Considering that
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
fluorescence, and the transcriptome were examined in white leaves of
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 (
/
) of the palisade mesophyll in white leaves was significantly lower than those of green ones, whereas
/
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 (
), glyeraldehyde-3-phosphate dehydrogenase (
) and RuBisCO activase (
) 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.
Low temperature thermal acclimation may require adjustments to nitrogen and water use to sustain photosynthesis due to slow enzyme functioning and high-water viscosity. However, understanding of ...photosynthetic acclimation to temperatures below 11°C is limited. Here, we acclimated Populus balsamifera to 6 °C and 10 °C (6A and 10A, respectively) and provided the trees with either high or low N fertilizer. We measured net CO2 assimilation rates (Anet), stomatal conductance (gs ), maximum rates of Rubisco carboxylation (Vcmax) and electron transport (Jmax), and dark respiration (Rd) at leaf temperatures of 2, 6, 10, 14 and 18 °C, along with leaf N concentrations. The 10A trees had higher Anet than the 6A trees at warmer leaf temperatures, which was correlated with higher gs in the 10A trees. The instantaneous temperature responses of Vcmax, Jmax and Rd were similar for trees from both acclimation temperatures. While soil N availability increased leaf N concentrations, this had no effect on acclimation of photosynthesis or respiration. Our results indicate that acclimation below 11°C occurred primarily through changes in stomatal conductance, not photosynthetic biochemistry, and was unaffected by short-term N supply. Thermal acclimation of stomatal conductance should therefore be a priority for future carbon cycle model development.
Terminal heat stress is one of the major constraints of cereal production. A two-year field investigation was performed to assess the response of Hordeum vulgare ssp. spontaneum genotypes to terminal ...heat stress using gas-exchange parameters, photosystem efficiency, proline accumulation, cell membrane leakage, and grain yield traits. Results of analysis of variance revealed the significant effects of heat stress (E), genotype (G), and G × E on the studied traits. The results of linear regression analysis showed that yield loss was inversely correlated with the maximum quantum yield of PSII photochemistry (Fv/Fm) and chlorophyll content. Path-coefficient analysis revealed that high Chl contents were either directly related to the grain yield or indirectly through the higher net photosynthetic rate and higher Fv/Fm values under high temperatures at the reproductive growth stage. Overall, the adapted wild genotypes exhibited physiological mechanisms capable of sustainable maintaining their yield capacity and plasticity flow, which could be exploited by crossing with cultivated barley to introgress heat tolerance.
The terrestrial biosphere plays a critical role in mitigating climate change by absorbing anthropogenic CO2 emissions through photosynthesis. The rate of photosynthesis is determined jointly by ...environmental variables and the intrinsic photosynthetic capacity of plants (i.e. maximum carboxylation rate; Vcmax25). A lack of an effective means to derive spatially and temporally explicit Vcmax25 has long hampered efforts towards estimating global photosynthesis accurately. Recent work suggests that leaf chlorophyll content (Chlleaf) is strongly related to Vcmax25, since Chlleaf and Vcmax25 are both correlated with photosynthetic nitrogen content. We used medium resolution satellite images to derive spatially and temporally explicit Chlleaf, which we then used to parameterize Vcmax25 within a terrestrial biosphere model. Modelled photosynthesis estimates were evaluated against measured photosynthesis at 124 eddy covariance sites. The inclusion of Chlleaf in a terrestrial biosphere model improved the spatial and temporal variability of photosynthesis estimates, reducing biases at eddy covariance sites by 8% on average, with the largest improvements occurring for croplands (21% bias reduction) and deciduous forests (15% bias reduction). At the global scale, the inclusion of Chlleaf reduced terrestrial photosynthesis estimates by 9 PgC/year and improved the correlations with a reconstructed solar‐induced fluorescence product and a gridded photosynthesis product upscaled from tower measurements. We found positive impacts of Chlleaf on modelled photosynthesis for deciduous forests, croplands, grasslands, savannas and wetlands, but mixed impacts for shrublands and evergreen broadleaf forests and negative impacts for evergreen needleleaf forests and mixed forests. Our results highlight the potential of Chlleaf to reduce the uncertainty of global photosynthesis but identify challenges for incorporating Chlleaf in future terrestrial biosphere models.
We used satellite‐derived leaf chlorophyll content (Chlleaf) to infer leaf photosynthetic capacity (Vcmax25) that varies temporally and spatially. The new Chlleaf‐based Vcmax25 data set was then incorporated into an established terrestrial biosphere model (i.e. BEPS) to estimate global photosynthesis. Our results show that Chlleaf‐based Vcmax25 and its seasonally average values (Chlavg‐based Vcmax25) can both effectively improve the estimates of photosynthesis when validated against observations at 124 sites of different plant functional types across the globe. This study highlights that Chlleaf is a valuable leaf physiological trait to add in future models to better simulate the terrestrial carbon cycle.
Leaves are exposed to different light conditions according to their canopy position, resulting in structural and anatomical differences with consequences for carbon uptake. While these ...structure-function relationships have been thoroughly explored in dense forest canopies, such gradients may be diminished in open canopies, and they are often ignored in ecosystem models. We tested within-canopy differences in photosynthetic properties and structural traits in leaves in a mature Eucalyptus tereticornis canopy exposed to long-term elevated CO2 for up to three years. We explored these traits in relation to anatomical variation and diffusive processes for CO2 (i.e., stomatal conductance, gs and mesophyll conductance, gm) in both upper and lower portions of the canopy receiving ambient and elevated CO2. While shade resulted in 13% lower leaf mass per area ratio (MA) in lower versus upper canopy leaves, there was no relationship between leaf Nmass and canopy gap fraction. Both maximum carboxylation capacity (Vcmax) and maximum electron transport (Jmax) were ~ 18% lower in shaded leaves and were also reduced by ~ 22% with leaf aging. In mature leaves, we found no canopy differences for gm or gs, despite anatomical differences in MA, leaf thickness and mean mesophyll thickness between canopy positions. There was a positive relationship between net photosynthesis and gm or gs in mature leaves. Mesophyll conductance was negatively correlated with mean parenchyma length, suggesting that long palisade cells may contribute to a longer CO2 diffusional pathway and more resistance to CO2 transfer to chloroplasts. Few other relationships between gm and anatomical variables were found in mature leaves, which may be due to the open crown of Eucalyptus. Consideration of shade effects and leaf-age dependent responses to photosynthetic capacity and mesophyll conductance are critical to improve canopy photosynthesis models and will improve understanding of long-term responses to elevated CO2 in tree canopies.
The atmospheric concentration of carbon dioxide (CO2) and oxygen (O2) directly influence rates of photosynthesis (PN) and photorespiration (RPR) through the enzyme ribulose-1,5-bisphosphate ...carboxylase/oxygenase (RubisCO). Levels of CO2 and O2 have varied over Earth history affecting rates of both CO2 uptake and loss, alongside associated transpirative water-loss. The availability of CO2 has likely acted as a stronger selective pressure than O2 due to the greater specificity of RubisCO for CO2. The role of O2, and the interaction of O2 and CO2, in plant evolutionary history is less understood. We exposed twelve phylogenetically diverse species to combinations of sub-ambient, ambient and super-ambient O2 and CO2 to examine the biochemical and diffusive components of PN and the possible role of O2 as a selective pressure. Photosynthesis, photosynthetic capacity and stomatal, mesophyll and total conductance to CO2 were higher in the derived eudicot and monocot angiosperms than the more basal ferns, gymnosperms and basal angiosperms which originated in atmospheres characterised by higher CO2:O2 ratios. The ratio of RPR:PN was lower in the monocots, consistent with greater carboxylation capacity and higher stomatal and mesophyll conductance making easier CO2 delivery to chloroplasts. The effect of O2 and CO2 on PN/RPR was less evident in more derived species with a higher conductance to CO2. The effect of O2 was less apparent at high CO2, suggesting that atmospheric O2 may only have exerted a strong selective pressure on plant photosynthetic processes during periods characterised by low atmospheric CO2:O2 ratios. Current rising CO2 will predominantly enhance PN rates in species with low diffusive conductance to CO2.
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•O2 strongly affected photosynthesis only at low CO2.•CO2 and O2 effects most apparent in species with low mesophyll conductance.•Monocots and eudicots exhibited the highest mesophyll conductance.•Falling CO2 (100 Ma to present) favoured higher stomatal and mesophyll conductance.•O2 is unlikely to have exerted strong selective pressures during Earth history.
Drought stress is considered the most adverse factor restricting plant survival, growth, and productivity. The identification of the key adaptive mechanisms to drought stress is essential to enhance ...the drought resistance of plants. In this study, differential responses of three alfalfa varieties to drought, including Medicago sativa L. cv. Longzhong (drought-tolerant), Longdong (moderate drought-tolerant), and Gannong No. 3 (drought-sensitive), were comparatively studied at morphological, physio-biochemical, and transcriptional levels after a 12-day period of drought stress simulated by −1.2 MPa polyethylene glycol (PEG-6000). The results showed that prolonged drought stress dramatically decreased growth and photosynthetic capacity of three alfalfa varieties while it increased the accumulation of malondialdehyde (MDA), reactive oxygen species (ROS), osmolytes and antioxidants including reduced ascorbate and glutathione, ascorbate peroxidase (APX) activities, and gene expression of antioxidative enzymes (MsCu/Zn-SOD, MsFeSOD, MtPOD, MsGPX, MsAPX, MsMDAR, MtDHAR, and MsGR). Nine days of treatment and some key traits, including the maximum quantum yield of photosystem II (Fv/Fm), the levels of MDA, O2−, and H2O2, the redox states of ascorbate and glutathione, APX activity, and the transcript levels of MsFeSOD, MsGR, and MsMDAR, might contribute to differentiating the drought stress tolerance in alfalfa. Overall, drought-tolerant Longzhong showed the highest water retention, photosynthetic performance, and osmoregulation capacity, the lowest lipid peroxidation, and the highest antioxidant enzyme activities and gene expression, which were mainly involved in the ascorbate-glutathione cycle to maintain the balance between the generation and scavenging of intracellular ROS. These findings highlight that enhanced antioxidative protection and declined lipid peroxidation play an important role in alfalfa tolerance against drought.
The rapid A/Ci response: a guide to best practices Stinziano, Joseph R.; McDermitt, Dayle K.; Lynch, Douglas J. ...
The New phytologist,
January 2019, 20190101, Letnik:
221, Številka:
2
Journal Article
Fluoride (F−) stress is one of the major environmental pollutant, affecting plant growth, development and production, globally. Acquisition of eco-friendly F− stress reliever seems to be the major ...concern these days. Consequently, application of engineered nanomaterials (ENMs) has been increasing to improve agri-economy. However, the impact of silicon nanoparticles (Si NPs) on mitigation of F− stress has not been investigated yet. Thus, the present study was conducted to compare their protective roles against F− stress by improving diurnal photosynthetic efficiency of sugarcane plant leaves. An ability of sugarcane (Saccharum officinarum cv. GT44) plants to ameliorate F− toxicity assessed through soil culture medium. After an adaptive growth phase, 45 days old plants select to examine F− mitigative efficacy of silicon nanoparticles (SiNPs: 0, 100, 300 and 500 ppm) on sugarcane plants, irrigated by F− contaminated water (0, 100, 200 and 500 ppm). Our results strongly favour that SiNPs enhanced diurnally leaf photosynthetic gas exchange viz., photosynthesis (∼1.0–29%), stomatal conductance (∼3.0–90%), and transpiration rate (∼0.5–43%), significantly, as revealed by increments in photochemical chlorophyll fluorescence efficiency of PS II linked with performance index and photosynthetic pigments during F− stress. To the best of our knowledge, this is the first investigation to explore the impact of SiNPs improving and/or maintaining the diurnal photosynthetic responses in sugarcane plants in response to F− stress. It may also precisely unlayer action of molecular mechanism(s) mediated by SiNPs, found essential for mitigation of F−-toxicity to explore nano-phytoremediation approach for crop improvement and agri-economy as well.
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•Silicon nanoparticles enhance diurnal photosynthetic efficiency during F− stress.•Foliar application of Si NPs alleviated negative impacts of fluoride contaminated water.•Development of analytical model to integrate physiological responses against F- stress.
•Overexpressed MdTYDC enhanced drought tolerance by increasing cellular ABA levels in apple plants.•MdTYDC overexpression improved ASA/DHA and GSH/GSSG ratios under drought.•MdTYDC overexpression ...modulated stomatal movement by increasing ABA levels and ABA sensitivity.•Transcriptomic analyses indicated that MdTYDC overexpression regulated the expression of drought-related transcription factors.
Dopamine is produced in plants and plays a vital role in improving plant responses to abiotic stress. Tyrosine decarboxylase (TYDC) synthesizes tyramine from tyrosine, thereby providing the substrate for dopamine production. However, the function of TYDC in response to drought stress in apple plants remains unclear. In this study, transgenic apple plants that overexpressed MdTYDC were exposed to drought, in order to explore the biological function of TYDC in drought stress. Overexpression of MdTYDC significantly increased apple dopamine content. Transgenic apple plants that overexpressed MdTYDC exhibited less electrolyte leakage, a lower water loss rate, higher photosynthetic pigment contents, and enhanced photosynthetic performance under drought conditions. MdTYDC overexpression also improved reducing power by increasing the ratios of ascorbate to dehydroascorbate and reduced to oxidized glutathione. It influenced leaf water retention capacity and stomatal movement by modulating cellular abscisic acid (ABA) levels and ABA sensitivity. Transcriptomic analyses indicated that MdTYDC overexpression enhanced drought tolerance by regulating the expression of ABA- and drought-related transcription factors, including those from the NAC, ERF, and WRKY families. These results provide evidence for the involvement of MdTYDC and dopamine in enhancing the drought tolerance of apple plants.
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