Quantum Efficiency Of PSII Research Articles

Photochemical efficiency and growth of soursop rootstocks subjected to salt stress and hydrogen peroxide

Hydrogen peroxide has been used in agriculture as a way to minimize the negative effects caused by biotic and abiotic stresses on plants. Thus, the objective of this study was to evaluate the mitigating effect of hydrogen peroxide on chlorophyll <em>a</em> fluorescence and growth of soursop subjected to salt stress in the rootstock production phase. The study was conducted in plastic bags under greenhouse conditions. The treatments were distributed in randomized blocks, in a 5 × 2 factorial arrangement, corresponding to five levels of irrigation water electrical conductivity—ECw (0.6; 1.2; 1.8; 2.4 and 3.0 dS m^-1) and two concentrations of hydrogen peroxide—H₂O₂ (0 and 20 μM), with four replicates and two plants per plot. Irrigation water salinity hamper the quantum efficiency of photosystem II in soursop plants, at 120 days after sowing and it inhibits the growth of rootstocks in the period from 80 to 140 days after sowing. Hydrogen peroxide applications at concentration of 20 μM minimized the negative effects of salinity on the soursop initial fluorescence and favored the variable fluorescence and quantum efficiency of PSII.

Effects of light-dependent herbicides on growth and physiology of Salvia officinalis

Background: Salvia officinalis a medicinal plant which is severely affected by weeds competition. Objective: The objective of this study was to determine the growth and physiological responses of S. officinalis to some light-dependent herbicides. Methods: A factorial experiment was conducted to determine the effects of oxadiargyl (T), bentazon (B), oxyfluorfen (O), metribuzin (M), phenmedipham+desmedipham (P) at 0.75 (1), 1 (2) and 1.25 (3) rates on growth and physiological parameters of S. officinalis. Results: All herbicides initially caused visual injury to S. officinalis. SPAD values were decreased by all herbicide treatments except for low rate of phenmedipham+desmedipham and oxadiargyl. The relative leaf water content (RLWC) decreased following herbicide treatments except in P1, P2, B1, and B2. Membrane stability index decreased by herbicide treatments however there were no differences among control and P1, P2, B1, B2, O1, O3, M3, T1, T2, and T3. All rates of oxyfluorfen and oxadiargyl, P1, B1 and B2 had no marked effect on the maximum quantum efficiency of PSII (Fv/Fm). Plant growth was not affected by herbicide treatments probably due to the recovery of the plants at the end of the experiment excepting for metribuzin. Essential oil content increased as the herbicide rate increased based on herbicide type. Conclusions: The results showed that S. officinalis had the ability to recover over time depending on the herbicide type and rate. Results showed that phenmedipham+desmedipham and bentazon are suitable and metribuzin unsuitable herbicides for weeds selective control in S. officinalis.

Physiological and biochemical responses of basil to some allelopathic plant residues and dodder infestation

In the present study, the effects of three allelopathic plant residues, namely Syrian bean-caper (Zygophyllum fabago L.), marigold (Calendula officinalis L.), and jimsonweed (Datura stramonium L.) on two cultivar of sweet basil (Ocimum basilicum L.) plants infested by dodder (Cuscuta campestris Yunck.) were examined using factorial experiment in randomized complete block design with three replications. Means comparison revealed that the degree of sensitivity to allelopathic plant residues and dodder infestation in Iranian cultivar (Mubarake) of the basil was more than that of the Italian cultivar. In the plants, infested by dodder, a significant increase in the content of total soluble sugars, peroxidase activity, catalase, superoxide dismutase, ascorbate peroxidase and the initial fluorescence (F0) was observed, while a noticeable decrease in their height, shoot dry weight, relative water content, pigment–protein content, the variable fluorescence (Fv) and the maximum quantum efficiency (Fv/Fm) of PSII was recorded. Depending on the allelopathic plants used in this study, the effect of the residues on dodder infestation and basil growth varied significantly. While the use of Z. fabago and D. stramonium residues positively correlated with the suppression of dodder emergence, D. stramonium residue use showed a negative impact on basils’ growth. In contrast, the usage of C. officinalis residues could not diminish dodder infestation, and in dodder-infested basils it decreased plant performance, RWC, pigment and protein content and the maximum quantum efficiency (Fv/Fm) of PSII. Meanwhile, the application of Z. fabago residues to dodder-infested basil plants decreased dodder emergence rate and increased basil plants’ height, dry weight of shoot, relative water content, pigment and protein content, and the maximum quantum efficiency (Fv/Fm) of PSII. Our findings suggest that as an environment-friendly treatment, Z. fabago residues could be used for controlling dodder infestation in basil plants.

Photochemical efficiency and growth of soursop rootstocks subjected to salt stress and hydrogen peroxide

Hydrogen peroxide has been used in agriculture as a way to minimize the negative effects caused by biotic and abiotic stresses on plants. Thus, the objective of this study was to evaluate the mitigating effect of hydrogen peroxide on chlorophyll a fluorescence and growth of soursop subjected to salt stress in the rootstock production phase. The study was conducted in plastic bags under greenhouse conditions. The treatments were distributed in randomized blocks, in a 5 × 2 factorial arrangement, corresponding to five levels of irrigation water electrical conductivity—ECw (0.6; 1.2; 1.8; 2.4 and 3.0 dS m-1) and two concentrations of hydrogen peroxide—H2O2 (0 and 20 μM), with four replicates and two plants per plot. Irrigation water salinity hamper the quantum efficiency of photosystem II in soursop plants, at 120 days after sowing and it inhibits the growth of rootstocks in the period from 80 to 140 days after sowing. Hydrogen peroxide applications at concentration of 20 μM minimized the negative effects of salinity on the soursop initial fluorescence and favored the variable fluorescence and quantum efficiency of PSII.

Leaf water status, physiological behavior and biochemical mechanism involved in young olive plants under water deficit

Changes in leaf relative water content (RWC), water potential (Ψw), transpiration rate (E & Tsp), stomatal conductance (gs), maximum quantum efficiency of PSII (Fv/Fm), total chlorophylls, carotenoids, proline and soluble sugars were investigated in young Moroccan olive varieties (‘Moroccan Picholine’, ‘Menara’ and ‘Haouzia’) grown in pots under three water regimes (well-watering, moderate stress and high stress). The water treatment was applied at different growth stages during three growing seasons (2015, 2016 and 2017). Results from ANOVA analyses showed that all parameters were found to be mainly under the impact of the water regime and growth stage. In fact, the severe stress led to significant reductions in Ψw, gs, E and Tsp by more than 24%, but also in RWC, Fv/Fm and total chlorophylls with percentages lower than 15%. In contrast, water shortage activated the accumulation of proline and soluble sugars by about 13%. Among growth stages, the bud development displayed the highest levels for RWC, Ψw, gs, E, Tsp and Fv/Fm, and the lowest ones for proline and soluble sugars, whilst, the opposite was observed during the fruiting stage. Although the impacts of variety, growing season and interactions were of minor extents, we observed some significant differences. In fact, the young olive trees belonging to 'Moroccan Picholine' have shown more resistance to water stress, especially during the 2017 season. Principal component analysis (PCA) showed that 92% of the total observed variability was explained by the first two principal components, and allowed a good discrimination among the tree water regimes and the five growth stages. In addition, positive relationship was established between proline and soluble sugars, which were found negatively associated with the remaining parameters.

Cotton leaf photosynthetic characteristics, biomass production, and their correlation analysis under different irrigation and phosphorus application

Water and fertilizer application are the yield improvement approaches in cotton production, especially in arid regions. We hypothesized that irrigation and phosphorus fertilization regimes would enhance cotton leaf photosynthesis capacity. We examined two irrigation levels, i.e., normal irrigation (W1: 3,750 m3 hm-2) and limited irrigation (W2: 2,500 m3 hm-2), combined with no phosphorus (P0) and P application (P1: applying P2O5 with the ratio of the fertilizer to dry soil being 0.15 g kg-1). Leaf area (LA), net photosynthetic rate (PN), transpiration rate (E), and quantum efficiency of PSII (YII) of cotton under P1 were higher than that under P0. Under P1 conditions, the increasing rate of fruiting branches LA with W2 was 12.6% higher than that of W1 after 69 d (DAE). PN and E were 9.8 and 6.3% higher, respectively; YII was 38.0% higher at 69 DAE. The total and reproductive organs dry mass (DM) were in the following pattern: W1P1 > W1P0 > W2P1 > W2P0. After 69 DAE, there was a highly significant correlation between the fruit-branch LA and YII, between the fruit-branch LA and PN, and between PN and reproductive organs DM and total DM. Therefore, application of P can enlarge leaf area and slow down chlorophyll degradation, thus promoting accumulation of photosynthetic products in reproductive organs, especially under drought conditions.

Chlorophyll fluorescence analysis in diverse rice varieties reveals the positive correlation between the seedlings salt tolerance and photosynthetic efficiency

BackgroundPhotosynthetic efficiency might be a key factor determining plant resistance to abiotic stresses. Plants can sense when growing conditions are not favorable and trigger an internal response at an early stage before showing external symptoms. When a high amount of salt enters the plant cell, the membrane system and function of thylakoids in chloroplasts could be destroyed and affect photosynthetic performance if the salt concentration is not regulated to optimal values. Oryza species have salt-tolerant and salt-sensitive genotypes; however, very few studies have investigated the genetic architecture responsible for photosynthetic efficiency under salinity stress in cultivated rice.ResultsWe used an imaging-based chlorophyll fluorometer to monitor eight rice varieties that showed different salt tolerance levels for four consecutive days under control and salt conditions. An analysis of the changes in chlorophyll fluorescence parameters clearly showed the maximum quantum efficiency of PSII in sensitive varieties was significantly reduced after NaCl treatment when compared to tolerant varieties. A panel of 232 diverse rice accessions was then analyzed for chlorophyll fluorescence under salt conditions, the results showed that chlorophyll fluorescence parameters such as F0 and NPQ were higher in Japonica subspecies, ΦPSII of Indica varieties was higher than that in other subgroups, which suggested that the variation in photosynthetic efficiency was extensively regulated under salt treatment in diverse cultivated rice. Two significant regions on chromosome 5 were identified to associate with the fraction of open PSII centers (qL) and the minimum chlorophyll fluorescence (F0). These regions harbored genes related to senescence, chloroplast biogenesis and response to salt stress are of interest for future functional characterization to determine their roles in regulating photosynthesis.ConclusionsRice plant is very sensitive to salinity stress, especially at young seedling stage. Our work identified the distribution pattern of chlorophyll fluorescence parameters in seedlings leaf and their correlations with salt tolerance level in a diverse gene pool. We also revealed the complexity of the genetic architecture regulating rice seedling photosynthetic performance under salinity stress, the germplasm analyzed in this study and the associated genetic information could be utilized in rice breeding program.

Physiological analysis and transcriptome sequencing reveal the effects of combined cold and drought on tomato leaf

BackgroundCo-occurrence of cold and drought stress can alter the response of plants at morphological, physiological and molecular levels, which finally affect crop production, more than individual stress. Understanding the responses of crop to combined stress is necessary to improve tolerance and maintain crop production especially in the field where combined stress frequently occurs. We aimed to clarify the underlying leaf physiological and molecular mechanisms of tomato by imposing combining cold and drought on one popular tomato cultivar ‘Jinlingmeiyu’ as an example.ResultsThe physiological and genetic responses were identified in tomatoes after 42 h exposure to control, cold, drought and combined treatments. As compared with control, water loss rate at the three stresses including cold, drought and combined stress significantly decreased until 40 min after taking samples from the plants. The content of H2O2, zeatin riboside (ZR) and melatonin in all stress treatments were significantly higher than the control. Drought stress alone and combined stress induced the accumulation of abscisic acid (ABA) and auxin (IAA) as compared with control. The individual cold and combined stress significantly decreased the maximum quantum efficiency of PSII (Fv/Fm), quantum yield of PSII (Fq′/Fm′) and electron transport rate (ETR). In total, 7141, 1850 and 7841 genes were involved in the stress response to cold, drought and their combination. Functional analysis of the stress-inducible genes provided more insights concerning the complex regulatory mechanisms that were involved in combined stress. The expression level of 12 genes were validated by quantitative real-time PCR (qRT-PCR).ConclusionsWe found that the expression of stress-specific genes changed with physiological variation, indicating the close crosstalk between physiological and genetic response especially under combined stress. This study provides new knowledge on the complex regulatory mechanism genes in tomato (‘Jinlingmeiyu’) leaf to abiotic stresses.

Maintenance of photosynthesis and the antioxidant defence systems have key roles for survival of Halopeplis perfoliata (Amaranthaceae) in a saline environment

Coastal salt marsh plants employ various combinations of morphological and physiological adaptations to survive under saline conditions. Little information is available on salinity tolerance mechanisms of Halopeplis perfoliata, a C3 stem succulent halophyte. We investigated the growth, photosynthesis and antioxidant defence mechanisms of H. perfoliata under saline conditions (0, 150, 300 and 600 mM NaCl) in an open greenhouse. Optimal shoot succulence, projected shoot area and relative growth rate were obtained in the low (150mm NaCl) salinity treatment, while growth was inhibited at the highest salinity (600mm NaCl). The CO2 compensation point and carbon isotope composition of biomass confirmed C3 photosynthesis. Increases in salinity did not affect the photosynthetic pigment content or maximum quantum efficiency of PSII of H.perfoliata. Assimilation of CO2 (A) also remained unaffected by salinity. A modest effect on some gas exchange and photochemistry parameters was observed at 600mm NaCl. With increasing salinity, there was a continual increase in respiration, suggesting utilisation of energy to cope with saline conditions. Under 300 and 600mm NaCl, there was an increase in H2 O2 and MDA with a concomitant rise in AsA, GR content and CAT activity. Hence, H.perfoliata appears to be an obligate halophyte that can grow up to seawater salinities by modulating photosynthetic gas exchange, photochemistry and the antioxidant defence systems.

Low Nitrogen Priming Enhances Photosynthesis Adaptation to Water-Deficit Stress in Winter Wheat (Triticum aestivum L.) Seedlings.

Drought is among the main environmental stressors that reduces wheat production. Nitrogen (N) availability affects plant adaptation to abiotic stress, but the effect of low N (LN) on drought tolerance is unclear. To identify the effect of LN priming on water-deficit stress tolerance in wheat seedlings, we primed cultivar Yangmai158 with 0.25 mM N for 7 days, and then added 20% polyethylene glycol 6000 as a water-deficit treatment for 5 days. The net photosynthetic rate (Pn), plant biomass, and plant growth rate (GR) were significantly reduced under water-deficit conditions; such decreases were less severe in LN-primed (LND) plants than non-primed (CKD) plants. The leaf relative water content (LRWC) decreased under water-deficit conditions, which in turn led to a reduced transpiration rate, stomatal conductance, and intercellular CO2 concentration (Ci), causing a stomatal limitation on photosynthesis. LN priming also enhanced root growth, resulting in a higher LRWC and less stomatal limitation in LND plants than CKD plants. PSII quantum efficiency, photochemical quenching, and maximum PSII quantum efficiency were reduced under water-deficit conditions, indicating photoinhibition. However, LN priming increased the electron flux to photorespiration and the Mehler pathway, reducing photoinhibition. In conclusion, LN priming improved the leaf water status and increased alternative electron flux to attenuate photoinhibition, thus alleviating the inhibition of photosynthesis, and growth due to water deficiency.

Cross talk between ROS homeostasis and antioxidative machinery contributes to salt tolerance of the xero-halophyte Haloxylon salicornicum

Salinity is a foremost environmental threat that challenges agriculture and food security worldwide. In the present work, physiological, biochemical and anatomical strategies adopted by the xero-halophyte Haloxylon salicornicum in response to salinity was investigated. H. salicornicum plant withstands a prolong treatment of salinity, even under high dose of NaCl (400 mM). Our results showed that both fresh and dry biomass of shoot, plant height, and shoot area increased under low salinity (100–200 mM NaCl), whereas these parameters remained unaffected under high salinity (300–400 mM NaCl). In H. salicornicum, shoot water content (SWC%) was maintained at all levels of salinity. Salt tolerance index of H. salicornicum did not decline with increasing doses of salinity indicating salt tolerance capability of the plant. Although, salinity caused an increase in Na+ content of shoot, but K+ content of shoot remained steady at all levels of salinity. The rate of photosynthesis (PN), stomatal conductance (gs), rate of transpiration (E), water use efficiency (WUE), quantum yield of PSII (ΦPSII), photochemical quenching (qP), and electron transport rate (ETR) remained at par to the control level under low salinity (100–200 mM NaCl) and then reduced significantly under high salinity (300–400 mM NaCl). Salinity had no significant impacts on maximum quantum efficiency of PSII (Fv/Fm) and non-photochemical quenching (NPQ) which implies that PS II remained unaffected by sanity-induced oxidative damage. The levels of H2O2 and NO increased significantly under salinity, whereas the level of O2•− remained unaffected under various levels of salinity. Higher level of H2O2 and NO indicates the signaling role of these molecules. Lipid peroxidation level remained unchanged under low salinity (0–300 mM NaCl), but increased significantly under extreme salinity (400 mM NaCl). Ratio of AsA/DHA (indicator of cellular redox potential) elevated under high salinity (300–400 mM NaCl). The activities of various enzymatic antioxidants like SOD, APX, POX, GR and CAT showed differential responses under salinity. The results propose that coordination between enzymatic and non-enzymatic antioxidative components regulates ROS levels in H. salicornicum and contribute in salt tolerance by maintaining water status, ion homeostasis, redox status of the cells, and efficient protection of PSII form salinity induced oxidative damage. Higher tolerance index, optimal growth and competent antioxidative system make this xero-halophyte a suitable candidate for reclamation of salt degraded agricultural lands and can be a potent genetic resource for the development of salinity tolerant crops.

Identification and expression of the Cucurbita WRKY transcription factors in response to water deficit and salt stress

WRKY transcription factors (TFs) have been reported to play important roles in plant responses to various stress conditions. Although several studies on the genomic organization of the WRKY gene family in various species have been reported, the information related to the genus Cucurbita is scarce, and null in the case of Cucurbita pepo. The present study aimed to examine the response of Cucurbita pepo to water deficit and salt stress. Additionally, WRKY gene family has been identified and characterized in this species. Shoot growth was negatively affected by both adverse situations. Similarly, both salt and water stress conditions reduced transpiration and stomatal conductance in C. pepo plants. However, the quantum efficiency of PSII decreased only in those plants exposed to salt stress. The increase in proline concentration recorded in C. pepo plants subjected to salt or drought stress point out the important role of this amino acid for plant tolerance to both stress conditions.Based on the genome sequence, 95 CmWRKY genes were found and classified into three main groups according to their orthologues in Arabidopsis. Among these, 24 and 14 CmWRKY genes were responsive to water and salt stresses, respectively. Three water stress-responsive genes were up-regulated under the adverse condition. The expression of six CmWRKY genes was induced by NaCl treatment. Therefore, a total of nine up-regulated genes related to both stresses were identified, suggesting their putative involvement in the plant response to water deficit and salt stress.

Salinity restricts light conversion efficiency during photo-acclimation to high irradiance in Stuckenia pectinata

Thick beds of Stuckenia pectinata, a submerged macrophyte, were lost from Te Waihora (Lake Ellesmere) in 1968, following an extreme storm event. Subsequently, it has failed to re-establish what is now a turbid coastal lagoon with a rapid light attenuation and fluctuating salinities. We investigated the interacting effects of irradiance and salinity on photosynthesis of S. pectinata in a laboratory experiment. S. pectinata plants were first acclimated to three irradiances: 340 ± 20 μmol photons m−2 s−1, 110 ± 10 μmol photons m−2 s−1, and 45 ± 5 μmol photons m−2 s−1. At each irradiance, half of the plants experienced increasing salinity stress in a stepwise manner (0, 6, 12 and 18 ppt), whereas the other half remained in freshwater. The intrinsic and effective quantum yield of photosystem II, photosynthesis-irradiance relationships, chlorophyll-a and total carotenoids content, and PSII quantum efficiency of regulated heat dissipation were determined. On a chlorophyll-a basis, light-saturated gross photosynthesis was reduced at high irradiance by 12 and 18 ppt salinity, and at medium irradiance by 18 ppt salinity. Coincidently, plants displayed lowered chlorophyll-a to carotenoids ratios and enhanced heat dissipation in the same treatments. The photosynthetic apparatus in leaves of S. pectinata responded to salinity stress as if in acclimation to high light stress. The response of photosynthesis to an interaction of high salinity and high-light reduces the light conversion efficiency of surface reaching leaves, undermining the default shade-avoidance strategy of S. pectinata of etiolation, and thus contributes to the reduced overall photosynthetic capacity and its ability to colonise the lake.

Effects of Pb and Zn toxicity on chlorophyll fluorescence and biomass production of Koelreuteria paniculata and Zelkova schneideriana young plants

The influence of Pb and Zn on chlorophyll (Chl) fluorescence and plant growth of one-year-old Koelreuteria paniculata and Zelkova schneideriana young plants was investigated. Pb and Zn contents in plant organs were measured. The results showed Pb and Zn stress decreased photochemical quenching and quantum efficiency of PSII, but increased energy dissipation in the tested plants. At the same time, maximum net photosynthetic rate, maximum quantum use efficiency, and organ biomass were reduced. Under the same concentration of heavy metals, the damage induced by Zn toxicity was more serious than that of Pb. Pb was less accumulated in leaves, with a mild effect on photosynthesis. Zn was mostly accumulated in leaves and strongly disturbed chloroplast functioning and affected photosynthesis. Pb and Zn had different pathway to influence biomass production, and both tested plants might use different mechanisms of action for heavy metal stress resistance.

ASSOCIATION MAPPING OF MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS OF FLAG LEAF RELATED TO DROUGHT TOLERANCE IN BARLEY

Association mapping has proven to be a powerful approach for dissecting the genetic basis of complex traits. In this study, QTLs controlling flag leaf characteristics under drought stress were detected in a set of 148 modern spring barley cultivars using AM analysis. Flag leaf length (FLL), flag leaf width (FLW), relative water content (RWC), chlorophyll content, and maximum quantum efficiency of PSII (Fv/Fm) which are important in photosynthetic rate, were evaluated under normal irrigation and drought stress conditions at grain filling stage. Population structure was estimated using Structure 2.3 and linkage disequilibrium (LD) was estimated by the ‘Full Matrix LD’ using Tassel 5.0 . Significant marker/trait associations were investigated based on K-Q matrix using Tassel 3.0 . The analysis of population structure divided the cultivars into two sub-groups. Significant LD values (P < 0.01) between polymorphic sites with regions of high and low LD were observed. A total of 84 significant putative genomic regions were identified, which delineated into 37 QTLs under two water treatments. Two stable QTLs on 2H and 3H were detected for FLL in drought stress treatment. A QTL for FLL were detected on 2H in normal treatment, which alone explained around 11% of phenotypic variance of FLL. This QTL was also associated with the expression of FLW and explained around 7.5% of phenotypic variance. The results suggest that major loci are located on chromosomes 2H, 3H, 4H and 5H involved in the development of flag leaf characteristics and could be used as selection criteria in barley breeding for drought tolerance.

Light-induced systemic signalling down-regulates photosynthetic performance of soybean leaves with different directional effects.

When plants are exposed to a heterogeneous environment, photosynthesis of leaves is not only determined by their local condition, but also by certain signals from other parts of the same plant, termed systemic regulation. Our present study was conducted to investigate the effects of light-dependent systemic regulation on the photosynthetic performance of soybean (Glycine max L. Merr.) under heterogeneous light conditions. Soybean plants were treated with heterogeneous light. Then gas exchange characteristics were measured to evaluate the photosynthetic performance of leaves. Parameters related to photosynthetic pigments, chlorophyll fluorescence, Rubisco and photosynthates were examined to study the mechanisms of light-dependent systemic regulation on photosynthesis. Light-induced systemic signalling by illuminated leaves reduced the Pn of both upper and lower non-illuminated leaves on the same soybean plant. The decrease in gs and increase in Ci in these non-illuminated leaves indicated restriction of carbon assimilation, which was further verified by the decline in content and activity of Rubisco. However, the activation state of Rubisco decreased only in upper non-illuminated leaves. Quantum efficiency of PSII (ΦPSII) and ETR also decreased only in upper non-illuminated leaves. Moreover, the effects of light-induced systemic signalling on carbohydrate content were also detectable only in upper non-illuminated leaves. Light-induced systemic signalling by illuminated leaves restricts carbon assimilation and down-regulates photosynthetic performance of non-illuminated leaves within a soybean plant. However, effects of such systemic regulation differed when regulated in upward or downward direction.

Unraveling the Role of Red:Blue LED Lights on Resource Use Efficiency and Nutritional Properties of Indoor Grown Sweet Basil.

Indoor plant cultivation can result in significantly improved resource use efficiency (surface, water, and nutrients) as compared to traditional growing systems, but illumination costs are still high. LEDs (light emitting diodes) are gaining attention for indoor cultivation because of their ability to provide light of different spectra. In the light spectrum, red and blue regions are often considered the major plants’ energy sources for photosynthetic CO2 assimilation. This study aims at identifying the role played by red:blue (R:B) ratio on the resource use efficiency of indoor basil cultivation, linking the physiological response to light to changes in yield and nutritional properties. Basil plants were cultivated in growth chambers under five LED light regimens characterized by different R:B ratios ranging from 0.5 to 4 (respectively, RB0.5, RB1, RB2, RB3, and RB4), using fluorescent lamps as control (CK1). A photosynthetic photon flux density of 215 μmol m−2 s−1 was provided for 16 h per day. The greatest biomass production was associated with LED lighting as compared with fluorescent lamp. Despite a reduction in both stomatal conductance and PSII quantum efficiency, adoption of RB3 resulted in higher yield and chlorophyll content, leading to improved use efficiency for water and energy. Antioxidant activity followed a spectral-response function, with optimum associated with RB3. A low RB ratio (0.5) reduced the relative content of several volatiles, as compared to CK1 and RB ≥ 2. Moreover, mineral leaf concentration (g g−1 DW) and total content in plant (g plant−1) were influences by light quality, resulting in greater N, P, K, Ca, Mg, and Fe accumulation in plants cultivated with RB3. Contrarily, nutrient use efficiency was increased in RB ≤ 1. From this study it can be concluded that a RB ratio of 3 provides optimal growing conditions for indoor cultivation of basil, fostering improved performances in terms of growth, physiological and metabolic functions, and resources use efficiency.

Physiological and transcriptional responses to low-temperature stress in rice genotypes at the reproductive stage

ABSTRACTRice growth and productivity is adversely affected by low-temperature stress. From a previous screen of diverse rice genotypes for cold tolerance parameters at the vegetative stage, we selected the tolerant Nipponbare and M202 genotypes and sensitive Cypress and Secano do Brazil genotypes for further analysis at the reproductive stage for physiological and yield parameters. Cold stress severely affected grain yield as estimated by the number of grain per panicle, panicle length, and 100 seed weight. Analysis of gene expression of 21 genes involved in physiological responses to low temperature tested, in the flag leaf and inflorescence tissue of these genotypes, showed an increased expression of the Lipid Transfer Protein genes LTP7 and LTP10 in flag leaf tissue of the tolerant Nipponbare and M202, along with a significant increase in the relative expression of stress-responsive transcription factors (TFs) and cold-inducible genes. In flag leaf tissue OsNAC9, OsNAC10 and OsNAP genes showed high correlation with photosynthesis, stomatal conductance, transpiration and Quantum Efficiency of PSII. In consequence of the foregoing results, we conclude that Nipponbare and M202 are cold tolerant genotypes and that LTP7, LTP10, OsNAC9, OsNAC10 and OsNAP genes can be used as markers in screening for cold tolerance at the reproductive stage. Furthermore based on the results we propose a model of low-temperature tolerance mechanism of how stress is perceived, and how the signal cascade acts to promote tolerance at below-ideal temperatures.

Photosystem photochemistry, prompt and delayed fluorescence, photosynthetic responses and electron flow in tobacco under drought and salt stress

The present study aimed to understand the photosynthetic responses and chlorophyll fluorescence transient in tobacco under drought and salt stress. Net CO2 assimilation rate, stomatal conductance, intercellular CO2 concentration and transpiration rate decreased significantly under drought and salt stress. The maximum quantum efficiency of PSII and electron transport rate were lower in tobacco under drought and salt stress. The maximum carboxylation rate, maximum electron transport rate, triosephosphate utilization efficiency, and mesophyll conductance decreased under drought and salt stress, while dark respiration increased. A pool size of the electron acceptors on reducing side of PSII and activity of water-splitting complex on the donor side of the PSII decreased during drought and salt stress. Present results suggested upregulation of the photorespiratory pathway as a strategy to maintain the ribulose-1,5-bisphosphate regeneration for maintenance of photosynthesis under drought and salt stress. Chlorophyll fluorescence indicated the impaired electron transfer and changes in the architecture of light-harvesting complex in tobacco leaves under drought and salt stress.

Photosynthetic activity assessment in mixotrophically cultured Chlorella vulgaris biofilms at various developmental stages

Biofilm reactors have been used to grow the microalga Chlorella vulgaris, which under mixotrophic conditions can effectively grow as biofilm with reduced liquid volumes and low energy consumption requirements. Under mixotrophic conditions, CO2 is internally generated and can be reduced to carbohydrates or lipids, with changes in gene expression. However, our knowledge of the photosynthetic activity and gene expression profiles of C. vulgaris cultured in a biofilm reactor using glycerol and urea in the absence of external CO2 is limited. Our goal was to assess the 1) chlorophyll-a fluorescence, 2) oxygen evolution, and 3) gene expression levels of C. vulgaris biofilms in the exponential growth (0–96 h) and stationary phases at the onset of lipid biosynthesis (168 h). The maximum quantum efficiency of PSII (Fv/Fm) varied between 0.64 and 0.69, indicating no stress during growth for the mixotrophic C. vulgaris biofilms. In photosynthetic oxygen evolution measurements C. vulgaris mixotrophic cells exhibited dark respiration (higher than 25 mg O2 mg Chl-a−1 s−1); at the same time, they were photosynthetically active with electron transport rate (ETR) values up to 50 μmol electrons m−2 s−1. The change in gene expression of light-regulated enzymes linked to carbon fixation, such as rbcl, was slightly higher in the stationary phase, while the gene expression of other enzymes, such as G3PD and PRK, was reduced in 168-hour-old biofilms. On the other hand, the gene expression of MDH for carbon metabolism and of enzymes ACC and DGAT for lipid biosynthesis was upregulated in 168-hour-old biofilms. These results show that in algal biofilms under mixotrophic growth conditions, autotrophy is not limited by glycerol and is fully complemented by the heterotrophic metabolism through a cycle in which photosynthesis utilizes the CO2 released by the respiration of C. vulgaris in the presence of glycerol and urea.