Plants — Open Access Journal

In this study, the allelopathic properties of Medicago sativa on different weeds were investigated under in vitro conditions. The compounds involved in the autotoxicity of M. sativa were analyzed using high-performance liquid chromatography. The extracts of all concentrations inhibited the growth of the calluses of Digitaria ciliaris, Chenopodium album, Amaranthuslividus, Portulaca oleracea, and Commelina communis. Six allelopathic compounds in alfalfa were identified and quantified, and the most predominant phenolic compounds were salicylic acid and p-hydroxybenzoic acid. Various concentrations (10⁻², 10⁻³, and 10⁻⁵ M) of all the tested phenolic compounds exerted inhibitory effects on callus fresh weight. Rutin, salicylic acid, scopoletin, and quercetin significantly inhibited alfalfa seed germination. Of the seven identified saponins, medicagenic acid saponins exhibited the highest autotoxic effect and significantly lowered seed germination rate. Principal component analysis showed that the phenolic compounds and saponin composition significantly contributed to the different variables. The highly phytotoxic properties of the alfalfa-derived phenolic compounds and saponins indicate that these phytochemicals can be a potential source of bioherbicides. Full article

Increasing consciousness regarding the nutritional value of olive oil has enhanced the demand for this product and, consequently, the expansion of olive tree cultivation. Although it is considered a highly resilient and tolerant crop to several abiotic stresses, olive growing areas are usually affected by adverse environmental factors, namely, water scarcity, heat and high irradiance, and are especially vulnerable to climate change. In this context, it is imperative to improve agronomic strategies to offset the loss of productivity and possible changes in fruit and oil quality. To develop more efficient and precise measures, it is important to look for new insights concerning response mechanisms to drought stress. In this review, we provided an overview of the global status of olive tree ecology and relevance, as well the influence of environmental abiotic stresses in olive cultivation. Finally, we explored and analysed the deleterious effects caused by drought (e.g., water status and photosynthetic performance impairment, oxidative stress and imbalance in plant nutrition), the most critical stressor to agricultural crops in the Mediterranean region, and the main olive tree responses to withstand this stressor. Full article

Natural products derived from plants play a vital role in the discovery of new drug candidates, and these are used for novel therapeutic drug development. Andrographis paniculata and Spilanthes paniculata are used extensively as medicinal herbs for the treatment of various ailments, and are reported to have neuroprotective properties. β-amyloid is a microscopic brain protein whose significant aggregation is detected in mild cognitive impairment and Alzheimer’s disease (AD) brains. The accumulation of β-amyloid disrupts cell communication and triggers inflammation by activating immune cells, leading to neuronal cell death and cognitive disabilities. The proteases acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and beta secretase-1 (BACE-1) have been reported to be correlated with the synthesis and growth of β-amyloid plaques in the brains of AD patients. In the present study, the phenolic compounds from A. paniculata and S. paniculata that have been reported in the literature were selected for the current investigation. Furthermore, we employed molecular docking and molecular dynamics studies of the phenolic compounds with the proteins AChE, BChE, and BACE-1 in order to evaluate the binding characteristics and identify potent anti-amyloid agents against the neurodegenerative diseases such as AD. In this investigation, we predicted three compounds from A. paniculata with maximum binding affinities with cholinesterases and BACE-1. The computational investigations predicted that these compounds follow the rule of five. We further evaluated these molecules for in vitro inhibition activity against all the enzymes. In the in vitro investigations, 3,4-di-o-caffeoylquinic acid (5281780), apigenin (5280443), and 7-o-methylwogonin (188316) were found to be strong inhibitors of AChE, BChE, and BACE-1. These findings suggest that these compounds can be potent multi-target inhibitors of the proteases that might cumulatively work and inhibit the initiation and formation of β-amyloid plaques, which is a prime cause of neurotoxicity and dementia. According to our knowledge, these findings are the first report on natural compounds isolated from A. paniculata as multi-target potent inhibitors and anti-amyloid agents. Full article

In this research, seven different models to predict leaf area (LA) of loquat (Eriobotrya japonica Lindl) were tested and evaluated. This species was chosen due to the relevant importance of its fruit as an appreciated early summer product and of its leaves and flower as a source of additional income within the nutraceutical and functional food markets. The analysis (calibration and validation) was made using a large dataset (2190) of leaf width (W), leaf length (L), and single LA collected in ten common loquat cultivars. During the analysis, the results obtained using one- and two-regressor models were also evaluated to assess the need for fast measurements against different levels of accuracy achieved during the final estimate. The analysis permitted to finally select two different models: 1) a model based on a single measurement and quadratic relationship between the single LA and W (R² = 0.894; root mean squared error [RMSE] = 12.98) and another model 2) based, instead, on two measurements (L and W), and on the linear relationship between single LA and the product of L × W (R² = 0.980; RMSE = 5.61). Both models were finally validated with an independent dataset (cultivar ‘Tanaka’) confirming the quality of fitting and accuracy already observed during the calibration phase. The analysis permitted to select two different models to be used according to the aims and accuracy required by the analysis. One, based on a single-regressor quadratic model and W (rather than L) as a proxy variable, is capable of obtaining a good quality of fitting of the single LA of loquat cultivars (R² = 0.894; RMSE = 12.98), whereas, the other, a linear two-regressor (i.e., W and L) model, permitted to achieve the highest prediction (R² = 0.980; RMSE = 5.61) of the observed variable, but double the time required for leaf measurement. Full article

Inactivation of ADP-glucose pyrophosphorylase1 (ADG1) causes a starchless phenotype in Arabidopsis. Mutants defective in ADG1 show severe growth retardation in day/night conditions but exhibit similar growth to wild type under continuous light, implying that starch plays an important role in supporting respiration, metabolism and growth at night. In addition to carbohydrates, lipids and proteins can serve as alternative respiratory substrates for the energy production in mature plants. To test the role of lipids in plant growth, we generated transgenic plants overexpressing phospholipid:diacylglycerol acyltransferase1 (PDAT1) in adg1. We found that PDAT1 overexpression caused an increase in both fatty acid synthesis and turnover and increased the accumulation of triacylglycerol (TAG) at the expense of sugars, and enhanced the growth of adg1. We demonstrated that unlike sugars, which were metabolized within a few hours of darkness, TAG breakdown was slow, occurring throughout the entire dark period. The slow pace of TAG hydrolysis provided a sustained supply of fatty acids for energy production, thereby alleviating energy deficiency at night and thereby improving the growth of the starchless mutants. We conclude that lipids can contribute to plant growth by providing a constant supply of fatty acids as an alternative energy source in mature starchless mutant plants. Full article

Despite the fact that the vegetation pattern and history of the Bale Mountains in Ethiopia were reconstructed using pollen, little is known about the former extent of Erica species. The main objective of the present study is to identify unambiguous chemical proxies from plant-derived phenolic compounds to characterize Erica and other keystone species. Mild alkaline CuO oxidation has been used to extract sixteen phenolic compounds. After removal of undesired impurities, individual phenols were separated by gas chromatography and were detected by mass spectrometry. While conventional phenol ratios such as syringyl vs. vanillyl and cinnamyl vs. vanillyl and hierarchical cluster analysis of phenols failed for unambiguous Erica identification, the relative abundance of coumaryl phenols (>0.20) and benzoic acids (0.05—0.12) can be used as a proxy to distinguish Erica from other plant species. Moreover, a Random Forest decision tree based on syringyl phenols, benzoic acids (>0.06), coumaryl phenols (<0.21), hydroxybenzoic acids, and vanillyl phenols (>0.3) could be established for unambiguous Erica identification. In conclusion, serious caution should be given before interpreting this calibration study in paleovegetation reconstruction in respect of degradation and underground inputs of soil organic matter. Full article

Heat and drought are two major limiting factors for perennial pasture production in south eastern Australia. Although previous studies have focused on the effects of prolonged heat and drought stresses on pasture growth and physiology, the effects of short term recurring combined heat and drought stresses and the recovery from them have not been studied in detail. A controlled environment experiment was conducted to investigate the growth and physiological responses of perennial ryegrass (Lolium perenne L.), cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.) and chicory (Cichorium intybus L.) plants exposed to two consecutive seven day heat (control = 25/15 °C day/night; moderate = 30/20 °C day/night and severe = 35/30 °C day/night) and/or drought stresses each followed by a seven day recovery period. During the first moderate and severe heat and drought treatments, maximum photochemical efficiency of photosystem II (Fv/Fm), cell membrane permeability and relative leaf water content decreased in chicory and tall fescue compared to perennial ryegrass and cocksfoot. However, during the second moderate heat and drought treatment, all species showed less reduction in the same parameters suggesting that these species acclimated to consecutive moderate heat and drought stresses. Chicory was the only species that was not affected by the second severe heat and drought stress while physiological parameters of all grass species were reduced closer to minimum values. Irrigation mitigated the negative effects of heat stress by cooling the canopies 1–3 °C below air temperatures with the most cooling observed in chicory. All the species exposed to moderate heat and drought were fully recovered and those exposed to severe heat and drought recovered partially at the end of the experiment. These findings suggest that chicory may be a potential species for areas subject to frequent heat and drought stress. Full article

The rooting of stem cuttings is a highly efficient procedure for the vegetative propagation of ornamental plants. In cultivated carnations, an increased auxin level in the stem cutting base produced by active auxin transport from the leaves triggers adventitious root (AR) formation from the cambium. To provide additional insight into the physiological and genetic basis of this complex trait, we studied AR formation in a collection of 159 F₁ lines derived from a cross between two hybrid cultivars (2003 R 8 and 2101-02 MFR) showing contrasting rooting performances. In three different experiments, time-series for several stem and root architectural traits were quantified in detail in a subset of these double-cross hybrid lines displaying extreme rooting phenotypes and their parental genotypes. Our results indicate that the water content and area of the AR system directly contributed to the shoot water content and shoot growth. Moreover, morphometric data and rooting quality parameters were found to be associated with some stress-related metabolites such as 1-aminocyclopropane-1-carboxylic acid (ACC), the ethylene precursor, and the conjugated auxin indol-3-acetic acid-aspartic acid (IAA-Asp). Full article

Plants both generate and shed organs throughout their lifetime. Cell separation is in function during opening of anthers to release pollen; floral organs are detached after pollination when they have served their purpose; unfertilized flowers are shed; fruits and seeds are abscised from the mother plant to secure the propagation of new generations. Organ abscission takes place in specialized abscission zone (AZ) cells where the middle lamella between adjacent cell files is broken down. The plant hormone ethylene has a well-documented promoting effect on abscission, but mutation in ethylene receptor genes in Arabidopsis thaliana only delays the abscission process. Microarray and RNA sequencing have identified a large number of genes differentially expressed in the AZs, especially genes encoding enzymes involved in cell wall remodelling and disassembly. Mutations in such genes rarely give a phenotype, most likely due to functional redundancy. In contrast, mutation in the INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) blocks floral organ abscission in Arabidopsis. IDA encodes a small peptide that signals through the leucine-rich repeat receptor-like kinases HAESA (HAE) and HAE-LIKE2 (HSL2) to control floral organ abscission and facilitate lateral root emergence. Untimely abscission is a severe problem in many crops, and in a more applied perspective, it is of interest to investigate whether IDA-HAE/HSL2 is involved in other cell separation processes and other species. Genes encoding IDA and HSL2 orthologues have been identified in all orders of flowering plants. Angiosperms have had enormous success, with species adapted to all kinds of environments, adaptations which include variation with respect to which organs they shed. Here we review, from an evolutionary perspective, the properties of the IDA-HAE/HSL2 signaling module and the evidence for its hypothesized involvement in various cell separation processes in angiosperms. Full article

Interspecific hybridization is one of the major actuators of evolutionary changes in plants. As the result of allopolyploid hybridization, offspring may gain different ploidy levels in comparison to parental species, which can provide them instant reproductive isolation. Two tetraploid sister species, Centaurium erythraea and C. littorale, readily cross-fertilize, resulting in hybrids of various ploidy. In northern Serbia, two stable populations of a hexaploid taxon C. pannonicum have been documented. It has been proposed previously that this taxon emerged after an interspecific hybridization event between two tetraploid sister-species: C. erythraea and C. littorale subsp. compressum. The existing populations of the hybridogenic taxon, as well as neighboring populations of the two parental taxa were here characterized by both morphometrics and molecular markers (EST-SSR and trnL-F). Three leaf and two flower characteristics were found to be informative in delimitation of the parental taxa and in their discernment from hybrid individuals, the latter having intermediate values. Eight microsatellite markers were found to have good ability to distinguish studied taxa, placing C. pannonicum in closer relationship with C. erythraea. Conversely, trnL-F plastid marker nominated C. littorale subsp. compressum to be the donor of the C. pannonicum plastid DNA. Reproductive isolation of the hexaploid hybrid individuals from the parental species should be examined as the next logical step in describing the new species. Full article

Frankincense, the oleogum resin from members of Boswellia, has been used as medicine and incense for thousands of years, and essential oils derived from frankincense are important articles of commerce today. A new source of frankincense resin, Boswellia dalzielii from West Africa has been presented as a new, alternative source of frankincense. In this work, the oleogum resins from 20 different Boswellia dalzielii trees growing in Burkina Faso, West Africa were collected. Hydrodistillation of the resins gave essential oils that were analyzed by GC-MS and GC-FID. The essential oils were dominated by α-pinene (21.0%–56.0%), followed by carvone (2.1%–5.4%) and α-copaene (1.8%–5.0%). Interestingly, there was one individual tree that, although rich in α-pinene (21.0%), also had a substantial concentration of myrcene (19.2%) and α-thujene (9.8%). In conclusion, the oleogum resin essential oil compositions of B. dalzielii, rich in α-pinene, are comparable in composition to other frankincense essential oils, including B. sacra, B. carteri, and B. frereana. Additionally, the differences in composition between samples from Burkina Faso and those from Nigeria are very slight. There is, however, a rare chemotype of B. dalzielii that is dominated by myrcene, found both in Burkina Faso as well as Nigeria. Full article

Lupins anthracnose is a destructive seed and airborne disease caused by Colletotrichum lupini, affecting stems and pods. Primary seed infections as low as 0.01–0.1% can cause very severe yield losses. One of the most effective management strategies is the development of a robust and sensitive seed detection assay to screen seed lots before planting. PCR-based detection systems exhibit higher levels of sensitivity than conventional techniques, but when applied to seed tests they require the extraction of PCR-quality DNA from target organisms in backgrounds of saprophytic organisms and inhibitory seed-derived compounds. To overcome these limitations, a new detection protocol for C. lupini based on a biological enrichment step followed by a PCR assay was developed. Several enrichment protocols were compared with Yeast Malt Broth amended with ampicillin, streptomycin, and lactic acid were the most efficient. A species-specific C. lupini primer pair was developed based on rDNA IGS sequences. The specificity was evaluated against 17 strains of C. lupini, 23 different Colletotrichum species, and 21 different organisms isolated from seeds of Lupinus albus cv. Multitalia, L. luteus cv. Mister, and L. angustifolius cv. Tango. The protocol described here enabled the detection of C. lupini in samples artificially infected with less than 1/10,000 infected seed. Full article

Plant specific NAC (NAM, ATAF1/2 and CUC2) transcription factors (TFs) play important roles in response to abiotic stress. In this study, we identified and characterized a NAC protein, ThNAC7, from Tamarix hispida. ThNAC7 is a nuclear localized protein and has transcriptional activation activity. ThNAC7 expression was markedly induced by salt and osmotic stresses. Transiently transformed T. hispida seedlings overexpressing ThNAC7 (OE) or with RNA interference (RNAi) silenced ThNAC7 were generated to investigate abiotic stress tolerance via the gain- and loss- of function. Overexpressing ThNAC7 showed an increased reactive oxygen species (ROS) scavenging capabilities and proline content, which was accomplished by enhancing the activities of superoxide dismutase (SOD) and peroxidase (POD) in transiently transformed T. hispida and stably transformed Arabidopsis plants. Additionally, ThNAC7 activated these physiological changes by regulating the transcription level of P5CS, SOD and PODgenes. RNA-sequencing (RNA-seq) comparison between wild-type and ThNAC7-transformed Arabidopsis showed that more than 40 known salt tolerance genes might regulated by ThNAC7, including stress tolerance-related genes and TF genes. The results indicated that ThNAC7 induces the transcription level of genes associated with stress tolerance to enhance salt and osmotic stress tolerance via an increase in osmotic potential and enhanced ROS scavenging. Full article

Ground-level ozone (O₃) pollution is known to adversely affect the production of O₃-sensitive crops such as wheat. The magnitude of impact is dependent on the accumulated stomatal flux of O₃ into the leaves. In well-irrigated plants, the leaf pores (stomata) tend to be wide open, which stimulates the stomatal flux and therefore the adverse impact of O₃ on yield. To test whether reduced irrigation might mitigate O₃ impacts on flag leaf photosynthesis and yield parameters, we exposed an O₃-sensitive Kenyan wheat variety to peak concentrations of 30 and 80 ppb O₃ for four weeks in solardomes and applied three irrigation regimes (well-watered, frequent deficit, and infrequent deficit irrigation) during the flowering and grain filling stage. Reduced irrigation stimulated 1000-grain weight and harvest index by 33% and 13%, respectively (when O₃ treatments were pooled), which compensated for the O₃-induced reductions observed in well-watered plants. Whilst full irrigation accelerated the O₃-induced reduction in photosynthesis by a week, such an effect was not observed for the chlorophyll content index of the flag leaf. Further studies under field conditions are required to test whether reduced irrigation can be applied as a management tool to mitigate adverse impacts of O₃ on wheat yield. Full article

Systemic acquired resistance (SAR) is a mechanism through which plants may respond to initial challenge by a pathogen through activation of inducible defense responses, thereby increasing resistance to subsequent infection attempts. Fitness costs are assumed to be incurred by plants induced for SAR, and several studies have attempted to quantify these costs. We developed a mathematical model, motivated by game-theoretic concepts, to simulate competition between hypothetical plant populations with and without SAR to examine conditions under which the phenomenon of SAR may have evolved. Data were gathered from various studies on fitness costs of induced resistance on life history traits in different plant hosts and scaled as a proportion of the values in control cohorts in each study (i.e., healthy plants unprimed for SAR). With unprimed healthy control plants set to a fitness value of 1, primed healthy plants incurred a fitness cost of about 10.4% (0.896, n = 157), primed diseased plants incurred a fitness cost of about 15.5% (0.845, n = 54), and unprimed diseased plants incurred a fitness cost of about 28.9% (0.711, n = 69). Starting from a small proportion of the population (0.5%) and competing against a population with constitutive defenses alone in stochastic simulations, the SAR phenotype almost always dominated the population after 1000 generations when the probability of disease was greater than or equal to 0.5 regardless of the probability for priming errors. Full article

Root architecture is a complex structure that comprises multiple traits of the root phenotype. Novel platforms and models have been developed to better understand root architecture. In this methods paper, we introduce a novel allometric model, named rhizochron index (m), which describes lateral root (LR) branching and elongation patterns across the primary root (PR). To test our model, we obtained data from 16 natural accessions of Arabidopsis thaliana at three stages of early root development to measure conventional traits of root architecture (e.g., PR and LR length), and extracted the rhizochron index (m). In addition, we tested previously published datasets to assess the utility of the rhizochron index (m) to distinguish mutants and environmental effects on root architecture. Our results indicate that rhizochron index (m) is useful to distinguish the natural variations of root architecture between A. thaliana accessions, but not across early stages of root development. Correlation analyses in these accessions showed that m is a novel trait that partially captures information from other root architecture traits such as total lateral root length, and the ratio between lateral root and primary root lengths. Moreover, we found that the rhizochron index was useful to distinguish ABA effect on root architecture, as well as the mutant pho1 phenotype. We propose the rhizochron index (m) as a new feature of the root architectural system to be considered, in addition to conventional traits in future investigations. Full article

The aim of the study was to evaluate the antioxidant activity of selenium in the roots of Cucumis sativus L. seedlings pre-treated with selenium (Se) in the form of sodium selenite at concentrations of 1, 5, and 10 µM, and then subjected to a water deficit (WD). It has been hypothesized that Se, in low concentrations, alleviates an oxidative stress caused by a WD in the cucumber roots. A WD was introduced by the surface dehydration of roots. The aim of the research was to compare the changes accompanying oxidative stress in plants growing in the presence of Se and in its absence. The study concerns the generation of reactive oxygen species (ROS)—superoxide anions (O₂^•−), hydrogen peroxide (H₂O₂), and hydroxyl radicals (^•OH)—as well the activities of the antioxidant enzymes lowering the ROS level—ascorbate peroxidase (APX), peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD). A WD caused oxidative stress, i.e., the enhanced generation of ROS. Selenium at the concentrations of 1 and 5 μM increased the tolerance of cucumber seedlings to oxidative stress caused by a WD by increasing the activities of the antioxidant enzymes, and it also limited the damage of plasma membranes as a result of the inhibition of lipid peroxidation. Full article

Anthurium andraeanum Lind. is a popular potted and cut-flower plant with an attractive spathe and foliage. It is native to tropical rainforest areas and is able to blossom throughout the year under suitable conditions. However, various abiotic stresses seriously restrict the ornamental value of A. andraeanum and increase the costs of cultivation. A dark green (dg) leaf color mutant of A. andraeanum ‘Sonate’, which accumulates high levels of anthocyanin, has shown increased vigor and tolerance to stresses during cultivation and is, thus, an ideal germplasm for studying stress tolerance in this species. Here, we show that the anthocyanin content in dg mutant plants at different stages of leaf development was higher than in wild-type (WT) plants, and the ability to tolerate under low-temperature (LT, 14 °C) stress was stronger in dg than in WT plants. RNA-Seq of cDNA libraries from young leaves of dg and WT identified AabHLH35 as a differentially expressed gene (DEG) that was significantly up-regulated in dg. Furthermore, heterologous expression of AabHLH35 improved tolerance to cold and drought stresses in Arabidopsis. These results have built an important molecular foundation for further study of stress tolerance in A. andraeanum. Full article

WUSCHEL-related homeobox (WOX) is a family of transcription factors that are unique to plants and is characterized by the presence of a homeodomain. The WOX transcription factor plays an important role in regulating plant growth and development and the response to abiotic stress. Soybean is one of the most important oil crops worldwide. In this study, based on the available genome data of soybean, the WOX gene family was identified by bioinformatics analysis. The chromosome distribution, gene and protein structures, phylogenetic relationship and gene expression patterns of this family were comprehensively compared. The results showed that a total of 33 putative WOX genes in the soybean genome were found and then designated as GmWOX1- GmWOX33, which were distributed across 19 chromosomes except chromosome 16. Multiple sequence analysis of the GmWOX gene family revealed a highly conserved homeodomain. Phylogenetic tree analysis showed that 33 WOX genes could be divided into three major clades (modern/WUS, intermediate and ancient) in soybean. Of these 33 WOX genes, some showed differential expression patterns in the tested tissues (leaves, pods, unopen and open flowers, nodules, seed, roots, root hairs, stems, shoot apical meristems and shoot tips). In addition, the expression profile and qRT-PCR analysis showed that most of the GmWOX genes responded to different abiotic stress treatments (cold and drought). According to the expression pattern of GmWOX genes in the high regeneration capacity soybean material P3, overexpression of GmWOX18 was selected for function analysis. The overexpression of GmWOX18 increased the regeneration ability of clustered buds. The results will provide valuable information for further studies on the roles of WOX genes in regulating soybean growth, development and responses to abiotic stress, as well as a basis for the functional identification and analysis of WOX genes in soybean. Full article