Higher Photosynthetic Capacity Research Articles

Effects of Pea (Pisum sativum L.) Cultivars for Mixed Cropping with Oats (Avena sativa L.) on Yield and Competition Indices in an Organic Production System.

The benefits of cereal-legume mixed cropping is a sustainable agricultural practice. However, knowledge of the genotypic differences of semi-leafless pea varieties is not enough to help them compete with cereals. In this study, the effects of Lithuania's newest Pisum sativum cultivars ('Egle DS' and 'Lina DS') and, for comparison, a control cultivar ('Jūra DS') established with Avena sativa in mixed cropping system were investigated. Three years of field trials (2018, 2019 and 2020) with four experiments involved three different mixtures of each field pea cultivar with oat. The aboveground biomass of mixed cropped new field pea cultivars was found to be significantly higher: biomass of cultivars 'Egle DS' increased by 17.0% and 'Lina DS' by 7.2% on average compared with the control cultivar 'Jūra DS'. For the mixed cropping system, statistically greater total aboveground biomass was observed with plant ratios of 50% pea + 50% oat and 60% pea + 40% oat compared to peas monocultures. Mixed cropped oat was the dominant species in all tested mixture compositions; however, the highest total grain yield of mixed crops was obtained when new pea 'Lina DS' and 'Egle DS' cultivars were included in the mixtures compared with the control cultivar. The new pea cultivar 'Egle DS' had a greater effect on protein content compared to other tested pea cultivars. In the new pea cultivars 'Lina DS' and 'Egle DS', the higher photosynthetic capacity and aboveground biomass of mixed cropped pea with oat showed mixture effects in the mixed cropped system and could increase total yield compared with pea monoculture. Generally, the new pea cultivars displayed a greater Land Equivalent Ratio (LER) value, resulting in the greatest yield among the mixtures on average for all three years and all four experiments. Future research could optimize the effects of pea cultivar mixtures with cereals to further improve the yield of organic mixed cropping systems.

Improving C3 photosynthesis by exploiting natural genetic variation: Hirschfeldia incana as a model species

AbstractDespite research efforts toward improving crop photosynthetic energy conversion efficiencies over the past 40 years, photosynthetic efficiencies remain far from their theoretical maxima. A major challenge has been that plant photosynthesis is a complex process, controlled by many underlying genetic factors and highly dynamic in response to short‐term environmental changes. Recent approaches to improving photosynthesis involved model‐based identification of the bottlenecks in photosynthesis followed by their genetic modification (GM). While these approaches were successful and inspirational, their dependency on the use of GM techniques may restrict their implementation in some jurisdictions. We therefore suggest greater research focus on a different, yet complementary, approach to improving photosynthetic efficiency: the exploration and exploitation of natural genetic variation in photosynthesis. A substantial improvement in phenotyping and genotyping technology over the past decade has highlighted natural variation in photosynthetic sub‐traits for crop and model species. However, a comprehensive understanding of all the factors responsible for photosynthetic limitations is still lacking. We therefore propose the use of high photosynthetic capacity species as models for the exploration of the physiological and genetic basis of high photosynthetic efficiency. While most high photosynthetic capacity species are not suitable as models due to complex genetics and evolutionary distance from crops, we have identified Brassicaceae species Hirschfeldia incana (L.) Lagr.‐Foss as a promising candidate. In this perspective paper, we describe and advocate the use of H. incana as a model for the exploration of high maximum CO2 assimilation rates (Pmax) found in some C3 species. We describe the basic biology and evolutionary history of the species and report preliminary data on its photosynthetic characteristics. Our findings suggest H. incana is an excellent model species for studies aiming at understanding natural genetic variation in photosynthetic efficiency.

Exogenous trehalose protects photosystem II in heat-stressed wheat

Background: Photosystem II (PSII) is susceptible to heat stress. Plants naturally accumulate trehalose to improve stress tolerance. However, the mechanism by which trehalose affects PSII during heat stress is still unknown.
 Questions: How does trehalose affect PSII during heat stress?
 Studied species: Triticum aestivum L.
 Study site and dates: Shanghai, China. 2019-2021.
 Methods: Trehalose -pretreated wheat seedlings suffered from heat stress and their photosynthetic parameters were measured.
 Results: Heat stress caused a reduction in the photochemical efficiency of PSII, the electron transfer rate (ETR(II)), the quantum yield of regulated energy dissipationY(NPQ) and the coefficient of photochemical quenching (qP), but increased the quantum yield of non-regulated energy dissipation of PSII (Y[NO]). The shape of the fast chlorophyll fluorescence induction kinetics (OJIP) curve in the heat-stressed wheat was altered and the primary photochemistry maximum yield of PSII (Fv/Fo) and the PSII performance indicator PIabs were reduced. Accordingly, the activities of PSII and electron transport chain, the amount of ordered α-helix structures and the content of D1 protein also decreased. However, in trehalose-pretreated wheat, D1 protein and protein secondary structures of PSII were both protected, the electron transport activities of PSII and the whole chain were improved and greater fluorescence parameters values were maintained. Lower Y(NO) and more stable OJIP were obtained.
 Conclusions: Exogenous trehalose acted a vital role in the protection of the function of PSII, resulting in higherphotosynthetic capacity under heat stress.

Hydrogen peroxide regulates the biosynthesis of phenolic compounds and antioxidant quality enhancement in lettuce under low nitrogen condition.

Reduced nitrogen availability is an efficient strategy for increasing the accumulation of phenolic compounds in vegetables, but related mechanisms remain unknown. Here, the production of hydrogen peroxide (H2O2) and its potential roles in regulating phenolic biosynthesis and enhancing the antioxidant quality of lettuce under low nitrogen (LN) conditions were investigated. The LN treatment caused a rapid production of H2O2, which effectively increased lettuce quality by enhancing the levels of phenolic compounds and other nutrients such as ascorbic acid, glutathione, soluble sugar, and soluble protein. The increased phenolic content was related to the higher expression levels of phenolic biosynthesis genes, including PAL, CHS, DFR, F35H, and UFGT, and higher photosynthetic capacity after H2O2 addition under LN conditions. However, these positive effects were suppressed by dimethylthiourea (DMTU), a scavenger of H2O2. These results suggest that H2O2 as an important signal molecular mediates the LN-caused phenolic accumulation and antioxidant quality enhancement in lettuce.

Production and use of Scenedesmus acuminatus biomass in synthetic municipal wastewater for integrated biorefineries.

Bioethanol production from algal biomass is a promising alternative for sustainable biofuel production. Algae possess a high photosynthetic capacity and an adaptive ability to thrive under harsh environmental conditions. The potential properties of Scenedesmus acuminatus CCALA 436 were assessed in this research for its bioethanol efficiency, and the effects of growing the algae in wastewater and at different concentrations of mepiquat chloride were studied. Also, pre-treatment efficiencies of different concentrations of calcium oxide were carried out on microalgae biomass. Superoxide dismutase, catalase activity, glutathione, and malondialdehyde contents of microalgae were examined, and the changes in chlorophyll, photoprotective carotenoid contents, and protein concentrations were determined. The results revealed that the maximum sugar and ethanol contents of Scenedesmus acuminatus CCALA 436 were 44.7 ± 1.5% and 20.32 g/L, respectively, for 50% wastewater and mepiquat chloride (2.5 mg/L) after pre-treatment with calcium oxide (0.08%). Additionally, the levels of oxidative enzymes varied depending on the wastewater concentrations. These findings indicate Scenedesmus acuminatus CCALA 436 grown in wastewater and mepiquat chloride can be used for the treatment of wastewater and the production of ethanol and high-value products such as carotenoid.

Assessment of Variability for Nutritional Traits of Burr Medic (Medicago polymorpha L.) Genotypes with Different Phenology

The objective of this study was to determine compatible genotypes for both grazing and ley farming systems concerning nutritional traits among burr medic (Medicago polymorpha L.) genotypes with different flowering times. Therefore, the variability for nutritional traits of early- (n=13), medium- (n=12) and late-flowering (n=19) genotypes from a breeding study carried out during the 2016-2018 years was assessed using one-way ANOVA and chemometric techniques such as principal component (PCA) and cluster (CA) analyses. Except for the acid detergent protein, calcium and magnesium contents, there were significant differences in the nutritional traits among the genotypes with different flowering times. The medium-flowering genotype had a significant advantage over especially early-flowering genotype in crude protein, acid detergent fiber, metabolizable energy, and relative feed value. There were significantly mutual correlations between most of the studied traits. Consequently, considerable amounts of variability were determined among the genotypes for all the traits under consideration. The 44 genotypes formed three clusters, in which cluster sizes ranged from 3 to 29 accessions per cluster. The PCA 1 and 2 had the highest eigenvalues of 6.44 and 1.35, describing 63.27% and 15.91% of the total variance, respectively. The PCA and CA results indicate that medium- and late-flowering genotypes had the best nutritional traits due to probably high photosynthetic capacity in the conditions of the present study.

Trait coordination in boreal mosses reveals a bryophyte economics spectrum

Abstract The study of plant trait spectra and their association with trade‐offs in resource use strategy has greatly advanced our understanding of vascular plant function, yet trait spectra remain poorly studied in bryophytes, particularly outside of the Sphagnum genus. Here, we measured 25 traits related to carbon, nutrient and water conservation in 60 moss canopies (each dominated by one of 15 moss species) across diverse boreal forest habitats and used bi‐variate correlations and multi‐variate analyses to assess trait coordination and trait spectra. We found substantial trait coordination along a main principal components axis driven by trade‐offs in carbon, nutrient and water conservation strategies. Along this trait spectrum, traits varied from resource‐acquisitive at one end (e.g. high maximum photosynthetic capacity, high tissue nitrogen content, low water‐holding capacity) to resource‐conservative at the other end, in line with resource economics theory. Traits related to carbon turnover (photosynthesis and respiration rates, litter decomposability) were positively related to nitrogen content and to desiccation rates, in line with global trait spectra in vascular plants. However, architectural traits of the moss shoots and of the moss canopy were generally unrelated to the main axis of trait variation and formed a secondary axis of trait variation, contrary to what is observed for vascular plants. Resource‐conservative trait spectra dominated in moss canopies from open and wet habitats (i.e. mires), indicating that high irradiance and possibly high moisture fluctuation induce a resource‐conservative trait strategy in mosses. Synthesis. Our work suggests that trait relationships that are well established for vascular plants can be extended for bryophytes as well. Bryophyte trait spectra can be powerful tools to improve our understanding of ecosystem processes in moss‐dominated ecosystems, such as boreal or arctic environments, where bryophyte communities exert strong control on nutrient and carbon cycling.

Intra-canopy leaf trait variation facilitates high leaf area index and compensatory growth in a clonal woody encroaching shrub.

Leaf trait variation enables plants to utilize large gradients of light availability that exist across canopies of high leaf area index (LAI), allowing for greater net carbon gain while reducing light availability for understory competitors. While these canopy dynamics are well understood in forest ecosystems, studies of canopy structure of woody shrubs in grasslands are lacking. To evaluate the investment strategy used by these shrubs, we investigated the vertical distribution of leaf traits and physiology across canopies of Cornus drummondii, the predominant woody encroaching shrub in the Kansas tallgrass prairie. We also examined the impact of disturbance by browsing and grazing on these factors. Our results reveal that leaf mass per area (LMA) and leaf nitrogen per area (Na) varied approximately threefold across canopies of C. drummondii, resulting in major differences in the physiological functioning of leaves. High LMA leaves had high photosynthetic capacity, while low LMA leaves had a novel strategy for maintaining light compensation points below ambient light levels. The vertical allocation of leaf traits in C. drummondii canopies was also modified in response to browsing, which increased light availability at deeper canopy depths. As a result, LMA and Na increased at lower canopy depths, leading to a greater photosynthetic capacity deeper in browsed canopies compared to control canopies. This response, along with increased light availability, facilitated greater photosynthesis and resource-use efficiency deeper in browsed canopies compared to control canopies. Our results illustrate how C. drummondii facilitates high LAI canopies and a compensatory growth response to browsing-both of which are key factors contributing to the success of C. drummondii and other species responsible for grassland woody encroachment.

Synchronization between photosynthetic responses to seasonality during fruit development and fatty acid profile of mesocarp oil in macauba (Acrocomia aculeata)

Macauba palm (Acrocomia aculeata (Jacq.) Lodd. ex Mart. Arecaceae) is a novel oil crop with wide industrial applicability. However, little is known about the photosynthetic responses to seasonality during fruit development in macauba palm and its effects on the fatty acid profile of mesocarp oil and its physicochemical and spectroscopic characteristics. The fatty acid profile changed in six fruit developmental stages (ranging from 180 days after anthesis to full ripening and dispersion). This occurred during the transition from dry to rainy season concomitant with adjustments in photosynthetic responses. The increase in mesocarp oil yield in the fruit was synchronized with the higher photosynthetic capacity at the beginning of the rainy season, being characterized by a raise in oleic acid. The dynamics of soluble solids, acidity, pH, total sugars and starch were proportional to the spectroscopic changes and allowed to determine the ideal harvest point: 360 days after anthesis, with fruits still in the bunch. The macauba palm fruits in this stage showed suitable physical and chemical characteristics for industrial use, as well as higher oil yield. The monitoring of chemical changes with Fournier transformed infrared spectroscopy techniques would aid fast and precise detection of the fruit development and its ideal harvest point.

Transcriptomic reprogramming of diatom Minutocellus polymorphus grown on urea

Minutocellus polymorphus MMDL5290, a minute diatom, can efficiently utilize organic nitrogen (N) urea as the sole N source and achieve equivalent growth rate and photosynthesis capacity as it does with nitrate. Interestingly, M. polymorphus MMDL5290 growing on urea-replete (400 µM) medium yields a similar growth rate to that on nitrate-replete (882 µM). So far, very few reports are available on the molecular regulation mechanisms of microalgae with similar growth potential under different N sources. To address this gap, our study aimed to characterize the differences in transcriptome-level responses of M. polymorphus MMDL5290 between nitrate-replete and urea-replete conditions. We identified 4075 differentially expressed genes between these two groups. Interestingly, gene expression in light-harvesting, electron transport chain, ATP synthesis, and chlorophyll and carotenoid synthesis was up-regulated under urea, while the expression of carbon fixation genes did not change significantly. Meanwhile, transcriptome profiling indicated that under the urea-replete condition, M. polymorphus MMDL5290 triggered massive gene expression reconfiguration, inducing cells to increase investment in protein synthesis and antioxidative stress. This may explain why higher photosynthetic capacity in urea-grown cells does not lead to higher growth. Furthermore, down-regulation of PT (signal peptide) genes was observed under the urea-replete condition, suggesting a repressed capacity of phosphate transport. In addition, we identified 139 stably and highly expressed genes, which have the potential to be used as candidate reference genes in future gene expression studies on M. polymorphus MMDL5290.

Comparative transcriptome and physiological analysis unravel proso millet (Panicum miliaceum L.) source leaf adaptation to nitrogen deficiency with high nitrogen use efficiency

Nitrogen (N) is an essential macronutrient that limits agricultural productivity; however, excessive N fertilizers are still used, especially in China. Improving crop N use efficiency (NUE) is an effective measure to reduce environmental pollution and is a primary direction in agricultural crop improvement. Although the physiological and molecular mechanisms for uncovering differences in NUE have become increasingly important, only a few crops have been studied to date. Two proso millet ( Panicum miliaceum L.) cultivars with contrasting NUE, the low–N–tolerant cultivar (T184) and the low–N–sensitive cultivar (S111), were used to explore physiological as well as comparative transcriptomic mechanisms for earning high NUE in field and hydroponic experiments. The results showed that T184 had higher N uptake and utilization efficiencies and better photosynthetic capacity than S111 in field trials, as measured by increased chlorophyll content and net photosynthetic rate. Meanwhile, improved NUE and yield of T184 were observed compared with S111 under different N regimes. In hydroponic experiments, T184 had higher photosynthetic capacities in leaves and higher N metabolism enzyme activities in leaves and roots than S111, despite the photosynthetic and physiological parameters exhibited decreasing tendency to N deficiency in both T184 and S111. Furthermore, transcriptomic analysis revealed that T184 had less differentially expressed genes (DEGs) than S111. Many genes involved in photosynthesis and N uptake and assimilation were implicated in conferring NUE. Four nitrate transporter genes and eight photosynthetic genes were higher in T184 than in S111 under low and recovery N conditions and were strongly associated with NUE. These results revealed that greater N uptake and utilization efficiencies, accelerated N assimilation and translocation, and enhanced photosynthetic activity confer higher NUE in proso millet. • The low N–tolerant proso millet had increased N uptake, N utilization efficiency (NUE), and grain yield. • Higher photosynthetic capacity and physiological metabolism of the low–N–tolerant proso millet were observed. • Identify photosynthesis candidate genes could facilitate breeding for enhanced NUE. • High N uptake and utilization efficiencies, maintained photosynthesis, and N transport resulted in a higher NUE.

Stomata on the abaxial and adaxial leaf surfaces contribute differently to leaf gas exchange and photosynthesis in wheat.

Summary Although stomata are typically found in greater numbers on the abaxial surface, wheat flag leaves have greater densities on the adaxial surface. We determine the impact of this less common stomatal patterning on gaseous fluxes using a novel chamber that simultaneously measures both leaf surfaces.Using a combination of differential illuminations and CO2 concentrations at each leaf surface, we found that mesophyll cells associated with the adaxial leaf surface have a higher photosynthetic capacity than those associated with the abaxial leaf surface, which is supported by an increased stomatal conductance (driven by differences in stomatal density).When vertical gas flux at the abaxial leaf surface was blocked, no compensation by adaxial stomata was observed, suggesting each surface operates independently. Similar stomatal kinetics suggested some co‐ordination between the two surfaces, but factors other than light intensity played a role in these responses.Higher photosynthetic capacity on the adaxial surface facilitates greater carbon assimilation, along with higher adaxial stomatal conductance, which would also support greater evaporative leaf cooling to maintain optimal leaf temperatures for photosynthesis. Furthermore, abaxial gas exchange contributed c. 50% to leaf photosynthesis and therefore represents an important contributor to overall leaf gas exchange.

Physiological and transcriptome analyses reveal the response of Ammopiptanthus mongolicus to extreme seasonal temperatures in a cold plateau desert ecosystem

Ammopiptanthus mongolicus is the only evergreen broad-leaved shrub present in arid areas of Northwest China and plays an important role in maintaining the stability of the local desert ecosystem. It can survive under extreme temperatures (e.g., extreme low temperature: − 24.8 °C and extreme high temperature: 37.7 °C). To understand the gene expression-physiological regulation network of A. mongolicus in extreme temperature environments, we monitored the changes in gene expression and photosynthetic traits of the leaves. The results showed that at low temperatures, the net photosynthetic rates (A), Fv'/Fm' and electron transport rate (ETR) decreased, the Fv/Fm ratio was only 0.32, and the proportion of nonregulatory heat dissipation Y(NO) increased. Based on a KEGG analysis of the differentially expressed genes, 15 significantly enriched KEGG pathways were identified, which were mainly related to circadian rhythm, photosynthesis, lipid metabolism, carbohydrate metabolism, plant hormones and other life activities. At high temperatures, the A value increased, and the proportion of regulatory energy dissipation Y(NPQ) increased. The KEGG analysis identified 24 significantly enriched KEGG pathways, which are mainly related to circadian rhythm, carbon sequestration of photosynthesis, carotenoid biosynthesis, secondary metabolites, cofactors and vitamin metabolism. In general, at the expense of photosynthesis, A. mongolicus can ensure the survival of leaves by increasing Y(NO) levels, regulating the circadian rhythm, increasing the synthesis of unsaturated fatty acids and changing the role of plant hormones. Under high-temperature stress, a high photosynthetic capacity was maintained by adjusting the stomatal conductance (gsw), increasing Y(NPQ), consuming excess light energy, continuously assembling and maintaining PSII, and changing the production of antioxidants.

DETERMINING THE GRAIN YIELD AND NUTRITIONAL COMPOSITION OF MAIZE CULTIVARS IN DIFFERENT GROWING GROUPS

Due to its adaptability to different climates, short growing period, high photosynthetic capacity and yield, maize is an important crop widely grown all over the world. This study was conducted to determine grain yield and some nutrition traits of 18 maize cultivars in Bilecik ecological conditions in 2019 and 2020 years. Experiments were carried out in randomized complete block design with three replications. There were significant (P

Trehalose Outperforms Chitosan, Humic Acid and Gamma-Aminobutyric Acid in Promoting the Growth of Field Maize.

Despite the fact that there are many distinct types of plant growth regulators (PGRs), the diverse ways in which they regulate plant development are rarely compared. In this study, four PGRs (trehalose, chitosan, humic acid and gamma-aminobutyric acid) were selected and sprayed folially, and plant samples were collected while maize was at vegetative leaf stages 6, 10, and 14 (V6, V10, and V14, respectively) to reveal the effects of different PGRs on photosynthesis, dry matter accumulation, oxidative stress, carbon and nitrogen metabolism, hormone levels, and gene expression of maize. Results showed that 100 mg/L PGRs did not induce oxidative damage or repair activities in maize. Trehalose significantly increased chlorophyll content at V6 and promoted dry matter (roots and shoots) accumulation at V6 and V10. The activities of carbon and nitrogen metabolizing enzymes were significantly enhanced by trehalose treatment, which promoted the accumulation of sucrose and soluble sugar, but did not affect the biosynthesis of auxin and gibberellin at V6. Changes in carbon and nitrogen metabolism enzymes are regulated by transcription of related synthetic genes. Lower starch content and higher sucrose content in trehalose-treated maize leaves are important biological characteristics. Further analysis revealed that the effect of trehalose on the metabolic activity of maize was a short-term promoting effect (0–12 days), while the effect on maize growth was a long-term cumulative effect (13–28 days). Overall, exogenous trehalose induced stronger carbon and nitrogen metabolic activity, higher photosynthetic capacity and more dry matter accumulation than chitosan, humic acid and gamma-aminobutyric acid.

Microalgae bioremediation and CO2 fixation of industrial wastewater

The present work evaluates the bioremediation potential of the microalgae Chlorella sp. cultivated in industrial wastewaters of a metallurgy facility for CO2 fixation. Its growth in wastewaters was investigated experimentally and growth rate was determined based on different dilutions. Taguchi's experimental design was carried out and values found in laboratory were compared to those of a mathematical model adjusted based on growth rate. Process efficiency was evaluated to reduce organic load, nutrient consumption, and cell count during the initial and final stages via microscopy. After the biological treatment, reduction percentages of 99% for COD (Chemical Oxygen Demand) and 95% for SS (Sedimentable Solids) were achieved, in addition to 86% and 93% of nutrient and cyanide removal, respectively, and average CO2 biofixation of 0.1854 gL-1d-1. These values are close to those found in literature for other cultivation media. It was also observed that biomass productivity and CO2 fixation data are in agreement with those obtained in other studies, thus evidencing the efficiency of Chlorella sp. microalgae and its high photosynthetic capacity.

Leaf trait association in relation to herbivore defense, drought resistance, and economics in a tropical invasive plant

Exploring how functional traits vary and covary is important to understand plant responses to environmental change. However, we have limited understanding of the ways multiple functional traits vary and covary within invasive species. We measured 12 leaf traits of an invasive plant Chromolaena odorata, associated with plant or leaf economics, herbivore defense, and drought resistance on 10 introduced populations from Asia and 12 native populations from South and Central America, selected across a broad range of climatic conditions, and grown in a common garden. Species' range and climatic conditions influenced leaf traits, but trait variation across climate space differed between the introduced and native ranges. Traits that confer defense against herbivores and drought resistance were associated with economic strategy, but the patterns differed by range. Plants from introduced populations that were at the fast-return end of the spectrum (high photosynthetic capacity) had high physical defense traits (high trichome density), whereas plants from native populations that were at the fast-return end of the spectrum had high drought escape traits (early leaf senescence and high percentage of withered shoots). Our results indicate that invasive plants can rapidly adapt to novel environmental conditions. Chromolaena odorata showed multiple different functional trait covariation patterns and clines in the native and introduced ranges. Our results emphasize that interaction between multiple traits or functions should be considered when investigating the adaptive evolution of invasive plants.

Functional characterization and comparison of lycopene epsilon-cyclase genes in Nicotiana tabacum

BackgroundLycopene epsilon-cyclase (ε-LCY) is a key enzyme in the carotenoid biosynthetic pathway (CBP) of higher plants. In previous work, we cloned two Ntε-LCY genes from allotetraploid tobacco (Nicotiana tabacum), Ntε-LCY2 and Ntε-LCY1, and demonstrated the overall effect of Ntε-LCY genes on carotenoid biosynthesis and stress resistance. However, their genetic and functional characteristics require further research in polyploid plants.ResultsHere, we used CRISPR/Cas9 to obtain Ntε-LCY2 and Ntε-LCY1 mutants in allotetraploid N.tabacum K326. Ntε-LCY2 and Ntε-LCY1 had similar promoter cis-acting elements, including light-responsive elements. The Ntε-LCY genes were expressed in roots, stems, leaves, flowers, and young fruit, and their highest expression levels were found in leaves. Ntε-LCY2 and Ntε-LCY1 genes responded differently to normal light and high light stress. Both the Ntε-LCY2 and the Ntε-LCY1 mutants had a more rapid leaf growth rate, especially ntε-lcy2-1. The expression levels of CBP genes were increased in the ntε-lcy mutants, and their total carotenoid content was higher. Under both normal light and high light stress, the ntε-lcy mutants had higher photosynthetic capacities and heat dissipation levels than the wild type, and this was especially true of ntε-lcy2-1. The reactive oxygen species content was lower in leaves of the ntε-lcy mutants.ConclusionIn summary, the expression patterns and biological functions of the Ntε-LCY genes Ntε-LCY1 and Ntε-LCY2 differed in several respects. The mutation of Ntε-LCY2 was associated with a greater increase in the content of chlorophyll and various carotenoid components, and it enhanced the stress resistance of tobacco plants under high light.

Enhancement of Photosynthetic Capacity in Spongy Mesophyll Cells in White Leaves of Actinidia kolomikta.

Considering that Actinidia kolomikta bears abundant white leaves on reproductive branches during blossoming, we hypothesized that the white leaves may maintain photosynthetic capacity by adjustments of leaf anatomy and physiological regulation. To test this hypothesis, leaf anatomy, gas exchange, chlorophyll a fluorescence, and the transcriptome were examined in white leaves of A. kolomikta during flowering. The palisade and spongy mesophyll in the white leaves were thicker than those in green ones. Chloroplast development in palisade parenchyma of white leaves was abnormal, whereas spongy parenchyma of white leaves contained functional chloroplasts. The highest photosynthetic rate of white leaves was ~82% of that of green leaves over the course of the day. In addition, the maximum quantum yield of PSII (Fv/Fm) of the palisade mesophyll in white leaves was significantly lower than those of green ones, whereas Fv/Fm and quantum yield for electron transport were significantly higher in the spongy mesophyll of white leaves. Photosynthetic capacity regulation of white leaf also was attributed to upregulation or downregulation of some key genes involving in photosynthesis. Particularly, upregulation of sucrose phosphate synthase (SPS), glyeraldehyde-3-phosphate dehydrogenase (GAPDH) and RuBisCO activase (RCA) in white leaf suggested that they might be involved in regulation of sugar synthesis and Rubisco activase in maintaining photosynthetic capacity of white leaf. Conclusions: white leaves contained a thicker mesophyll layer and higher photosynthetic activity in spongy parenchyma cells than those of palisade parenchyma cells. This may compensate for the lowered photosynthetic capacity of the palisade mesophyll. Consequently, white leaves maintain a relatively high photosynthetic capacity in the field.

Proline-rich protein MdPRP6 alters low nitrogen stress tolerance by regulating lateral root formation and anthocyanin accumulation in transgenic apple (Malus domestica)

Nitrogen (N) is the main nutrient element limiting plant growth and crop yield. Plant proline-rich proteins (PRPs) are a group of structural proteins that are rich in proline and hydroxyproline . Previously, we identified 9 PRPs from the apple genome and found that they were induced by different stress treatments. In this study, we showed that the expression of MdPRP6 was inhibited by low N stress. Transgenic apple plants with decreased MdPRP6 expression were generated by RNA interference (Ri) to explore the biological role of MdPRP6 under low N stress. Ri transgenic apple plants grew better than wild-type (WT) plants under low N stress, as indicated by their well-developed roots; greater height, stem diameter, number of leaves, and biomass; and higher photosynthetic capacity and N content. N and starch metabolism were more active in Ri plants than in WT plants. Ri plants accumulated greater amounts of starch and soluble sugar under low N stress, which was consistent with the higher expression levels of related genes in Ri plants relative to WT plants. The accumulation of anthocyanins was higher in Ri plants than in WT plants under low N stress, which helped plants resist the effects of low N stress. The indole acetic acid (IAA) content was higher in the roots of Ri plants, which strengthened the root system. Overall, our data suggested that MdPRP6 negatively regulates low N stress tolerance by modulating anthocyanin accumulation and IAA metabolism in the roots of apple plants. • RNAi of MdPRP6 resulted in more LR in transgenic apples under LN stress. • RNAi of MdPRP6 conferred more accumulation of anthocyanins in transgenic apples under LN stress. • The tolerance of LN stress conferred by MdPRP6 was related to the soluble sugars content.