C4 and crassulacean acid metabolism within a single leaf: deciphering key components behind a rare photosynthetic adaptation.

Although biochemically related, C4 and crassulacean acid metabolism (CAM) systems are expected to be incompatible. However, Portulaca species, including P. oleracea, operate C4 and CAM within a single leaf, and the mechanisms behind this unique photosynthetic arrangement remain largely unknown. Here, we employed RNA-seq to identify candidate genes involved exclusively or shared by C4 or CAM, and provided an in-depth characterization of their transcript abundance patterns during the drought-induced photosynthetic transitions in P. oleracea. Data revealed fewer candidate CAM-specific genes than those recruited to function in C4 . The putative CAM-specific genes were predominantly involved in night-time primary carboxylation reactions and malate movement across the tonoplast. Analysis of gene transcript-abundance regulation and photosynthetic physiology indicated that C4 and CAM coexist within a single P. oleracea leaf under mild drought conditions. Developmental and environmental cues were shown to regulate CAM expression in stems, whereas the shift from C4 to C4 -CAM hybrid photosynthesis in leaves was strictly under environmental control. Moreover, efficient starch turnover was identified as part of the metabolic adjustments required for CAM operation in both organs. These findings provide insights into C4 /CAM connectivity and compatibility, contributing to a deeper understanding of alternative ways to engineer CAM into C4 crop species.

An insight from tolerance to salinity stress in halophyte Portulaca oleracea L.: Physio-morphological, biochemical and molecular responses.

Salinity represents one of the environmental conditions with adverse effects on the productivity of most crops throughout the world. The response of plants to salt stress is of great interest for research to understand the mechanism involved in tolerance to salinity and highlight insights into the improvement of salt tolerance-crops of importance. In this study, the effect of salt stress was observed in wild and cultivated populations of P. oleracea originated from Tunisia and Italy. The results showed that at various concentrations of NaCl (0 mM, 50 mM, 100 mM and 150 mM), salinity has led to changes in growth parameters marked mainly by an increase in fresh and dry biomass. Beside, one of the salinity-induced side effects corresponds to the competition of Na+ and K+ ions for potassium root transporters. Our results suggested that purslane deployed an important element of tolerance such as the transporters ability to discriminate cations. In addition, the variation of PC5S gene expression tested by semi-quantitative RT-PCR revealed that proline synthesis is important in plants adaptation in saline conditions. A correlation between the gene expression varying by population and saline concentration and the level of proline assayed on the leaves of P. oleracea was highlighted.

Deciphering the mechanisms involved in Portulaca oleracea (C4) response to drought: metabolic changes including crassulacean acid-like metabolism induction and reversal upon re-watering.

Portulaca oleracea is a C(4) plant; however, under drought it can change its carbon fixation metabolism into a crassulacean acid metabolism (CAM)-like one. While the C(3) -CAM shift is well known, the C(4) -CAM transition has only been described in Portulaca. Here, a CAM-like metabolism was induced in P. oleracea by drought and then reversed by re-watering. Physiological and biochemical approaches were undertaken to evaluate the drought and recovery responses. In CAM-like plants, chlorophyll fluorescence parameters were transitory affected and non-radiative energy dissipation mechanisms were induced. Induction of flavonoids, betalains and antioxidant machinery may be involved in photosynthetic machinery protection. Metabolic analysis highlights a clear metabolic shift, when a CAM-like metabolism is induced and then reversed. Increases in nitrogenous compounds like free amino acids and urea, and of pinitol could contribute to withstand drought. Reciprocal variations in arginase and urease in drought-stressed and in re-watered plants suggest urea synthesis is strictly regulated. Recovery of C(4) metabolism was accounted by CO(2) assimilation pattern and malate levels. Increases in glycerol and in polyamines would be of importance of re-watered plants. Collectively, in P. oleracea multiple strategies, from induction of several metabolites to the transitory development of a CAM-like metabolism, participate to enhance its adaptation to drought.

Comparative proteomic analysis of the thermotolerant plant Portulaca oleracea acclimation to combined high temperature and humidity stress.

Elevated temperature and humidity are major environmental factors limiting crop yield and distribution. An understanding of the mechanisms underlying plant tolerance to high temperature and humidity may facilitate the development of cultivars adaptable to warm or humid regions. Under conditions of 90% humidity and 35 °C, the thermotolerant plant Portulaca oleracea exhibits excellent photosynthetic capability and relatively little oxidative damage. To determine the proteomic response that occurs in leaves of P. oleracea following exposure to high temperature and high humidity, a proteomic approach was performed to identify protein changes. A total of 51 differentially expressed proteins were detected and characterized functionally and structurally; these identified proteins were involved in various functional categories, mainly including material and energy metabolism, the antioxidant defense responses, protein destination and storage, and transcriptional regulation. The subset of antioxidant defense-related proteins demonstrated marked increases in activity with exposure to heat and humidity, which led to lower accumulations of H(2)O(2) and O(2)(-) in P. oleracea compared with the thermosensitive plant Arabidopsis thaliana. The quickly accumulations of proline content and heat-shock proteins, and depleting abscisic acid (ABA) via increasing ABA-8'-hydroxylase were also found in P. oleracea under stress conditions, that resulted into greater stomata conductance and respiration rates. On the basis of these findings, we propose that P. oleracea employs multiple strategies to enhance its adaptation to high-temperature and high-humidity conditions.

The impact of horse purslane (Trianthema portulacastrum L.) infestation on soybean [Glycine max (L.) Merrill] productivity in northern irrigated plains of Pakistan.

Horse purslane (Trianthema portulacstrum L.) is an important weed of soybean crop capable of causing significant yield reduction. Therefore, this study assessed the impact of horse purslane and other weeds' infestation on the productivity of soybean. Ten treatments, i.e., weed-free throughout the growing season, horse purslane-free till 20, 40 and 60 days after emergence (DAE), all weeds-free till 20, 40 and 60 DAE, weedy-check (excluding horse purslane), weedy-check (horse purslane alone) and weedy-check (all weeds) were included in the study. Data relating to density and dry weight of recorded weed species, and yield and related traits of soybean were recorded. Overall, infestation percentage of horse purslane was 33.10 and 51%, whereas dry weight was 12 and 44 g m-2 during 1st and 2nd year, respectively. The highest dry weight of all weed species was recorded at 45 DAE in weedy-check all weeds treatment during both years. The lowest relative density and frequency of horse purslane were recorded in the treatment where it was controlled until 20 DAE during 2018 at 30 DAE, whereas the same treatment recoded the lowest density of horse purslane at 45 DAE during 2019. The relative frequency of horse purslane was non-significant for weedy-check horse purslane and weedy-check all weeds treatments during 2018, whereas former treatment had higher relative frequency of horse purslane in weedy-check all weeds than the later during 2019. Yield and related traits significantly differed among different treatments used in the study. The treatment all weeds controlled until 40 DAE recorded higher number of pods per plant, 1000-seed weight and seed yield during both years. The yield reduction in weedy-check treatments was; weedy-check all weeds > weedy-check all weeds except horse purslane > weedy-check horse purslane only. It is concluded that horse purslane was not the sole weed interfering soybean fields and weed flora consisted of false amaranth [Digera muricata (L.) Mart.] and purple nut sedge (Cyperus rotundus L.). Hence, if the soybean fields in northern irrigated plains of Pakistan are infested with horse purslane or heavily infested with horse purslane or other weeds, these should be controlled in initial 40 DAE to improve soybean productivity.

Revealing diversity in structural and biochemical forms of C4 photosynthesis and a C3-C4 intermediate in genus Portulaca L. (Portulacaceae).

Portulacaceae is one of 19 families of terrestrial plants in which species having C(4) photosynthesis have been found. Representative species from major clades of the genus Portulaca were studied to characterize the forms of photosynthesis structurally and biochemically. The species P. amilis, P. grandiflora, P. molokiniensis, P. oleracea, P. pilosa, and P. umbraticola belong to the subgenus Portulaca and are C(4) plants based on leaf carbon isotope values, Kranz anatomy, and expression of key C(4) enzymes. Portulaca umbraticola, clade Umbraticola, is NADP-malic enzyme (NADP-ME)-type C(4) species, while P. oleracea and P. molokiniensis in clade Oleracea are NAD-ME-type C(4) species, all having different forms of Atriplicoid-type leaf anatomy. In clade Pilosa, P. amilis, P. grandiflora, and P. pilosa are NADP-ME-type C(4) species. They have Pilosoid-type anatomy in which Kranz tissues enclose peripheral vascular bundles with water storage in the centre of the leaf. Portulaca cf. bicolor, which belongs to subgenus Portulacella, is an NADP-ME C(4) species with Portulacelloid-type anatomy; it has well-developed Kranz chlorenchyma surrounding lateral veins distributed in one plane under the adaxial epidermis with water storage cells underneath. Portulaca cryptopetala (clade Oleracea), an endemic species from central South America, was identified as a C(3)-C(4) based on its intermediate CO(2) compensation point and selective localization of glycine decarboxylase of the photorespiratory pathway in mitochondria of bundle sheath cells. The C(4) Portulaca species which were examined also have cotyledons with Kranz-type anatomy, while the stems of all species have C(3)-type photosynthetic cells. The results indicate that multiple structural and biochemical forms of C(4) photosynthesis evolved in genus Portulaca.

Effect of nitrogen source in the fertilizing solution on nutritional quality of three members of the Portulaca oleracea aggregate.

BACKGROUND: Portulaca oleracea (purslane) is nutritious but, in addition to the essential alpha-linolenic acid, vitamin C and tocopherols, it contains undesirable oxalic acid. Knowing the effects of nitrate and ammonium on oxalate accumulation, we tested the agronomic potential of three members of the P. oleracea aggregate under various nitrogen fertilization conditions, by measuring biomass production and accumulation of fatty acids, organic acids and tocopherol in the commercial P. sativa (Pos) and two natural members: P. nitida (Pon) and P. papillato-stellulata (Pop). RESULTS: With nitrate as the sole N source, we measured differences between Pon and Pos in concentrations of the essential omega-3 fatty acid alpha-linolenic acid. Pos also gained less dry biomass under these conditions, implying a higher agronomical and nutritional value for Pon. Increasing the fertilizer ammonium concentration and reducing that of nitrate significantly decreased oxalic acid by factors of up to 1.7, 2.6 and 3.4 in Pos, Pop and Pon, respectively, significantly increased concentrations of tocopherol and malic acid, had no effect on fatty acids or ascorbic acid, but reduced biomass. CONCLUSION: In spite of the recumbent growth habit of Pon, the present findings indicate its agronomic potential. Because early flowering and seed production may be the limiting factors in purslane agriculture, growing Pon in nitrate-poor conditions might be agriculturally favorable.

Exploring C4-CAM plasticity within the Portulaca oleracea complex.

Portulaca oleracea is a C4 herb capable of performing CAM under drought stress. It is distributed worldwide and is either considered a polymorphic species or a complex of subspecies, due to its numerous morphological variations. We evaluated CAM plasticity within P. oleracea genotypes since the complexity surrounding this species may be reflected in intraspecific variations in photosynthetic behavior. Eleven subspecies of P. oleracea from distant geographical locations and one cultivar were morphologically and physiologically characterized. C4 and CAM photosynthesis were monitored in plants exposed to well-watered, droughted and rewatered treatments, and data obtained were compared among individual genotypes. All subspecies expressed CAM in a fully-reversible manner. Transcript abundance of C4-CAM signature genes was shown to be a useful indicator of the C4-CAM-C4 switches in all genotypes. C4-related genes were down-regulated and subsequently fully expressed upon drought and rewatering, respectively. CAM-marker genes followed the opposite pattern. A gradient of morphological traits and drought-induced nighttime malate accumulation was observed across genotypes. Therefore, different combinations of CAM expression levels, plant sizes and shapes are available within the P. oleracea complex, which can be a valuable tool in the context of C4/CAM photosynthesis research.

[Impacts of Vegetation on Hydrological Performances of Green Roofs Under Different Rainfall Conditions].

Vegetation is an important component of green roofs and may affect their hydrological performance through the processes of rainwater interception and evapotranspiration. Based on the rainfall-runoff observations of green roofs with four types of vegetation covers (Portulaca grandiflora, Sedum lineare, Festuca elata, and bare substrate) located in Beijing during 26 rainfall events from April to October 2017, the impacts of vegetation cover on the hydrological performance of green roofs were investigated using runoff and peak discharge reduction rates and time-delay of runoff generation and peak discharge as indices. For the 12 green roofs, there was a significantly negative correlation (P<0.01) between runoff reduction rate and rainfall event volume. For low rainfall (<10 mm), the runoff reduction rates of all the green roofs were equal or close to 100%. When the rainfall volume increased to about 30 mm, the runoff reduction rates dropped to below 70%. For the heaviest rainfall event during the observation period (81.4 mm), the runoff reduction rates of all the green roofs were less than 55%. The impacts of vegetation on the hydrological performance of green roofs changed with rainfall conditions. The differences between runoff reduction rates of green roofs with different types of vegetation cover were largest for the heavy rainfall events. For the moderate rainstorm events, the differences were slightly lower. For light rainfall events, however, no significant differences were observed among the runoff reduction rates of green roofs with different types of vegetation cover, as little runoff was generated. Vegetation cover could enhance the hydrological performance of green roofs, as the runoff and peak discharge reduction rates and time-delay of runoff generation and peak discharge of green roofs covered with vegetation were all better than those of the bare substrate for all the groups of rainfall events except the light rainfall. Vegetation-covered green roofs with P. grandiflora performed the best, as the average height and aboveground biomass per unit area of P. grandiflora were the largest.

Optional use of CAM photosynthesis in two C4 species, Portulaca cyclophylla and Portulaca digyna.

Low levels of crassulacean acid metabolism (CAM) are demonstrated in two species with C4 photosynthesis, Portulaca cyclophylla and P. digyna. The expression of CAM in P. cyclophylla and P. digyna is facultative, i.e. optional. Well-watered plants did not accumulate acid at night and exhibited gas-exchange patterns consistent with C4 photosynthesis. CAM-type nocturnal acidification was reversible in that it was induced following drought and lost when droughted plants were rewatered. In P. cyclophylla, droughting was accompanied by a small but discernible net uptake of CO2 during the dark, whereas in P. digyna, net CO2 exchange at night approached the CO2 compensation point but did not transition beyond it. This report brings the number of known C4 species with a capacity for expressing CAM to six. All are species of Portulaca. The observation of CAM in P. cyclophylla and P. digyna is the first for species in the opposite-leaved (OL) Portulacelloid-anatomy lineage of Portulaca and for the Australian clade therein. The other four species are within the alternate-leaved (AL) lineage, in the Atriploid-anatomy Oleracea and the Pilosoid-anatomy Pilosa clades. Studies of the evolutionary origins of C4 and CAM in Portulaca will benefit from a more wide-range survey of CAM across its species, particularly in the C3-C4 intermediate-containing Cryptopetala clade.

Effect of salinity on biomass yield and physiological and stem-root anatomical characteristics of purslane (Portulaca oleracea L.) accessions.

13 selected purslane accessions were subjected to five salinity levels 0, 8, 16, 24, and 32 dS m(-1). Salinity effect was evaluated on the basis of biomass yield reduction, physiological attributes, and stem-root anatomical changes. Aggravated salinity stress caused significant (P < 0.05) reduction in all measured parameters and the highest salinity showed more detrimental effect compared to control as well as lower salinity levels. The fresh and dry matter production was found to increase in Ac1, Ac9, and Ac13 from lower to higher salinity levels but others were badly affected. Considering salinity effect on purslane physiology, increase in chlorophyll content was seen in Ac2, Ac4, Ac6, and Ac8 at 16 dS m(-1) salinity, whereas Ac4, Ac9, and Ac12 showed increased photosynthesis at the same salinity levels compared to control. Anatomically, stem cortical tissues of Ac5, Ac9, and Ac12 were unaffected at control and 8 dS m(-1) salinity but root cortical tissues did not show any significant damage except a bit enlargement in Ac12 and Ac13. A dendrogram was constructed by UPGMA based on biomass yield and physiological traits where all 13 accessions were grouped into 5 clusters proving greater diversity among them. The 3-dimensional principal component analysis (PCA) has also confirmed the output of grouping from cluster analysis. Overall, salinity stressed among all 13 purslane accessions considering biomass production, physiological growth, and anatomical development Ac9 was the best salt-tolerant purslane accession and Ac13 was the most affected accession.

Characterization of Cd-, Pb-, Zn-resistant endophytic Lasiodiplodia sp. MXSF31 from metal accumulating Portulaca oleracea and its potential in promoting the growth of rape in metal-contaminated soils.

The aim of this study was to characterize the features of a Cd-, Pb-, and Zn-resistant endophytic fungus Lasiodiplodia sp. MXSF31 and to investigate the potential of MXSF31 to remove metals from contaminated water and soils. The endophytic fungus was isolated from the stem of Portulaca oleracea growing in metal-contaminated soils. The maximum biosorption capacities of MXSF31 were 3.0 × 10(3), 1.1 × 10(4), and 1.3 × 10(4) mg kg(-1) for Cd, Pb, and Zn, respectively. The biosorption processes of Cd, Pb, and Zn by MXSF31 were well characterized with the pseudo-second-order kinetic model. The biosorption isotherm processes of Pb and Zn by the fungus were fitted better with the Langmuir model, while the biosorption processes of Cd was better fitted with the Freundlich model. The biosorption process of MXSF31 was attributed to the functional groups of hydroxyl, amino, carbonyl, and benzene ring on the cell wall. The active biomass of the strain removed more Cd, Pb, and Zn (4.6 × 10(4), 5.6 × 10(5), and 7.0 × 10(4) mg kg(-1), respectively) than the dead biomass. The inoculation of MXSF31 increased the biomass of rape (Brassica napus L.), the translocation factor of Cd, and the extraction amount of Cd by rape in the Cd+Pb-contaminated soils. The results indicated that the endophytic fungus strain had the potential to remove heavy metals from water and soils contaminated by multiple heavy metals, and plants accumulating multiple metals might harbor diverse fungi suitable for bioremediation of contaminated media.

The neuroprotective effects of purslane (Portulaca oleracea) on rotenone-induced biochemical changes and apoptosis in brain of rat.

Purslane (Portulaca oleraceae L.), a member of the Portulacaceae family, is widespread as a weed and has been ranked as the eighth most common plant in the world. In order to evaluate purslane herbal aqueous juice as a neuroprotective agent, the antioxidant activity of purslane juice was assessed in vitro and the neuroprotective effects of purslane (1.5 mL/Kg bwt) on rotenone (12 mg/Kg bwt for 12 days) induced biochemical changes and apoptosis in striatum of rats were also examined. The repeated administration of rotenone produced dramatic increases in intercellular content of calcium, dopamine metabolites and apoptosis in the striatum. In addition, rotenone administration caused significant decrease in complex I activity. These biochemical changes and apoptosis inductions were effectively counteracted by administration of purslane. Overall, the present study demonstrated the neuroprotective role of purslane in the striatum and proposes its prophylactic potential against developing brain damage and Parkinson's disease induction followed by rotenone administration, and that purslane may be considered as a potential neuroprotective agent against environmental factors affecting the function of the dopaminergic system.

Omega-3 fatty acid desaturase genes isolated from purslane (Portulaca oleracea L.): expression in different tissues and response to cold and wound stress.

Two full-length cDNA clones PoleFAD7 and PoleFAD8, encoding plastidial omega-3 fatty acid desaturases were isolated from purslane (Portulaca oleracea). The encoded enzymes convert linoleic to alpha-linolenic acid (C18:3n-3). Three histidine clusters characteristic of fatty acid desaturases, a putative chloroplast transit peptide in the N-terminal, and three putative transmembrane domains were identified in the sequence. Both genes were expressed in all analyzed tissues showing different levels of expression. PoleFAD7 was up-regulated by wounding but not by low temperature. PoleFAD8 was up-regulated by cold stress but not by wounding. Total fatty acid and linolenic acid content were higher both, in wounded and intact leaves of plants exposed to low temperature.