The Responses of Light Reaction of Photosynthesis to Dynamic Sunflecks in a Typically Shade-Tolerant Species Panax notoginseng

Light is highly heterogeneous in natural conditions, and plants need to evolve a series of strategies to acclimate the dynamic light since it is immobile. The present study aimed to elucidate the response of light reaction of photosynthesis to dynamic sunflecks in a shade-tolerant species Panax notoginseng and to examine the regulatory mechanisms involved in an adaptation to the simulated sunflecks. When P. notoginseng was exposed to the simulated sunflecks, non-photochemical quenching (NPQ) increased rapidly to the maximum value. Moreover, in response to the simulated sunflecks, there was a rapid increase in light-dependent heat dissipation quantum efficiency of photosystem II (PSII) (ΦNPQ), while the maximum quantum yield of PSII under light (Fv′/Fm′) declined. The relatively high fluorescence and constitutive heat dissipation quantum efficiency of PSII (Φf,d) in the plants exposed to transient high light (400, 800, and 1,600 μmol m–2 s–1) was accompanied by the low effective photochemical quantum yield of PSII (ΦPSII) after the dark recovery for 15 min, whereas the plants exposed to transient low light (50 μmol m–2 s–1) has been shown to lead to significant elevation in ΦPSII after darkness recovery. Furthermore, PSII fluorescence and constitutive heat dissipation electron transfer rate (Jf,d) was increased with the intensity of the simulated sunflecks, the residual absorbed energy used for the non-net carboxylative processes (JNC) was decreased when the response of electron transfer rate of NPQ pathway of PSII (JNPQ) to transient low light is restricted. In addition, the acceptor-side limitation of PSI [Y(NA)] was increased, while the donor-side limitation of photosystems I (PSI) [Y(ND)] was decreased at transient high light conditions accompanied with active cyclic electron flow (CEF). Meanwhile, when the leaves were exposed to transient high light, the xanthophyll cycle (V cycle) was activated and subsequently, the JNPQ began to increase. The de-epoxidation state [(Z + A)/(V + A + Z)] was strongly correlated with NPQ in response to the sunflecks. In the present study, a rapid engagement of lutein epoxide (Lx) after the low intensity of sunfleck together with the lower NPQ contributed to an elevation in the maximum photochemical quantum efficiency of PSII under the light. The analysis based on the correlation between the CEF and electron flow devoted to Ribulose-1, 5-bisphosphate (RuBP) oxygenation (JO) indicated that at a high light intensity of sunflecks, the electron flow largely devoted to RuBP oxygenation would contribute to the operation of the CEF. Overall, photorespiration plays an important role in regulating the CEF of the shade-tolerant species, such as P. notoginseng in response to transient high light, whereas active Lx cycle together with the decelerated NPQ may be an effective mechanism of elevating the maximum photochemical quantum efficiency of PSII under light exposure to transient low light.

Does a Large Ear Type Wheat Variety Benefit More From Elevated CO2 Than That From Small Multiple Ear-Type in the Quantum Efficiency of PSII Photochemistry?

Recently, several reports have suggested that the growth and grain yield of wheat are significantly influenced by high atmospheric carbon dioxide concentration (CO2) because of it photosynthesis enhancing effects. Moreover, it has been proposed that plants with large carbon sink size will benefit more from CO2 enrichment than those with small carbon sink size. However, this hypothesis is yet to be test in winter wheat plant. Therefore, the aim of this study was to examine the effect of elevated CO2 (eCO2) conditions on the quantum efficiency of photosystem II (PSII) photochemistry in large ear-type (cv. Shanhan 8675; greater ear C sink strength) and small multiple ear-type (cv. Early premium; greater vegetative C source strength) winter wheat varieties. The experiment was conducted in a free air CO2 enrichment (FACE) facility, and three de-excitation pathways of the primary reaction of PSII of flag leaf at the anthesis stage were evaluated under two CO2 concentrations (ambient [CO2], ∼415 μmol⋅mol–1, elevated [CO2], ∼550 μmol⋅mol–1) using a non-destructive technique of modulated chlorophyll fluorescence. Additionally, the grain yield of the two varieties was determined at maturity. Although elevated CO2 increased the quantum efficiency of PSII photochemistry (ΦPSII) of Shanhan 8675 (SH8675) flag leaves at the anthesis stage, the grain number per ear and 1,000-kernel weight were not significantly affected. In contrast, the ΦPSII of early premium (ZYM) flag leaves was significantly lower than that of SH8675 flag leaves at the anthesis stage, which was caused by an increase in the regulatory non-photochemical energy dissipation quantum (ΦNPQ) of PSII, suggesting that light energy absorbed by PSII in ZYM flag leaf was largely dissipated as thermal energy. The findings of our study showed that although SH8675 flag leaves exhibited higher C sink strength and quantum efficiency of PSII photochemistry at the anthesis stage, these factors alone do not ensure improved grain yield under eCO2 conditions.

Regulation of Photosystem II Heterogeneity and Photochemistry in Two Cultivars of C4 Crop Sugarcane Under Chilling Stress

In subtropical regions, chilling stress is one of the major constraints for sugarcane cultivation, which hampers yield and sugar production. Two recently released sugarcane cultivars, moderately chilling tolerant Guitang 49 and chilling tolerant Guitang 28, were selected. The experiments were conducted in the controlled environment, and seedlings were exposed to optimum (25°C/15°C), chilling (10°C/5°C), and recovery (25°C/15°C) temperature conditions. PSII heterogeneity was studied in terms of reducing side and antenna size heterogeneity. Under chilling, reducing side heterogeneity resulted in increased number of QB non-reducing centers, whereas antenna side heterogeneity resulted in enhanced number of inactive β centers in both cultivars, but the magnitude of change was higher in Guitang 49 than Guitang 28. Furthermore, in both cultivars, quantum efficiency of PSII, status of water splitting complex, and performance index were adversely affected by chilling, along with reduction in net photosynthesis rate and nighttime respiration and alterations in leaf optical properties. The extents of negative effect on these parameters were larger in Guitang 49 than in Guitang 28. These results reveal a clear differentiation in PSII heterogeneity between differentially chilling tolerant cultivars. Based on our studies, it is concluded that PSII heterogeneity can be used as an additional non-invasive and novel technique for evaluating any type of environmental stress in plants.

Drought stress strengthens the link between chlorophyll fluorescence parameters and photosynthetic traits

Chlorophyll fluorescence (ChlF) has been used to understand photosynthesis and its response to climate change, particularly with satellite-based data. However, it remains unclear how the ChlF ratio and photosynthesis are linked at the leaf level under drought stress. Here, we examined the link between ChlF ratio and photosynthesis at the leaf level by measuring photosynthetic traits, such as net CO2 assimilation rate (An), the maximum carboxylation rate of Rubisco (Vcmax), the maximum rate of electron transport (Jmax), stomatal conductance (gs) and total chlorophyll content (Chlt). The ChlF ratio of the leaf level such as maximum quantum efficiency of PSII (Fv/Fm) is based on fluorescence kinetics. ChlF intensity ratio (LD685/LD740) based on spectrum analysis was obtained. We found that a combination of the stomatal limitation, non-stomatal limitation, and Chlt regulated leaf photosynthesis under drought stress, while Jmax and Chlt governed the ChlF ratio. A significant link between the ChlF ratio and An was found under drought stress while no significant correlation in the control, which indicated that drought stress strengthens the link between the ChlF ratio and photosynthetic traits. These results suggest that the ChlF ratio can be a powerful tool to track photosynthetic traits of terrestrial ecosystems under drought stress.

Photosynthetic Performance of Guaranazeiro Plants as Affected by Glyphosate Application

The unsuitable use of herbicides damages many cultures. In cases of high infestations and presence of aggressive weed species in guarana (Paullinia cupana) culture, glyphosate application is advisable, but its impact on guarana physiology is unknown. Therefore, leaf photosynthetic characteristics were measured with the aim of identifying if the photosynthetic performance of guaranazeiro plants is affected in response to glyphosate application. Three glyphosate doses (0 (control); 324 and 432 g a.i. ha-1) were applied to two guaranazeiro cultivars (BRS-Andirá and BRS-Maués) selected on the basis of productive performance. An analysis was made of the effects of these doses on characteristics that represent the photosynthetic process: gas exchange, maximum quantum efficiency of PSII, performance index and chlorophyll content. The application of glyphosate did not affect the short-term responses relative chlorophyll content (SPAD index) and light use (chlorophyll a fluorescence). After 168 h, there were changes only in gas exchange variables. The effects of glyphosate doses on gas exchange was different between guaranazeiro cultivars. The photosynthetic performance of the guaranazeiro seems to be tolerant to the effects of short-term of glyphosate application.

Phytoremediation effect of Medicago sativa colonized by Piriformospora indica in the phenanthrene and cadmium co-contaminated soil

Background: The coexistence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals has deleterious effects on environmental quality. Few reports have studied the mechanisms of plant inoculation with Piriformospora indica to remediate PAH-metal co-contaminated soil by analyzing the chemical speciation of the contaminants. This study investigated the influence of the inoculation of Medicago sativa with P. indica to remediate soil co-contaminated with phenanthrene (a kind of PAH) and cadmium (a heavy metal) by analyzing plant growth, physiological parameters and chemical speciation in rhizosphere and nonrhizosphere soils.Results: The presence of P. indica significantly increased plant tolerance, chlorophyll a, chlorophyll b, maximum quantum efficiency of PSII photochemistry and electron transport rate values in phenanthrene- and/or cadmium-contaminated soil. P. indica inoculation in M. sativa roots increased fluorescein diacetate activities in soils contaminated with phenanthrene, cadmium or both, especially in the nonrhizosphere. The presence of phenanthrene prevented the inoculated plant from accumulating cadmium to some extent, whereas the presence of cadmium did not prevent the degradation of phenanthrene in either the rhizosphere or the nonrhizosphere after P. indica colonization. Although the low bioavailability of cadmium in the rhizosphere restricted its transportation into the stem, P. indica colonization in plants effectively increased cadmium accumulation in roots in soil co-contaminated with cadmium and phenanthrene.Conclusions: In conclusion, this work provides a theoretical basis for the use of P. indica combined with M. sativa for the remediation of PAH-metal co-contaminated soil.

Phytoremediation effect of Medicago sativa colonized by Piriformospora indica in the phenanthrene and cadmium co-contaminated soil

Background: Coexistence of polycylic aromatic hydrocarbons (PAHs) and heavy metals deleteriously threatens the quality of environmental health . Few reports uncover the mechanism of inoculation plants with Piriformospora indica for remediating PAH- m etal co-contaminated soil by analyzing the chemical speciations of contaminants . This study investigated the influence of inoculation Medicago sativa with P. indica to remediate phenanthrene (kind of PAHs ) , and cadmium (one of heavy metals ) co-contaminated soil by analyzing the plant growth, physiological parameters and chemical speciation in rhizosphere and non-rhizosphere . Results: T he presence of P. indica significantly increased plants tolerance, Chlorophyll a , Chlorophyll b , maximum quantum efficiency of PSII photochemistry and electron transport rate values in phenanthrene an d /or cadmium contaminated soil. P. indica inoculation in M edicago sativa root increased f luorescein diacetate activities in phenanthrene, cadmium and both of that co-contaminated soil, especially in non-rhizosphere . The presence of phenanthrene hindered the inoculated plant from accumulating cadmium to some extent ; Whereas the presence of cadmium did not hinder the degradation of phenanthrene in both rhizosphere and non-rhizosphere after P. indica colonization. Although the poor bioavailability of cadmium in rhizosphere restricted the transportation into stem, P. indica colonization in plant efficiently increased cadmium accumulation in root in cadmium and phenanthrene co-contaminated soil. Conclusions: In conclusion, t he work provides the theoretical basis that Piriformospora indica combined with Medicago sativa contributed to the remediation of PAH-Metal co-contaminated soil.

Phytoremediation effect of Medicago sativa colonized by Piriformospora indica in the phenanthrene and cadmium co-contaminated soil

Background: Coexistence of polycylic aromatic hydrocarbons (PAHs) and heavy metals deleteriously threatens the quality of environmental health . F ew reports uncover the mechanism of inoculation plants with Piriformospora indica for remediating PAH- m etal co-contaminated soil by analyzing the chemical speciations of contaminants . This study investigated the influence of inoculation Medicago sativa with P. indica to remediate phenanthrene (kind of PAHs ) , and cadmium (one of heavy metals ) co-contaminated soil by analyzing the plant growth, physiological parameters and chemical speciation in rhizosphere and non-rhizosphere . Results: T he presence of P. indica significantly increased plants tolerance, Chlorophyll a , Chlorophyll b , maximum quantum efficiency of PSII photochemistry and electron transport rate values in phenanthrene an d /or cadmium contaminated soil. P. indica inoculation in M edicago sativa root increased f luorescein diacetate activities in phenanthrene, cadmium and both of that co-contaminated soil, especially in non-rhizosphere . The presence of phenanthrene hindered the inoculated plant from accumulating cadmium to some extent ; Whereas the presence of cadmium did not hinder the degradation of phenanthrene in both rhizosphere and non-rhizosphere after P. indica colonization. Although the poor bioavailability of cadmium in rhizosphere restricted the transportation into stem, P. indica colonization in plant efficiently increased cadmium accumulation in root in cadmium and phenanthrene co-contaminated soil. Conclusions: In conclusion, t he work provides the theoretical basis that Piriformospora indica combined with Medicago sativa contributed to the remediation of PAH-Metal co-contaminated soil.

Phytoremediation effect of Medicago sativa colonized by Piriformospora indica in the phenanthrene and cadmium co-contaminated soil

Background:Coexistence of polycylic aromatic hydrocarbons (PAHs) and heavy metals deleteriously threatens the quality of environmental health. Few reports uncover the mechanism of inoculation plants with Piriformospora indica for remediating PAH-metal co-contaminated soil by analyzing the chemical speciations of contaminants. This study investigated the influence of inoculation Medicago sativa with Piriformospora indica to remediate phenanthrene (kind of PAHs), and cadmium (one of heavy metals) co-contaminated soil by analyzing the plant growth, physiological parameters and chemical speciation in rhizosphere and non-rhizosphere. Results:The presence of P. indica significantly increased plants tolerance, Chlorophyll a, Chlorophyll b, maximum quantum efficiency of PSII photochemistry and electron transport rate values in phenanthrene and/or cadmium contaminated soil. P. indica inoculation in Medicago sativa root increased fluorescein diacetate activities in phenanthrene, cadmium and both of that co-contaminated soil, especially in non-rhizosphere. The presence of phenanthrene hindered the inoculated plant from accumulating cadmium to some extent; Whereas the presence of cadmium did not hinder the degradation of phenanthrene in both rhizosphere and non-rhizosphere after P. indica colonization. Although the poor bioavailability of cadmium in rhizosphere restricted the transportation into stem, P. indica colonization in plant efficiently increased cadmium accumulation in root in cadmium and phenanthrene co-contaminated soil. Conclusions: In conclusion, the work provides the theoretical basis that Piriformospora indica combined with Medicago sativa contributed to the remediation of PAH-Metal co-contaminated soil.

Herbicide selectivity in pre-sprouted seedlings of ‘CTC14’ sugarcane

ABSTRACT: A new sugarcane planting system, using pre-sprouted seedlings (PSS) to replace sugarcane stem fragments, substantiates the hypothesis of this study that there might be seedling toxicity by herbicides that are sprayed at pre-emergence in traditional systems. Therefore, the aim of this paper was to study the selectivity of herbicides applied at pre-planting in PSS. A field experiment was conducted in a randomized block design, using seven treatments and four replications. Herbicides were sprayed and, 24 hours later, the seedlings were planted. At the beggining of seedling development, all herbicide treatments showed phytotoxicity, but the symptoms decreased with the growth and development of seedlings, with no difference in height, stem diameter, number of leaves, quantum efficiency of PSII (Fv/Fm) and dry matter of plants between treatments. There was also no significant difference in the yield and technological characteristics of stems. All herbicides used were selective to sugarcane seedlings when applied at pre-planting in the PSS system.