The increasing salinity in soils and irrigation water is a major concern for growers of strawberry, a salt-sensitive horticultural crop. The hormone melatonin (N-acetyl-5-methoxytryptamine) is ...involved in many biological processes and affects plant responses to environmental stresses. The effects of weekly 100 and 200 μM melatonin sprays on leaf composition parameters (photosynthetic pigment and macronutrient concentrations, oxidative stress markers, antioxidant defense systems and abscisic acid concentrations), fruit yield and quality parameters (soluble solids, total acidity, ascorbic acid, total antioxidants and phenolics and sugars), and leaf and fruit melatonin have been studied in strawberry grown under non-saline, moderate and intense salinity conditions (0, 40 and 80 mM NaCl, respectively). Salinity led to decreases in yield, fruit quality parameters and leaf photosynthetic pigments and macronutrient concentrations, as well as to increases in oxidative stress, with melatonin foliar application alleviating all these changes. On the other hand, salinity led to increases in the leaf levels of antioxidant enzymes, abscisic acid and melatonin, with foliar applications of melatonin boosting those increases. In the absence of salinity stress, melatonin led to smaller changes in all parameters in the same direction to that observed in the presence of salinity. Furthermore, melatonin resulted in increases in strawberry fruit yield and quality, especially in plants grown under salinity. Results indicate that the effects of melatonin application are associated with a boost in leaf antioxidant enzymes and abscisic acid, and support that the application of melatonin is a promising tool for mitigating salt stress in strawberry.
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•Salinity stress reduced strawberry fruit yield and quality.•Foliar melatonin alleviated the reduction of fruit yield and quality caused by salinity.•Salinity stress activated antioxidant systems and increased abscisic acid in leaves.•Foliar melatonin boosted the increases in leaf antioxidant systems and abscisic acid caused by salinity.•Foliar melatonin also had positive effects in the absence of salinity.
Glycyrrhiza glabra L. (licorice) is a medicinal species rich in the specialised plant metabolite glycyrrhizin. It has been previously proposed that drought, which is increasing in importance due to ...the climatic change and scarcity of water resources, can promote the synthesis of glycyrrhizin. The effects of slight, moderate and intense drought (70, 35 and 23% of the regular irrigation, respectively) on growth parameters, osmolyte content, oxidative stress markers, antioxidant enzymes, glycyrrhizin biosynthesis genes and root glycyrrhizin concentration and contents, have been assessed in five Iranian licorice genotypes grown in the field. Drought decreased progressively biomass and leaf relative water contents, and increased progressively osmolyte (proline, glycine-betaine and soluble sugars) concentrations in leaves and roots. Drought caused oxidative stress in leaves, as indicated by lipid peroxidation and hydrogen peroxide concentrations, and increased the activities of antioxidant enzymes in leaf extracts (catalase, peroxidase, superoxide dismutase and pholyphenoloxidase). Drought promoted the synthesis of glycyrrhizin, as indicated by the increases in the expression of the glycyrrhizin biosynthesis pathway genes SQS1, SQS2, bAS, CYP88D6, CYP72A154 and UGT73, and increased the root concentrations of glycyrrhizin with drought in some genotypes. However, the large decreases in root biomass caused by drought led to general decreases in the amount of glycyrrhizin per plant with moderate and intense drought, whereas the slight drought treatment led to significant decreases in glycyrrhizin content in only one genotype. Under intense drought two of the genotypes were still capable to maintain half of the control glycyrrhizin yield, whereas in the other three genotypes glycyrrhizin yield was 22–33% of the control values. Results indicate that under intense drought, with only 23% of the normal water dose being applied, an appropriate choice of genotype can still lead to acceptable glycyrrhizin yields.
Hypothetical interaction network in response to drought stress in Licorice. The red rectangle includes genes involved in the glycyrrhizin biosynthesis pathway in licorice plants. The expression of genes encoding these enzymes in slight (S), moderate (M) and intense (I) drought stress is shown in the heatmap. Genes are depicted using fold change values and colour coded to reflect changes in relative expression. Each arrow represents the enzyme reactions: FPP, farnesyl pyrophosphate; SQS, squalene synthase; bAS, beta-amyrin synthase; LUS, lupeol synthase; CAS, cycloartenol synthase; CYP88D6 and CYP72A154, cytochrome P450 monooxygenases; UGTs, UDP-glucuronosyltransferases. Display omitted
•Drought caused progressive decreases in the biomass of five licorice genotypes grown in the field.•Drought caused oxidative stress, and increases in osmolytes and in antioxidant enzymes.•Drought caused increases in the expression of several genes in the glycyrrhizin biosynthesis pathway.•Root glycyrrhizin concentrations only increased in some genotypes under slight/moderate drought.•Glycyrrhizin contents per plant were maintained in four genotypes but only under slight drought.
•A single foliar spray with relatively low amounts of B or Zn nano-fertilizers (34mgBtree−1 or 636mgZntree−1, respectively) led to increases in pomegranate fruit yield.•Fertilization with the highest ...of the two doses led to significant improvements in fruit quality, including TSS, decreases in TA, and increases in maturity index and pH in juice.•Physical fruit characteristics were unaffected. Changes in total sugars and total phenolic compounds were only minor, whereas the antioxidant activity and total anthocyanin were unaffected.
This study was carried out to assess the effects of the foliar application of nano-fertilizers of zinc (Zn) and boron (B) on pomegranate (Punica granatum cv. Ardestani) fruit yield and quality. A factorial experiment was conducted based on a completely randomized block design, with nine treatments and four replications per treatment. Foliar sprays of nano-Zn chelate fertiliser at three concentrations (0, 60 and 120mgZnL−1) and nano-B chelate fertiliser (0, 3.25 and 6.5mgBL−1) were applied as a single spray before full bloom at a rate of 5.3Ltree−1. The application of Zn and B increased the leaf concentrations of both microelements in August, reflecting the improvements in tree nutrient status. A single foliar spray with relatively low amounts of B or Zn nano-fertilizers (34mgBtree−1 or 636mgZntree−1, respectively) led to increases in pomegranate fruit yield, and this was mainly due to increases in the number of fruits per tree. The effect was not as large with Zn as with B. Fertilization with the highest of the two doses led to significant improvements in fruit quality, including 4.4–7.6% increases in TSS, 9.5–29.1% decreases in TA, 20.6–46.1% increases in maturity index and 0.28–0.62pH unit increases in juice pH, whereas physical fruit characteristics were unaffected. Changes in total sugars and total phenolic compounds were only minor, whereas the antioxidant activity and total anthocyanins were unaffected.
Iron (Fe) is abundant in soils but generally poorly soluble. Plants, with the exception of Graminaceae, take up Fe using an Fe(III)‐chelate reductase coupled to an Fe(II) transporter. Whether or not ...nongraminaceous species can convert scarcely soluble Fe(III) forms into soluble Fe forms has deserved little attention so far. We have used Beta vulgaris, one among the many species whose roots secrete flavins upon Fe deficiency, to study whether or not flavins are involved in Fe acquisition. Flavins secreted by Fe‐deficient plants were removed from the nutrient solution, and plants were compared with Fe‐sufficient plants and Fe‐deficient plants without flavin removal. Solubilization of a scarcely soluble Fe(III)‐oxide was assessed in the presence or absence of flavins, NADH (nicotinamide adenine dinucleotide, reduced form) or plant roots, and an Fe(II) trapping agent. The removal of flavins from the nutrient solution aggravated the Fe deficiency‐induced leaf chlorosis. Flavins were able to dissolve an Fe(III)‐oxide in the presence of NADH. The addition of extracellular flavins enabled roots of Fe‐deficient plants to reductively dissolve an Fe(III)‐oxide. We concluded that root‐secretion of flavins improves Fe nutrition in B. vulgaris. Flavins allow B. vulgaris roots to mine Fe from Fe(III)‐oxides via reductive mechanisms.
Root secretion of coumarin-phenolic type compounds has been recently shown to be related to
tolerance to Fe deficiency at high pH. Previous studies revealed the identity of a few simple coumarins ...occurring in roots and exudates of Fe-deficient
plants, and left open the possible existence of other unknown phenolics. We used HPLC-UV/VIS/ESI-MS(TOF), HPLC/ESI-MS(ion trap) and HPLC/ESI-MS(Q-TOF) to characterize (identify and quantify) phenolic-type compounds accumulated in roots or secreted into the nutrient solution of
plants in response to Fe deficiency. Plants grown with or without Fe and using nutrient solutions buffered at pH 5.5 or 7.5 enabled to identify an array of phenolics. These include several coumarinolignans not previously reported in
(cleomiscosins A, B, C, and D and the 5'-hydroxycleomiscosins A and/or B), as well as some coumarin precursors (ferulic acid and coniferyl and sinapyl aldehydes), and previously reported cathecol (fraxetin) and non-cathecol coumarins (scopoletin, isofraxidin and fraxinol), some of them in hexoside forms not previously characterized. The production and secretion of phenolics were more intense when the plant accessibility to Fe was diminished and the plant Fe status deteriorated, as it occurs when plants are grown in the absence of Fe at pH 7.5. Aglycones and hexosides of the four coumarins were abundant in roots, whereas only the aglycone forms could be quantified in the nutrient solution. A comprehensive quantification of coumarins, first carried out in this study, revealed that the catechol coumarin fraxetin was predominant in exudates (but not in roots) of Fe-deficient
plants grown at pH 7.5. Also, fraxetin was able to mobilize efficiently Fe from a Fe(III)-oxide at pH 5.5 and pH 7.5. On the other hand, non-catechol coumarins were much less efficient in mobilizing Fe and were present in much lower concentrations, making unlikely that they could play a role in Fe mobilization. The structural features of the array of coumarin type-compounds produced suggest some can mobilize Fe from the soil and others can be more efficient as allelochemicals.
The metal chelator nicotianamine promotes the bioavailability of Fe and reduces cellular Fe toxicity. For breeding Fe-efficient crops, we need to explore the fundamental impact of nicotianamine on ...plant development and physiology. The quadruple nas4x-2 mutant of Arabidopsis thaliana cannot synthesize any nicotianamine, shows strong leaf chlorosis, and is sterile. To date, these phenotypes have not been fully explained. Here, we show that sink organs of this mutant were Fe deficient, while aged leaves were Fe sufficient. Upper organs were also Zn deficient. We demonstrate that transport of Fe to aged leaves relied on citrate, which partially complemented the loss of nicotianamine. In the absence of nicotianamine, Fe accumulated in the phloem. Our results show that rather than enabling the long-distance movement of Fe in the phloem (as is the case for Zn), nicotianamine facilitates the transport of Fe from the phloem to sink organs. We delimit nicotianamine function in plant reproductive biology and demonstrate that nicotianamine acts in pollen development in anthers and pollen tube passage in the carpels. Since Fe and Zn both enhance pollen germination, a lack of either metal may contribute to the reproductive defect. Our study sheds light on the physiological functions of nicotianamine.
Iron deficiency is a yield-limiting factor with major implications for field crop production in one-third of the world’s agricultural areas, especially those with high soil CaCO3. In the present ...work, a two-dimensional gel electrophoresis proteomic approach was combined with a study on the riboflavin synthesis pathway, including qPCR and riboflavin determination, to investigate Fe-deficiency responses in Medicago truncatula plants grown with and without CaCO3. Iron deficiency caused a de novo accumulation of DMRLs and GTPcII, proteins involved in riboflavin biosynthesis, as well as marked increases in root riboflavin concentrations and in the expression of four genes from the riboflavin biosynthetic pathway. Two novel changes found were the increased accumulation of proteins related to N recycling and protein catabolism. Other identified changes were consistent with previously found increases in glycolysis, TCA cycle, and stress-related processes. All effects were more marked in the presence of CaCO3. Our results show that the riboflavin biosynthesis pathway was up-regulated at the genomic, proteomic, and metabolomic levels under both Fe-deficiency treatments, especially in the presence of CaCO3. Results also indicate that N recycling occurs in M. truncatula upon Fe deficiency, possibly constituting an additional anaplerotic N and C source for the synthesis of secondary metabolites, carboxylates, and others.
In response to iron deficiency, Nicotiana tabacum secretes both flavins and O-methylated coumarins to the rhizosphere, the latter being transported by NtPDR3, an ABC transporter.
Abstract
Although ...iron is present in large amounts in the soil, its poor solubility means that plants have to use various strategies to facilitate its uptake. In this study, we show that expression of NtPDR3/NtABCG3, a Nicotiana tabacum plasma-membrane ABC transporter in the pleiotropic drug resistance (PDR) subfamily, is strongly induced in the root epidermis under iron deficiency conditions. Prevention of NtPDR3 expression resulted in N. tabacum plants that were less tolerant to iron-deficient conditions, displaying stronger chlorosis and slower growth than those of the wild-type when not supplied with iron. Metabolic profiling of roots and root exudates revealed that, upon iron deficiency, secretion of catechol-bearing O-methylated coumarins such as fraxetin, hydroxyfraxetin, and methoxyfraxetin to the rhizosphere was compromised in NtPDR3-silenced plants. However, exudation of flavins such as riboflavin was not markedly affected by NtPDR3-silencing. Expression of NtPDR3 in N. tabacum Bright Yellow-2 (BY-2) cells resulted in altered intra- and extracellular coumarin pools, supporting coumarin transport by this transporter. The results demonstrate that N. tabacum secretes both coumarins and flavins in response to iron deficiency and that NtPDR3 plays an essential role in the plant response to iron deficiency by mediating secretion of O-methylated coumarins to the rhizosphere.
The study was aimed to determine the effects of foliar applications of thidiazuron and putrescine, two compounds that may cause iron (Fe) remobilization, in pot marigold (
Calendula officinalis
L.) ...grown in controlled conditions under a limited Fe supply. In a first experiment, plants were grown in a greenhouse in a mixture of sand and perlite with pre-growth/growth Fe concentrations ranging from 0 to 20 µM, and treated three consecutive times with foliar sprays of 0 or 45.4 µM thidiazuron. In a second experiment, plants were grown in a greenhouse in hydroponics with pre-growth/growth Fe concentrations in the nutrient solution ranging from 0 to 20 µM, and treated three consecutive times with foliar sprays of 0, 2.27, or 5.67 mM putrescine. Parameters measured included leaf photosynthetic pigments and Fe concentrations, root ferric chelate reductase activities, photosynthesis rates and peroxidase in leaf extracts in the first experiment, and leaf photosynthetic pigments, leaf and root micronutrient concentrations, root ferric chelate reductase activities, and superoxide dismutase and peroxidase activities in leaf extracts in the second experiment. Results indicate that foliar thidiazuron and putrescine treatments in the µM and mM ranges, respectively, improve Fe transport to the leaf under zero or low supply of Fe. This indicates that foliar treatments with thidiazuron and putrescine increase remobilization of pre-existing plant Fe pools. This could be an additional tool for the optimization of Fe nutrition in ornamental plants such as
C. officinalis
when grown in controlled conditions.
Summary
Many metal transporters in plants are promiscuous, accommodating multiple divalent cations including some which are toxic to humans. Previous attempts to increase the iron (Fe) and zinc (Zn) ...content of rice endosperm by overexpressing different metal transporters have therefore led unintentionally to the accumulation of copper (Cu), manganese (Mn) and cadmium (Cd). Unlike other metal transporters, barley Yellow Stripe 1 (HvYS1) is specific for Fe. We investigated the mechanistic basis of this preference by constitutively expressing HvYS1 in rice under the control of the maize ubiquitin1 promoter and comparing the mobilization and loading of different metals. Plants expressing HvYS1 showed modest increases in Fe uptake, root‐to‐shoot translocation, seed accumulation and endosperm loading, but without any change in the uptake and root‐to‐shoot translocation of Zn, Mn or Cu, confirming the selective transport of Fe. The concentrations of Zn and Mn in the endosperm did not differ significantly between the wild‐type and HvYS1 lines, but the transgenic endosperm contained significantly lower concentrations of Cu. Furthermore, the transgenic lines showed a significantly reduced Cd uptake, root‐to‐shoot translocation and accumulation in the seeds. The underlying mechanism of metal uptake and translocation reflects the down‐regulation of promiscuous endogenous metal transporters revealing an internal feedback mechanism that limits seed loading with Fe. This promotes the preferential mobilization and loading of Fe, therefore displacing Cu and Cd in the seed.
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