DC group), DM + CEPO + EPO receptor (EPOR) blocking peptide treatment group (DCEB group), and DM + CEPO + CD131 blocking peptide treatment group (DCCB group). Meanwhile, a normal control group (NC group, n=6) was set up. Kidney tissues and blood samples were obtained for evaluation of oxidative stress and renal function. The results showed that diabetic rats exhibited increased oxidative stress in the kidney and early pathological changes associated with DKD. Treatment with CEPO reduced oxidative stress and attenuated renal dysfunction. However, diabetic rats treated with the combination of CEPO and EPOR blocking peptide or CD131 blocking peptide showed increased oxidative stress and reduced renal function when compared with CEPO treatment alone group. These results suggested that CEPO can protect against kidney damage in DKD by inhibiting oxidative stress injury via EPOR-CD131 heterodimers.

First Report of Bacterial Rot Caused by Pantoea endophytica on Tobacco in Liuyang, China.

Tobacco, Nicotiana tabacum L., is produced largely in China (~1/3 of the global market). In the monsoon summer of 2020, tobacco plant petioles, where axillary buds were removed, became black-rotten, and thick ooze appeared, when squeezed. Lesions encompassed more than half of petiole circumference. Ten tobacco fields (100 plant/field) were investigated in Liuyang, China and 5% disease severity founded in each infected field (Fig. 1A, B, C). Six infected stalks leave of different tobacco were sampled from severe field in Liuyang (N28°21', E113°52') and were surface sterilized (1% sodium hypochlorite for 3 min.), rinsed thrice in sterile distilled water, grounded, and streaked on Luria Bertani agar (LBA). After 24 hours at 28ºC, circular and convex colonies appeared. Hundred colony from ten plates were picked, amplified, and sequenced with the primer 16S-27F/16S-1492R by colony PCR (Lane et al. 1991). 16S rRNA sequence from 100 colony were assembled and fell into two sequences, either similar to Leclercia sp. (86%), or Pantoea sp. (14%). Identification and homology search was done by BLASTn analysis against NCBI and the EzBio Cloud database (Yoon et al. 2017). The Pantoea isolate HN-23 (1,408 bp, MW405831) and the other 16S sequence of 13 Pantoea showed 99.57% identity to the type strain P. endophyitca 596T (PJRT0100022) based on the EzBio Cloud database to identify novel bacteria. Colonies of HN-23 were smooth, translucent, convex with entire margin on LBA, and 1mm and 3mm (diameter), white to yellow, after 24h and 48h (Fig.1 H, I), respectively but white (Fig.1 J, K) on Nutrient Agar (NA). Phenotype of HN-23 (S-1) was performed using API 20E and API ZYM system (bioMérieux, France) and found identical to P. endophytica 596T (Gao et al. 2019). Draft genome of HN-23 (size 4.96Mbp, total Scaffold 79, Scaf N50 218,098bp and Scaf N90 61,041bp) was studied by Illumina sequencing (JAFLWX000000000) and was found to have 98.24% nucleotide identity with the genome of P. endophytica type strain 596. Average nucleotide identity (ANI) values were calculated using Ortho ANIu algorithm (Yoon et al 2017a). HN-23 had 83.89% and 83.65% ANI with P. rodasii LMG26273T and P. dispersa CCUG25232T, respectively (S-2). Six tobacco seedlings (cultivar K326, 30cm height plants grown at greenhouse at 28℃ and 70-80% humidity) were injected by 20µl of culture (109 CFU/ml) of HN-23 and three with dominant species Leclercia sp. HN-7, and reisolated from infected tissues. Pathogenic tissue extract and sterile water were also used as positive and negative control, respectively and experiments were performed in triplicate. After 20h, symptoms of water-soaked decay appeared in the injected leaf axils (Fig. 1D). After 2 days, a severe rot is developed (Fig.1 E). Though, the controls were symptomless (Fig.1 F, G). The bacterium was then isolated from the rotten tissues and identity was confirmed by 16S rDNA sequencing, thus fulfilling Koch's postulates. This species was also reported as endophytes to be isolated from root, stem and leaf of maize planted in diverse parts of China and identified as P. endophytica. To our knowledge, this is the first report of P. endophytica as a plant pathogen, which was firstly isolated from Tobacco planted in southern China.

Photosystem I is tolerant to fluctuating light under moderate heat stress in two orchids Dendrobium officinale and Bletilla striata.

Under natural field conditions, plants usually experience fluctuating light (FL) under moderate heat stress in summer. However, responses of photosystems I and II (PSI and PSII) to such combined stresses are not well known. Furthermore, the role of water-water cycle (WWC) in photoprotection in FL under moderate heat stress is poorly understood. In this study, we examined chlorophyll fluorescence and P700 redox state in FL at 42 °C in two orchids, Dendrobium officinale (with high WWC activity) and Bletilla striata (with low WWC activity). After FL treatment at 42 °C, PSI activity maintained stable while PSII activity decreased significantly in these two orchids. In D. officinale, the WWC could rapidly consume the excess excitation energy in PSI and thus avoided an over-reduction of PSI upon any increase in illumination. Therefore, in D. officinale, WWC likely protected PSI in FL at 42 °C. In B. striata, heat-induced PSII photoinhibition down-regulated electron flow from PSII and thus prevented an over-reduction of PSI after transition from low to high light. Consequently, in B. striata moderate PSII photoinhibition could protected PSI in FL at 42 °C. We conclude that, in addition to cyclic electron flow, WWC and PSII photoinhibition-repair cycle are two important strategies for preventing PSI photoinhibition in FL under moderate heat stress.

Differential Response of the Photosynthetic Machinery to Fluctuating Light in Mature and Young Leaves of Dendrobium officinale.

A key component of photosynthetic electron transport chain, photosystem I (PSI), is susceptible to the fluctuating light (FL) in angiosperms. Cyclic electron flow (CEF) around PSI and water-water cycle (WWC) are both used by the epiphytic orchid Dendrobium officinale to protect PSI under FL. This study examined whether the ontogenetic stage of leaf has an impact on the photoprotective mechanisms dealing with FL. Thus, chlorophyll fluorescence and P700 signals under FL were measured in D. officinale young and mature leaves. Upon transition from dark to actinic light, a rapid re-oxidation of P700 was observed in mature leaves but disappeared in young leaves, indicating that WWC existed in mature leaves but was lacking in young leaves. After shifting from low to high light, PSI over-reduction was clearly missing in mature leaves. By comparison, young leaves showed a transient PSI over-reduction within the first 30 s, which was accompanied with highly activation of CEF. Therefore, the effect of FL on PSI redox state depends on the leaf ontogenetic stage. In mature leaves, WWC is employed to avoid PSI over-reduction. In young leaves, CEF around PSI is enhanced to compensate for the lack of WWC and thus to prevent an uncontrolled PSI over-reduction induced by FL.

The Light Dependence of Mesophyll Conductance and Relative Limitations on Photosynthesis in Evergreen Sclerophyllous Rhododendron Species.

Mesophyll conductance (gm) limits CO2 diffusion from sub-stomatal internal cavities to the sites of RuBP carboxylation. However, the response of gm to light intensity remains controversial. Furthermore, little is known about the light response of relative mesophyll conductance limitation (lm) and its effect on photosynthesis. In this study, we measured chlorophyll fluorescence and gas exchange in nine evergreen sclerophyllous Rhododendron species. gm was maintained stable across light intensities from 300 to 1500 µmol photons m-2 s-1 in all these species, indicating that gm did not respond to the change in illumination in them. With an increase in light intensity, lm gradually increased, making gm the major limiting factor for area-based photosynthesis (AN) under saturating light. A strong negative relationship between lm and AN was found at 300 µmol photons m-2 s-1 but disappeared at 1500 µmol photons m-2 s-1, suggesting an important role for lm in determining AN at sub-saturating light. Furthermore, the light-dependent increase in lm led to a decrease in chloroplast CO2 concentration (Cc), inducing the gradual increase of photorespiration. A higher lm under saturating light made AN more limited by RuBP carboxylation. These results indicate that the light response of lm plays significant roles in determining Cc, photorespiration, and the rate-limiting step of AN.

Clinical characteristics of coronavirus disease 2019 in patients aged 80 years and older.

OBJECTIVE: Coronavirus disease 2019 (COVID-19) has raised concern around the world as an epidemic or pandemic. As data on COVID-19 has grown, it has become clear that older adults have a disproportionately high rate of death from COVID-19. This study describes the early clinical characteristics of COVID-19 in patients with more than 80 years of age. METHODS: Epidemiological, clinical, laboratory, radiological, and treatment data from 17 patients diagnosed with COVID-19 between January 20 and February 20, 2020 were collected and analyzed retrospectively. Treatment outcomes among subgroups of patients with non-severe and severe symptoms of COVID-19 were compared. RESULTS: Of the 17 hospitalized patients with COVID-19, the median age was 88.0 years (interquartile range, 86.6-90.0 years; range, 80.0-100.0 years) and 12 (70.6%) were men. The age distribution of patients was not significantly different between non-severe group and severe group. All patients had chronic pre-existing conditions. Hypertension and cardiovascular diseases were the most common chronic conditions in both subgroups. The most common symptoms at the onset of COVID-19 were fever (n = 13; 76.5%), fatigue (n = 11; 64.7%), and cough (n = 5; 29.4%). Lymphopenia was observed in all patients, and lymphopenia was significantly more severe in the severe group than that in non-severe group (0.4 × 109/L vs 1.2 × 109/L, P = 0.014). The level of serum creatinine was higher in the severe group than in the non-severe group (99.0 µmol/L vs 62.5 µmol/L, P = 0.038). The most common features of chest computed tomography images were nodular foci in 10 (58.8%) patients and pleural thickening in 7 (41.2%) patients. All patients received antiviral therapy, while some patients also received intravenous antibiotics therapy (76.5%), Chinese medicinal preparation therapy (Lianhuaqingwen capsule, 64.7%), corticosteroids (35.3%) or immunoglobin (29.4%). Eight patients (47.1%) were transferred to the intensive care unit because of complications. Ten patients (58.8%) received intranasal oxygen, while 3 (17.6%) received non-invasive mechanical ventilation, and 4 (23.5%) received high-flow oxygen. As of June 20, 7 (41.2%) patients had been discharged and 10 (58.8% of this cohort, 77.8% of severe patients) had died. CONCLUSION: The mortality of patients aged 80 years and older with severe COVID-19 symptoms was high. Lymphopenia was a characteristic laboratory result in these patients, and the severity of lymphopenia was indicative of the severity of COVID-19. However, the majority of patients with COVID-19 in this age cohort had atypical symptoms, and early diagnosis depends on prompt use of a viral nucleic acid test.

The water-water cycle is more effective in regulating redox state of photosystem I under fluctuating light than cyclic electron transport.

Photosynthetic electron flux from water via photosystem II (PSII) and PSI to oxygen (water-water cycle) may act as an alternative electron sink under fluctuating light in angiosperms. We measured the P700 redox kinetics and electrochromic shift signal under fluctuating light in 11 Camellia species and tobacco leaves. Upon dark-to-light transition, these Camellia species showed rapid re-oxidation of P700. However, this rapid re-oxidation of P700 was not observed when measured under anaerobic conditions, as was in experiment with tobacco performed under aerobic conditions. Therefore, photo-reduction of O2 mediated by water-water cycle was functional in these Camellia species but not in tobacco. Within the first 10 s after transition from low to high light, PSI was highly oxidized in these Camellia species but was over-reduced in tobacco leaves. Furthermore, such rapid oxidation of PSI in these Camellia species was independent of the formation of trans-thylakoid proton gradient (ΔpH). These results indicated that in addition to ΔpH-dependent photosynthetic control, the water-water cycle can protect PSI against photoinhibition under fluctuating light in these Camellia species. We here propose that the water-water cycle is an overlooked strategy for photosynthetic regulation under fluctuating light in angiosperms.

Moderate heat stress accelerates photoinhibition of photosystem I under fluctuating light in tobacco young leaves.

Moderate heat stress and fluctuating light are typical conditions in summer in tropical and subtropical regions. This type of stress can cause photodamage to photosystems I and II (PSI and PSII). However, photosynthetic responses to the combination of heat and fluctuating light in young leaves are little known. In this study, we investigated chlorophyll fluorescence and P700 redox state under fluctuating light at 25 °C and 42 °C in young leaves of tobacco. Our results indicated that fluctuating light caused selective photodamage to PSI in the young leaves at 25 °C and 42 °C. Furthermore, the moderate heat stress significantly accelerated photoinhibition of PSI under fluctuating light. Within the first 10 s after transition from low to high light, cyclic electron flow (CEF) around PSI was highly stimulated at 25 °C but was slightly activated at 42 °C. Such depression of CEF activation at moderate heat stress were unable to maintain energy balance under high light. As a result, electron flow from PSI to NADP+ was restricted, leading to the over-reduction of PSI electron carriers. These results indicated that moderate heat stress altered the CEF performance under fluctuating light and thus accelerated PSI photoinhibition in tobacco young leaves.

The decline in photosynthetic rate upon transfer from high to low light is linked to the slow kinetics of chloroplast ATP synthase in Bletilla striata.

Upon a sudden transition from high to low light, the rate of CO2 assimilation (AN) in some plants first decreases to a low level before gradually becoming stable. However, the underlying mechanisms remain controversial. The activity of chloroplast ATP synthase (gH+) is usually depressed under high light when compared with low light. Therefore, we hypothesize that upon a sudden transfer from high to low light, the relatively low gH+ restricts ATP synthesis and thus causes a reduction in AN. To test this hypothesis, we measured gas exchange, chlorophyll fluorescence, P700 redox state, and electrochromic shift signals in Bletilla striata (Orchidaceae). After the transition from saturating to lower irradiance, AN and ETRII decreased first to a low level and then gradually increased to a stable value. Within the first seconds after transfer from high to low light, gH+ was maintained at low levels. During further exposure to low light, gH+ gradually increased to a stable value. Interestingly, a tight positive relationship was found between gH+ and ETRII. These results suggested that upon a sudden transition from high to low light, AN was restricted by gH+ at the step of ATP synthesis. Taken together, we propose that the decline in AN upon sudden transfer from high to low light is linked to the slow kinetics of chloroplast ATP synthase.

Responses of photosystem I compared with photosystem II to combination of heat stress and fluctuating light in tobacco leaves.

Moderate heat stress is usually accompanied with fluctuating light in summer. Although either heat stress or fluctuating light can cause photoinhibition of photosystems I and II (PSI and PSII), it is unclear whether moderate heat stress accelerate photoinhibition under fluctuating light. Here, we measured chlorophyll fluorescence, P700 redox state and the electrochromic shift signal under fluctuating light at 25 °C and 42 °C for tobacco leaves. We found that (1) the thylakoid proton conductance was significantly enhanced at 42 °C, leading to a decline in trans-thylakoid proton gradient (ΔpH); (2) this low ΔpH at 42 °C did not decrease donor-side limitation of PSI and thermal energy dissipation in PSII; (3) the activation of cyclic electron flow (CEF) around PSI was elevated at 42 °C; and (4) the moderate heat stress did not accelerate photoinhibition of PSI and PSII under fluctuating light. These results strongly indicate that under moderate heat stress the stimulation of CEF protects PSI under fluctuating light in tobacco leaves.

Genomic, Transcriptomic and Enzymatic Insight into Lignocellulolytic System of a Plant Pathogen Dickeya sp. WS52 to Digest Sweet Pepper and Tomato Stalk.

Abstract:Dickeya sp., a plant pathogen, causing soft rot with strong pectin degradation capacity was taken for the comprehensive analysis of its corresponding biomass degradative system, which has not been analyzed yet. Whole genome sequence analysis of the isolated soft-rotten plant pathogen Dickeya sp. WS52, revealed various coding genes which involved in vegetable stalk degradation-related properties. A total of 122 genes were found to be encoded for putative carbohydrate-active enzymes (CAZy) in Dickeya sp. WS52. The number of pectin degradation-related genes, was higher than that of cellulolytic bacteria as well as other Dickeya spp. strains. The CAZy in Dickeya sp.WS52 contains a complete repertoire of enzymes required for hemicellulose degradation, especially pectinases. In addition, WS52 strain possessed plenty of genes encoding potential ligninolytic relevant enzymes, such as multicopper oxidase, catalase/hydroperoxidase, glutathione S-transferase, and quinone oxidoreductase. Transcriptome analysis revealed that parts of genes encoding lignocellulolytic enzymes were significantly upregulated in the presence of minimal salt medium with vegetable stalks. However, most of the genes were related to lignocellulolytic enzymes, especially pectate lyases and were downregulated due to the slow growth and downregulated secretion systems. The assay of lignocellulolytic enzymes including CMCase and pectinase activities were identified to be more active in vegetable stalk relative to MSM + glucose. However, compared with nutrient LB medium, it needed sufficient nutrient to promote growth and to improve the secretion system. Further identification of enzyme activities of Dickeya sp.WS52 by HPLC confirmed that monosaccharides were produced during degradation of tomato stalk. This identified degradative system is valuable for the application in the lignocellulosic bioenergy industry and animal production.

Photorespiration is the major alternative electron sink under high light in alpine evergreen sclerophyllous Rhododendron species.

Owing to the high leaf mass per area, alpine evergreen sclerophyllous Rhododendron have low values of mesophyll conductance (gm). The resulting low chloroplast CO2 concentration aggravates photorespiration, which requires a higher ATP/NADPH ratio. However, the significance of photorespiration and underlying mechanisms of energy balance in these species are little known. In this study, eight alpine evergreen sclerophyllous Rhododendron species grown in a common garden were tested for their gm, electron flow to photorespiration, and energy balancing. Under saturating light, gm was the most limiting factor for net photosynthesis (AN) in all species, and the species differences in AN were primarily driven by gm rather than stomatal conductance. The total electron flow through photosystem II (ETRII) nearly equaled the electron transport required for Rubisco carboxylation and oxygenation. Furthermore, blocking electron flow to photosystem I with appropriate inhibitors showed that electron flow to plastic terminal oxidase was not observed. As a result, these studied species showed little alternative electron flow mediated by water-water cycle or plastic terminal oxidase. By comparison, the ratio of electron transport consumed by photorespiration to ETRII (JPR/ETRII), ranging from 43%∼55%, was negatively correlated to AN and gm. Furthermore, the increased ATP production required by enhanced photorespiration was regulated by cyclic electron flow around photosystem I. These results indicate that photorespiration is the major electron sink for dissipation of excess excitation energy in the alpine evergreen sclerophyllous Rhododendron species. The coordination of gm, photorespiration and cyclic electron flow is important for sustaining leaf photosynthesis.

Stimulation of cyclic electron flow around photosystem I upon a sudden transition from low to high light in two angiosperms Arabidopsis thaliana and Bletilla striata.

In angiosperms, cyclic electron flow (CEF) around photosystem I (PSI) is more important for photoprotection under fluctuating light than under constant light. However, the underlying mechanism is not well known. In the present study, we measured the CEF activity, P700 redox state and electrochromic shift signal upon a sudden transition from low to high light in wild-type plants of Arabidopsis thaliana and Bletilla striata (Orchidaceae). Within the first 20 s after transition from low to high light, P700 was highly reduced in both species, which was accompanied with a sufficient proton gradient (ΔpH) across the thylakoid membranes. Meanwhile, the level of CEF activation was elevated. After transition from low to high light for 60 s, the plants generated an optimal ΔpH. Under such condition, PSI was highly oxidized and the level of CEF activation decreased to the steady state. Furthermore, the CEF activation was positively correlated to the P700 reduction ratio. These results indicated that upon a sudden transition from low to high light, the insufficient ΔpH led to the over-reduction of PSI electron carriers, which in turn stimulated the CEF around PSI. This transient stimulation of CEF not only favored the rapid ΔpH formation but also accepted electrons from PSI, thus protecting PSI at donor and acceptor sides. These findings provide new insights into the important role of CEF in regulation of photosynthesis under fluctuating light.