The replacement of long-chained per- and polyfluoroalkyl substances (PFAS) with their short-chained homologues may have an impact on the accumulation in plants. The extent to which PFAS are absorbed by plants may differ among species and may depend on environmental factors, including temperature. The effect of an increased temperature on root uptake and translocation of PFAS in plants has been poorly studied. In addition, very few studies have examined toxicity of environmentally realistic PFAS concentrations to plants. Here, we investigated the bioaccumulation and tissue-distribution of fifteen PFAS in Arabidopsis thaliana L. grown in vitro at two different temperatures. Additionally, we examined the combined effects of temperature and PFAS accumulation on plant growth. Short-chained PFAS mainly accumulated in the leaves. The perfluorocarboxylic acid (PFCA) concentrations in roots and leaves, and the relative contribution of PFCAs to the ΣPFAS concentrations increased with carbon chain length regardless of temperature, with the exception of perfluorobutanoic acid (PFBA). An increased uptake of PFAS in leaves and roots at higher temperatures was observed for PFAS containing either eight or nine carbon atoms and could hence potentially result in higher risks for human intake. Leaf:root ratios of PFCAs followed a U-shaped pattern with carbon chain length, which is attributed to both hydrophobicity and anion exchange. Overall, no combined effects of realistic PFAS concentrations and temperature on the growth of A. thaliana were observed. PFAS exposure positively affected early root growth rates and root hair lengths, indicating a potential effect on factors involved in root hair morphogenesis. However, this effect on root growth rate became negligible later on in the exposure, and solely a temperature effect was observed after 6 days. Temperature also affected the leaf surface area. The underlying mechanisms on how PFAS stimulates root hair growth require further examination.

In this study, we grew radish (Raphanus raphanistrum subsp. sativus L.) and broad beans (Vicia faba L.) in a greenhouse on soils spiked with a mixture of 15 per- and polyfluoroalkyl substances (PFASs) and investigated the association between accumulated ∑PFAS concentrations, growth, and hormone levels. Short-chained PFASs dominated aboveground tissues, whereas long-chained PFASs were most abundant in the plant roots. Our results showed that the presence or absence of exodermal Casparian strips, as well as the hydrophobicity and anion exchange capacities of PFASs, could explain the translocation of PFASs within plants. Significant associations found between accumulated PFAS concentrations and levels of gibberellins (GA1 and GA15), methionine, and indole-3-acetic acid (IAA) imply potential effects of PFASs on plant development and growth. This study provides the first evidence of associations between PFAS accumulation in plants and growth hormone levels, possibly leading to growth reduction of the apical dome and effects on the cell cycle in pericycle cells and methionine metabolism in plants.

The chemical composition of olive leaves and roots of Chemlali variety was evaluated regarding the contents of amino acids and endogenous phytohormones under foliar application of biofertilizers (F1: rich in nitrogen (N), phosphorus (P), potassium (K); F2: rich in calcium (Ca); F3: application of F1 and F2). The results of this study demonstrated significant effects of tested fertilizers on the concentrations of amino acids. Glutamic acid and asparagine had the highest concentrations in leaves and the lowest concentrations in roots under F1 and F3. Regarding the concentrations of endogenous phytohormones, high contents of indole-3-acetic acid and salicylic acid were found in leaves and roots under the application of F1 biofertilizer. Jasmonic acid (JA) was of higher concentration in root than leaves, while abscisic acid occurred in lower concentration. Moreover, the analysis of isoprenoid cytokinins by ultra-performance liquid-chromatography tandem mass spectrometry (UPLC-MS/MS) showed that these cytokinins were improved and became more abundant in roots under foliar treatments. Particularly, Zeatin-N7-glucoside and Dihydrozeatin-N9-Glucoside were enhanced under F1 and F3. The results of this study suggest that foliar application of biological fertilizers may improve physiological status of olive trees throughout the enhancement of some phytohormones and amino acids. Key words: Foliar fertilization, olive trees, amino acids, indole-3-acetic acid, isoprenoid cytokinins.

Growth and biochemical parameters of leaves, flower buds and flowers of olive (Olea europaea L. cv. Chemlali) treated by foliar biofertilization (T0: untreated trees; T1: rich in nitrogen (N), phosphorus (P), potassium (K); T2: rich in calcium (Ca); T3: application of T1 and T2) were analyzed during the flowering stage. The results showed that T1 resulted in higher contents of leaf N, K, and Na. T1 and T3 resulted in an increase of pigment concentration in leaves. All foliar treatments affected negatively the contents of total polyphenols and orthodiphenols in leaves and flower buds. Lower amounts of individual phenolic compounds were detected in the leaves under all foliar bio-fertilizations and in flower buds of olive trees sprayed with T2 and T3. This decrease is explained by the lower enzymatic activity of l-phenylalanine ammonia-lyase. In flowers, T1 exhibits the highest levels of total polyphenols, o-diphenols, and individual phenolic compounds compared to T0.

Recently, we reported that the novel mitochondrial RNA editing factor SLO2 is essential for mitochondrial electron transport, and vital for plant growth through regulation of carbon and energy metabolism. Here, we show that mutation in SLO2 causes hypersensitivity to ABA and insensitivity to ethylene, suggesting a link with stress responses. Indeed, slo2 mutants are hypersensitive to salt and osmotic stress during the germination stage, while adult plants show increased drought and salt tolerance. Moreover, slo2 mutants are more susceptible to Botrytis cinerea infection. An increased expression of nuclear-encoded stress-responsive genes, as well as mitochondrial-encoded NAD genes of complex I and genes of the alternative respiratory pathway, was observed in slo2 mutants, further enhanced by ABA treatment. In addition, H2O2 accumulation and altered amino acid levels were recorded in slo2 mutants. We conclude that SLO2 is required for plant sensitivity to ABA, ethylene, biotic, and abiotic stress. Although two stress-related RNA editing factors were reported very recently, this study demonstrates a unique role of SLO2, and further supports a link between mitochondrial RNA editing events and stress response.

The role and metabolism of indole-3-acetic acid in gram-negative bacteria is well documented, but little is known about indole-3-acetic acid biosynthesis and regulation in gram-positive bacteria. The phytopathogen Rhodococcus fascians, a gram-positive organism, incites diverse developmental alterations, such as leafy galls, on a wide range of plants. Phenotypic analysis of a leafy gall suggests that auxin may play an important role in the development of the symptoms. We show here for the first time that R. fascians produces and secretes the auxin indole-3-acetic acid. Interestingly, whereas noninfected-tobacco extracts have no effect, indole-3-acetic acid synthesis is highly induced in the presence of infected-tobacco extracts when tryptophan is not limiting. Indole-3-acetic acid production by a plasmid-free strain shows that the biosynthetic genes are located on the bacterial chromosome, although plasmid-encoded genes contribute to the kinetics and regulation of indole-3-acetic acid biosynthesis. The indole-3-acetic acid intermediates present in bacterial cells and secreted into the growth media show that the main biosynthetic route used by R. fascians is the indole-3-pyruvic acid pathway with a possible rate-limiting role for indole-3-ethanol. The relationship between indole-3-acetic acid production and the symptoms induced by R. fascians is discussed.

The culture of pasture legumes is of special interest for the world's agriculture because it results in the production of high value protein accompanied by improvement of soil fertility, since they undergo symbioses with dinitrogen-fixing bacteria. Alfalfa is the most important forage crop for the arid and semi-arid areas, where increased salinity of irrigated fields is one of the major constraints that limit crop productivity. Recently, using in vitro selection, we obtained alfalfa genotypes with increased tolerance to PEG 6000, an agent that mimics drought. Here, we present studies on salt tolerance with adult plants of these alfalfa genotypes grown either on nitrate or diazotrophically at various non-lethal salt concentrations. Growth parameters and parameters related to nodule physiology and development have been analysed. All R lines had a higher salt tolerance than their explant source genotype (T1) in germination and growth on nitrate-containing medium. Under diazotrophic growth conditions, R1 and R3 were with higher relative salt tolerance than T1. Nodule biomass was depressed at high salt concentrations in all genotypes. This growth decline went in pair with changes in carbohydrate partitioning and in the hormonal balance.

Plant hormones are present and active in minor concentrations in plant tissue. To allow quantification in a restricted amount of material, i.e., protoplasts, chloroplasts, seedlings, seeds, buds, or apical root- and stem regions, a sensitive analytical technique is a prerequisite. During the last two decades, procedures for phytohormone analysis as well as the available hardware have improved substantially. Fluorimetry is widely used for the analysis of indole-3-acetic acid (IAA) because it is more specific and therefore more sensitive than ultraviolet detection (for a review see ref. 1). Good detection limits for derivatized IAA are obtained in Electron Impact (EI+) (2,3) or negative ion chemical ionization (NICI) GC-MS* (4,5).