Non-photochemical Quenching Research Articles

Role of membrane H+ transport and plasmalemma excitability in pattern formation, long-distance transport and photosynthesis of Characean algae

Illuminated giant cells of Characeae comprise alternating areas with H+ pump activity and zones with high conductivity for H+/OH–, which create counter-directed H+ flows between the medium and the cytoplasm. In areas where H+ enters the cell, the pH on the surface (pHo) increases to pH 10, while the cytoplasmic pH (pHc) decreases. The lack of the permeant substrate of photosynthesis (CO2) and the acidic pHc shift in the region of external alkaline zones redirect electron transport in chloroplasts from CO2-dependent (assimilatory) pathway to O2 reduction. This electron transport route is associated with an increase in thylakoid membrane ΔpH and an enhanced nonphotochemical quenching (NPQ) of chlorophyll excitations, which underlies strict coordination between nonuniform distributions of pHo and photosynthetic activity in resting cells. When the action potential (AP) is generated, the longitudinal pH profile is temporarily smoothed out, while the heterogeneity of the distribution of NPQ and PSII photochemical activity (YII) sharply increases. The damping of the pHo profile is due to the suppression of the H+ pump and passive H+ conductance under the influence of an almost 100-fold increase in the cytoplasmic of Ca2+ level ([Ca2+]c) during AP. The increase in [Ca2+]c stimulates photoreduction of O2 in chloroplasts under external alkaline zones and, at the same time, arrests the cytoplasmic streaming, which causes the accumulation of excess amounts of H2O2 in the cytoplasm in areas of intense production of this metabolite, with a weak effect on areas of CO2 assimilation. These changes enhance the nonuniform distribution of cell photosynthesis and account for the long-term oscillations of chlorophyll fluorescence Fm' and the quantum efficiency of linear electron flow in microscopic cell areas after the AP generation.

Identifying the gene responsible for non-photochemical quenching reversal in Phaeodactylum tricornutum.

Algae such as diatoms and haptophytes have distinct photosynthetic pigments from plants, including a novel set of carotenoids. This includes a primary xanthophyll cycle comprised of diadinoxanthin and its de-epoxidation product diatoxanthin that enables the switch between light harvesting and non-photochemical quenching (NPQ)-mediated dissipation of light energy. The enzyme responsible for the reversal of this cycle was previously unknown. Here, we identified zeaxanthin epoxidase 3 (ZEP3) from Phaeodactylum tricornutum as the candidate diatoxanthin epoxidase. Knocking out the ZEP3gene caused a loss of rapidly reversible NPQ following saturating light exposure. This correlated with the maintenance of high concentrations of diatoxanthin during recovery in low light. Xanthophyll cycling and NPQ relaxation were restored via complementation of the wild-type ZEP3 gene. The zep3 knockout strains showed reduced photosynthetic rates at higher light fluxes and reduced specific growth rate in variable light regimes, likely due to the mutant strains becoming locked in a light energy dissipation state. We were able to toggle the level of NPQ capacity in a time and dose dependent manner by placing the ZEP3 gene under the control of a β-estradiol inducible promoter. Identification of this gene provides a deeper understanding of the diversification of photosynthetic control in algae compared to plants and suggests a potential target to improve the productivity of industrial-scale cultures.

Photoinhibition Sensitivity of Abies sachalinensis Saplings Under Different Leaf Mass per Area Conditions: Insights into Acclimation to Current and Future Light Environments

Photoinhibition, a common physiological obstacle in forest regeneration, results from rapid light elevations after removing upper-layer trees, thereby impeding sapling growth and survival. The leaf mass per area (LMA), which reflects the current light environment, may predict saplings’ responses to future elevations in light intensity. However, the relationship between the LMA and photoinhibition sensitivity in boreal forest evergreen conifers remains unclear. In this study, we explored whether the LMA was related to photoinhibition sensitivity in A. sachalinensis saplings. Saplings with a high LMA exhibited higher excitation pressure (1−qP) under the current light environment, leading to increased stress even at low relative light intensities of 3%–17%. A model illustrating the dependence of photosynthetic physiological parameters on the photosynthetic photon flux density (PPFD) revealed that 1−qP significantly decreased with an increasing LMA, while the electron transfer rate (ETR) and non-photochemical quenching (NPQ) significantly increased. Additionally, regardless of the LMA, 1−qP reached near saturation (≈1.0) at a PPFD of 1000 μmol m−2 s−1, likely owing to the inefficient consumption of excess energy by electron transfer, as indicated by the low maximum ETR (approximately 25 μmol m−2 s−1). These findings suggest that although A. sachalinensis exhibits high sensitivity to photoinhibition, a high LMA may reflect physiological acclimation to forthcoming elevations in light exposure, thereby reducing the susceptibility to photoinhibition at present and in the future.

Ecophysiological variables retrieval and early stress detection: insights from a synthetic spatial scaling exercise

ABSTRACT The ability to access physiologically driven signals, such as surface temperature, photochemical reflectance index (PRI), and sun-induced chlorophyll fluorescence (SIF), through remote sensing (RS) are exciting developments for vegetation studies. Accessing this ecophysiological information requires considering processes operating at scales from the top-of-the-canopy to the photosystems, adding complexity compared to reflectance index-based approaches. To investigate the maturity and knowledge of the growing RS community in this area, COST Action CA17134 SENSECO organized a Spatial Scaling Challenge (SSC). Challenge participants were asked to retrieve four key ecophysiological variables for a field each of maize and wheat from a simulated field campaign: leaf area index (LAI), leaf chlorophyll content (C ab), maximum carboxylation rate (V cmax,25), and non-photochemical quenching (NPQ). The simulated campaign data included hyperspectral optical, thermal and SIF imagery, together with ground sampling of the four variables. Non-parametric methods that combined multiple spectral domains and field measurements were used most often, thereby indirectly performing the top-of-the-canopy to photosystem scaling. LAI and C ab were reliably retrieved in most cases, whereas V cmax,25 and NPQ were less accurately estimated and demanded information ancillary to RS imagery. The factors considered least by participants were the biophysical and physiological canopy vertical profiles, the spatial mismatch between RS sensors, the temporal mismatch between field sampling and RS acquisition, and measurement uncertainty. Furthermore, few participants developed NPQ maps into stress maps or provided a deeper analysis of their parameter retrievals. The SSC shows that, despite advances in statistical and physically based models, the vegetation RS community should improve how field and RS data are integrated and scaled in space and time. We expect this work will guide newcomers and support robust advances in this research field.

Chemical topping enhances the cotton (Gossypium hirsutum L.) yield formation through improving leaf photosynthesis and assimilating the partitioning to reproductive organs

Chemical topping with 1,1-dimethylpiperidinium chloride (DPC) has attracted widespread attention because of its potential to replace manual topping in cotton production. However, the effects of DPC chemical topping remain poorly understood. Therefore, a two-year field experiment (2019–2020) was conducted with two cultivars (DPC-insensitive cultivar Xinluzao 60, C60, and DPC-sensitive cultivar Jinken 1402, C1402), and four topping methods (manual topping (T1), no topping (T2), fortified DPC chemical topping (T3) and DPC chemical topping (T4)) were used as the experimental treatments. Compared with those in T1 and T2, the seed cotton yield and boll weight in both T3 and T4 in C60 and C1402 were greater; the leaf area in T3 and T4 in C60 and C1402 increased on average by 15.6 % 40 days after treatment; the chlorophyll a and a+b contents in T3 and T4 in C1402 increased on average by 8.4 % at 5060 days after treatment; the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) in T3 and T4 in C60 and C1402 increased on average by 37.5 % 40 days after treatment; the actual photosynthetic efficiency of PSII (φPSII) and relative electron transport rate of PSII (ETR) in T3 and T4 in C60 and C1402 increased on average by 22.5 %, the non-photochemical quenching (NPQ) decreased on average by 26.4 % at 50 days after treatment; and the contents of the soluble sugars, sucrose and starch in T3 and T4 in C1402 significantly decreased on average by 17.3 % at 20 days after treatment; the reproductive organ biomass in T3 and T4 in C1402 increased on average by 15.7 % at 5060 days after treatment. Overall, DPC chemical topping increased the photosynthetic performance of the cotton varieties with different sensitivities to DPC and carbohydrate translocation and was beneficial for increasing the reproductive organ biomass and exploiting the yield potential.

Chromium uptake and its impact on antioxidant level, photosynthetic machinery, and related gene expression in Brassica napus cultivars.

The development of heavy metals, particularly chromium (Cr)-tolerant crop cultivars, is hampered due to lack of understanding of the mechanisms behind Cr stress tolerance. In this study, two Brassica napus cultivars, ZS758 and ZD622, were compared for Cr stress resistance by using the chlorophyll a fluorescence technique and biochemical characteristics. In both cultivars, Cr stress dramatically decreased PSII and PSI efficiency, biomass accumulation, and antioxidant enzyme levels. Although, cultivar ZS758 showed reduction in oxidative stress by decreasing the production of reactive oxygen species (ROS) in terms of reduced H2O2 and MDA content and increased enzymatic activities of key antioxidants enzymes including SOD, APX, CAT, and POD activities that play a crucial role in the regulation of numerous transcriptional pathways involved in oxidative stress responses. Higher non-photochemical quenching (NPQ) and QY were found in tolerant ZS758 cultivar under Cr stress, indicating that tolerant cultivar had a greater capacity to preserve PSII activity under Cr stress by enhancing heat dissipation as a photo-protective component of NPQ. Lower PSI activity and electron transfer from PSII were confirmed by lower PSI efficiency and higher donor end limitation of PSI in both rapeseed cultivars. The Cr concentration was greater in the ZD622 as compared to ZS758, which affected the mineral nutrients profile and damaged the cellular ultrastructure and related gene expression levels. However, current study suggest that cultivar ZS758 is more resistant to Cr stress than ZD622 due to improved metabolism and structural integrity and Cr stress tolerance that is linked with the increased PSII activity, NPQ, and antioxidant potential; these physiological characteristics can be exploited to select cultivars for Cr stress tolerance.

Zinc Nano and Zinc Ethylenediaminetetraacetic acid (EDTA) Mediated Water Deficit Stress Alleviation in Pearl Millet (Pennisetum glaucum (L.) R. Br.): Photosystem II Electron Transport and Pigment Dynamics

Water stress adversely affects the photosynthetic apparatus and pigment composition in plants, leading to reduced yields and compromised plant health. Zinc (Zn) foliar spray in nano form presents a potential solution to ameliorate water deficit stress. We attempt here a detailed dissection of electron transport in Photosystem II (PSII) through studies on chlorophyll a fast fluorescence kinetics and non-photochemical quenching (NPQ) and pigment dynamics in response to water stress. We also investigated the possible changes in these processes and the regulation of it by Zn Nano and Zn Ethylenediaminetetraacetic acid (EDTA) foliar sprays that may lead to amelioration of stress. Our results indicated that water stress created a "traffic jam" like situation in the electron transport system of Photosystem II, leading to decreased photosynthetic efficiency. Treatments with Water deficit stress + Zn Nano (particle size < 90 nm) spray with Zn concentration at 20 mg L−1 and Water deficit stress + Zn EDTA spray (solid material size ∼ 100 mm) with Zn concentration at 240 mg L−1 effectively ameliorated water deficit stress by its action on flux ratio parameters viz., quantum yield for electron transport (φE0), probability of electron transport beyond QA (ψ0) and quantum yield of electron transport from QA⁻ to PS1 end electron acceptors (ϕR0) and also the specific fluxes and phenomenological fluxes. These treatments positively influenced chlorophyll content, and xanthophyll components, including violaxanthin, antheraxanthin, and zeaxanthin, and reduced NPQ and the de expoxidation state. Higher concentrations of Zn Nano foliar spray (water stress + Zn Nano spray Zn @ 30 mg L⁻¹) did not ameliorate water deficit stress as effectively as the lower concentrations, although this higher concentration was not in any way toxic. This lack of stress amelioration at higher concentrations of Zn Nano spray may be due to physiological limitations of elemental zinc action within the plant. Our findings suggest that Zn foliar sprays in Nano and EDTA form at optimum concentrations can significantly improve plant resilience to water stress.

Optimized irrigation practices with fertilizer utilization strategies to improve photo-fluorescence efficiency, vascular bundles and maize production in semi-arid regions

The mechanism of irrigation models combined with fertilizer utilization strategies under the biodegradable film mulching could greatly promote crop photosynthesis, vascular bundles structure; resource utilization and maize production are unclear in semi-arid areas. Unfortunately, this mechanism provides a scientific basis for improving irrigation and fertilizer utilization. A field study was carried out during 2021–2022 years. Seven treatments were established: two nitrogen levels: low-N (150 kg N ha−1) and high-N (300 kg N ha−1) combined with three different irrigation models: drip irrigation (DI), ridge irrigation (RI) and border irrigation (BI) under the biodegradable film mulching with (CK) treatment have no irrigation, fertilizer and mulching. Our results revealed that DIH treatment considerably increased soil water storage, enhanced photosynthesis rate (Pn) of maize by mainly to facilitate stomatal opening compared to the rest of all treatments. In addition, it also enhances the differentiation of the vascular bundle system and maintains its post silk function under better environmental conditions, greatly improving nitrogen storage in soil and plants, and enhancing maize productivity. DIH and RIH treatments significantly increased net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum quantum yield of PSII photochemistry (Fv/Fm), and effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching (qP), non-photochemical quenching (NPQ), and yield were observed, but evapotranspiration (ET) decreased at different growth stages. The results showed that DIH treatment was an effective tillage strategy, which increased biomass yield by 32.6 %, grain yield by 46.0 %, water use efficiency (WUE) by 46.2 %, and nitrogen use efficiency (NUE) by 86.4 % compared to other treatments. Given these results, thus we recommend the drip irrigation combined with a high-N level under a biodegradable film mulching increase photo-fluorescence efficiency, maize production and resource utilization efficiency in semi-arid regions.

Exogenous strigolactones alleviate low-temperature stress in peppers seedlings by reducing the degree of photoinhibition.

The growth and yield of pepper, a typical temperature-loving vegetable, are limited by low-temperature environments. Using low-temperature sensitive 'Hangjiao No. 4' (Capsicum annuum L.) as experimental material, this study analyzed the changes in plant growth and photosynthesis under different treatments: normal control (NT), low-temperature stress alone (LT), low-temperature stress in strigolactone pretreated plants (SL_LT), and low-temperature stress in strigolactone biosynthesis inhibitor pretreated plants (Tis_LT). SL pretreatment increased the net photosynthetic rate (Pn) and PSII actual photochemical efficiency (φPSII), reducing the inhibition of LT on the growth of pepper by 17.44% (dry weight of shoot). Due to promoting the accumulation of carotenoids, such as lutein, and the de-epoxidation of the xanthophyll cycle [(Z + A)/(Z + A + V)] by strigolactone after long-term low-temperature stress (120h), non-photochemical quenching (NPQ) of pepper was increased to reduce the excess excitation energy [(1-qP)/NPQ] and the photoinhibition degree (Fv/Fm) of pepper seedlings under long-term low-temperature stress was alleviated. Twelve cDNA libraries were constructed from pepper leaves by transcriptome sequencing. There were 8776 differentially expressed genes (DEGs), including 4473 (51.0%) upregulated and 4303 (49.0%) downregulated genes. Gene ontology pathway annotation showed that based on LT, the DEGs of SL_LT and Tis_LT were significantly enriched in the cellular component, which is mainly related to the photosystem and thylakoids. Further analysis of the porphyrin and chlorophyll biosynthesis, carotenoid biosynthesis, photosynthesis-antenna protein, and photosynthetic metabolic pathways and the Calvin cycle under low-temperature stress highlighted 18, 15, 21, 29, and 31 DEGs for further study, which were almost all highly expressed under SL_LT treatment and moderately expressed under LT treatment, whereas Tis_LT showed low expression. The positive regulatory effect of SLs on the low-temperature tolerance of pepper seedlings was confirmed. This study provided new insights for the development of temperature-tolerant pepper lines through breeding programs.

Photoprotective mechanisms activated in Antarctic moss &lt;i&gt;Chorisodontium aciphyllum&lt;/i&gt; during desiccation

We investigated the relationship between relative water content (RWC) of Antarctic moss Chorisodontium aciphyllum and several chlorophyll fluorescence parameters evaluating primary photochemical processes of photosynthesis. During the gradual dehydration of Ch. aciphyllum from fully wet (RWC=100%) to dry (RWC=0%) state, progression of NPQ (non-photochemical quenching) induction curves were recorded; the maximum NPQ (NPQmax) attained at the end of illumination period (10 min.), and NPQ relaxation in dark were all analysed. Induction curves of photosynthetic electron transport rate (ETR) were also evaluated, as well as two parameters, ETRmax and initial slop, were derived from the curve: (1) ETRmax; (2) initial slope (a parameter). The two parameters were related to the degree of desiccation (RWC decdlining from 100 to 0%). It was found that NPQ induction curves and the parameters derived from them were sensitive to dehydration and may be used as markers for dehydration-induced changes in photosystem II functioning of desiccating Ch. aciphyllum. The activation of non-photochemical quenching during desiccatin and the underlying mechanisms are discussed.

Photoinhibition and recovery of primary photosynthesis in Antarctic and subantarctic lichens. Analysis of interspecific differences

This study meticulously investigates the dynamics of photoinhibition and the mechanisms of primary photosynthetic activity recovery in lichens found in Antarctica and the sub-Antarctic regions. Advanced methodologies were utilised, such as Kautsky's kinetic analysis and the OJIP test. The study carefully details the response of various lichen species to intense light stress, outlining both immediate effects and subsequent recovery processes. Our findings reveal that these lichens employ a range of adaptive strategies, specific to each species, to mitigate the effects of photoinhibition, thereby emphasizing their remarkable resilience and ecological importance in harsh environments. Notably, the investigation reveals the sophisticated interplay between inherent photoprotective mechanisms and the ecological adaptations that enable these lichens to thrive under such harsh conditions. The study not only advances our knowledge of plant physiology under stress but also enriches our insights into the survival strategies of terrestrial organisms facing global environmental changes. Three types of photoinhibitory treatments differing in their duration and strength were applied to 7 lichen species from Antarctica and South America (Isla Navarino). The lichens responded with a decrease in photosynthetic processes in photosystem II (FV/FM and ΦPSII declined), although they showed almost complete recovery in the following 5 h. This was attributed to the activation of photoprotective mechanisms, non-photochemical quenching (NPQ) in particular, during photoinhibitory treatments. Chlorophyll fluorescence parameters derived from slow Kautsky kinetics were correlated with those derived from the OJIP curve. Our study presents data that supports the conclusion of significant photoresistance of the studied lichen species in the hydrated state to photoinhibition induced by high doses of photosynthetically active radiation (PAR).

Selecting the Most Sustainable Phosphorus Adsorbent for Lake Restoration: Effects on the Photosynthetic Activity of Chlorella sp.

To promote the conservation of aquatic ecosystems, it is essential to delve into restoration techniques for selecting the most sustainable option for combating eutrophication. Hence, we study the effects of novel phosphorus (P) adsorbents (magnetic carbonyl iron particles, HQ, and two non-magnetic P adsorbents: CFH-12® and Phoslock®) on the growth and photosynthetic activity of Chlorella sp. More specifically, the intrinsic photochemical efficiency of PSII (ΦPSII) and the nonphotochemical quenching (NPQ) were measured in Chlorella sp. after different contact times with different concentrations of these adsorbents. Our initial hypothesis was that non-magnetic P adsorbents have more effects on the organisms than magnetic ones. However, our results did not show strong evidence of inhibitory effects caused by HQ nor CFH-12® (no significant effect size on ΦPSII), while Phoslock® showed inhibitory effects on the photosynthetic activity of Chlorella sp. for any of its concentrations (NPQ = 0). Lastly, we compared the effect of the studied P adsorbents in a real application scenery (Honda wetland, Spain). For this study case, it is likely that CFH-12® and HQ doses would not cause any negative effects on photosynthetic efficiency while Phoslock®, by limiting light availability, will drastically reduce it.

Photosynthetic Responses to Salt Stress in Two Rice (Oryza sativa L.) Varieties

Assessing salt tolerance in plants under field conditions is a challenging task. The objective of this research was to assess the effectiveness of different methods (leaf disc assay and pot experiment) for evaluating salt tolerance in rice. Using two varieties with different salt tolerance, Changmaogu (CM) and 9311, under three NaCl levels (0, 0.3%, and 1.0%), we evaluated the photosynthetic performance in terms of chlorophyll content in leaf disc assays, as well as the photosynthetic rate (Pn), chlorophyll content, linear electron flow (LEF), and non-photochemical quenching (NPQ), in a semi-controlled pot experiment. In the leaf disc assay, CM showed a smaller decrease in chlorophyll content compared to 9311, especially under 1.0% salinity. Simultaneously, in the pot experiment, the CM variety employed flexible photosynthetic strategies, actively decreasing LEF and Pn after 5 days of salt stress (day 5) and then increasing photosynthetic capacity (chlorophyll content, LEF, and Pn) on day 10. Notably, the total chlorophyll content for the CM variety under 1.0% salinity was significantly higher than in the control, showing a 25.0% increase. Additionally, CM demonstrated NPQt sensitivity under 0.3% salinity, requiring an LEF of 150 to achieve an NPQt value of 3.0, compared to an LEF of 180 in the control. These results suggest that a simple leaf disc assay may not fully capture the adaptive mechanisms of rice plants under salinity stress. Therefore, we advocate for the use of more comprehensive methods, such as outdoor pot or field experiments, to gain a deeper understanding and more accurate evaluation of salt tolerance in rice.

Deciphering the Mechanism of Melatonin-Induced Enhancement of Photosystem II Function in Moderate Drought-Stressed Oregano Plants.

Melatonin (MT) is considered as an antistress molecule that plays a constructive role in the acclimation of plants to both biotic and abiotic stress conditions. In the present study, we assessed the impact of 10 and 100 μM MT foliar spray, on chlorophyll content, and photosystem II (PSII) function, under moderate drought stress, on oregano (Origanum vulgare L.) plants. Our aim was to elucidate the molecular mechanism of MT action on the photosynthetic electron transport process. Foliar spray with 100 μM MT was more effective in mitigating the negative impact of moderate drought stress on PSII function, compared to 10 μM MT. MT foliar spray significantly improved the reduced efficiency of the oxygen-evolving complex (OEC), and PSII photoinhibition (Fv/Fm), which were caused by drought stress. Under moderate drought stress, foliar spray with 100 μM MT, compared with the water sprayed (WA) leaves, increased the non-photochemical quenching (NPQ) by 31%, at the growth irradiance (GI, 205 μmol photons m-2 s-1), and by 13% at a high irradiance (HI, 1000 μmol photons m-2 s-1). However, the lower NPQ increase at HI was demonstrated to be more effective in decreasing the singlet-excited oxygen (1O2) production at HI (-38%), in drought-stressed oregano plants sprayed with 100 μM MT, than the corresponding decrease in 1O2 production at the GI (-20%), both compared with the respective WA-sprayed leaves under moderate drought. The reduced 1O2 production resulted in a significant increase in the quantum yield of PSII photochemistry (ΦPSII), and the electron transport rate (ETR), in moderate drought-stressed plants sprayed with 100 μM MT, compared with WA-sprayed plants, but only at the HI (+27%). Our results suggest that the enhancement of PSII functionality, with 100 μM MT under moderate drought stress, was initiated by the NPQ mechanism, which decreased the 1O2 production and increased the fraction of open PSII reaction centers (qp), resulting in an increased ETR.

The Ratio of A400/A1800 Mapping Identifies Chromosomal Regions Containing Known Photoprotection Recovery-Related Genes in Rice

The rice, like other plants, undergoes photoprotection mode by increasing nonphotochemical quenching (NPQ) in high light intensity (> 1200 µmol m− 2s− 1 PPFD), which attenuates photosystem II yield (φPSII) drastically. The plant remains in photoprotection mode even after light intensity becomes not stressful for an extended period. While there are significant differences in the time it takes for photoprotection to recover among different genotypes, its use is limited in plant breeding because measuring the chlorophyll fluorescence parameters in progressive actinic light after dark adaptation takes more than forty-five minutes per genotype. The study finds that instantly measured A400/A1800 ratio by five minutes in flag leaves of 25 diverse genotypes strongly associated with the φPSII400 differences between theoretical and actual, qPd400 and NPQ400 with R2 values 0.74, 0.65 and 0.60, respectively. In two consecutive years, GWAS of A400/A1800 ratio identified the regions with genes reported earlier for plant photoprotection recovery. Additionally, QTL analysis in a RIL population also identified the regions carrying known genes related to photoprotection. Thus, the A400/A1800 ratio can quickly phenotype many plants for easier introgression of the traits in popular cultivars. The identified genotypes, genes, and QTLs can be used to improve yield potential and allele mining.

Genotype-specific morphophysiological adaptations and proline accumulation uncover drought adaptation complexity in hemp (Cannabis sativa and Cannabis indica)

Hemp, which has a wide range of industrial applications, has been marginalized due to its association with marijuana. This stigma has hindered research into improving its resilience to various stressors, resulting in underutilization and neglect. As cultivation expands globally, particularly in hot, dry regions of Africa, understanding drought stress mechanisms in hemp is crucial. This study investigates the drought adaptation mechanisms of three CBD flower hemp genotypes: Cannabis indica (MP) from Switzerland, Cannabis sativa (AQ) from South Africa, and Cannabis sativa (ZB) from Zimbabwe. Conducted under well-watered (WW-75% field capacity [FC]), mild drought (MD-40% FC), and severe drought (SD-0% FC) conditions, the research examines morphophysiological adaptations and proline accumulation in these genotypes, assessed 55 days after transplanting. Results revealed genotype-specific responses to watering regimes. MP demonstrated controlled water use and inherent drought tolerance, maintaining high assimilation rates (A) and superior photosynthetic performance (ΦPSII) under drought conditions. ZB maintained proline levels during drought recovery, suggesting optimized resource allocation and alternative stress-responsive mechanisms, while exhibiting effective morning water use and high non-photochemical quenching (NPQ) for photoprotection. AQ showed conservative water use strategies beneficial in water-limited environments. These findings provide a foundation for breeding programs aimed at developing robust and resilient hemp varieties suited to specific environmental conditions.

Dynamic responses of chlorophyll fluorescence parameters to drought across diverse plant families.

Chlorophyll fluorescence measurement is a quick and efficient tool for plant stress-level detection. The use of Pulse amplitude modulation (PAM), allows the detection of the plant stress level under field conditions. Over the years, several parameters estimating different parts of the chlorophyll and photosystem response were developed to describe the plant stress level. Despite all fluorescence parameters being based on the same measurements, their relationship remains unclear, and their response to drought stress is significantly influenced by the incoming light intensity. In this study, we use six different annual plants from different families, both C3 and C4 photosynthesis types, to describe the plant response to drought through the fluorescence parameters response (NPQ, Y(NPQ), and qN). To describe the dynamic response to drought, we employed light-response curves, adapting and fitting an equation for each curve to compare the drought response for each fluorescence parameter. The results demonstrated that the non-photochemical quenching (NPQ) and the quantum yield of non-photochemical quenching [Y(NPQ)] maximal values decrease when the PSII functionality (Fv/Fm) is lower than ~0.7. The basal fluorescence level ( and remained unaffected by the stress level and stayed stable across the various plants and stress levels. Our results indicate that the response of different stress parameters follows a distinct order under continuous drought. Consequently, monitoring just one parameter during long-term stress assessments may result in biased analysis outcomes. Incorporating multiple chlorophyll fluorescence parameters offers a more accurate reflection of the plant's stress level.

Improving photosynthetic efficiency of rice via over-expressing a ferredoxin-like protein gene from Methanothermobacter thermautotrophicus.

Ferredoxins (Fds) are crucial in various essential plant metabolic processes, including photosynthesis, fermentation and aerobic nitrogen fixation, due to their role in electron transport rate (ETR). However, the full scope of ferredoxin's function across prokaryotes and eukaryotic plants remains less understood. This study investigated the effect of MtFd from Methanothermobacter thermoautotrophicus on rice photosynthetic efficiency. We found that MtFd was localized in the chloroplasts of rice protoplasts. Transgenic analysis showed that MtFd significantly enhanced the photosynthetic capacity compared to the wild-type plants. This enhancement was evident through increased ETR, NADPH content and net photosynthetic rates, as well as decreased non-photochemical quenching (NPQ). Despite similar biomass to wild type plants, MtFd transgenic plants exhibited a marked increase in grain size and the 1000-grian weight. The elevated ETR and surplus free electrons in transgenic plants result in a considerable rise in cellular ROS content, which in turn enhances the enzymatic activity of the antioxidant system. In summary, our findings suggest that introducing the Fd protein from M. thermoautotrophicus into transgenic rice improves photosynthetic efficiency by accelerating ETR, which triggers the cellular oxidative stress response.

Reduced diffusional limitations in carnation stems facilitate higher photosynthetic rates and reduced photorespiratory losses compared with leaves.

Green stem photosynthesis has been shown to be relatively inefficient but can occasionally contribute significantly to the carbon budget of desert plants. Although the possession of green photosynthetic stems is a common trait, little is known about their photosynthetic characteristics in non-desert species. Dianthus caryophyllus is a semi-woody species with prominent green stems, which show similar photosynthetic anatomy with leaves. In the present study, we used a combination of gas exchange and chlorophyll fluorescence measurements, some of which were taken under varying O2 and CO2 partial pressures, to investigate whether the apparent anatomical similarities between the species' leaves and stems translate into similar photosynthetic physiology and capacity for CO2 assimilation. Both organs displayed high photosynthetic electron transport rates (ETR) and similar values of steady-state non-photochemical quenching (NPQ), albeit leaves could attain them faster. The analysis of OJIP transients showed that the quantum efficiencies and energy fluxes along the photosynthetic electron transport chain are largely similar between leaves and stems. Stems displayed higher total conductance to CO2 diffusion, similar biochemical properties, significantly higher photosynthetic rates and lower water use efficiency than leaves. Leaf ETR was more sensitive to sub-ambient O2 and super-ambient CO2 partial pressures, while leaves also displayed a higher relative rate of Rubisco oxygenation. We conclude that the highly responsive NPQ and the enhanced photorespiration and WUE in leaves represent photoprotective and water-conserving adaptations to the high incident light intensities they experience naturally, at the expense of higher CO2 assimilation rates, which the vertically orientated stems can readily attain.

Contrasting Dynamic Photoprotective Mechanisms under Fluctuating Light Environments between an Andean and a Mesoamerican Genotype of Phaseolus vulgaris L.

Plants have evolved various photosynthetic adaptations and photoprotective mechanisms to survive in fluctuating and extreme light environments. Many light-activated photosynthetic proteins and enzymes adjust to plant leaf anatomy and leaf pigments to facilitate these processes. Under excessive amounts of light, plants use non-photochemical quenching (NPQ) mechanisms to dissipate excess absorbed light energy as heat to prevent photoinhibition and, therefore, mitigate damage to the plant’s photosystems. In this study, we examined photosynthetic adaptations to the light environment in common beans using representative genotypes of the Andean (Calima) and the Mesoamerican (Jamapa) gene pools. We estimated their leaf chlorophyll fluorescence characteristics using dark- and light-adapted mature leaves from three-week-old plants. Our results indicated a higher chlorophyll fluorescence of the light-adapted leaves in the Mesoamerican genotype. NPQ induction was early and extended in the Andean genotype. A similar response in the Mesoamerican counterpart required high light intensity (≥1500 PAR). The NPQ relaxation was rapid in the Mesoamerican genotype (t1/2: 6.76 min) but sluggish in the Andean genotype (t1/2: 9.17 min). These results indicated variable adaptation to light environments between the two common bean genotypes and suggested different strategies for surviving fluctuating light environments that can be exploited for developing plants with environmentally efficient photosynthesis under light limitations.