Characterization of strigolactones exuded by Asteraceae plants

Strigolactones (SLs), originally characterized as germination stimulants for root parasitic weeds, are now recognized as hyphal branching factors for symbiotic arbuscular mycorrhizal fungi and as a novel class of plant hormones inhibiting shoot branching. In the present study, SLs in root exudates of 13 Asteraceae plants including crops, a weed, and ornamental plants were characterized. High performance liquid chromatography/tandem mass spectrometry (LC–MS/MS) analyses revealed that all the Asteraceae plants examined exuded known SLs and, except for sunflower (Helianthus annuus), high germination stimulant activities at retention times corresponding to these SLs were confirmed. The two major SLs exuded by these Asteraceae plants were orobanchyl acetate and orobanchol. 5-Deoxystrigol and 7-hydroxyorobanchyl acetate were detected in root exudates from several Asteraceae species examined in this study.     

Study on the extraction, purification and quantification of jasmonic acid, abscisic acid and indole-3-acetic acid in plants

Introduction  – Jasmonic acid (JA), abscisic acid (ABA) and indole‐3‐acetic acid (IAA) are important plant hormones. Plant hormones are difficult to analyse because they occur in small concentrations and other substances in the plant interfere with their detection. Objective  – To develop a new, inexpensive procedure for the rapid extraction and purification of IAA, ABA and JA from various plant species. Methodology  – Samples were prepared by extraction of plant tissues with methanol and ethyl acetate. Then the extracts were further purified and enriched with C₁₈ cartridges. The final extracts were derivatised with diazomethane and then measured by GC‐MS. The results of the new methodology were compared with those of the Creelman and Mullet procedure. Results  – Sequential elution of the assimilates from the C₁₈ cartridges revealed that IAA and ABA eluted in 40% methanol, while JA subsequently eluted in 60% methanol. The new plant hormone extraction and purification procedure produced results that were comparable to those obtained with the Creelman and Mullet's procedure. This new procedure requires only 0.5 g leaf samples to quantify these compounds with high reliability and can simultaneously determine the concentrations of the three plant hormones. Conclusion  – A simple, inexpensive method was developed for determining endogenous IAA, ABA and JA concentrations in plant tissue. Copyright © 2008 John Wiley & Sons, Ltd.     

Tomato strigolactones: A more detailed look

Strigolactones are plant signaling molecules that induce germination of parasitic plant seeds, initiate host plant - arbuscular mycorrhizal fungus symbiosis and act as plant hormones controlling shoot branching and root architecture. To date four unique strigolactones (e.g., orobanchol, didehydroorobanchol isomers 1 and 2 and the aromatic strigolactone solanacol) have been reported in the root exudates and extracts of tomato (Solanum lycopersicum). Here we report on the presence of several additional strigolactones in tomato root exudates and extracts, orobanchyl acetate, two 7-hydroxyorobanchol isomers, 7-oxoorobanchol and two additional didehydroorobanchol isomers and discuss their possible biological relevance.     

Strigolactones activate different hormonal pathways for regulation of root development in response to phosphate growth conditions

Background

Strigolactones (SLs) – a group of plant hormones and their derivatives – have been found to play a role in the regulation of root development, in addition to their role in suppression of lateral shoot branching: they alter root architecture and affect root-hair elongation, and SL signalling is necessary for the root response to low phosphate (Pi) conditions. These effects of SLs have been shown to be associated with differential activation of the auxin and ethylene signalling pathways.

Scope

The present review highlights recent findings on the activity of SLs as regulators of root development, in particular in response to low Pi stress, and discusses the different hormonal networks putatively acting with SLs in the root''s Pi response.

Conclusions

SLs are suggested to be key regulators of the adaptive responses to low Pi in the root by modulating the balance between auxin and ethylene signalling. Consequently, they impact different developmental programmes responsible for the changes in root system architecture under differential Pi supply.     

Quantitative Analysis of Ingenol in Euphorbia species via Validated Isotope Dilution Ultra‐high Performance Liquid Chromatography Tandem Mass Spectrometry

Introduction

Various species of the Euphorbia genus contain diterpene ingenol and ingenol mebutate (ingenol‐3‐angelate), a substance found in the sap of the plant Euphorbia peplus and an inducer of cell death. A gel formulation of the drug has been approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the topical treatment of actinic keratosis.

Objective

To develop a rapid and reliable method for quantification of ingenol in various plant extracts.

Methodology

Methanolic extracts of 38 species of the Euphorbia genus were analysed via ultra‐high performance liquid chromatography with tandem mass spectrometry (UHPLC–MS/MS) after methanolysis and solid‐phase extraction (SPE) purification. The ¹⁸O–labelled ingenol analogue was prepared and used as an internal standard for ingenol content determination and method validation.

Results

The highest ingenol concentration (547 mg/kg of dry weight) was found in the lower leafless stems of E. myrsinites. The screening confirms a substantial amount of ingenol in species studied previously and furthermore, reveals some new promising candidates.

Conclusion

The newly established UHPLC–MS/MS method shows to be an appropriate tool for screening of the Euphorbia genus for ingenol content and allows selection of species suitable for raw material production and/or in vitro culture initiation. Copyright © 2017 John Wiley & Sons, Ltd.     

Expression of <Emphasis Type="Italic">MAX2</Emphasis> under <Emphasis Type="Italic">SCARECROW</Emphasis> promoter enhances the strigolactone/MAX2 dependent response of <Emphasis Type="Italic">Arabidopsis</Emphasis> roots to low-phosphate conditions

Main conclusion

MAX2/strigolactone signaling in the endodermis and/or quiescent center of the root is partiallysufficient to exert changes in F-actin density and cellular trafficking in the root epidermis, and alter gene expression during plant response to low Pi conditions.Strigolactones (SLs) are a new group of plant hormones that regulate different developmental processes in the plant via MAX2, an F-box protein that interacts with their receptor. SLs and MAX2 are necessary for the marked increase in root-hair (RH) density in seedlings under conditions of phosphate (Pi) deprivation. This marked elevation was associated with an active reduction in actin-filament density and endosomal movement in root epidermal cells. Also, expression of MAX2 under the SCARECROW (SCR) promoter was sufficient to confer SL sensitivity in roots, suggesting that SL signaling pathways act through a root-specific, yet non-cell-autonomous regulatory mode of action. Here we show evidence for a non-cell autonomous signaling of SL/MAX2, originating from the root endodermis, and necessary for seedling response to conditions of Pi deprivation. SCR-derived expression of MAX2 in max2-1 mutant background promoted the root low Pi response, whereas supplementation of the synthetic SL GR24 to these SCR:MAX2 expressing lines further enhanced this response. Moreover, the SCR:MAX2 expression led to changes in actin density and endosome movement in epidermal cells and in TIR1 and PHO2 gene expression. These results demonstrate that MAX2 signaling in the endodermis and/or quiescent center is partially sufficient to exert changes in F-actin density and cellular trafficking in the epidermis, and alter gene expression under low Pi conditions.

     

Optimised separation procedures for the simultaneous assay of three plant hormones in liquid biofertilisers

Introduction – The overuse of petrochemical‐based synthetic fertilisers has caused detrimental effects to soil, water supplies, foods and animal health. This, in addition to increased awareness of organic farming, has generated considerable interest in the evaluation of renewable biofertilisers. Objective – The three objectives of the current research were: (1) to evaluate and optimise a solid phase extraction procedure for extraction of three plant hormones, IAA, GA₃ and ABA from two model biofertilisers produced from coconut shells and pineapple peels; (2) to develop an HPLC analysis procedure for the simultaneous separation and quantification of three plant hormones (IAA, GA₃ and ABA); and (3) to evaluate the changes in three plant hormones levels at four different fermentation time periods and varying number of general bacteria, lactic acid bacteria and yeast. Result – An optimised procedure for sample preparation, separation and simultaneous analysis of three plant hormones [indole‐3‐acetic acid (IAA), gibberellic acid (GA₃) and abscisic acid (ABA)] produced in liquid biofertilisers was developed. This method involves sample cleanup using a Sep‐pack Oasis^®MAX cartridge containing mixed‐mode anion‐exchange and reverse‐phase sorbents that provided optimum recovery of 85.6, 91.9 and 94.3%, respectively, for the three hormones, IAA, GA₃, and ABA. Baseline separation of three hormones was achieved using mobile phase consisting of 1% acetic acid and acetonitrile (75:25, v/v) at pH 4.0. The amounts of hormones produced in liquid biofertilisers were influenced by fruit types, fermentation time and total number of general bacteria, lactic acid bacteria and yeasts. The quantities of three plant hormones produced during fermentation correlated well with the total number of microorganisms present in the liquid biofertilisers. Conclusion – A simple and rapid sample preparation procedure followed by RP‐HPLC with UV detection was optimised and developed for simultaneous quantification and identification of three plant hormones namely, IAA, GA₃ and ABA in the liquid biofertilisers. This procedure allows quantification of the three plant hormones in their natural states without any prior derivatisation step. The results presented illustrate that the contents of the three plant hormones depended on the type of fruit wastes, fermentation time and the number of microorganisms found in liquid biofertilisers. This method can be extended to determine the quantity of three hormones in other matrices. This assay procedure will aid in the development of liquid biofertilisers, a valuable alternative fertilisers to promote plant growth. This process will help farmers to reduce production cost and pollution problems. Copyright © 2009 John Wiley & Sons, Ltd.     

Strigolactones: new plant hormones in action

Main conclusion

The key step in the mode of action of strigolactones is the enzymatic detachment of the D-ring. The thus formed hydroxy butenolide induces conformational changes of the receptor pocket which trigger a cascade of reactions in the signal transduction.

Abstract

Strigolactones (SLs) constitute a new class of plant hormones which are of increasing importance in plant science. For the last 60 years, they have been known as germination stimulants for parasitic plants. Recently, several new bio-properties of SLs have been discovered such as the branching factor for arbuscular mycorrhizal fungi, regulation of plant architecture (inhibition of bud outgrowth and of shoot branching) and the response to abiotic factors, etc. To broaden horizons and encourage new ideas for identifying and synthesising new and structurally simple SLs, this review is focused on molecular aspects of this new class of plant hormones. Special attention has been given to structural features, the mode of action of these phytohormones in various biological actions, the design of SL analogs and their applications.

     

The role of strigolactones during plant interactions with the pathogenic fungus <Emphasis Type="Italic">Fusarium</Emphasis><Emphasis Type="Italic">oxysporum</Emphasis>

Main conclusion

Strigolactones (SLs) do not influence spore germination or hyphal growth of Fusarium oxysporum. Mutant studies revealed no role for SLs but a role for ethylene signalling in defence against this pathogen in pea. Strigolactones (SLs) play important roles both inside the plant as a hormone and outside the plant as a rhizosphere signal in interactions with mycorrhizal fungi and parasitic weeds. What is less well understood is any potential role SLs may play in interactions with disease causing microbes such as pathogenic fungi. In this paper we investigate the influence of SLs on the hemibiotrophic pathogen Fusarium oxysporum f.sp. pisi both directly via their effects on fungal growth and inside the plant through the use of a mutant deficient in SL. Given that various stereoisomers of synthetic and naturally occuring SLs can display different biological activities, we used (+)-GR24, (?)-GR24 and the naturally occurring SL, (+)-strigol, as well as a racemic mixture of 5-deoxystrigol. As a positive control, we examined the influence of a plant mutant with altered ethylene signalling, ein2, on disease development. We found no evidence that SLs influence spore germination or hyphal growth of Fusarium oxysporum and that, while ethylene signalling influences pea susceptibility to this pathogen, SLs do not.

     

A Comprehensive Characterisation of Rosemary tea Obtained from Rosmarinus officinalis L. Collected in a sub‐Humid Area of Tunisia

Introduction

Rosemary (Rosmarinus officinalis L.) is an aromatic plant common in Tunisia and it is widely consumed as a tea in traditional cuisine and in folk medicine to treat various illnesses. Currently, most research efforts have been focused on rosemary essential oil, alcoholic and aqueous extracts, however, little is reported on rosemary infusion composition.

Objective

To investigate compounds present in rosemary tea obtained from Rosmarinus officinalis L. collected in a sub‐humid area of Tunisia in order to assess whether the traditional rosemary tea preparation method could be considered as a reference method for rosemary's compounds extraction.

Methodology

Qualitative characterisation of Rosmarinus officinalis tea obtained after rosemary infusion in boiled water was determined by high performance liquid chromatography coupled with electrospray ionisation quadrupole time‐of‐flight mass spectrometry (HPLC‐ESI‐QTOF‐MS). Quantitative analysis relies on high performance liquid chromatography with diode array detector (HPLC‐DAD).

Results

Forty‐nine compounds belonging to six families, namely flavonoids, phenolic acids, phenolic terpenes, jasmonate, phenolic glycosides, and lignans were identified. To the best of the authors' knowledge eucommin A is characterised for the first time in rosemary. Rosmarinic acid (158.13 μg/g dried rosemary) was the main compound followed then by feruloylnepitrin (100.87 μg/g) and luteolin‐3′‐O‐(2″‐O‐acetyl)‐β‐d ‐glucuronide (44.04 μg/g). Among quantified compounds, luteolin‐7‐O‐rutinoside was the compound with the lowest concentration.

Conclusion

The infusion method allows several polyphenols present in rosemary tea to be extracted, therefore it could be a reference method for rosemary's compounds extraction. Moreover, traditional Tunisian Rosmarinus officinalis tea consumption is of interest for its rich phenolic content. Copyright © 2017 John Wiley & Sons, Ltd.     

Quantitative analysis of tetrahydrofolate metabolites from <Emphasis Type="Italic">clostridium autoethanogenum</Emphasis>

Introduction

Quantification of tetrahydrofolates (THFs), important metabolites in the Wood–Ljungdahl pathway (WLP) of acetogens, is challenging given their sensitivity to oxygen.

Objective

To develop a simple anaerobic protocol to enable reliable THFs quantification from bioreactors.

Methods

Anaerobic cultures were mixed with anaerobic acetonitrile for extraction. Targeted LC–MS/MS was used for quantification.

Results

Tetrahydrofolates can only be quantified if sampled anaerobically. THF levels showed a strong correlation to acetyl-CoA, the end product of the WLP.

Conclusion

Our method is useful for relative quantification of THFs across different growth conditions. Absolute quantification of THFs requires the use of labelled standards.

     

Strigolactones are regulators of root development

Strigolactones (SLs) have been defined as a new group of plant hormones or their derivatives that suppress lateral shoot branching. Recently, a new role for SLs was discovered, in the regulation of root development. Strigolactones were shown to alter root architecture and affect root-hair elongation. Here, I review the recent findings regarding the effects of SLs on root growth and development, and their association with changes in auxin flux. The networking between SLs and other plant hormones that regulate root development is also presented. Strigolactone regulation of plant development suggests that they are coordinators of shoot and root development and mediators of plant responses to environmental conditions.     

Colonization cues of leaf- and root-inhabiting bacterial microbiota of <Emphasis Type="Italic">Atractylodes lancea</Emphasis> derived in vitro and in vivo

Background and aims

Earthworms effect on plant growth is mediated by their dejections or “casts”, a complex mixture of organic matter, minerals and microbes. In casts, different processes such as organic matter mineralization and signal molecule production follow a complex temporal dynamics. An adaptation of root morphology to cast dynamics could allow an efficient nitrogen capture by the plant.

Methods

The plant Brachypodium distachyon was grown in a laboratory experiment with different proportions of casts of increasing ages. Casts were labelled with ¹⁵N to quantify the plant N uptake from the casts. Plant biomass and morphology, especially root system structure, were analysed.

Results

The age of casts had an effect on fine root length, highlighting the importance of the dynamics of cast maturation in root adaptation. Plant biomass production was affected by the interaction between the age and proportion of casts. A positive correlation between the ¹⁵N proportion in plant tissues and plant biomasses indicated that plants were more efficient in foraging N in casts than in the bulk soil.

Conclusions

Our results suggested that both a timely adaptation of the root system structure and a significant proportion of casts are necessary to observe a positive effect of casts on plant growth.

     

Identification of some Bioactive Metabolites in a Fractionated Methanol Extract from Ipomoea aquatica (Aerial Parts) through TLC,HPLC, UPLC‐ESI‐QTOF‐MS and LC‐SPE‐NMR Fingerprints Analyses

Introduction

The plant species Ipomoea aquatica contains various bioactive constituents, e.g. phenols and flavonoids, which have several medical uses. All previous studies were executed in Asia; however, no reports are available from Africa, and the secondary metabolites of this plant species from Africa are still unknown.

Objective

The present study aims finding suitable conditions to identify the bioactive compounds from different fractions.

Methodology

Chromatographic fingerprint profiles of different fractions were developed using high‐performance liquid chromatography (HPLC) and then these conditions were transferred to thin‐layer chromatography (TLC). Subsequently, the chemical structure of some bioactive compounds was elucidated using ultra‐performance liquid chromatography‐quadrupole time of flight‐tandem mass spectrometry (UPLC‐QTOF‐MS) and liquid chromatography‐solid phase extraction‐nuclear magnetic resonance (LC‐SPE‐NMR) spectroscopy.

Results

The HPLC fingerprints, developed on two coupled Chromolith RP‐18e columns, using a gradient mobile phase (methanol/water/trifluoroacetic acid, 5:95:0.05, v/v/v), showed more peaks than the TLC profile. The TLC fingerprint allows the identification of the types of chemical constituents, e.g. flavonoids. Two flavonoids (nicotiflorin and ramnazin‐3‐O‐rutinoside) and two phenolic compounds (dihydroxybenzoic acid pentoside and di‐pentoside) were tentatively identified by QTOF‐MS, while NMR confirmed the structure of rutin and nicotiflorin.

Conclusion

The HPLC and TLC results showed that HPLC fingerprints give more and better separated peaks, but TLC helped in determining the class of the active compounds in some fractions. Bioactive constituents were identified as well using MS and NMR analyses. Two flavonoids and two phenolic compounds were tentatively identified in this species for the first time, to the best of our knowledge. Copyright © 2017 John Wiley & Sons, Ltd.     

Quantification of the Pyrrolizidine Alkaloid Jacobine in Crassocephalum crepidioides by Cation Exchange High‐Performance Liquid Chromatography

Introduction

Pyrrolizidine alkaloids (PAs) are secondary plant metabolites with considerable hepatoxic, tumorigenic and genotoxic potential. For separation, reversed phase chromatography is commonly used because of its excellent compatibility with detection by mass spectrometry. However, reversed phase chromatography has a low selectivity for PAs.

Objective

The objective of this work was to investigate the suitability of cation exchange chromatography for separation of PAs and to develop a rapid method for quantification of jacobine in Crassocephalum crepidioides that is suitable for analysis of huge sample numbers as required for mutant screening procedures.

Results

We demonstrate that cation exchange chromatography offers excellent selectivity for PAs allowing their separation from most other plant metabolites. Due to the high selectivity, plant extracts can be directly analysed after simple sample preparation. Detection with UV at 200 nm instead of mass spectrometry can be applied, which makes the method very simple and cost‐effective. The recovery rate of the method exceeded 95%, the intra‐day and inter‐day standard deviations were below 7% and the limit of detection and quantification were 1 mg/kg and 3 mg/kg, respectively.

Conclusion

The developed method is sufficiently sensitive for reproducible detection of jacobine in C. crepidioides. Simple sample preparation and rapid separation allows for quantification of jacobine in plant material in a high‐throughput manner. Thus, the method is suitable for genetic screenings and may be applicable for other plant species, for instance Jacobaea maritima. In addition, our results show that C. crepidioides cannot be considered safe for human consumption. Copyright © 2017 John Wiley & Sons, Ltd.     

Microscale magnetic microparticle‐based immunopurification of cytokinins from Arabidopsis root apex

Cytokinins (CKs) are pivotal plant hormones that have crucial roles in plant growth and development. However, their isolation and quantification are usually challenging because of their extremely low levels in plant tissues (pmol g^?1 fresh weight). We have developed a simple microscale magnetic immunoaffinity‐based method for selective one‐step isolation of CKs from very small amounts of plant tissue (less than 0.1 mg fresh weight). The capacity of the immunosorbent and the effect of the complex plant matrix on the yield of the rapid one‐step purification were tested using a wide range of CK concentrations. The total recovery range of the new microscale isolation procedure was found to be 30–80% depending on individual CKs. Immunoaffinity extraction using group‐specific monoclonal CK antibodies immobilized onto magnetic microparticles was combined with a highly sensitive ultrafast mass spectrometry‐based method with a detection limit close to one attomole. This combined approach allowed metabolic profiling of a wide range of naturally occurring CKs (bases, ribosides and N⁹‐glucosides) in 1.0‐mm sections of the Arabidopsis thaliana root meristematic zone. The magnetic immunoaffinity separation method was shown to be a simple and extremely fast procedure requiring minimal amounts of plant tissue.     

Nitrogen and phosphorus fertilization negatively affects strigolactone production and exudation in sorghum

Strigolactones (SLs) are essential host recognition signals for both root parasitic plants and arbuscular mycorrhizal fungi, and SLs or their metabolites function as a novel class of plant hormones regulating shoot and root architecture. Our previous study indicated that nitrogen (N) deficiency as well as phosphorus (P) deficiency in sorghum enhanced root content and exudation of 5-deoxystrigol, one of the major SLs produced by sorghum. In the present study, we examined how N and P fertilization affects SL production and exudation in sorghum plants subjected to short- (5 days) or long-term (10 days) N or P deficiency and demonstrated their common and distinct features. The root contents and exudation of SLs in the N- or P-deficient sorghum plants grown for 6, 12 or 24 h with or without N or P fertilization were quantified by LC–MS/MS. In general, without fertilization, root contents and exudation of SLs stayed at similar levels at 6 and 12 h and then significantly increased at 24 h. The production of SLs responded more quickly to P fertilization than the secretion of SLs, while regulation of SL secretion began earlier after N fertilization. It is suggested that sorghum plants regulate SL production and exudation when they are subjected to nutrient deficiencies depending on the type of nutrient and degree of deficiency.     

Fabacyl acetate, a germination stimulant for root parasitic plants from Pisum sativum

A germination stimulant, fabacyl acetate, was purified from root exudates of pea (Pisum sativum L.) and its structure was determined as ent-2′-epi-4a,8a-epoxyorobanchyl acetate [(3aR,4R,4aR,8bS,E)-4a,8a-epoxy-8,8-dimethyl-3-(((R)-4-methyl-5-oxo-2,5-dihydrofuran-2-yloxy)methylene)-2-oxo-3,3a,4,5,6,7,8,8b-decahydro-2H-indeno[1,2-b]furan-4-yl acetate], by 1D and 2D NMR spectroscopic, ESI- and EI-MS spectrometric, X-ray crystallographic analyses, and by comparing the ¹H NMR spectroscopic data and relative retention times (RR_t) in LC-MS and GC-MS with those of synthetic standards prepared from (+)-orobanchol and (+)-2′-epiorobanchol. The ¹H NMR spectroscopic data and RR_t of fabacyl acetate were identical with those of an isomer prepared from (+)-2′-epiorobanchol except for the opposite sign in CD spectra. This is the first natural ent-strigolactone containing an epoxide group. Fabacyl acetate was previously detected in root exudates of other Fabaceae plants including faba bean (Vicia faba L.) and alfalfa (Medicago sativa L.).     

Strigolactones as mediators of plant growth responses to environmental conditions

Strigolactones (SLs) have been recently identified as a new group of plant hormones or their derivatives thereof, shown to play a role in plant development. Evolutionary forces have driven the development of mechanisms in plants that allow adaptive adjustments to a variety of different habitats by employing plasticity in shoot and root growth and development. The ability of SLs to regulate both shoot and root development suggests a role in the plant''s response to its growth environment. To play this role, SL pathways need to be responsive to plant growth conditions, and affect plant growth toward increased adaptive adjustment. Here, the effects of SLs on shoot and root development are presented, and possible feedback loops between SLs and two environmental cues, light and nutrient status, are discussed; these might suggest a role for SLs in plants'' adaptive adjustment to growth conditions.Key words: strigolactones, light, nutrient status, root, shoot, branching, lateral roots, root hairsStrigolactones (SLs) are carotenoid-derived terpenoid lactones suggested to stem from the carotenoid pathway¹ via the activity of various oxygenases.^2,3 SLs production has been demonstrated in both monocotyledons and eudicotyledons (reviewed in ref. ⁴), suggesting their presence in many plant species.⁵ SLs are synthesized mainly in the roots and in some parts of the stem and then move towards the shoot apex (reviewed ref. ⁷).^6,8,9SLs were first characterized more than 40 years ago as germination stimulants of the parasitic plants Striga and Orobanche and later, as stimulants of arbuscular mycorrhiza hyphal branching as well (reviewed in ref. ^{4, 10–13}). Recently, SLs or derivatives thereof, have been identified as a new group of plant hormones, shown to play a role in inhibition of shoot branching,^2,3,8,9 thereby affecting shoot architecture; more recently they have also been shown to affect root growth by affecting auxin efflux.¹⁴Plants have developed mechanisms that allow adaptive adjustments to a variety of different habitats by employing plasticity in their growth and development.¹⁵ Shoot architecture is affected by environmental cues, such as light quality and quantity and nutrient status.^16–19 Root-system architecture and development are affected by environmental conditions such as nutrient availability (reviewed in ref. ^{20, 21}). At the same time, plant hormones are known to be involved in the regulation of plant growth, development and architecture (reviewed in ref. ^22–24) and to be mediators of the effects of environmental cues on plant development; one classic example is auxin''s role in the plant''s shade-avoidance response (reviewed in ref. ²⁵).The ability of SLs to regulate shoot and root development suggests that these phytohormones also have a role in the plant''s growth response to its environment. To play this putative role, SL pathways need to be responsive to plant growth conditions, and affect plant growth toward enhancing its adaptive adjustment. The present review examines the SLs'' possible role in adaptive adjustment of the plant''s response to growth conditions, by discussing their effect on plant development and the possible associations and feedback loops between SLs and two environmental cues: light and nutrient status.     

Capacity of biological soil crusts colonized by the lichen <Emphasis Type="Italic">Diploschistes</Emphasis> to metabolize simple phenols

Background and aims

Soil compaction strongly affects water uptake by roots. The aim of the work was to examine soil—plant interactions with focus on the impact of distribution of compacted soil layers on growth and water uptake by wheat roots.

Methods

The growth-chamber experiment was conducted on wheat growth in soil with compacted soil layers. The system for maintaining constant soil water potential and measurement of daily water uptake from variously compacted soil layers was used.

Results

Layered soil compaction differentiated vertical root distribution to higher extent for root length than root mass. The propagation rate of a water extraction front was the highest through layers of moderately compacted soil. The root water uptake rate was on average 67 % higher from moderately than heavily compacted soil layers. Correlations between water uptake and the length of thick roots were increasing with increasing level of soil compaction.

Conclusions

The study shows that root amount, water uptake, propagation of water extraction and shoot growth strongly depend on the existence of compacted layers within soil profile. The negative effects of heavily compacted subsoil layer on water uptake were partly compensated by increased uptake from looser top soil layers and significant contribution of thicker roots in water uptake.