Maximum Efficiency Of PSII Research Articles

The Leafless Orchid Cymbidium macrorhizon Performs Photosynthesis in the Pericarp during the Fruiting Season.

Photosynthesis with highly photoreactive chlorophyll (Chl) provides energy for plant growth but with simultaneous risk of photooxidative damage and photoprotection costs. Although the leafless orchid Cymbidium macrorhizon mostly depends on mycorrhizal fungi for carbon, it accumulates Chl particularly during fruiting and may not be fully mycoheterotrophic. In fact, stable isotopic analysis suggested that the fruiting C. macrorhizon specimens obtain a significant proportion of its carbon demands through photosynthesis. However, actual photosynthetic characteristics of this leafless orchid are unknown. To reveal the functionality of photosynthetic electron transport in C. macrorhizon, we compared its photosynthetic properties with those of its relative mixotrophic orchid Cymbidium goeringii and the model plant Arabidopsis thaliana. Compared with C. goeringii and A. thaliana, maximum photochemical efficiency of PSII was substantially low in C. macrorhizon. Chl fluorescence induction kinetics revealed that the electron transport capacity of PSII was limited in C. macrorhizon. Chl fluorescence analysis at 77 K suggested partial energetic disconnection of the light-harvesting antenna from the PSII reaction center in C. macrorhizon. Despite its low PSII photochemical efficiency, C. macrorhizon showed photosynthetic electron transport activity both in the field and under laboratory conditions. Cymbidium macrorhizon developed strong nonphotochemical quenching in response to increased light intensity as did C. goeringii, suggesting the functionality of photoprotective systems in this orchid. Moreover, C. macrorhizon fruit developed stomata on the pericarp and showed net O2-evolving activity. Our data demonstrate that C. macrorhizon can perform photosynthetic electron transport in the pericarp, although its contribution to net carbon acquisition may be limited.

Chlorophyll retention caused by STAY-GREEN (SGR) gene mutation enhances photosynthetic efficiency and yield in soybean hybrid Z1

To study the effect of a stay-green mutation on photosynthetic efficiency in hybrid offspring of soybean (Glycine max [L.] Merr.), the parameters of photosynthesis and chlorophyll (Chl) fluorescence were compared between a new stay-green variety Jinda Zhilv No. 1 (Z1) and one of its parents Jinda No. 74 (JD74). During leaf natural senescence, the Chl degradation attenuated in Z1. The net photosynthetic rate, stomatal conductance, and transpiration rate were consistently higher in Z1 than that in JD74 after flowering. The decreases of maximum photochemical efficiency of PSII, actual photochemical efficiency of PSII, and photochemical quenching coefficient were greater in JD74 than in Z1. Transcriptional levels of most genes involved in photosystems were much higher in Z1. All these effectively contributed to maintained photosystem stability and enhanced photosynthetic efficiency and yield in Z1. We also revealed that the STAY-GREEN gene mutation was responsible for inhibiting Chl degradation in Z1.

Light quality-dependent regulation of photoprotection and antioxidant properties in rice seedlings grown under different light-emitting diodes

We examined light quality-dependent regulation of photoprotection and antioxidant properties in rice seedlings. Seedlings grown under red or green light-emitting diodes (LEDs) showed declines in quantum yield of electron transport through PSII, maximum relative electron transport rates, and photochemical quenching compared to the white and blue LED, but no difference in maximum photochemical efficiency of PSII was found. Blue LED treatment resulted in greater increases in not only nonphotochemical quenching, but also zeaxanthin formation, expressions of β-carotene hydroxylase and violaxanthin de-epoxidase, and anthocyanin compared to other LED treatments. By contrast, green and red LEDs increased activities of superoxide dismutase and ascorbate peroxidase as well as expression levels of catalase (CAT)a and CATb to white and blue LEDs. Green and red LEDs also greatly upregulated expressions of phytochrome (PHY) A, PHYB, PHYC, and cryptochrome 2 compared to white and blue LEDs, whereas blue LED upregulated CRY1. Our results demonstrate that specific wavelengths of different LEDs differentially influence photosynthetic performance, photoprotection, and antioxidant properties, possibly through regulating expressions of phytochrome and cryptochrome genes in a light-quality-dependent manner.

Ecophysiology of Pilocarpus microphyllus in response to temperature, water availability and vapour pressure deficit

The jaborandi is a natural source of alkaloids used in the treatment of important diseases and, therefore, relevant for the pharmaceutical industry. However, the lack of information on the jaborandi ecophysiological responses under different climatic conditions is the major limitation for its expansion in Brazil. Thus, we investigated the effects of different environmental conditions on the ecophysiology of jaborandi seedlings, combining several ranges of mean air temperature (T), vapour pressure deficit (VPD) and water availability. For this, jaborandi seedlings were cultivated in four different environments: cold and humid (Temp: 21.1 °C, VPD: 0.31 kPa), hot and humid (Temp: 26.8 °C, VPD: 0.34 kPa), hot and dry (Temp: 26.3 °C, VPD: 1.09 kPa) and cold and dry (Temp: 20.8 °C, VPD: 0.84 kPa); all the environments had two water availability levels: well-watered (control: C) and water-stressed (45% of the maximum substrate water holding capacity). Growth and fluorescence parameters, crop water stress index and enzymatic antioxidant activity were evaluated. Our results revealed that the seedlings reduced their growth when subjected to water restriction in all treatments, resulting in a lower total dry mass production, mainly due to the reduction of the root system. In the well-watered treatments, jaborandi seedlings showed higher growth when cultivated in warmer environments, regardless of the VPD. Under low-temperature conditions, there was a reduction in maximum quantum yield efficiency of PSII, indicating damage to photosystem II; also, the minimum fluorescence and the enzymatic antioxidants activity increased. The highest dry mass accumulation was obtained when the seedlings were submitted to high temperatures, indicating that the regions that experience such conditions are the most suitable for jaborandi cultivation.

On the Relationship between a Novel Prorocentrum sp. and Colonial Phaeocystis antarctica under Iron and Vitamin B12 Limitation: Ecological Implications for Antarctic Waters

We collected live mixed natural samples from the northeastern Ross Sea during the austral summer of 2017 and isolated a novel Prorocentrum sp. (Dinophyceae) associated with mucilaginous Phaeocystis antarctica (Coccolithophyceae) colonies. The haptophyte P. antarctica is a key species of the phytoplankton community in the Ross Sea, where blooms are subjected to iron limitation and/or co-limitation with other micronutrients (e.g., vitamin B12) during the summer. We first performed preliminary genetic analyses to determine the specific identity of the novel Prorocentrum sp., which indicated that it represented a previously undescribed species. The formal description of this new species is in process. To further assess its relationship with P. antarctica, we obtained their monospecific and mixed cultures and evaluated their responses to different irradiance levels and iron and vitamin B12 limitation. Our results indicated differential susceptibility of the two species to iron limitation and differential photosynthetic plasticity under high irradiance. Iron limitation reduced colony formation in P. antarctica and decreased the chlorophyll-a content in Prorocentrum sp., whereas B12 limitation did not affect growth or photosynthetic efficiency in either species. In addition, P. antarctica could photosynthesize efficiently under different irradiance levels, due to its ability to modulate the light adsorption cross-section of PSII, whereas Prorocentrum sp. exhibited lower photosynthetic plasticity and an inability to modulate both the maximum photochemical efficiency and effective adsorption cross-section of PSII under high irradiance. The trophic interaction between Prorocentrum sp. and P. antarctica could present ecological implications for the food webs and biogeochemical cycles of the Antarctic ecosystem. Considering the predicted climate-driven shifts in global ocean surface light regimes and changes in iron or vitamin B12 transfer, which are most likely to impact changes in the phytoplankton community structure, our results present implications for carbon export to deeper waters, ecological functioning, and associated biogeochemical changes in the future.

Foliar nitrogen supply enhances the recovery of photosynthetic performance of cold-stressed coffee (Coffea arabica L.) seedlings

Cold-stressed leaves possess an elevated risk of photodamage due to an inefficient photosynthetic apparatus during winter conditions. Recovery of cold-stressed coffee seedlings treated with different concentrations of nitrogen applied as foliar urea sprays [control (0), 5, 10, 20, and 40 mM], was investigated under optimum growth chamber conditions (25/20°C) for three months. Concentrations of nitrogen and photosynthetic pigments in the leaves increased with increasing concentration of the foliar sprays up to 20 mM. This was accompanied with a recovery of the photosynthetic apparatus and increased net carbon assimilation rate. In addition, 10 and 20 mM-treated plants also had the highest maximal efficiency of PSII compared to their lower or higher nitrogen concentration treated counterparts. Conversely, these plants contained lower concentrations of 5-caffeoylquinic acid, mangiferin, trigonelline, and caffeine than control plants. We concluded therefore that foliar sprays of the appropriate nitrogen concentration were adequate for recuperating the photosynthetic apparatus and improved the photosynthetic performance of the cold-stressed coffee seedlings.

Role of rhizospheric microorganisms in mitigating the adverse effect of salinity stress in Plantago ovata growth, biochemical and photosynthetic traits

ABSTRACT This pot experiment was carried out to investigate the efficiency of plant rhizospheric microorganisms (PRMs) to counteract salinity stress in Plantago ovata. The treatments included soil salinity (2.5 (as control), 5 and 10 dS m−1), arbuscular mycorrhizal fungi (Control, Glomus mosseae, Rhizophagus intraradices and Funneliformis mosseae) and phosphate solubilizing bacteria (Control and Pseudomonas fluorescens). The highest amount of growth and yield parameters, relative water content (RWC), potassium (K+) and phosphorus (P) concentration, photosynthetic traits (chlorophyll a and b, carotenoid, maximal efficiency of PSII (fv/fm), variable fluorescence to initial fluorescence (fv/f0) and stomatal conductance (gs)), antioxidant enzymes and the lowest sodium (Na+) concentration, malondialdehyde (MDA) and electrolyte leakage were observed in the plants treated with mixture of Rhizophagus intraradices and Pseudomonas fluorescens under all salinity levels. Although all previously mentioned traits significantly and severely decreased under salinity stress, mucilage percentage, electrolyte leakage and Na+ concentration were increased under salinity levels. In conclusion, the results suggested that inoculation of AMF (particularly Rhizophagus intraradices) in combination with Pseudomonas fluorescens by the accumulation of proline along with decreased electrolyte leakage, maintenance of relative water content in leaves and selective uptake of K+ ions could overcome detrimental effects of salinity stress in isabgol. Abbreviations AMF: arbuscular mycorrhizal fungi; APX: ascorbate peroxidase; CAT: catalase; Chl: chlorophyll; CAR: carotenoids; ECe: electrical conductivity of soil saturation extract; EL: Electrolyte leakage; Fv/Fm: maximal efficiency of PSII; gs: stomatal conductance; Fv/F0: variable fluorescence to initial fluorescence; K+: potassium; MDA: malondialdehyde; Na+: Sodium; PGPR: plant growth-promoting rhizobacteria; P: phosphorus; PRM: plant rhizospheric microorganisms; PSB: phosphate solubilizing bacteria; RWC: relative water content; SOD: superoxide dismutase

High light intensity aggravates latent manganese deficiency in maize.

Manganese (Mn) plays an important role in the oxygen-evolving complex, where energy from light absorption is used for water splitting. Although changes in light intensity and Mn status can interfere with the functionality of the photosynthetic apparatus, the interaction between these two factors and the underlying mechanisms remain largely unknown. Here, maize seedlings were grown hydroponically and exposed to two different light intensities under Mn-sufficient or -deficient conditions. No visual Mn deficiency symptoms appeared even though the foliar Mn concentration in the Mn-deficient treatments was reduced to 2 µg g-1. However, the maximum quantum yield efficiency of PSII and the net photosynthetic rate declined significantly, indicating latent Mn deficiency. The reduction in photosynthetic performance by Mn depletion was further aggravated when plants were exposed to high light intensity. Integrated transcriptomic and proteomic analyses showed that a considerable number of genes encoding proteins in the photosynthetic apparatus were only suppressed by a combination of Mn deficiency and high light, thus indicating interactions between changes in Mn nutritional status and light intensity. We conclude that high light intensity aggravates latent Mn deficiency in maize by interfering with the abundance of PSII proteins.

Functional trade-off of hydration strategies in old forest epiphytic cephalolichens

Although water is essential for photosynthetic activation in lichens, rates of vapor uptake and activation in humid air, which likely influence their niche preferences and distribution ranges, are insufficiently known. This study simultaneously quantifies rehydration kinetics and PSII reactivation in sympatric, yet morphologically and functionally distinct cephalolichens (Lobaria amplissima, Lobaria pulmonaria, Lobaria virens). High-temporal resolution monitoring of rehydrating thalli by automatic weighing combined with chlorophyll fluorescence imaging of maximal PSII efficiency (FV/FM) was applied to determine species-specific rates of vapor uptake and photosynthetic activation. The thin and loosely attached growth form of L. pulmonaria rehydrates and reactivates faster in humid air than the thick L. amplissima, with L. virens in between. This flexible hydration strategy is consistent with L. pulmonaria’s wide geographical distribution stretching from rainforests to continental forests. By contrast, the thick and resupinate L. amplissima reactivates slowly in humid air but stores much water when provided in abundance. This prolongs active periods after rain, which could represent an advantage where abundant rain and stem flow alternates with long-lasting drying. Understanding links between morphological traits and functional responses, and their ecological implications for species at risk, is crucial to conservation planning and for modelling populations under various climate scenarios.

Application of Trichoderma asperellum T34 on maize (Zea mays) seeds protects against drought stress.

Coating maize seeds with the microbial plant protection product Trichoderma asperellum strain T34 is an effective form of inoculation that enhances plant performance when faced with drought stress, and it improves nutrient and kernel parameters differently in drought and non-stressed conditions. Drought is currently one of the biggest threats to maize production. Trichoderma spp. is mainly used in agriculture as plant protection product with secondary beneficial effects on plants: improved growth, nutrient uptake and plant immunity. Here, we studied the physiological performance of maize plants under two different water regimes (fully irrigated and drought conditions) and three different seed treatments: application of Trichoderma asperellum strain T34, application of a chemical fungicide (CELEST XL) or the combination of both. Regardless of water regime, T34 treatment improved kernel P and C, kernel number and dry weight. Higher populations of T34 on the rhizosphere (T34 treatment) alleviated water stress better than lower T34 populations (T34+Q treatment). Under drought, T34 treatment improved leaf relative water content, water use efficiency, PSII maximum efficiency and photosynthesis. T34-treated maize seeds maintained sufficient T34 populations to alleviate drought throughout crop development suggesting an optimal dose of 104 and 105 colony forming unitsg-1dry weight of rhizosphere under the studied conditions. This work helps to demonstrate the beneficial interaction between T. asperellum strain T34 and maize plants under drought.

Neodymium improves the activity of ascorbate-glutathione cycle and chloroplast function of wheat seedlings under chromium stress

We investigated the roles of neodymium trichloride (NdCl3) in regulating ascorbate-glutathione (AsA-GSH) cycle and chloroplast function of chromium (Cr)-stressed wheat seedlings. The findings showed that Cr stress markedly increased malondialdehyde (MDA) content, electrolytic leakage (EL), nonphotochemical quenching, and the activities of enzymes in AsA-GSH cycle, compared with control. However, Cr stress markedly reduced the ratios of reduced ascorbate to dehydroascorbate and reduced glutathione to oxidized glutathione, net photosynthetic rate, the contents of chlorophylls and carotenoids, maximum photochemical efficiency of PSII, photochemical quenching, and quantum efficiency of PSII photochemistry, as well as plant height, root length, and plant biomass. NdCl3 plus Cr stress markedly reduced MDA content and EL and improved other indicators, compared with Cr stress alone. Meanwhile, NdCl3 alone also markedly improved above indicators except MDA and EL, compared with control. Current results implied that NdCl3 improved AsA-GSH cycle and chloroplast function of wheat seedlings under Cr stress.

Phytoremediation of Waste Water Containing Phenol by Salix Matsudana Seedlings and their Physiological Response

In order to study the tolerance and removal capability of Salix matsudana to phenol wastewater, we determined the effects of different concentrations of phenol on the photosynthesis, chlorophyll fluorescence parameters and enzyme activities of S. matsudana cut seedlings and their purification effects to phenol using hydroponics. The results show that wastewater containing 30 mg L-1 and 60 mg L-1 phenol increased Pn, Gs and Tr of S. matsudana, however, the maximum photochemical efficiency (Fv/Fm) of PSII changed little. When the concentration of phenol increased to 90 mg L-1-180 mg L-1, Pn and Fv/Fm of S. matsudana were significantly lower than those in the control group, while the Ci increased significantly. The 30 mgL-1-150 mgL-1 of phenol can increase the SOD and POD activities in leaves and roots of S. matsudana and the 180 mgL-1 of phenol decreased their activities. The percent removal of phenol decreased with increasing concentration of phenol ranging from 87% to 98% in 10 days. In conclusion, S. matsudana can be used to purify waste water containing phenol in concentration less than 150 mg L-1.

Seasonal variation of fig tree (Ficus carica L.) physiological characteristics reveals its adaptation performance

In the context of climate change, understanding fig trees physiology is very important, since the areas of fig production registered a large climate variability that severely affects fruit quality. The present study was conducted to evaluate the seasonal changes of physiological leaf behaviour of two Tunisian fig cultivars, Zidi and Bither Abiadh during two years. Plants were subjected to full irrigation to maintain the soil moisture around pot capacity through the experimental period. Leaf gas exchange characteristics (net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E)), chlorophyll content index, leaf temperature and the maximum photochemical efficiency of PSII (Fv/Fm) were measured. Results showed that the photosynthetic characteristics changed during the growing season. Changes of photosynthetic CO2 assimilation, stomatal conductance, and chlorophyll content were not significantly affected by cultivar, and their variation was attributed to year. Seasonal changes of PN and gs were similar suggesting that both processes are dependent. Indeed the best photosynthetic performance of fig occurred about 80-87 days after bud break (spring) of the second season of growth, being supported by a high stomatal aperture. The lowest values of PN, E and gs were recorded 156 days after bud break (summer) for 2017. The decrease of gas exchange rates and high temperatures were registered during the same dates. A little increase of the photosynthetic characteristics and chlorophyll content was noticed in the autumn period, about 180 days after bud break, until a definitive decrease at the end of the growing season with the occurrence of low winter temperature. These results revealed particular adaptive behaviour and could be used as preliminary criteria to predict the future impact of environmental abiotic stresses on ecophysiological fig tree behaviour.

Nitric Oxide is Required for Aminolevulinic Acid-Induced Salt Tolerance by Lowering Oxidative Stress in Maize (Zea mays)

Although some investigations show that 5-aminolevulinic acid (ALA) participates in plant stress tolerance, the role of nitric oxide (NO) in ALA-induced improvement in tolerance to salt stress in plants necessitates to be understood. So, a NO scavenger, 0.1 mM 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO); was applied jointly with ALA. Of four ALA concentrations tested in a preliminary experiment, 20 mg L−1 was chosen to apply as seed treatment or foliage spray to saline-stressed maize seedlings. Salinity (100 mM NaCl) significantly led to reduction in plant biomass, PSII maximum efficiency (Fv/Fm), total chlorophyll, leaf potassium (K+) and calcium (Ca2+) as well as leaf water potential in both cultivars, but it led to enhanced contents of proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), electrolyte leakage (EL) and leaf sodium (Na+) as well as internal NO and nitric oxide synthase (NOS). ALA treatments improved plant growth, activities of antioxidant enzymes, and leaf Ca2+ and K+, but it led to further increases in leaf NO and NOS activity as well as ALA levels. ALA-induced salt tolerance was completely abolished by cPTIO application by eliminating the internal NO generation. This evidently showed that ALA triggered the synthesis of NO through activation of NOS, which in turn improved salt tolerance of the maize plants.

Exogenously supplied silicon (Si) improves cadmium tolerance in pepper (Capsicum annuum L.) by up-regulating the synthesis of nitric oxide and hydrogen sulfide

The current research was aimed to observe the interactive role of silicon-generated hydrogen sulfide (H2S) and nitric oxide (NO) on tolerance of pepper (Capsicum annum L.) plants to cadmium (Cd). Thus, the pepper plants were subjected to control (no Cd) or cadmium stress with and without Si supplementation. Significant decreases were found in plant dry weights, water potential, PSII maximum efficiency, glutathione (GSH), total chlorophyll, relative water content, Ca2+ and K+ concentrations and ascorbate, but there was a significant increase in H2O2, MDA, electron leakage (EL), proline, key antioxidant enzymes’ activities, and endogenous Cd, NO and H2S in the Cd-stressed plants. Silicon enhanced Cd tolerance of the pepper plants by lowering the leaf Cd concentration, oxidative stress, enhancing the antioxidant defence system, leaf Si content, photosynthetic traits and plant growth as well as the contents of NO, proline and H2S. Furthermore, foliar-applied NO scavenger, cPTIO, and that of H2S, hypotaurine (HT), significantly decreased the levels of H2S alone, but cPTIO effectively reduced the concentrations of NO and H2S accumulated by Si in the Cd-stressed plants. The positive effect of Si was eliminated by cPTIO, but not by HT, suggesting that both molecules were involved in Si-induced improvement in Cd tolerance of the pepper plants.

Melatonin alleviates nickel phytotoxicity by improving photosynthesis, secondary metabolism and oxidative stress tolerance in tomato seedlings.

Arable land contamination with nickel (Ni) has become a major threat to worldwide crop production. Recently, melatonin has appeared as a promising stress-relief substance that can alleviate heavy metal-induced phytotoxicity in plants. However, the plausible underlying mechanism of melatonin function under Ni stress has not been fully substantiated in plants. Herein, we conducted an experiment that unveiled critical mechanisms in favor of melatonin-mediated Ni-stress tolerance in tomato. Ni stress markedly inhibited growth and biomass by impairing the photosynthesis, photosystem function, mineral homeostasis, root activity, and osmotic balance. In contrast, melatonin application notably reinforced the plant growth traits, increased photosynthesis efficiency in terms of chlorophyll content, upregulation of chlorophyll synthesis genes, i.e. POR, CAO, CHL G, gas exchange parameters, and PSII maximum efficiency (Fv/Fm), decreased Ni accumulation and increased mineral nutrient homeostasis. Moreover, melatonin efficiently restricted the hydrogen peroxide (H2O2) and superoxide radical production and increased RBOH expression and restored cellular integrity (less malondialdehyde and electrolyte leakage) through triggering the antioxidant enzyme activities and modulating AsA-GSH pools. Notably, oxidative stress was effectively mitigated by upregulation of several defense genes (SOD, CAT, APX, GR, GST, MDHAR, DHAR) and melatonin biosynthesis-related genes (TDC, T5S, SNAT, ASMT). Besides, melatonin treatment enhanced secondary metabolites (phenols, flavonoids, and anthocyanin) contents along with their encoding genes (PAL, CHS) expression, and these metabolites potentially restricted excess H2O2 accumulation. In conclusion, our findings deciphered the potential functions of melatonin in alleviating Ni-induced phytotoxicity in tomato through boosting the biomass production, photosynthesis, nutrient uptake, redox balance, and secondary metabolism.

Involvement of abscisic acid, ABI5, and PPC2 in plant acclimation to low CO2.

Phosphoenolpyruvate carboxylase (PEPC) plays a pivotal role in the photosynthetic CO2 fixation of C4 plants. However, the functions of PEPCs in C3 plants are less well characterized, particularly in relation to low atmospheric CO2 levels. Of the four genes encoding PEPC in Arabidopsis, PPC2 is considered as the major leaf PEPC gene. Here we show that the ppc2 mutants suffered a growth arrest when transferred to low atmospheric CO2 conditions, together with decreases in the maximum efficiency of PSII (Fv/Fm) and lower levels of leaf abscisic acid (ABA) and carbohydrates. The application of sucrose, malate, or ABA greatly rescued the growth of ppc2 lines under low CO2 conditions. Metabolite profiling analysis revealed that the levels of glycine and serine were increased in ppc2 leaves, while the abundance of photosynthetic metabolites was decreased under these conditions. The transcript levels of encoding enzymes involved in glycine or serine metabolism was decreased in ppc2 in an ABI5-dependent manner. Like the ppc2 mutants, abi5-1 mutants had lower photosynthetic rates and Fv/Fm compared with the wild type under photorespiratory conditions (i.e. low CO2 availability). However, the growth of these mutants was similar to that of the wild type under non-photorespiratory (low O2) conditions. The constitutive expression of ABI5 prevented the growth arrest of ppc2 lines under low CO2 conditions. These findings demonstrate that PPC2 plays an important role in the acclimation of Arabidopsis plants to low CO2 availability by linking photorespiratory metabolism to primary metabolism, and that this is mediated, at least in part, through ABA- and ABI5-dependent processes.

Moderate drought followed by re-watering initiates beneficial changes in the photosynthesis, biomass production and Rubiaceae-type cyclopeptides (RAs) accumulation of Rubia yunnanensis

Roots and rhizomes of Rubia yunnanensis are important Chinese medicine materials with significant anti-tumor activity, which is mainly obtained from wild resources. There is an urgent need to develop the production practice for the cultivation of R. yunnanensis. The current study was performed to investigate the changes in the photosynthetic pigment content, photosynthetic characteristics, chlorophyll fluorescence parameters, biomass production, and secondary metabolites Rubiaceae-type cyclopeptides (RAs) contents in roots and rhizomes by drought and re-watering in R. yunnanensis grown in four water conditions: well-watered control (C), moderate drought (MD), severe drought (SD), and re-watering after moderate drought (RMD). The results indicated that compared with the control, drought stresses (MD and SD) significantly decreased photosynthetic pigments and impaired photochemical efficiency, as revealed by the reductions of maximum potential PSII efficiency (Fv/Fm), effective quantum yield of photochemical energy conversion (Yield) and electron transport rate (ETR), etc., resulting in limited photosynthetic capacity, and hence reduced biomass accumulation and RAs contents and yields in roots and rhizomes. The RMD plants could produce compensation effect and their photosynthetic ability recovered to control level; they showed the comparable dry biomass of roots and rhizomes and higher contents and yields of RAs compared with the control. This implied that moderate drought-induced injury in R. yunnanensis was reversible. These results reinforce the importance of water management and recommend the re-water operation for the cultivation of R. yunnanensis.

Foliar application of nanoparticles mitigates the chilling effect on photosynthesis and photoprotection in sugarcane

Chilling is one of the main abiotic stresses that adversely affect the productivity of sugarcane, in marginal tropical regions where chilling incidence occurs with seasonal changes. However, nanoparticles (NPs) have been tested as a mitigation strategy against diverse abiotic stresses. In this study, NPs such as silicon dioxide (nSiO2; 5–15 nm), zinc oxide (nZnO; <100 nm), selenium (nSe; 100 mesh), graphene (graphene nanoribbons [GNRs] alkyl functionalized; 2–15 μm × 40–250 nm) were applied as foliar sprays on sugarcane leaves to understand the amelioration effect of NPs against negative impact of chilling stress on photosynthesis and photoprotection. To this end, seedlings of moderately chilling tolerant sugarcane variety Guitang 49 was used for current study and spilt plot was used as statistical design. The changes in the level chilling tolerance after the application of NPs on Guitang 49 were compared with tolerance level of chilling tolerant variety Guitang 28. NPs treatments reduced the adverse effects of chilling by maintaining the maximum photochemical efficiency of PSII (Fv/Fm), maximum photo-oxidizable PSI (Pm), and photosynthetic gas exchange. Furthermore, application of NPs increased the content of light harvesting pigments (chlorophylls and cartinoids) in NPs treated seedlings. Higher carotenoid accumulation in leaves of NPs treated seedlings enhanced the nonphotochemical quenching (NPQ) of PSII. Among the NPs, nSiO2 showed higher amelioration effects and it can be used alone or in combination with other NPs to mitigate chilling stress in sugarcane.

Arbuscular Mycorrhizal Fungi Mediate Drought Tolerance and Recovery in Two Contrasting Carob (Ceratonia siliqua L.) Ecotypes by Regulating Stomatal, Water Relations, and (In)Organic Adjustments.

Irregular precipitation and drought caused an increase in tree mortality rates in multiple forest biomes with alterations in both ecosystem services and carbon balance. Carob (Ceratonia siliqua) growth and production in arid and semi-arid ecosystems are likely affected by climate change-induced droughts. Understanding the physiological responses of drought-induced early-stage tree death and strategies to enhance drought tolerance and optimize growth will help tree improvement programs. Mycorrhizal inoculation has a pronounced impact on plant growth, water absorption, mineral nutrition, and protection from abiotic stresses. However, a better understanding of these complex interconnected cellular processes and arbuscular mycorrhizal fungi (AMF)-mediated mechanisms regulating drought tolerance in plants will enhance its potential application as an efficient approach for bio-amelioration of stresses. The objectives of this work were to elucidate the different effects of autochthone AMF on inorganic solute and water content uptakes, organic adjustments (sugar and proteins content), leaf gas exchange (stomatal conductance and efficiency of photosystems I and II), and oxidative damage of two contrasting ecotypes of carob seedlings: coastal (southern ecotype (SE)) and in-land (northern ecotype (NE)) under control (C), drought (by cessation of irrigation for 15 days (15D)), and recovery (R) conditions. Our findings showed that AMF promoted growth, nutrient content, and physiological and biochemical parameters in plants of both ecotypes during C, 15D, and R conditions. After four days of recovery, stomatal conductance (gs), the maximum photochemical efficiency of PSII (Fv/Fm), water content, and plant uptake of mineral nutrients (P, K, Na, and Ca) were significantly higher in shoots of mycorrhizal (AM) than non-mycorrhizal (NM) control plants. Consequently, AMF reduced to a greater degree the accumulation of hydrogen peroxide (H2O2) and oxidative damage to lipid (malondialdehyde (MDA)) content in AM than NM plants in NE and SE, after recovery. Altogether, our findings suggest that AMF can play a role in drought resistance of carob trees at an early stage by increasing the inorganic solutes (P, K, Na, and Ca), water content uptake, organic solutes (soluble sugars and protein content), stomatal conductance, and defense response against oxidative damage during re-watering after drought stress.