Shoot Responses Research Articles

Cadmium and arsenic provoke mostly distinct but partly overlapping responses in

Among the toxic heavy metal(loid)s, cadmium (Cd) and arsenic (As) have devastating effects on crop productivity and human health. In plants, mechanisms of detoxification of Cd and As proceed via a glutathione (GSH) dependent common pathway, despite their different modes of toxicity. In this context, the present study aimed to investigate how the common detoxification mechanisms for Cd and As influence the physiological and biochemical responses of seedlings of an important plant used for phytoremediation purposes, Brassica juncea, under Cd and As stress. We demonstrated that Cd and As trigger mostly distinct, but partly overlapping, responses in B. juncea. Exposure of B. juncea seedlings to 100 μM Cd stress for 12 days in a hydroponic system led to a significant reduction in the growth of roots and shoots, and in total chlorophyll content. However, As stress caused a decline in root length only. High-performance liquid chromatography analyses revealed a significant increase in cysteine levels in roots and shoots in response to As stress compared with control and Cd-treated plants. Concomitant elevated sulfur content in response to As stress was observed in roots and shoots. In terms of GSH content, Cd and As triggered similar responses, with a significant decrease in GSH in roots, and non-significant changes in shoots, compared with untreated plants. Inductively coupled plasma-atomic emission spectroscopy revealed that under Cd stress, plants preferentially accumulated zinc (Zn) in the roots compared with iron (Fe) and manganese (Mn). Responses in roots under As and Cd stress were similar with respect to Fe accumulation but opposite in terms of Zn and Mn accumulation. Our data provide valuable insights for design of future strategies for sustainable plant growth on As and Cd polluted soils.

An efficient protocol for in vitro regeneration from the nodal explants of Withania coagulans (Stocks) Dunal: a valuable medicinal herb

In order to develop a protocol for the effective micropropagation of the important medicinal plant Withania coagulans (Stocks) Dunal, the effects of different concentrations and combinations of growth regulators on the nodal explants in two independent experiments were investigated. For shooting, a MS medium fortified with different concentrations and combinations of IBA (0.01, 0.1 and 0.5 mg l-1), BA (0.5, 1 and 2 mg l-1), Kin (0.5 and 1 mg l-1), PG (0.5 mg l-1) and GA (0.5 mg l-1) was used and the highest shooting response, shoot number and shoot length were obtained in the MS + IBA (0.01 mg l-1) + BA (0.5 mg l-1) + PG (0.5 mg l-1) + GA (0.5 mg l-1) treatment. In the second experiment, the effect of MS supplemented with different combinations and concentrations of IBA (0.1, 0.5, 1 and 2 mg l-1), NAA (0.1 and 1 mg l-1) and PG (1 mg l-1) on rooting of the nodal explants was investigated, which showed that the highest rooting response (%) was observed in the MS fortified with NAA (0.1 mg l-1), NAA (1 mg l-1), NAA (0.1 mg l-1) + PG (1 mg l-1), and NAA (1 mg l-1) + PG (1 mg l-1) treatments, as well as the highest number of roots at NAA (0.1 mg l-1) and the highest root length at IBA (1 mg l-1). Our findings highlight a complete micropropagation method for W. coagulans from the nodal explant that can make a significant contribution to the development of W. coagulans material for medical applications.

In vitro growth of Sempur (Dillenia philippinensis Rolfe) shoots in response to different types of plants growth regulators supplemented on MS medium

Plant tissue culture of Sempur (Dillenia philippinensis Rolfe) has not been widely reported. The previous study showed that BAP added to Murashige & Skoog (MS) basal medium promoted the growth of D. philippinensis shoot culture. This research aimed to investigate the growth of D. philippinensis shoot tip cultures on MS medium containing three types of cytokinins namely BAP, Kinetin, and 2-iP compared with Gibberelic acid (GA3). The results showed that the type and concentrations of cytokinins significantly affected all growth parameters observed except the number of roots which was only influenced by cytokinin concentrations alone. However, different levels of GA3 did not significantly affect all growth parameters observed. After eight weeks of culture, MS medium containing 1 mg/l 2-iP gave the best response for plant height, (3.68± 0.26 cm). The highest number of leaves (20.33±3.14) and nodes (6.67± 0.21) were found in MS medium containing 0.5 mg/l BAP. While the highest number of roots (1.83±0.17) was found in MS medium without the addition of cytokinins. The range of average values of plant height at different levels of GA3 was 3.08-3.74 cm; the number of leaves was 5.1-7.5; the number of nodes was 3.9-5.4 and the number of roots was 1.0-2.8.

Large variation in waterlogging tolerance and recovery among the three subspecies of Trifolium subterranean L. is related to root and shoot responses

Tolerance to waterlogging and recovery ability was compared among the three subspecies of subterranean clover (Trifolium subterraneum L.) to identify tolerance mechanisms, in order to guide future subclover breeding activities. Three cultivars each of ssp. yanninicum, subterraneum and brachycalycinum were grown in a controlled environment glasshouse with T. michelianum as a waterlogging-tolerant control. After 28 days of growth two treatments were imposed for 35 days: free-draining (control) and waterlogged. A 21-day recovery period followed. After 35 days, waterlogging reduced shoot dry weight (DW) to 58–27% and root DW to 35–21% of respective controls in each subspecies. Shoot relative growth rate (RGR) of yanninicum was least affected (78–104% of control), compared to subterraneum (51–100%) and brachycalycinum (45–69%). The subterraneum cv. Denmark had a similar response to subspecies yanninicum. Shoot RGR of T. michelianum was 138% of its control. After recovery, all traits (except tap root length) recovered to control values. Up to 21 days, the main traits associated with waterlogging tolerance (shoot and root growth) were high petiole length, less petiole anthocyanin pigmentation and high leaf chlorophyll content, but by 35 days these were a high proportion of leaf biomass, high stomatal conductance and enhanced root porosity. Average root diameter and nodulation rates were unrelated to waterlogging tolerance. Subspecies yanninicum had superior waterlogging tolerance. Priority traits for easily-assessed indicators of waterlogging tolerance are less reduction of leaf size and high stomatal conductance.

Acetic-acid-induced jasmonate signaling in root enhances drought avoidance in rice

Conferring drought resistant traits to crops is one of the major aims of current breeding programs in response to global climate changes. We previously showed that exogenous application of acetic acid to roots of various plants could induce increased survivability under subsequent drought stress conditions, but details of the metabolism of exogenously applied acetic acid, and the nature of signals induced by its application, have not been unveiled. In this study, we show that rice rapidly induces jasmonate signaling upon application of acetic acid, resulting in physiological changes similar to those seen under drought. The major metabolite of the exogenously applied acetic acid in xylem sap was determined as glutamine—a common and abundant component of xylem sap—indicating that acetic acid is not the direct agent inducing the observed physiological responses in shoots. Expression of drought-responsive genes in shoot under subsequent drought conditions was attenuated by acetic acid treatment. These data suggest that acetic acid activates root-to-shoot jasmonate signals that partially overlap with those induced by drought, thereby conferring an acclimated state on shoots prior to subsequent drought.

Root and Shoot Response to Nickel in Hyperaccumulator and Non-Hyperaccumulator Species.

The soil–root interface is the micro-ecosystem where roots uptake metals. However, less than 10% of hyperaccumulators’ rhizosphere has been examined. The present study evaluated the root and shoot response to nickel in hyperaccumulator and non-hyperaccumulator species, through the analysis of root surface and biomass and the ecophysiological response of the related aboveground biomass. Ni-hyperaccumulators Alyssoides utriculata (L.) Medik. and Noccaea caerulescens (J. Presl and C. Presl) F.K. Mey. and non-hyperaccumulators Alyssum montanum L. and Thlaspi arvense L. were grown in pot on Ni-spiked soil (0–1000 mg Ni kg−1, total). Development of root surfaces was analysed with ImageJ; fresh and dry root biomass was determined. Photosynthetic efficiency was performed by analysing the fluorescence of chlorophyll a to estimate the plants’ physiological conditions at the end of the treatment. Hyperaccumulators did not show a Ni-dependent decrease in root surfaces and biomass (except Ni 1000 mg kg−1 for N. caerulescens). The non-hyperaccumulator A. montanum suffers metal stress which threatens plant development, while the excluder T. arvense exhibits a positive ecophysiological response to Ni. The analysis of the root system, as a component of the rhizosphere, help to clarify the response to soil nickel and plant development under metal stress for bioremediation purposes.

Magnetic Field Induced Changes in the Shoot and Root Proteome of Barley (Hordeum vulgare L.).

The geomagnetic field (GMF) has been present since the beginning of plant evolution. Recently, some researchers have focused their efforts on employing magnetic fields (MFs) higher than GMF to improve the seed germination, growth, and harvest of agriculturally important crop plants, as the use of MFs is an inexpensive and environment-friendly technique. In this study, we have employed different treatments of MF at 7 mT (milliTesla) at different time points of exposure, including 1, 3, and 6 h. The extended exposure was followed by five consecutive days at 6 h per day in barley seeds. The results showed a positive impact of MF on growth characteristics for 5-day-old seedlings, including seed germination rate, root and shoot length, and biomass weight. Furthermore, ~5 days of delay of flowering in pre-treated plants was also observed. We used a shotgun proteomics approach to identify changes in the protein signatures of root and shoot tissues under MF effects. In total, we have identified 2,896 proteins. Thirty-eight proteins in the shoot and 15 proteins in the root showed significant changes under the MF effect. Proteins involved in primary metabolic pathways were increased in contrast to proteins with a metal ion binding function, proteins that contain iron ions in their structure, and proteins involved in electron transfer chain, which were all decreased significantly in the treated tissues. The upregulated proteins' overall biological processes included carbohydrate metabolic process, oxidation-reduction process, and cell redox homeostasis, while down-regulated processes included translation and protein refolding. In general, shoot response was more affected by MF effect than root tissue, leading to the identification of 41 shoot specific proteins. This study provides an initial insight into the proteome regulation response to MF during barley's seedling stage.

Main Molecular Pathways Associated with Copper Tolerance Response in Imperata cylindrica by de novo Transcriptome Assembly.

The metallophyte Imperata cylindrica inhabits copper (Cu) polluted soils in large areas from Central Chile. Here, we subjected clonal vegetative plantlets to 300 mg Cu kg−1 of substrate for 21 days to identify the main molecular pathways involved in the response to Cu stress. Transcriptomic analyses were performed for shoots and roots, with and without Cu supply. RNA-Seq and de novo transcriptome assembly were performed to identify the gene response associated with molecular mechanisms of Cu tolerance in I. cylindrica. De novo transcriptome revealed a total of 200,521 transcripts (1777 bp) comprising ~91% complete ultra-conserved genes in the eukaryote and Plantae database. The differentially expressed genes (DEGs) in roots were 7386, with 3558 of them being up-regulated and the other 3828 down-regulated. The transcriptome response in shoots was significantly less, showing only 13 up-regulated and 23 down-regulated genes. Interestingly, DEGs mainly related with actin and cytoskeleton formation, and to a minor degree, some DEGs associated with metal transporters and superoxide dismutase activity in root tissues were found. These transcriptomic results suggest that cytoskeleton could be acting as a mechanism of Cu-binding in the root, resulting in a high Cu tolerance response in this metallophyte, which deserve to be analyzed ultra-structurally. Our study contributes to reinforcing the potential of I. cylindrica as a candidate plant species to be used as a phytoremediation agent in Cu-contaminated environments.

A comprehensive study of the proteins involved in salinity stress response in roots and shoots of the FL478 genotype of rice (Oryza sativa L. ssp. indica)

Rice, a major staple, is the most salt-sensitive cereal. High salinity triggers several adaptive responses in rice to cope with osmotic and ionic stress at the physiological, cellular, and molecular levels. A major QTL for salinity tolerance, named Saltol, is present on chromosome 1 of Indian landraces such as Pokkali and Nona Bokra. The early proteomic and physiological responses to salinity in roots and shoots of FL478, an inbred rice line harboring the Saltol QTL, were characterized. Plantlets were cultured in hydroponic cultures with 100 mmol L−1 NaCl and evaluated at 6, 24, and 48 h. At the physiological level, root length significantly increased at 48 h, whereas shoot length was reduced. The Na+/K+ ratio was maintained at lower levels in shoots than in roots, suggesting that roots play a protective role. More than 2000 proteins were detected in both tissues. Roots showed a faster and more coordinated proteomic response than shoots, evident after only 6 h of treatment. These responses showed clear correspondence with those of proteins involved in transcription and translation. Maintenance of mitochondrial activity and amino acid metabolism in roots, and activation of stress-responsive proteins such as dehydrins and PLAT in shoots, may play a key role during the response of the plant to salinity stress. Proteomic and physiological responses showed that roots respond in a more highly adaptive manner than shoots to salinity stress, suggesting that this tissue is critical to the tolerance observed in cultivars harboring Saltol.

Sugarcane Plant Growth and Physiological Responses to Soil Salinity during Tillering and Stalk Elongation

A pot study was conducted to investigate influences of salinity on sugarcane (Saccharum spp.) plant growth, leaf photosynthesis, and other physiological traits during tillering and stalk elongation. Treatments included two commercial sugarcane cultivars (Canal Point (CP) 96-1252 and CP 00-1101) and an Erianthus with five different soil salt concentrations (0 [Control], 38, 75, 150, and 300 mM of NaCl added). Growth (tillers, plant height, and nodes) and physiological (leaf net photosynthetic rate [Pn], stomatal conductance [gs], intercellular CO2 concentration, and leaf water soluble sugar concentrations) characters were determined during the experiment. Responses of sugarcane growth, photosynthesis, and photoassimilate translocation to salinity depended on soil salt concentration. Plant height was the most sensitive while the number of nodes was the most tolerant to soil salinity among the three growth traits measured. CP 96-1252 differed from CP 00-1101 significantly in response of shoot:root ratio to high salt concentration. Leaf Pn of plants treated with the 38 mM salt did not differ from that of the control plant, but plants treated with the 75, 150, and 300 mM salt had 12.7, 18.7, and 35.3% lower leaf Pn, respectively, than the control. The low leaf Pn due to salinity was associated with not only the decrease in gs, but also the non-stomatal factors. Results of leaf sugar composition and concentrations revealed that high salt concentration also depressed photoassimilate translocation from leaves to other plant tissues. These findings are important for better understanding of some physiological mechanisms of salinity influence on sugarcane growth and yields.

Preliminary Investigation on Crop Growth, Physiology, and Yield of Rice under Partial Root-Zone Irrigation

Rice is a staple food predominantly consumed by more than half of the global population. Water deficit is a crucial threat to produce rice globally. Prevailing water-saving techniques for rice can reduce water inputs but are not widely adopted due to the high yield penalty. Partial root-zone irrigation (PRI) is an innovative water-saving technique that allows simultaneous wet and dry areas within the root zone. We hypothesized that optimized PRI improves the water use and reduces the yield penalty of rice. A split root experiment was conducted on rice grown in pots with six defined PRI treatments, that is, PRI1, PRI2, PRI3, PRI4, PRI5, and PRI6. Half of the root system was wetted and alternated between halves with one- (PRI1), two- (PRI2), three- (PRI3), four- (PRI4), five- (PRI5), and six- (PRI6) day intervals. Conventionally irrigated rice plants where the whole root zone of rice was wetted and grown in the nonsplit pot were maintained and considered as control. Control and PRI treatments were irrigated based on 100% potential evapotranspiration demand (ETc). In particular, one PRI treatment (PRI3) showed a remarkable increase in active roots and leaf photosynthesis (PN) by wet and dry cycles within the root zone. Distinctive shoot responses of rice under PRI indicated enriched physiological responses for superior water productivity. The third-day-interval partial root-zone irrigation (PRI3) and conventional irrigation had similar leaf water potential (Ψleaf), while PRI3 had higher grain yield than conventional treatment and higher root surface area that may have compensated for the moderate level of stress in PRI. The finding that PRI scheduled at three-day intervals (PRI3) was superior to conventional irrigation for a single rice plant is promising and needs to be tested and adapted to field conditions.

Sugarcane of Rapid Multiplication by Callogenesis

The results showed that shoot apical meristem of sugarcane has the ability to stimulate and induction to callus in vitro by plant tissue culture. The results showed 2,4-D regulator 1.5 mg/L was more potent in the induction of the callus and callus subsequent growth. The effected interactions of auxin and cytokinin regulators were not significant with respect to the formation of callus. The best regeneration response was achieved by using growth regulators. In Co8371, best induction of the shoot response was found on MS medium with concentration of 1.0 mg/L BAP compared to Co85004. MS medium with the using of 0.5 mg/L BAP and 0.25 mg/L Kinetin regulator exhibited best organogenesis responding.

Molecular Dialog between Root and Shoot via Regulatory Peptides and Its Role in Systemic Control of Plant Development

Plant developmental processes are very flexible and highly depend on environmental factors. This is largely due to the existence of regulatory mechanisms that systemically control development on the whole plant level. In plants, regulatory peptides produced in the roots have been identified that are activated in response to different factors influencing root system, such as variation in the level of macronutrients (first of all, nitrogen and phosphorus) in the soil, influence of symbiotic microorganisms (soil rhizobial bacteria and arbuscular mycorrhiza fungi), and water deficiency. Among the systemically acting peptides, the most thoroughly investigated are CLE (CLAVATA3/EMBRYO SURROUNDING REGION-related) and CEP (C-TERMINALLY ENCODED PEPTIDES) peptides that are capable of travelling through the xylem from the roots to the shoot and triggering responses via binding to specific receptors operating in the phloem of the leaf. This review focuses on the role of these two groups of peptides in molecular dialog between the root and shoot.

LAZY1 Controls Tiller Angle and Shoot Gravitropism by Regulating the Expression of Auxin Transporters and Signaling Factors in Rice.

Tiller angle is a key factor determining rice plant architecture, planting density, light interception, photosynthetic efficiency, disease resistance and grain yield. However, the mechanisms underlying tiller angle control are far from clear. In this study, we identified a mutant, termed bta1-1, with an enlarged tiller angle throughout its life cycle. A detailed analysis reveals that BTA1 has multiple functions because tiller angle, shoot gravitropism and tolerance to drought stress are changed in bta1-1 plants. Moreover, BTA1 is a positive regulator of shoot gravitropism in rice. Shoot responses to gravistimulation are disrupted in bta1-1 under both light and dark conditions. Gene cloning reveals that bta1-1 is a novel mutant allele of LA1 renamed la1-SN. LA1 is able to rescue the tiller angle and shoot gravitropism defects observed in la1-SN. The nuclear localization signal of LA1 is disrupted by la1-SN, causing changes in its subcellular localization. LA1 is required to regulate the expression of auxin transporters and signaling factors that control shoot gravitropism and tiller angle. High-throughput mRNA sequencing is performed to elucidate the molecular and cellular functions of LA1. The results show that LA1 may be involved in the nucleosome and chromatin assembly, and protein-DNA interactions to control gene expression, shoot gravitropism and tiller angle. Our results provide new insight into the mechanisms whereby LA1 controls shoot gravitropism and tiller angle in rice.

A king and vassals' tale: Molecular signatures of clonal integration in Posidonia oceanica under chronic light shortage

Abstract Under unfavourable conditions, clonal plants benefit from physiological integration among ramets, sharing resources and information. Clonal integration can buffer against environmental changes and lets the plant clone work as a ‘macro’ organism. Molecular signals that regulate this phenomenon are completely unknown in marine plants. Here we present a first comprehensive study providing insights into the metabolic role of different types of ramets (i.e. apical vs. vertical) in the foundation species Posidonia oceanica. Plants were exposed to 80% diminishing irradiance level (LL) in a controlled mesocosm system. Subsequent multiscale variations in whole transcriptome expression, global DNA methylation level, photo‐physiology, morphology and fitness‐related traits, were explored at different exposure times. We tested the hypothesis that vertical shoots (the ‘vassals’) can provide vital resources to apical shoots (the ‘kings’) under energy shortage, thus safeguarding the whole clone survival. Whole transcriptome analysis of leaves and shoot‐apical meristems (SAMs) emphasized signatures of molecular integration among ramets, which strongly correlated with higher organization‐level responses. In both shoots types, the exposure to LL resulted in a growth slowdown throughout the experiment, which started from immediate signals in SAMs. In apical shoots, this was linked to an acclimative response, where they were suffering a mild stress condition, while in vertical ones it fell in a more severe stress response. Yet, they suffered from sugar starvation and showed a clear cellular stress response in terms of protein refolding and DNA repair mechanisms. Several epigenetic mechanisms modulated the observed gene‐expression patterns and the cross‐talk between DNA methylation and the cellular energetic status appeared to regulate shoot metabolism under LL. Synthesis. Our results demonstrate a high level of specialization of integrated ramets within seagrass clones and a ‘division of labour’ under adverse conditions. Vertical shoots appear to do ‘most of the job’ especially in terms of resource providing, whereas activated functions in apical shoots were restricted to few important processes, according to an ‘energy‐saving’ strategy. The response of vertical shoots could be seen as a ‘sacrificing response’ allowing the survival of ‘the king’ that is key for ensuring propagation and population maintenance, and for the colonization of new environments.

Effect of commercial plant growth regulator on the growth of dragon fruit (Hyolocereus sp) cuttings under greenhouse condition

Information is limited on the effects of commercial plant growth regulators (PGRs) on dragon fruit. Most studies on rooting effects on dragon fruit cuttings employed very high doses of plant growth regulators (PGRs), which are not deemed practical for greenhouse and field applications. This study was initiated to evaluate the responses of four genotypes of dragon fruit (‘Royal Red’, ‘Moroccan Red’, ‘Mexican White’, and ‘Hawaiian White’) during greenhouse acclimatization to diluted concentrations of commercial PGRs that are readily available in the market. A single factorial experiment on genotype effects on root and shoot responses, without PGR, was conducted. A second experiment with a 4x3x2 completely randomized design, with four genotypes, three diluted commercial PGR formulations and two exposure times as factors was also done. Root length, number of roots, number of days to first shoot emergence and number of new shoots were measured after 50 days of acclimatization in the greenhouse. In the single factorial experiment, only ‘genotype’ had an effect on number of new shoots (P<0.05). In the multifactorial experiment, all factors tested did not have significant interaction effects. However, the main effect of ‘genotype’ on number of new shoots and number of days to first shoot emergence was also significant (P<0.05). The lack of significant effect of other factors and their interactions on most growth responses suggest that it is difficult to resolve differences among the four genotypes using highly diluted commercial PGR formulations after a 50-day observation period. However, our data still suggest that the ‘Red’ genotypes are more superior than the ‘White’ genotypes in terms of shoot growth.

Barley microRNAs as metabolic sensors for soil nitrogen availability

Barley (Hordeum vulgare) is one of the most important crops in the world, ranking 4th in the worldwide production. Crop breeders are facing increasing environmental obstacles in the field, such as drought, salinity but also toxic over fertilization which not only impacts quality of the grain but also an yield. One of the most prevalent mechanisms of gene expression regulation in plants is microRNA-mediated silencing of target genes. We identified 13 barley microRNAs and 2 microRNAs* that are nitrogen excess responsive. Four microRNAs respond only in root, eight microRNAs only in shoot and one displays broad response in roots and shoots. We demonstrate that 2 microRNAs* are induced in barley shoot by nitrogen excess. For all microRNAs we identified putative target genes and confirmed microRNA-guided cleavage sites for ten out of thirteen mRNAs. None of the identified microRNAs or their target genes is known as nitrogen excess responsive. Analysis of expression pattern of thirteen target mRNAs and their cognate microRNAs showed expected correlations of their levels. The plant microRNAs analyzed are also known to respond to nitrogen deprivation and exhibit the opposite expression pattern when nitrogen excess/deficiency conditions are compared. Thus, they can be regarded as metabolic sensors of the regulation of nitrogen homeostasis in plants.

Root-to-shoot signalling in mycorrhizal tomato plants upon Botrytis cinerea infection

Arbuscular mycorrhizal symbiosis is restricted in roots, but it also improves shoot responses against leaf challenges, a phenomenon known as Mycorrhiza-Induced Resistance (MIR). This study focuses on mycorrhizal root signals that may orchestrate shoot defence responses. Metabolomic analysis of non-mycorrhizal and mycorrhizal plants upon Botrytis cinerea infection showed that roots rearrange their metabolome mostly in response to the symbiosis, whereas in shoots a stronger impact of the infection is observed. Specific clusters of compounds in shoots and roots display a priming profile suggesting an implication in the enhanced resistance observed in mycorrhizal plants. Among the primed pathways in roots, lignans showed the highest number of hits followed by oxocarboxylic acids, compounds of the amino acid metabolism, and phytohormones. The lignan yatein was present at higher concentrations in roots, root efflux and leaves of mycorrhizal plants This lignan displayed in vitro antimicrobial activity against B. cinerea and it was also functional protecting tomato plants. Besides, several JA defence-related genes were upregulated in mycorrhizal roots regardless of the pathogen infection, whereas PIN-II was primed in roots of mycorrhizal infected plants. These observations suggest that the enhanced resistance in shoots during MIR may be coordinated by lignans and oxylipins with the participation of roots.

Cadmium phytoremediation potential of Gnaphalium affine D. Don and physiological response in metal tolerance

In this study, the plant growth, physiological responses and phytoremediation potential of the herbaceous plant Gnaphalium affine D. Don were evaluated in varying extents of Cd contaminated soil and 40 days cultivation. The results demonstrated that the plant had a high Cd tolerance of up to 300 mg.kg-1 in which Cd content in roots and shoots reached a maximum of 733.9 and 404.6 mg.kg-1 respectively. Cd exposure enhances the malondialdehyde (MDA) level and antioxidative response (SOD, POD and CAT) in shoots of Gnaphalium affine D. Don. The bioconcentration factor (BCF) values in all treatments were greater than 1 and the translocation factor (TF) values were almost 2 at the high Cd concentration treatments. These findings indicated that Gnaphalium affine D. Don as a Cd-accumulator can be considered as a potential candidate for phytoremediation in Cd polluted sites.

Response of grafting tobacco to low potassium stress

BackgroundIn the previous study, we investigated the alleviation effect of grafting on potassium uptake in roots and tobacco growth inhibition under low potassium stress. However, the effect of grafting on the low potassium stress perception and coping mechanism of tobacco at the whole plant level is not clear now. In order to clearly understand the impact of grafting on potassium deficit responding mechanism in tobacco, a mutual grafting experiment has been conducted in two varieties of tobacco (‘Wufeng No.2’ and ‘Yunyan 87’) in different K supply level (5 mmol L− 1 and 0.5 mmol L− 1 K).ResultsThe results show that compared with the self-rooted seedlings, grafting significantly increased the potassium content of the whole plant of Yunyan 87 (97.57 and 189.74% under normal potassium and low potassium conditions, respectively), and the increase in shoots was greater. The data of whole plant K content distribution and tobacco hypocotyls net K+ flux demonstrates that potassium stress makes plants more inclined to maintain K+ in the shoot rather than root. In addition, when K deficiency occurs, grafting could reduce the time required for downward net K+ flux in tobacco hypocotyl to decrease to stable levels. The results of net K+ flux in the roots indicated that K channel proteins and transporters play different roles in two rootstocks in terms of potassium tolerance. Transcription level analysis suggested that the increased circulating efficiency of K+ between the shoots and roots in tobacco constitutes one means to low potassium stress adaptation.ConclusionsGrafting can activate more K+ channels in tobacco ‘Yunyan 87’, this means a more active K+ cycle, higher potassium content in shoot and faster response to low potassium stress signals in grafting tobacco. In addition, grafting can also change the K+ absorption mode of tobacco root from being dominated by HATS to being jointly responsible by HATS and LATS, greatly improving the ability of K+ transmembrane transportation on root surface under low potassium stress. These are undoubtedly the reasons why grafting tobacco performs better in coping with low potassium stress.