Transcriptome analysis of germinating maize kernels exposed to smoke-water and the active compound KAR1

Plant-derived smoke water and karrikinolide (KAR1) enhance physiological activities, essential oil yield and bioactive constituents of Mentha arvensis L

Introduction

The current study was carried out with the hypothesis that foliar application of plant-derived smoke water (PDSW) and karrikinolide (KAR₁) might enhanced the plant growth, physiology, and essential oil production of the Mentha arvensis L. Karrikinolide (KAR₁) is one of the most important bioactive constituents of PDSW.

Methods

Mint (Mentha arvensis L.) was grown in natural conditions in the net-house. Different concentrations of PDSW (1:125, 1:250, 1:500 and 1:1000 v/v) and KAR₁ (10^-9 M, 10^-8 M, 10^-7 M and 10^-6 M) were used as foliar-spray treatments, using double-distilled water as control. The PDSW was prepared by burning the dried wheat-straw that acted as a growth-promoting substance.

Results

Foliar-spray treatment 1:500 v/v of PDSW and 10^-8 M of KAR₁ proved optimal for enhancing all morphological, physiological, and essential-oil yield related parameters. In comparison with the control, 1:500 v/v of PDSW and 10^-8 M of KAR₁ increased significantly (p ≤ 0.05) the height of mint plant (19.23% and 16.47%), fresh weight (19.30% and 17.44%), dry weight (35.36% and 24.75%), leaf area (18.22% and 17.46%), and leaf yield per plant (28.41% and 23.74%). In addition, these treatments also significantly increased the photosynthetic parameters, including chlorophyll fluorescence (12.10% and 11.41%), total chlorophyll content (25.70% and 20.77%), and total carotenoid content (29.77% and 27.18%). Likewise, 1:500 v/v of PDSW and 10^-8 M of KAR₁ significantly increased the essential-oil content (37.09% and 32.25%), essential oil productivity per plant (72.22% and 66.66%), menthol content (29.94% and 25.42%), menthyl acetate content (36.90% and 31.73%), and menthone content (44.38% and 37.75%). Furthermore, the TIC chromatogram of the GCMS analysis revealed the presence of 34 compounds, 12 of which showed major peak areas.

Discussion

Treatment 1: 500 v/v of PDSW proved better than the treatment 10^-8 M of KAR₁ with regard to most of the parameters studied. The outcome of the study can be used as a recommendation tool for agricultural and horticultural crops, since it costs much lesser than that of KAR₁. In fact, the foliar application of PDSW proved economical and played bioactive role at very low concentrations.

Smoke promotes germination of peatland bryophyte spores

Northern peatlands are globally important carbon stores. With increasing fire frequency, the re-establishment of bryophytes becomes crucial for their carbon sequestration. Smoke-responsive germination is a common trait of seeds in fire-prone ecosystems but has not been demonstrated in bryophytes. To investigate the potential role of smoke in post-fire peatland recovery, we tested the germination of spores of 15 bryophyte species after treatment with smoke-water. The smoke responsiveness of spores with different laboratory storage times and burial depths/age (3-200 years) was subsequently tested. Smoke increased the germination percentage for 10 of the species and the germination speed for four of these. Smoke responsiveness increased along the fire frequency gradient from open expanse to forest margin, consistent with the theory that this selects for the maintenance of fire-adapted traits. Smoke enhanced the germinability of 1-year but not 4-year laboratory-stored spores, and considerably increased the germinability of spores naturally buried in peat for up to ~200 years. The effect of fire may be overlooked in non-fire-prone ecosystems, such as those in which wetland bryophytes dominate. Our study reveals a mechanism by which an increase in fire frequency may lead to shifts in species dominance, which may affect long-term carbon sequestration in peatlands.

Mechanism for enhancing the growth of mung bean seedlings under simulated microgravity

To elucidate a mechanism for enhancing mung bean seedlings’ growth under microgravity conditions, we measured growth, gene expression, and enzyme activity under clinorotation (20 rpm), and compared data obtained to those grown under normal gravity conditions (control). An increase in fresh weight, water content, and lengths were observed in the clinostat seedlings, compared to those of the control seedlings. Real-time PCR showed that aquaporin expression and the amylase gene were upregulated under clinorotation. Additionally, seedlings under clinorotation exhibited a significantly higher amylase activity. Near-infrared image showed that there was no restriction of water evaporation from the seedlings under clinorotation. Therefore, these results indicate that simulated microgravity could induce water uptake, resulting in enhanced amylase activity and seedling growth. Upregulated aquaporin expression could be the first trigger for enhanced growth under clinorotation. We speculated that the seedlings under clinorotation do not use energy against gravitational force and consumed surplus energy for enhanced growth.

Transcriptome profiling unveils the mechanism of phenylpropane biosynthesis in rhizome development of Caucasian clover

Caucasian clover is the only perennial herb of the genus Leguminous clover with underground rhizomes. However, we know very little about its development process and mechanism. Transcriptome studies were conducted on the roots of Caucasian clover without a rhizome (NR) at the young seedling stage and the fully developed rhizome, including the root neck (R1), main root (R2), horizontal root (R3), and rhizome bud (R4), of the tissues in the mature phase. Compared with the rhizome in the mature phase, NR had 893 upregulated differentially expressed genes (DEGs), most of which were enriched in 'phenylpropanoid biosynthesis', 'phenylalanine metabolism', 'DNA replication' and 'biosynthesis of amino acids'. A higher number of transcription factors (AP2/ERF, C2H2 and FAR1) were found in NR. There were highly expressed genes for R4, such as auxin response factor SAUR, galacturonosyltransferase (GAUT), and sucrose synthase (SUS). Phenylpropanoids are very important for the entire process of rhizome development. We drew a cluster heat map of genes related to the phenylpropanoid biosynthesis pathway, in which the largest number of genes belonged to COMT, and most of them were upregulated in R4.

Bioassays for the Effects of Strigolactones and Other Small Molecules on Root and Root Hair Development

Growth and development of plant roots are highly dynamic and adaptable to environmental conditions. They are under the control of several plant hormone signaling pathways, and therefore root developmental responses can be used as bioassays to study the action of plant hormones and other small molecules. In this chapter, we present different procedures to measure root traits of the model plant Arabidopsis thaliana. We explain methods for phenotypic analysis of lateral root development, primary root length, root skewing and straightness, and root hair density and length. We describe optimal growth conditions for Arabidopsis seedlings for reproducible root and root hair developmental outputs; and how to acquire images and measure the different traits using image analysis with relatively low-tech equipment. We provide guidelines for a semiautomatic image analysis of primary root length, root skewing, and root straightness in Fiji and a script to automate the calculation of root angle deviation from the vertical and root straightness. By including mutants defective in strigolactone (SL) or KAI2 ligand (KL) synthesis and/or signaling, these methods can be used as bioassays for different SLs or SL-like molecules. In addition, the techniques described here can be used for studying seedling root system architecture, root skewing, and root hair development in any context.

Plant-Derived Smoke Affects Biochemical Mechanism on Plant Growth and Seed Germination

The role of plant-derived smoke, which is changed in mineral-nutrient status, in enhancing germination and post-germination was effectively established. The majority of plant species positively respond to plant-derived smoke in the enhancement of seed germination and plant growth. The stimulatory effect of plant-derived smoke on normally growing and stressed plants may help to reduce economic and human resources, which validates its candidature as a biostimulant. Plant-derived smoke potentially facilitates the early harvest and increases crop productivity. Karrikins and cyanohydrin are the active compound in plant-derived smoke. In this review, data from the latest research explaining the effect of plant-derived smoke on morphological, physiological, biochemical, and molecular responses of plants are presented. The pathway for reception and interaction of compounds of plant-derived smoke at the cellular and molecular level of plant is described and discussed.

Plant-derived smoke enhances plant growth through ornithine-synthesis pathway and ubiquitin-proteasome pathway in soybean

To investigate the mechanism of promotive effect of plant-derived smoke on the soybean growth, a gel-free/label-free proteomics was performed. Smoke solutions were irrigated on soybean or supplied simultaneously with flooding stress. Morphological and physiological analyses were performed for the confirmation of proteomic result. Metabolomic change was investigated to correlate proteomic change with metabolism regulation. Under normal condition, the length of root including hypocotyl increased in soybean treated with 2000 ppm plant-derived smoke within 4 days, as well as nitric oxide content. Proteins related to protein synthesis especially arginine metabolism were altered; metabolites related to amino acid, carboxylic acids, and sugars were mostly altered. Integrated analysis of omics data indicated that plant-derived smoke regulated nitrogen‑carbon transformation through ornithine synthesis pathway and promoted soybean normal growth. Under flooding, the number of lateral roots increased with root tip degradation in soybean treated with smoke solutions. Proteins related to ubiquitin-proteasome pathway were altered and led to sacrifice-for-survival-mechanism-driven degradation of root tip in soybean, which enabled accumulation of metabolites and guaranteed lateral root development during soybean recovery after flooding. These findings suggest that plant-derived smoke improves early stage of growth in soybean with regulation of ornithine-synthesis pathway and ubiquitin-proteasome pathway. BIOLOGICAL SIGNIFICANCE: Plant-derived smoke plays a key role in crop growth, however, the understanding of soybean in response to smoke treatment remains premature. Therefore, gel-free/label-free proteomic analysis was used for comprehensive study on the dual effect of smoke to soybean under normal and flooding conditions. Under normal condition, plant-derived smoke regulated nitrogen‑carbon transformation through ornithine synthesis pathway and resulted in the increase of the length of root including hypocotyl in soybean within 4 days. Under flooding condition, plant-derived smoke induced inhibition of ubiquitin-proteasome pathway and led to sacrifice-for-survival-mechanism-driven degradation of root tip in soybean, which enabled accumulation of metabolites and promoted lateral root development during soybean recovery after flooding.

Melatonin Priming Alleviates Aging-Induced Germination Inhibition by Regulating β-oxidation, Protein Translation, and Antioxidant Metabolism in Oat (Avena sativa L.) Seeds

Although melatonin has been reported to play an important role in regulating metabolic events under adverse stresses, its underlying mechanisms on germination in aged seeds remain unclear. This study was conducted to investigate the effect of melatonin priming (MP) on embryos of aged oat seeds in relation to germination, ultrastructural changes, antioxidant responses, and protein profiles. Proteomic analysis revealed, in total, 402 differentially expressed proteins (DEPs) in normal, aged, and aged + MP embryos. The downregulated DEPs in aged embryos were enriched in sucrose metabolism, glycolysis, β-oxidation of lipid, and protein synthesis. MP (200 μM) turned four downregulated DEPs into upregulated DEPs, among which, especially 3-ketoacyl-CoA thiolase-like protein (KATLP) involved in the β-oxidation pathway played a key role in maintaining TCA cycle stability and providing more energy for protein translation. Furthermore, it was found that MP enhanced antioxidant capacity in the ascorbate-glutathione (AsA-GSH) system, declined reactive oxygen species (ROS), and improved cell ultrastructure. These results indicated that the impaired germination and seedling growth of aged seeds could be rescued to a certain level by melatonin, predominantly depending on β-oxidation, protein translation, and antioxidant protection of AsA-GSH. This work reveals new insights into melatonin-mediated mechanisms from protein profiles that occur in embryos of oat seeds processed by both aging and priming.

Potential of Smoke-Water and One of Its Active Compounds (karrikinolide, KAR1) on the Phytochemical and Antioxidant Activity of Eucomis autumnalis

Eucomis autumnalis (Mill.) Chitt. subspecies autumnalis is a popular African plant that is susceptible to population decline because the bulbs are widely utilized for diverse medicinal purposes. As a result, approaches to ensure the sustainability of the plants are essential. In the current study, the influence of smoke-water (SW) and karrikinolide (KAR₁ isolated from SW extract) on the phytochemicals and antioxidant activity of in vitro and greenhouse-acclimatized Eucomis autumnalis subspecies autumnalis were evaluated. Leaf explants were cultured on Murashige and Skoog (MS) media supplemented with SW (1:500, 1:1000 and 1:1500 v/v dilutions) or KAR₁ (10⁻⁷, 10⁻⁸ and 10⁻⁹ M) and grown for ten weeks. In vitro regenerants were subsequently acclimatized in the greenhouse for four months. Bioactive phytochemicals in different treatments were analyzed using ultra-high performance liquid chromatography (UHPLC-MS/MS), while antioxidant potential was evaluated using two chemical tests namely: DPPH and the β-carotene model. Smoke-water and KAR₁ generally influenced the quantity and types of phytochemicals in in vitro regenerants and acclimatized plants. In addition to eucomic acid, 15 phenolic acids and flavonoids were quantified; however, some were specific to either the in vitro regenerants or greenhouse-acclimatized plants. The majority of the phenolic acids and flavonoids were generally higher in in vitro regenerants than in acclimatized plants. Evidence from the chemical tests indicated an increase in antioxidant activity of SW and KAR₁-treated regenerants and acclimatized plants. Overall, these findings unravel the value of SW and KAR₁ as potential elicitors for bioactive phytochemicals with therapeutic activity in plants facilitated via in vitro culture systems. In addition, it affords an efficient means to ensure the sustainability of the investigated plant. Nevertheless, further studies focusing on the use of other types of antioxidant test systems (including in vivo model) and the carry-over effect of the application of SW and KAR₁ for a longer duration will be pertinent. In addition, the safety of the resultant plant extracts and their pharmacological efficacy in clinical relevance systems is required.

Fire-Borne Life: A Brief Review of Smoke-Induced Germination

Naturally occurring fires have been shaping landscapes long before mankind existed. Presumably, it is an early observation that in some habitats, fire is crucial to maintaining species diversity and for the rejuvenation of the vegetation, and so early settled farmers might have started to take advantage of the controlled burning of a desired area. The heat of fire is essential to break the dormancy of many fire ephemerals and for the seed release of some serotinous or woody taxa. Besides the physical effects caused by the heat on seeds, smoke and burnt organic material contain chemical cues that regulate the germination of seeds and the early development of seedlings. The scientific community really started to reveal the secrets of these enigmatic components from the early 1990s, although there are still a number of questions to be answered. In this review, we briefly introduce the path which leads to our current knowledge on smoke-derived compounds and their enormous effects on plant life.

SMAX1/SMXL2 regulate root and root hair development downstream of KAI2-mediated signalling in Arabidopsis

Karrikins are smoke-derived compounds presumed to mimic endogenous signalling molecules (KAI2-ligand, KL), whose signalling pathway is closely related to that of strigolactones (SLs), important regulators of plant development. Both karrikins/KLs and SLs are perceived by closely related α/β hydrolase receptors (KAI2 and D14 respectively), and signalling through both receptors requires the F-box protein MAX2. Furthermore, both pathways trigger proteasome-mediated degradation of related SMAX1-LIKE (SMXL) proteins, to influence development. It has previously been suggested in multiple studies that SLs are important regulators of root and root hair development in Arabidopsis, but these conclusions are based on phenotypes observed in the non-specific max2 mutants and by use of racemic-GR24, a mixture of stereoisomers that activates both D14 and KAI2 signalling pathways. Here, we demonstrate that the majority of the effects on Arabidopsis root development previously attributed to SL signalling are actually mediated by the KAI2 signalling pathway. Using mutants defective in SL or KL synthesis and/or perception, we show that KAI2-mediated signalling alone regulates root hair density and root hair length as well as root skewing, straightness and diameter, while both KAI2 and D14 pathways regulate lateral root density and epidermal cell length. We test the key hypothesis that KAI2 signals by a non-canonical receptor-target mechanism in the context of root development. Our results provide no evidence for this, and we instead show that all effects of KAI2 in the root can be explained by canonical SMAX1/SMXL2 activity. However, we do find evidence for non-canonical GR24 ligand-receptor interactions in D14/KAI2-mediated root hair development. Overall, our results demonstrate that the KAI2 signalling pathway is an important new regulator of root hair and root development in Arabidopsis and lay an important basis for research into a molecular understanding of how very similar and partially overlapping hormone signalling pathways regulate different phenotypic outputs.

Smoke-Isolated Karrikins Stimulated Tanshinones Biosynthesis in Salvia miltiorrhiza through Endogenous Nitric Oxide and Jasmonic Acid

Although smoke-isolated karrikins (KAR₁) could regulate secondary metabolism in medicinal plants, the signal transduction mechanism has not been reported. This study highlights the influence of KAR₁ on tanshinone I (T-I) production in Salvia miltiorrhiza and the involved signal molecules. Results showed KAR₁-induced generation of nitric oxide (NO), jasmonic acid (JA) and T-I in S. miltiorrhiza hairy root. KAR₁-induced increase of T-I was suppressed by NO-specific scavenger (cPTIO) and NOS inhibitors (PBITU); JA synthesis inhibitor (SHAM) and JA synthesis inhibitor (PrGall), which indicated that NO and JA play essential roles in KAR₁-induced T-I. NO inhibitors inhibited KAR₁-induced generation of NO and JA, suggesting NO was located upstream of JA signal pathway. NO-induced T-I production was inhibited by SHAM and PrGall, implying JA participated in transmitting signal NO to T-I accumulation. In other words, NO mediated the KAR₁-induced T-I production through a JA-dependent signaling pathway. The results helped us understand the signal transduction mechanism involved in KAR₁-induced T-I production and provided helpful information for the production of S. miltiorrhiza hairy root.

NMR-based metabolomics reveals that plant-derived smoke stimulates root growth via affecting carbohydrate and energy metabolism in maize

INTRODUCTION

It is well known that plant-derived smoke stimulates seed germination and seedling growth in many plants. Although a number of transcriptomics and proteomics studies have been carried out to understand the mode of action of smoke, less is known about the biochemical alterations associated with smoke exposure in plants.

OBJECTIVES

The aims of this study were (1) to determine the metabolic alterations in maize roots pre-treated with various concentrations of smoke solution, and (2) to identify the smoke-responsive metabolic pathways during early root growth period.

METHODS

Maize seeds were pre-treated with different concentrations of smoke solutions for 24 h and then grown for 10 days. 600-MHz ¹H NMR spectroscopy was performed on the aqueous root extracts of maize seedlings. The metabolite data obtained from the NMR spectra were analyzed by several statistical and functional methods, including one-way ANOVA, PCA, PLS-DA and pathway analysis.

RESULTS

Our study identified a total of 29 metabolites belonging to various chemical groups. Concentrations of 20 out of these 29 metabolites displayed significant (p < 0.05) changes after at least one smoke pre-treatment compared to the control. Moreover, functional analyses revealed that smoke pre-treatments markedly affected the carbohydrate- and energy-related metabolic pathways, such as galactose metabolism, glycolysis, glyoxylate metabolism, tricarboxylic acid cycle, and starch/sucrose metabolism.

CONCLUSIONS

To our knowledge, this is the first study that investigates smoke-induced biochemical alterations in early root growth period using NMR spectroscopy. Our findings clearly indicate that smoke either directly or indirectly influences many metabolic processes in maize roots.

Long-Term Effects of Cold on Growth, Development and Yield of Narrow-Leaf Lupine May Be Alleviated by Seed Hydropriming or Butenolide

In this article, the effects of cold on the development of Lupine angustifolius and the possibility of mitigating it, via seed hydropriming or pre-treatment with butenolide (10-6 M⁻10-4 M), are investigated in two cultivars, differing in their ability to germinate at low temperature. Physiological background of plant development after cold stress was investigated in imbibed seeds. For the first four weeks, the seedlings grew at 7 °C or 13 °C. Seeds well germinating at 7 °C demonstrated higher activity of α-amylase and higher levels of gibberellins, IAA and kinetin. Germination ability at low temperature correlated with dehydrogenase activity and membrane permeability. Seed pre-treatment improved germination at low temperature by decreasing abscisic acid content. Seed hydropriming alleviated cold effects on plant development rate and yield, while butenolide accelerated vegetative development but delayed the generative phase. Potential seed yield may be predicted based on the seed germination vigour and the photosynthetic efficiency measured before flowering.

Seed Hydropriming and Smoke Water Significantly Improve Low-Temperature Germination of Lupinus angustifolius L

Seed imbibition under cold temperature is dangerous when dry seeds have relatively low water content. The aim of this study was to investigate germination of 20 lines/cultivars of narrow-leaf lupine at 7 °C (cold) and 13 °C (control) under the influence of smoke water and following seed hydropriming for 3 h at 20 °C. The efficacy of individual treatments was examined with regard to seed protection during low-temperature germination. Based on seed germination, vigour at cold was evaluated four days after sowing by means of hypocotyl length, the studied lines/cultivars were divided into three groups with low, high and very high germination rates. Germination vigour correlated with cell membrane permeability, dehydrogenase activity and abscisic acid (ABA) content and was analysed in the seeds one day after sowing. Gibberellin content did not correlate with germination vigour. The seeds of weakly germinating lines/cultivars had the highest cell permeability and ABA content as well as the lowest amylolytic activity at both studied temperatures. Additionally, the vigour of weakly germinating seeds at 7 °C correlated with dehydrogenase activity. Three-hour hydropriming was the most effective for seed germination under cold due to reduced cell membrane permeability and ABA level. Stimulating effects of smoke water on germination under cold could be explained by enhanced dehydrogenase activity.

Proteomic analysis of the promotive effect of plant-derived smoke on plant growth of chickpea

Plant-derived smoke plays a key role in seed germination and plant growth. To investigate the effect of plant-derived smoke on chickpea, a gel-free/label-free proteomic technique was used. Germination percentage, root/shoot length, and fresh biomass were increased in chickpea treated with 2000 ppm plant-derived smoke within 6 days. On treatment with 2000 ppm plant-derived smoke for 6 days, the abundance of 90 proteins including glycolysis-related proteins significantly changed in chickpea root. Proteins related to signaling and transport were increased; however, protein metabolism, cell, and cell wall were decreased. The sucrose synthase for starch degradation was increased and total soluble sugar was induced. The proteins for nitrate pathway were increased and nitrate content was improved. On the other hand, although secondary metabolism related proteins were decreased, flavonoid contents were increased. Based on proteomic and immuno-blot analyses, proteins related to redox homeostasis were decreased and increased in root and shoot, respectively. Furthermore, fructose‑bisphosphate aldolase was increased; while, phosphotransferase and phosphoglycero mutase were decreased in glycolysis. In addition, phosphoglyceraldehyde‑3‑phosphate dehydrogenase and glutamine synthetase related genes were up-regulated. These results suggest that plant-derived smoke improves early stage of growth in chickpea with the balance of many cascades such as glycolysis, redox homeostasis, and secondary metabolism.

BIOLOGICAL SIGNIFICANCE

The current study examined the effects of plant-derived smoke on root of chickpea seedlings using a gel-free/label-free proteomic technique. Based on functional categorization of results from proteomics, proteins related to glycolysis, signaling, transport, protein metabolism, cell wall, and cell were predominantly changed in chickpea. The proteins related to carbohydrate and nitrate pathways were increased, while, those of secondary metabolism were decreased. Physiological analysis indicated that flavonoid, total soluble sugar, and nitrate content were increased in root of chickpea treated with plant-derived smoke for 6 days. Moreover, accumulated protein abundance of glyceraldehyde‑3‑phosphate dehydrogenase and fructose-bisphosphate aldolase was in agreement with immuno-blot results, which suggests that glycolysis process might be enhanced in root of chickpea in response to plant-derived smoke.

Polyamines may influence phytochelatin synthesis during Cd stress in rice

Although the metabolism of phytochelatins and higher polyamines are linked with each other, the direct relationship between them under heavy metal stress has not yet been clarified. Two approaches were used to reveal the influence of polyamine content on cadmium stress responses, particularly with regard to phytochelatin synthesis: putrescine pre-treatment of rice plants followed by cadmium stress, and treatment with the putrescine synthesis inhibitor, 2-(difluoromethyl)ornithine combined with cadmium treatment. The results indicated that putrescine pre-treatment enhanced the adverse effect of cadmium, while the application of 2-(difluoromethyl)ornithine reduced it to a certain extent. These differences were associated with increased polyamine content, more intensive polyamine metabolism, but decreased thiol and phytochelatin contents. The gene expression level and enzyme activity of phytochelatin synthase also decreased in rice treated with putrescine prior to cadmium stress, compared to cadmium treatment alone. In contrast, the inhibition of putrescine synthesis during cadmium treatment resulted in higher gene expression level of phytochelatin synthase. The results suggest that polyamines may have a substantial influence on phytochelatin synthesis at several levels under cadmium stress in rice.

Hydroquinone; A Novel Bioactive Compound from Plant-Derived Smoke Can Cue Seed Germination of Lettuce

Plant-derived smoke has been known to play an important role in distribution and growth of vegetation. Using a proficiently designed furnace, we extracted smoke from the leaves of four plant viz. Helianthus annuus,Aloe vera,Ginkgo biloba, and Cymbopogon jwarancusa. Smoke dilutions obtained from these plants were obtained in different concentrations to identify potential lettuce growth promoting smoke solution. Results revealed that smoke obtained from G. biloba significantly enhanced the lettuce seed germination. This solution was then partitioned into ethyl acetate, dichloromethane, n-hexane, chloroform and ether fractions. Ethyl acetate fraction was found to be potent to enhance seed germination. This fraction was subjected to column chromatography and spectroscopic techniques to obtain compound 1. This compound was identified as hydroquinone using 1D and 2D NMR techniques. At low concentrations (5, 10, and 20 ppm), compound 1 enhanced the lettuce seed germination; however, higher concentrations inhibited its growth as compared to control.

Cytokinin profiles in ex vitro acclimatized Eucomis autumnalis plants pre-treated with smoke-derived karrikinolide

The current evidence of regulatory effect of smoke-water (SW) and karrikinolide (KAR(1)) on the concentrations of endogenous cytokinins in plants partly explain the basis for their growth stimulatory activity. Karrikinolide (KAR1) which is derived from smoke-water (SW) is involved in some physiological aspects in the life-cycle of plants. This suggests a potential influence on the endogenous pool (quantity and quality) of phytohormones such as cytokinins (CKs). In the current study, the effect of SW (1:500; 1:1000; 1:1500 v/v dilutions) and KAR1 (10(-7); 10(-8); 10(-9) M) applied during micropropagation of Eucomis autumnalis subspecies autumnalis on the ex vitro growth and CKs after 4 months post-flask duration was evaluated. The interactions of SW and KAR(1) with benzyladenine (BA), α-naphthaleneacetic acid (NAA) or BA+NAA were also assessed. Plants treated with SW (1:500) and KAR1 (10(-8) M) demonstrated superior growth in terms of the rooting, leaf and bulb sizes and fresh biomass than the control and plants treated with BA and BA+NAA. However, plant growth was generally inhibited with either SW (1:500) or KAR1 (10(-8) M) and BA when compared to BA (alone) treatment. Relative to NAA treatment, the presence of KAR(1) (10(-7) M) with NAA significantly increased the leaf area and fresh biomass. Both SW and KAR1-treated plants accumulated more total CKs, mainly isoprenoid-type than the control and NAA-treated plants. The highest CK content was also accumulated in SW (1:500) with BA+NAA treatments. Similar stimulatory effects were observed with increasing concentrations of KAR(1) and BA. The current findings establish that SW and KAR1 exert significant influence on the endogenous CK pools. However, the better growth of plants treated with SW and KAR1 treatments was not exclusively related to the endogenous CKs.

Integrated RNA-Seq and sRNA-Seq Analysis Identifies Chilling and Freezing Responsive Key Molecular Players and Pathways in Tea Plant (Camellia sinensis)

Tea [Camellia sinensis (L) O. Kuntze, Theaceae] is one of the most popular non-alcoholic beverages worldwide. Cold stress is one of the most severe abiotic stresses that limit tea plants’ growth, survival and geographical distribution. However, the genetic regulatory network and signaling pathways involved in cold stress responses in tea plants remain unearthed. Using RNA-Seq, DGE and sRNA-Seq technologies, we performed an integrative analysis of miRNA and mRNA expression profiling and their regulatory network of tea plants under chilling (4℃) and freezing (-5℃) stress. Differentially expressed (DE) miRNA and mRNA profiles were obtained based on fold change analysis, miRNAs and target mRNAs were found to show both coherent and incoherent relationships in the regulatory network. Furthermore, we compared several key pathways (e.g., ‘Photosynthesis’), GO terms (e.g., ‘response to karrikin’) and transcriptional factors (TFs, e.g., DREB1b/CBF1) which were identified as involved in the early chilling and/or freezing response of tea plants. Intriguingly, we found that karrikins, a new group of plant growth regulators, and β-primeverosidase (BPR), a key enzyme functionally relevant with the formation of tea aroma might play an important role in both early chilling and freezing response of tea plants. Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis further confirmed the results from RNA-Seq and sRNA-Seq analysis. This is the first study to simultaneously profile the expression patterns of both miRNAs and mRNAs on a genome-wide scale to elucidate the molecular mechanisms of early responses of tea plants to cold stress. In addition to gaining a deeper insight into the cold resistant characteristics of tea plants, we provide a good case study to analyse mRNA/miRNA expression and profiling of non-model plant species using next-generation sequencing technology.

Arabidopsis proteome responses to the smoke-derived growth regulator karrikin

Karrikins are butenolide plant growth regulators in smoke from burning plant material that have proven ability to promote germination and seedling photomorphogenesis. However, the molecular mechanisms underlying these processes are unclear. Here we provide the first proteome-wide analysis of early responses to karrikin in plants (Arabidopsis seedlings). Image analysis of two-dimensionally separated proteins, Rubisco-depleted proteomes and phosphoproteomes, together with LC-MS profiling, detected >1900 proteins, 113 of which responded to karrikin treatment. All the differentially abundant proteins (except HSP70-3) are novel karrikin-responders, and most are involved in photosynthesis, carbohydrate metabolism, redox homeostasis, transcription control, proteosynthesis, protein transport and processing, or protein degradation. Our data provide functionally complementary information to previous identifications of karrikin-responsive genes and evidence for a novel karrikin signalling pathway originating in chloroplasts. We present an updated model of karrikin signalling that integrates proteomic data and is supported by growth response observations.

BIOLOGICAL SIGNIFICANCE

Karrikin has shown promising potential in agricultural applications, yet this process is poorly understood at the molecular level. To the best of our knowledge, this is the first survey of early global proteomic responses to karrikin in plants (Arabidopsis seedlings). The combination of label-free LC-MS profiling and 2-DE analyses provided highly sensitive snapshots of protein abundance and quantitative information on proteoform-level changes. These results present evidence of proteasome-independent karrikin signalling pathways and provide novel targets for detailed mechanistic studies using, e.g., mutants and transgenic plants.

Structure-activity relationships of analogs of 3,4,5-trimethylfuran-2(5H)-one with germination inhibitory activities

Smoke-derived butenolide compounds have, in recent years, been shown to be important germination signaling molecules, which also affect seedling growth. The butenolide 3,4,5-trimethylfuran-2(5H)-one was previously isolated from plant-derived smoke and was found to significantly reduce the effect on germination by the highly active promotor karrikinolide (KAR1, 3-methyl-2H-furo[2,3-c]pyran-2-one), another smoke-derived compound. In this study, 11 analogs of 3,4,5-trimethylfuran-2(5H)-one were synthesized and their effect on the germination of light-sensitive 'Grand Rapids' lettuce seeds (Lactua sativa cv. 'Grand Rapids') were evaluated. A concentration series (1mM-1μM) of the analogs were tested alone, or in combination with 0.01μM KAR1. Only two compounds were found to reduce the germination promotory effect of 0.01μM KAR1 in a similar manner as observed with 3,4,5-trimethylfuran-2(5H)-one, with activity ranging from 1mM to 10μM. Four compounds were found to have inhibitory activity at 1mM and 100μM. The retention of activity by some of the analogs may be useful for designing novel compounds with improved activity. Furthermore, understanding the structure-activity relationships of these compounds may be helpful in synthesizing molecular probes that can be used to further investigate the mechanism of action of these compounds in regulating seed germination.

Molecular aspects of the antagonistic interaction of smoke-derived butenolides on the germination process of Grand Rapids lettuce (Lactuca sativa) achenes

Smoke-derived compounds provide a strong chemical signal to seeds in the soil seed bank, allowing them to take advantage of the germination niche created by the occurrence of fire. The germination stimulatory activity of smoke can largely be attributed to karrikinolide (KAR(1) ), while a related compound, trimethylbutenolide (TMB), has been shown to have an inhibitory effect on germination. The aim of this study was to characterize the interaction of these potent fire-generated compounds. Dose-response analysis, leaching tests and a detailed transcriptome study were performed using highly KAR(1) -sensitive lettuce (Lactuca sativa cv 'Grand Rapids') achenes. Dose-response analysis demonstrated that the compounds are not competitors and TMB modulates germination in a concentration-dependent manner. The transcriptome analysis revealed a contrasting expression pattern induced by the compounds. KAR(1) suppressed, while TMB up-regulated ABA, seed maturation and dormancy-related transcripts. The effect of TMB was reversed by leaching the compound, while the KAR(1) effect was only reversible by leaching within the first 2 h of KAR(1) treatment. Our findings suggest that the compounds may act in concert for germination-related signaling. After the occurrence of fire, sufficient rainfall would contribute to post-germination seedling recruitment by reducing the concentration of the inhibitory compound.

Regulation of seed germination and seedling growth by chemical signals from burning vegetation

It is well known that burning of vegetation stimulates new plant growth and landscape regeneration. The discovery that char and smoke from such fires promote seed germination in many species indicates the presence of chemical stimulants. Nitrogen oxides stimulate seed germination, but their importance in post-fire germination has been questioned. Cyanohydrins have been recently identified in aqueous smoke solutions and shown to stimulate germination of some species through the slow release of cyanide. However, the most information is available for karrikins, a family of butenolides related to 3-methyl-2H-furo[2,3-c]pyran-2-one. Karrikins stimulate seed germination and influence seedling growth. They are active in species not normally associated with fire, and in Arabidopsis they require the F-box protein MAX2, which also controls responses to strigolactone hormones. We hypothesize that chemical similarity between karrikins and strigolactones provided the opportunity for plants to employ a common signal transduction pathway to respond to both types of compound, while tailoring specific developmental responses to these distinct environmental signals.