Photosynthetic and Growth Responses of Arundo donax L. Plantlets Under Different Oxygen Deficiency Stresses and Reoxygenation

Waterlogging resistance and evaluation of physiological mechanism of three peach (Prunus persica) rootstocks

Waterlogging occurs due to poor soil drainage or excessive rainfall. It is a serious abiotic stress factor that negatively affects crop growth. Waterlogging often causes plants to shed leaves, fruits, and, ultimately, to die. Peach (Prunus persica) trees are generally intolerant to waterlogging, and the primary peach rootstock used in Chinais "Maotao," which has very poor resistance to sensitivity. Therefore, waterlogging has become a restriction on the development of the peach industry in many regions. In this experiment, we tested the waterlogging resistance of "Maotao (Prunus persica (L.) Batsch)" (MT), "Shannong1 (GF677 × Cadaman)" (SN1), and "Mirabolano 29C (Prunus cerasifera)" (M29C) rootstocks. Using a simulated waterlogging method, the effects of waterlogging on the photosynthetic system, leaf pigments, osmotic adjustment, lipid membrane peroxidation, and antioxidant system of these three peach rootstocks were studied, and the changes of chlorophyll fluorescence parameters and fluorescence imaging were observed. The results showed that, with prolonged waterlogging, the photosynthetic pigment content and photosynthesis of the three peach rootstocks decreased rapidly, but the decomposition rate of SN1 and M29C chlorophyll was slower, and it still had high light energy absorption and energy transfer capabilities under waterlogging stress, which reduced the damage caused by waterlogging stress; under the stress of flooding, the osmoregulatory substances of the three rootstocks increased to varying degrees compared with normal conditions. At the same time, the enzyme activity of superoxide dismutase (SOD) activity, peroxidase (POD) activity, and catalase (CAT) activity in the leaves of the three rootstocks under flooding stress all increased and then decreased; during this period, malondialdehyde (MDA) continued to increase, and SN1 and M29C were significantly lower than MT; and chlorophyll fluorescence parameters, including the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), and electron transfer rate (ETR) decreased significantly. The tolerance of SN1 and M29C to waterlogging was significantly better than that of MT rootstocks. The rootstock and grafted seedlings of SN1 have good waterlogging tolerance.

Physiological, biochemical, and metabolic changes in diploid and triploid watermelon leaves during flooding

BACKGROUND

Flooding is a major stress factor impacting watermelon growth and production globally. Metabolites play a crucial role in coping with both biotic and abiotic stresses.

METHODS

In this study, diploid (2X) and triploid (3X) watermelons were investigated to determine their flooding tolerance mechanisms by examining physiological, biochemical, and metabolic changes at different stages. Metabolite quantification was done using UPLC-ESI-MS/MS and a total of 682 metabolites were detected.

RESULTS

The results showed that 2X watermelon leaves had lower chlorophyll content and fresh weights compared to 3X. The activities of antioxidants, such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), were higher in 3X than in 2X. 3X watermelon leaves showed lower O₂ production rates, MDA, and hydrogen peroxide (H₂O₂) levels in response to flooding, while higher ethylene production was observed. 3X had higher levels of dehydrogenase activity (DHA) and ascorbic acid + dehydrogenase (AsA + DHA), but both 2X and 3X showed a significant decline in the AsA/DHA ratio at later stages of flooding. Among them, 4-guanidinobutyric acid (mws0567), an organic acid, may be a candidate metabolite responsible for flooding tolerance in watermelon and had higher expression levels in 3X watermelon, suggesting that triploid watermelon is more tolerant to flooding.

CONCLUSION

This study provides insights into the response of 2X and 3X watermelon to flooding and the physiological, biochemical, and metabolic changes involved. It will serve as a foundation for future in-depth molecular and genetic studies on flooding response in watermelon.

Multi-stress resilience in plants recovering from submergence

Submergence limits plants' access to oxygen and light, causing massive changes in metabolism; after submergence, plants experience additional stresses, including reoxygenation, dehydration, photoinhibition and accelerated senescence. Plant responses to waterlogging and partial or complete submergence have been well studied, but our understanding of plant responses during post-submergence recovery remains limited. During post-submergence recovery, whether a plant can repair the damage caused by submergence and reoxygenation and re-activate key processes to continue to grow, determines whether the plant survives. Here, we summarize the challenges plants face when recovering from submergence, primarily focusing on studies of Arabidopsis thaliana and rice (Oryza sativa). We also highlight recent progress in elucidating the interplay among various regulatory pathways, compare post-hypoxia reoxygenation between plants and animals and provide new perspectives for future studies.

Exploring the Physiological Multiplicity of Native Microalgae from the Ecuadorian Highland, Italian Lowland and Indoor Locations in Response to UV-B

The differential effects of UV-B on the inhibition or activation of protective mechanisms to maintain cells photosynthetically active were investigated in native microalgae. Four strains were used, including two Chlorella sorokiniana strains, F4 and LG1, isolated from a Mediterranean inland swamp and a recycled cigarette butt's substrate, respectively, and two isolates from an Ecuadorian highland lake related to Pectinodesmus pectinatus (PEC) and Ettlia pseudoalveolaris (ETI). Monocultures were exposed to acute UV-B (1.7 W m^-2) over 18 h under controlled conditions. UV-B-untreated microalgae were used as the control. Comparative physiological responses, including photosynthetic pigments, non-enzymatic antioxidants, and chlorophyll a fluorescence, were evaluated at specific time points. Results showed that UV-B significantly compromised all the physiological parameters in F4, thereby resulting in the most UV-B-sensitive strain. Contrarily, UV-B exposure did not lead to changes in the PEC physiological traits, resulting in the best UV-B-resistant strain. This could be attributed to the acclimation to high light habitat, where maintaining a constitutive phenotype (at the photosynthetic level) is strategically advantageous. Differently, LG1 and ETI at 12 h of UV-B exposure showed different UV-B responses, which is probably related to acclimation, where in LG1, the pigments were recovered, and the antioxidants were still functioning, while in ETI, the accumulation of pigments and antioxidants was increased to avoid further photodamage. Consequently, the prolonged exposure in LG1 and ETI resulted in species-specific metabolic regulation (e.g., non-enzymatic antioxidants) in order to constrain full photoinhibition under acute UV-B.

UV-B Irradiation Effect on Microalgae Performance in the Remediation of Effluent Derived from the Cigarette Butt Cleaning Process

In this study, the potential of ultraviolet B (UV-B) radiation to alleviate the effects of pollutants in cigarette butt wastewater (CBW) was investigated using different Chlorella sorokiniana strains (F4, R1 and LG1). Microalgae were treated with UV-B (1.7 W m⁻²) for 3 days prior to their exposure to CBW and then incubated for 4 days in the absence or presence of UV-B. UV-B-untreated microalgae were used as the control. Comparative physiological responses, including photosynthetic pigments and non-enzymatic antioxidants, as well as nicotine and nicotyrine removal, were evaluated in 7-day cultures. UV-B treatments did not negatively impact algal chlorophyll or carotenoid production. UV-B acclimation was strain-dependent, correlating with native environment adaptations and genetic constitutions. UV-B as a pretreatment had long-term positive effects on non-enzymatic antioxidant capacity. However, LG1 needed more time to readjust the pro-oxidant/antioxidant balance, as it was the most UV-B-sensitive. Phenolic compounds played an important role in the antioxidant system response to UV-B, while flavonoids did not contribute to the total antioxidant capacity. Although cross-resistance between UV-B and CBW was observed in F4 and R1, only R1 showed nicotine/nicotyrine catabolism induction due to UV-B. Overall, the results suggest that UV-B activates defense pathways associated with resistance or tolerance to nicotine and nicotyrine.

Growth and Photosynthetic Responses of Cowpea Genotypes under Waterlogging at the Reproductive Stage

Waterlogging is an important environmental stress limiting the productivity of crops worldwide. Cowpea (Vigna unguiculata L.) is particularly sensitive to waterlogging stress during the reproductive stage, with a consequent decline in pod formation and yield. However, little is known about the critical processes underlying cowpea’s responses to waterlogging during the reproductive stage. Thus, we investigated the key parameters influencing carbon fixation, including stomatal conductance (g_s), intercellular CO₂ concentration, chlorophyll content, and chlorophyll fluorescence, of two cowpea genotypes with contrasting waterlogging tolerance. These closely related genotypes have starkly contrasting responses to waterlogging during and after 7 days of waterlogging stress (DOW). In the intolerant genotype (‘EpicSelect.4’), waterlogging resulted in a gradual loss of pigment and decreased photosynthetic capacity as a consequent decline in shoot biomass. On the other hand, the waterlogging-tolerant genotype (‘UCR 369’) maintained CO₂ assimilation rate (A), stomatal conductance (g_s), biomass, and chlorophyll content until 5 DOW. Moreover, there was a highly specific downregulation of the mesophyll conductance (g_m), maximum rate of Rubisco (V_cmax), and photosynthetic electron transport rate (J_max) as non-stomatal limiting factors decreasing A in EpicSelect.4. Exposure of EpicSelect.4 to 2 DOW resulted in the loss of PSII photochemistry by downregulating the PSII quantum yield (F_v/F_m), photochemical efficiency (Φ_PSII), and photochemical quenching (qP). In contrast, we found no substantial change in the photosynthesis and chlorophyll fluorescence of UCR 369 in the first 5 DOW. Instead, UCR 369 maintained biomass accumulation, chlorophyll content, and Rubisco activity, enabling the genotype to maintain nutrient absorption and photosynthesis during the early period of waterlogging. However, compared to the control, both cowpea genotypes could not fully recover their photosynthetic capacity after 7 DOW, with a more significant decline in EpicSelect.4. Overall, our findings suggest that the tolerant UCR 369 genotype maintains higher photosynthesis under waterlogging stress attributable to higher photochemical efficiency, Rubisco activity, and less stomatal restriction. After recovery, the incomplete recovery of A can be attributed to the reduced g_s caused by severe waterlogging damage in both genotypes. Thus, promoting the rapid recovery of stomata from waterlogging stress may be crucial for the complete restoration of carbon fixation in cowpeas during the reproductive stage.

Short waterlogging events differently affect morphology and photosynthesis of two cucumber (Cucumis sativus L.) cultivars

Waterlogging induces growth and developmental changes in sensitive crops such as cucumber (Cucumis sativus L.) during early plant development. However, information on the physiological mechanisms underpinning the response of cucumber plants to waterlogging conditions is limited. Here, we investigated the effects of 10-day waterlogging stress on the morphology, photosynthesis, and chlorophyll fluorescence parameters in two cultivars of cucumber seedlings. Waterlogging stress hampered cultivars' growth, biomass accumulation, and photosynthetic capacity. Both cultivars also developed adventitious roots (ARs) after 10 days of waterlogging (DOW). We observed differential responses in the light- and carbon-dependent reactions of photosynthesis, with an increase in light-dependent reactions. At the same time, carbon assimilation was considerably inhibited by waterlogging. Specifically, the CO₂ assimilation rate (A) in leaves was significantly reduced and was caused by a corresponding decrease in stomatal conductance (g_s). The downregulation of the maximum rate of Rubisco efficiency (V_cmax) and the maximum rate of photosynthetic electron transport (J_max) were non-stomatal limiting factors contributing to A reduction. Exposure of cucumber to 10 DOW affected the PSII photochemistry by downregulating the PSII quantum yield (Φ_PSII). The redox state of the primary quinone acceptor in the lake model (1-qL), a measure of the regulatory balance of the light reactions, became more oxidized after 10 DOW, indicating enhanced electron sink capacity despite a reduced A. Overall, the results suggest that waterlogging induces alterations in the photochemical apparatus efficiency of cucumber. Thus, developing cultivars that resist inhibition of PSII photochemistry while maintaining carbon metabolism is a potential approach for increasing crops' tolerance to waterlogged environments.

Molecular Mechanism of Organic Pollutant-Induced Reduction of Carbon Fixation and Biomass Yield in Oryza sativa L

Photosynthetic carbon fixation is fundamental for plant growth and is a key process driving the global carbon cycle. This study explored the mechanism of disturbed carbon fixation in Oryza sativa L. by organic pollutants 2,3,4,5-tetrachlorobiphenyl (CB 61), 4'-hydroxy-2,3,4,5-tetrachlorobiphenyl (4'-OH-CB 61), 2,2',4,4'-tetrabromo diphenyl ether (BDE 47), tricyclazole (TRI), and pyrene. The biomass of rice exposed to 4'-OH-CB 61, TRI, and BDE 47 was on average 80.63% of that of the control (p < 0.05), and the inhibition of net photosynthetic rate was 59.15% by 4'-OH-CB 61. Proteomics confirmed that 4'-OH-CB 61 significantly downregulated the enzymes in the photosynthetic carbon fixation pathway, which was attributed to the decrease in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the rate-limiting enzyme in the Calvin cycle. In detail, decreased Rubisco activity (6.96-33.44%) and downregulated OsRBCS2-5 encoding small Rubisco subunits (-6.80 < log₂FC < -2.13) by 4'-OH-CB 61, TRI, and BDE 47 were in line with biomass yield reduction. Molecular docking and dynamic simulation suggested that the three pollutants potentially competed with CO₂ for binding to the active sites in Rubisco, leading to reduced CO₂ capture efficiency. These results revealed the molecular mechanism of organic pollution-induced rice yield reduction, contributing to improving the understanding of crop growth and carbon sequestration capacity of organics-contaminated soils globally.

Waterlogging tolerance and recovery capability screening in peanut: a comparative analysis of waterlogging effects on physiological traits and yield

Fifteen peanut varieties at the pod filling stage were exposed to waterlogging stress for 7 days, the enzyme activities and fluorescence parameters were measured after 7 days of waterlogging and drainage. The waterlogging tolerance and recovery capability of varieties were identified. After waterlogging, waterlogging tolerance coefficient (WTC) of relative electrolyte linkage (REL), malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, and catalase (CAT) activity, non-photochemical quenching (NPQ) and photochemical quenching (qL) of leaves of most peanut varieties were increased, while the WTC of the soil and plant analysis development (SPAD) value, PS II actual quantum yield (Φ _PS II ), maximum photochemical efficiency (Fv/Fm) were decreased. After drainage, the WTC of REL, MDA content, SOD and CAT activity of leaves were decreased compared with that of after waterlogging, but these indicators of a few cultivars were increased. Φ _PS II , Fv/Fm and qL can be used as important indexes to identify waterlogging recovery capability. There was a significant negative correlation between recovery capability and the proportion of reduction in yield, while no significant correlation was found between waterlogging tolerance and the proportion of reduction in yield. Therefore, it is recommended to select varieties with high recovery capability and less pod number reduction under waterlogging in peanut breeding and cultivation.

Maintenance of photosynthetic capacity in flooded tomato plants with reduced ethylene sensitivity

Ethylene is considered one of the most important plant hormones orchestrating plant responses to flooding stress. However, ethylene may induce deleterious effects on plants, especially when produced at high rates in response to stress. In this paper, we explored the effect of attenuated ethylene sensitivity in the Never ripe (Nr) mutant on leaf photosynthetic capacity of flooded tomato plants. We found out that reduced ethylene perception in Nr plants was associated with a more efficient photochemical and non-photochemical radiative energy dissipation capability in response to flooding. The data correlated with the retention of chlorophyll and carotenoids content in flooded Nr leaves. Moreover, leaf area and specific leaf area were higher in Nr, indicating that ethylene would exert a negative role in leaf growth and expansion under flooded conditions. Although stomatal conductance was hampered in flooded Nr plants, carboxylation activity was not affected by flooding in the mutant, suggesting that ethylene is responsible for inducing non-stomatal limitations to photosynthetic CO₂ uptake. Upregulation of several cysteine protease genes and high protease activity led to Rubisco protein loss in response to ethylene under flooding. Reduction of Rubisco content would, at least in part, account for the reduction of its carboxylation efficiency in response to ethylene in flooded plants. Therefore, besides its role as a trigger of many adaptive responses, perception of ethylene entails limitations in light and dark photosynthetic reactions by speeding up the senescence process that leads to a progressive disassembly of the photosynthetic machinery in leaves of flooded tomato plants.

Photosynthetic performance of five cool-season turfgrasses under UV-B exposure

Turfgrasses are monocotyledonous plants from the family Poaceae. They are widely used in green spaces and are considered one of the most economically important horticultural crops in the world. Turfgrass quality is affected by several environmental factors including light, which is involved in the quality decline of transplanted sod. Ultraviolet-B (UV-B) is an important regulator of plant growth and development. Plants growing and/or stored in protected systems, such as in sod production, may be more vulnerable to UV-B damage than those growing in the field due to acclimation. Few studies on the effects of UV-B on turfgrass physiology have been published. Therefore, the aim of this study was to evaluate the influence of UV-B irradiation on the photosynthetic performance of five cool-season turfgrasses, namely Agrostis stolonifera L., Festuca arundinacea Schreb., Poa supina Schrad., Poa pratensis L. and Lolium perenne L. Turfgrasses were exposed to 18.25 kJ m^-2 d^-1 biologically effective UV-B in growth chambers under controlled conditions. Measurements included photosynthetic pigments, chlorophyll fluorescence and gas exchanges monitored for 16 d-UV-B treatment and after recovery. Content of pigments decreased with UV-B exposure with significant differences among the species. UV-B also affected the photosystem II (PSII) efficiency depending on the exposure period and species. Similarly, gas exchange parameters showed different effects among species after UV-B exposure compromising the assimilation of CO₂. Multivariate analysis highlighted three main clusters of species confirming their different UV-B tolerance and ability to restore PSII photochemistry after recovery, from which Festuca arundinacea resulted to be the most tolerant.