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Clerodendrum viscosum is a traditionally used medicinal plant. The present study aimed to analyze a detailed cytotoxic effect of the nonpolar petroleum ether fraction (AQPEF) of leaf aqueous extract of C. viscosum Vent. (LAECV) in Allium cepa root tip cells. The LAECV was fractionated with petroleum ether and tested for A. cepa toxicity at early hours (2 and 4 h treatment) at concentrations 0, 50, 100, 150 and 200 {micro}g mL-1. The highest aberrant cell percentage (10.45{+/-}0.46%) was scored from 150 {micro}g mL-1 followed by100 {micro}g mL-1 (8.75{+/-}0.26%) concentration at 4 h treated samples. The AQPEF treatment induced a significant (p

Saccharin has been a controversial dietary component because of its potential to aggravate a number of human health disorders. The genotoxic properties of saccharin affect the normal karyokinesis process and results in chromosomal aberrations. In this backdrop, the current study has been formulated to evaluate the genotoxic potential of aqueous saccharin solution using Allium cepa L. assay. Three different concentrations of saccharin solution (0.25%, 0.5% and 1%) and a negative control were used for the root growth inhibition assay. The root length of Allium cepa significantly reduced under saccharin treatments and the effective concentration (EC50) value of the aqueous saccharin solution was determined as 0.587%. The genotoxic effects were determined for the root tip meristematic cells through mitotic index (MI) and mitotic depression (MD) at 3, 6 and 12 h of study. The MI registered highest value without saccharin at low exposure period (17.0 ± 1.5%) while a significant reduction with saccharin application culminated in the lowest MI for 1% saccharin solution at 12 h (3.4 ± 0.4%). MD was found to have a concomitant increase regarding the exposure of the chemical. Higher dose of saccharin for longer exposure time had a gradual decrease in the prophase and simultaneous increase in metaphase and anaphase. Further microscopic observations revealed eight different types of chromosomal aberrations in the A. cepa root tip cells with Anaphase Bridge assuming the highest score. Thus the current study clearly establishes the genotoxic consequences of aqueous solution of saccharin warranting its moderate and regulated dietary intake.

Exploration of novel genetic resources against root-knot nematode (RKN) is necessary to strengthen the resistance breeding program in cultivated rice, and investigations on the role of genotype-specific root anatomy in conferring a structural barrier against nematode invasion are largely underexplored. Here, we reported a highly-resistant rice germplasm Phule Radha that conferred remarkably lower RKN parasitic fitness in terms of reduced penetration and delayed development and reproduction when compared with susceptible cultivar PB1121. Using histological and biochemical analyses, we demonstrated that an enhanced suberin deposition in the exodermal root tip tissue of Phule Radha compared to PB1121 can effectively form a penetrative barrier against RKN infection, and this preformed barrier in the control tissue did not necessarily alter to a greater extent when challenged with RKN stress. Using qRT-PCR analysis, we showed that a number of suberin biosynthesis genes were greatly expressed in the exodermis of Phule Radha compared to PB1121. In sum, the present study established the role of rice exodermal barrier system in defense against an important soil-borne pathogen.

Avocados (Persea americana Mill.) are one of the crops with the highest water footprints in Chile and the production is at risk due to severe and frequent droughts. The current production is mostly based on sexually (seed) propagated rootstocks, while clonally propagated rootstocks are on the rise. In a recent study, we found differences in aerial, root growth and water use efficiency between trees grown on these two different rootstocks under controlled continuous fertigation and environmental conditions. In this study, we further describe possible mechanisms which drive the differences. Avocado cv. “Hass” grafted on “Dusa” (D, clonally propagated) and “Mexicola” (M, sexually propagated) rootstocks and different root segments (3, 5 and 8 cm from root tip) were investigated using a combination of hydraulic measurements and polar metabolite (GC-MS) techniques. The results show significant differences in root hydraulic properties, indicating that “Mexicola” fine roots have higher water uptake capacity. The polar metabolites analysis revealed 13 compounds significantly different between rootstocks while nine were found significantly different among root segments. Principal component analysis (PCA) revealed differences between rootstocks and root segments. The data presented here highlight the importance of considering key physiological knowledge in avocado rootstocks breeding programs to be better prepared for future challenging environmental conditions.

Flooding is an environmental stress that leads to a shortage of O2 that can be detrimental for plants. When flooded, deepwater rice grow floating adventitious roots to replace the dysfunctional soil-borne root system, but the features that ensure O2 supply and hence growth of aquatic roots have not been explored. We investigate the sources of O2 in aquatic adventitious roots and relate aerenchyma and barriers for gas diffusion to local O2 gradients, as measured by microsensor technology, to link O2 distribution in distinct root zones to their anatomical features. The mature root part receives O2 exclusively from the stem. It has aerenchyma that, together with suberin and lignin depositions at the water–root and cortex–stele interfaces, provides a path for longitudinal O2 movement toward the tip. The root tip has no diffusion barriers and receives O2 from the stem and floodwater, resulting in improved aeration of the root tip over mature tissues. Local formation of aerenchyma and diffusion barriers in the mature root channel O2 towards the tip which also obtains O2 from the floodwater. These features explain aeration of floating roots and their ability to grow under water.

Made available in DSpace on 2020-12-12T02:44:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Styrax camporum Pohl. (Styracaceae) is a woody species that grows on acidic soils from the Brazilian savanna with high aluminum (Al) saturation (m% > 50%), where it accumulates ~ 1500 mg Al per kg dry leaves. Using nutrient solution, a previous study showed that 1480 μM Al causes toxicity symptoms, which raises the question whether less than 1480 μM Al could cause beneficial effects on this species. Here, we checked possible altered gas exchange rates, damage to organelles in root tips and the association between Al exposure and mitochondria occurrence in cells of root tips, once organic acids from Krebs cycle exuded by the roots of this species when exposed to Al have been recently evidenced. Five-month-old plants were grown in nutrient solution with 0, 740 and 1480 μM Al for 90 days. Plants exposed to 1480 μM Al showed less developed root system, reduced plant height and low gas exchange rates in relation to those exposed to 0 and 740 μM Al, confirming that 1480 μM Al is toxic to S. camporum. However, plants exposed to 0 and 740 μM Al had similar number of leaves, plant height, root biomass, root length, total plant biomass and gas exchange rates, indicating that no beneficial effects from 740 μM Al could be noted on this species. In plants exposed to 0 and 740 μM Al, mitochondria were noted at the root tip, while at 1480 μM Al these organelles were not evident due to the conspicuous vacuolation of root cells. S. camporum shows limited tolerance to Al in nutrient solution. In addition, this species is not dependent on Al to grow and develop because the plants grew well under 0 and 740 μM Al. Departamento de Biodiversidade Instituto de Biociências Programa de Pós-Graduação Em Ciências Biológicas (Biologia Vegetal) Universidade Estadual Paulista UNESP, Av. 24-A, 1515 Departamento de Fitopatologia e Nematologia Escola Superior de Agricultura “Luiz de Queiróz”-Universidade de São Paulo ESALQ-USP, Av. Pádua Dias, 11 Departamento de Biodiversidade Instituto de Biociências Universidade Estadual Paulista UNESP, Av. 24-A, 1515 Departamento de Biodiversidade Instituto de Biociências Programa de Pós-Graduação Em Ciências Biológicas (Biologia Vegetal) Universidade Estadual Paulista UNESP, Av. 24-A, 1515 Departamento de Biodiversidade Instituto de Biociências Universidade Estadual Paulista UNESP, Av. 24-A, 1515 FAPESP: 2014/14386-0 FAPESP: 2018/25658-2 CNPq: 309149/2017-7

We present a simple and generic model, based on mechanistic hypotheses, to represent the longitudinal variations of the diameter of individual roots and the associated diversity of growth patterns., In a given root system, individual roots usually exhibit a rather homogeneous tip structure although highly different diameters and growth patterns, and this diversity is of prime importance in the definition of the whole root system architecture and foraging characteristics. In order to represent and predict this diversity, we built a simple and generic model at root tip level combining structural and functional knowledge on root elongation. The tip diameter, reflecting meristem size, is used as a driving variable of elongation. It varies, in response to the fluctuations of photo-assimilate availability, between two limits (minimal and maximal diameter). The elongation rate is assumed to be dependent on the transient value of the diameter. Elongation stops when the tip reaches the minimal diameter. The model could satisfactorily reproduce patterns of root elongation and tip diameter changes observed in various species at different scales. Although continuous, the model could generate divergent root classes as classically observed within populations of lateral roots. This model should help interpret the large plasticity of root elongation patterns which can be obtained in response to different combinations of endogenous and exogenous factors. The parameters could be used in phenotyping the root system.

Structural changes during severe drought stress greatly modify the hydraulic properties of fine roots. Yet, the physiological basis behind the restoration of fine root water uptake capacity during water recovery remains unknown. Using neutron radiography (NR), X-ray micro-computed tomography (micro-CT), fluorescence microscopy, and fine root hydraulic conductivity measurements (Lpr ), we examined how drought-induced changes in anatomy and hydraulic properties of contrasting grapevine rootstocks are coupled with fine root growth dynamics during drought and return of soil moisture. Lacunae formation in drought-stressed fine roots was associated with a significant decrease in fine root Lpr for both rootstocks. However, lacunae formation occurred under milder stress in the drought-resistant rootstock, 110R. Suberin was deposited at an earlier developmental stage in fine roots of 101-14Mgt (i.e. drought susceptible), probably limiting cortical lacunae formation during mild stress. During recovery, we found that only 110R fine roots showed rapid re-establishment of elongation and water uptake capacity and we found that soil water status surrounding root tips differed between rootstocks as imaged with NR. These data suggest that drought resistance in grapevine rootstocks is associated with rapid re-establishment of growth and Lpr near the root tip upon re-watering by limiting competing sites along the root cylinder.

Plants display extraordinary ability to revive tissues and organs lost or damaged in injury. This is evident from the root tip restoration and classical experiments in stem demonstrating re-establishment of vascular continuity. While recent studies have begun to unravel the mechanistic understanding of tissue restoration in response to injury in underground plant organs, the molecular mechanisms of the same in aerial organs remain to be ventured deeper. Here, we discuss the possibility of unearthing the regulatory mechanism that can confer universal regeneration potential to plant body and further provide a comprehensive understanding of how tissue and organ regeneration gets triggered in response to mechanical injury and later gets terminated after re-patterning and regaining the appropriate size.

Already a short-term Cd treatment induces changes in gene expression in barley root tips via IAA and ROS signaling during mild and severe Cd stress, respectively. Even a short, 30 min, Cd treatment of roots induced a considerable alteration in gene expression in the barley root tips within an hour after the treatments. The very early activation of MYB1 transcription factor expression is partially regulated by auxin signaling in mildly stressed seedlings. An increase in allene oxide cyclase and NADPH oxidase expression was a distinguishing feature of root tips response to mild Cd stress and their expression is activated via IAA signaling. Meanwhile, early changes in the level of dehydrin transcripts were detected in moderately and severely stressed root tips, and their induction is related to altered ROS homeostasis in cells. The early activation of glutathione peroxidase expression by mild Cd stress indicates the involvement of IAA in the signaling process. In contrast, early ascorbate peroxidase expression was induced only with Cd treatment causing severe stress and ROS play central roles in its induction. The expression of cysteine protease was activated similarly in both mildly and severely Cd-stressed roots; consequently, both increased IAA and ROS levels take part in the regulation of cysteine protease expression. The Cd-evoked accumulation of BAX Inhibitor-1 mRNA was characteristic for moderately and severely stressed roots. Whereas decreased IAA level did not affect its expression, rotenone-mediated ROS depletion markedly reduced the Cd-induced expression of BAX Inhibitor-1. An early increase of alternative oxidase levels in the root tip cells indicated that the reduction of mitochondrial superoxide generation is an important component of barley root response to severe Cd stress.

Callose is cell wall constitutive component of some plant tissues and it is synthesized and deposited in response to stresses (abiotic and biotic). Considering physiological seed quality as an attribute that determines the rapid and uniform emergence of seedlings under a wide range of environmental conditions, this study verified the callose accumulation in seedling roots of soybean cultivars showing contrasting seed vigor under water deficit. Six soybean cultivars were used and the physiological seed quality was determined by germination and vigor tests. Water deficit simulation was performed by germination tests with polyethylene glycol solution at − 0.4 MPa, and the control (0.0 MPa; deionized water). 24 h after radicle protrusion, three samples of 13 root tips were prepared for callose determination. The cultivar ‘BMX Potencia RR’ presented lower germination (87%) when compared to the other cultivars. Vigor results allowed the separation of cultivars into two vigor categories, high and low. The callose concentration deposited on soybean root tissues ranged from 0.0511 to 0.1244 μg per root tip. This allowed the observation of the contrast in callose accumulation between the cultivars during the water deficit, and this is responsive to the greater susceptibility of low vigor cultivars to stress in order to isolate plant tissue through the deposition of a physical barrier. Callose accumulation can be used as indicative of susceptibility to water stress in soybean cultivars.

Meloidogyne hapla is the most prevalent plant-parasitic nematode in Washington state wine grape vineyards. Understanding the developmental dynamics of M. hapla can improve the timing of diagnostic sampling and nematicide application. Three Vitis vinifera vineyards in Washington were sampled March 2015 to March 2017 to determine the developmental dynamics of M. hapla by measuring second-stage juveniles (J2) in soil, eggs and adult females in roots, and fine root tips. A model of M. hapla J2 development based on soil growing degree days using a base temperature (Tb) of 0°C (GDDsoil) and a start date of 1 March was developed. This model was validated at two additional vineyards in Washington and was robust with R2 values > 0.74. M. hapla has one generation per year and overwinters primarily as the J2 infective stage. Juvenile populations declined after 1 March, reaching their lowest density in early July and reaching a maximum density over the winter. M. hapla egg and root tip densities reached a maximum in early August. The number of females per root tip did not vary throughout the year. A single generation with defined peaks in J2 population densities will allow for specific timing of nematicide interventions.

SUMMARY Axial resistance (Ra) was estimated from xylem diameter measurements obtained from periodic acid and toluidinc blue O (PAS-TBO) stained sections of Vitis vinifera L. ev. Shiraz. Multiple linear regression showed a strong negative relationship between axial resistance and either root diameter or distance from the root tip. Water stress treatments did not affect the relationships, but plant age significantly influenced the intercept of the regression. The use of both lignin and cytoplasm stain showed that some vessels retained degenerating protoplasm which would impede water flow. Inclusion of these vessels in calculations of axial resistance could account for the underestimation reported by some authors in comparison with experimental determinations. Calculations based on the assumption that all xylem vessels, large and small, are involved in axial water conduction showed that use of mean xylem diameter might result in overestimating values by a magnitude of between 1.7 and 4.4. The use of individual xylem vessel diameters gave more accurate estimation of axial resistance. Some adjacent secondary xylem and metaxylem vessels were observed to merge into single vessels as a result of breakdown of the wall between them. Implications of such a developmental phenomenon are discussed.

The mutation Ageotropic (Agt) results in defective development of the surface pellicle which overlies the young epidermal cells of mesocotyl and nodal roots of maize. In roots of plants of the parent, cv. Kys, pellicle development is normal. This structure forms a coherent, smooth covering, up to ∼ 13/μm thick, over the epidermal cells distal to the elongation zone. This pellicle is external to the helicoidal outer wall of the epidermal cells and is composed of a thick inner layer with close-packed, longitudinally oriented fibrils, and a thin outer layer with less regularly oriented fibrils. Both layers of the normal pellicle and the underlying epidermal wall are strongly stained by the periodic acid-Schiff's (PAS) reaction. In Agt plants, the pellicle is irregular and diffuse, lacks definition of the two layers and is largely amorphous with occasional wisps of fibrils. Neither this mutant pellicle nor the underlying epidermal wall are PAS-positive. Mesocotyl and nodal roots of Agt are sensitive to gravity but grow crookedly through soil. It is proposed that a normal pellicle maintains the smooth outer contour of young roots and provides stiffness in the region distal to the zone of elongation. When the pellicle is defective, the root tip is more compliant and bends result when the tip encounters small air spaces and barriers in the soil.

In flooded soils, an efficient internal aeration system is essential for root growth and plant survival. Roots of many wetland species form barriers to restrict radial O2 loss (ROL) to the rhizosphere. The formation of such barriers greatly enhances longitudinal O2 diffusion from basal parts towards the root tip, and the barrier also impedes the entry of phytotoxic compounds produced in flooded soils into the root. Nevertheless, ROL from roots is an important source of O2 for rhizosphere oxygenation and the oxidation of toxic compounds. In this paper, we review the methodological aspects for the most widely used techniques for the qualitative visualization and quantitative determination of ROL from roots. Detailed methodological approaches, practical set-ups and examples of ROL from roots with or without barriers to ROL are included. This paper provides practical knowledge relevant to several disciplines, including plant–soil interactions, biogeochemistry and eco-physiological aspects of roots and soil biota.

Aluminium (Al) toxicity inhibits soybean root growth, leading to insufficient water and nutrient uptake. Two soybean lines (‘Magellan’ and PI 567731) were identified differing in Al tolerance, as determined by primary root length ratio, total root length ratio, and root tip number ratio under Al stress. Serious root necrosis was observed in PI 567731, but not in Magellan under Al stress. An F8 recombinant inbred line population derived from a cross between Magellan and PI 567731 was used to map the quantitative trait loci (QTL) for Al tolerance. Three QTL on chromosomes 3, 13, and 20, with tolerant alleles from Magellan, were identified. qAl_Gm13 and qAl_Gm20 explained large phenotypic variations (13–27%) and helped maintain root elongation and initiation under Al stress. In addition, qAl_Gm13 and qAl_Gm20 were confirmed in near-isogenic backgrounds and were identified to epistatically regulate Al tolerance via internal detoxification instead of Al3+ exclusion. Phylogenetic and pedigree analysis identified the tolerant alleles of both loci derived from the US ancestral line, A.K.[FC30761], originally from China. Our results provide novel genetic resources for breeding Al-tolerant soybean and suggest that internal detoxification contributes to soybean tolerance to excessive soil Al.

Differences in the storability of sugar beet genotypes have been reported to be related to the marc content of beets. Hence, this study aimed at identifying 1) general patterns to characterize varieties and growing sites for low storage losses, 2) the causal relationship between marc content of varieties and their damage susceptibility, infestation with mould and rots and sugar losses after storage, and 3) the environmental stability of the marc content of varieties. For the storage experiments, 10 varieties were grown at 8 sites in Germany, the Netherlands, Belgium and Sweden in 2015, 2016. After harvest, roots were stored for 8 weeks under controlled conditions. To evaluate the environmental stability, the same 10 varieties were grown at 12 sites in D, NL, B, S and Moldova in 2015 and 11 sites in D, NL, B, S in 2016. The results demonstrate a marked effect of the site on the extent of root tip breakage and surface damages, on infestation with mould and rots and on storage losses (invert sugar content, sugar losses). A general pattern could be identified: in most cases, a higher marc content of varieties coincided with less damages and less infestation with mould and rots, resulting in lower sugar losses. With the exception of variety 1, the marc content provided an indication of the storability of the varieties. The marc content turned out to be a very stable variety trait. These results indicate possibilities for breeding and selection for higher marc content and presumed better storability.

Lentil is now an integral part of prairie cropping systems. Climate forecasts point to variable and increased drought frequency, putting lentil production in jeopardy. Future lentil genotypes will require root systems that can extract more water under drought conditions. This study focuses on root diameter and root tip number, traits known to play an important role in water uptake during drought. We compared the total root length (TRL) in three soil horizons of both wild and cultivated lentil genotypes for three root diameter classes when plants were grown under moderate or severe drought, and when re-watered after exposure to moderate drought conditions. Our study demonstrates that roots of both wild and cultivated lentil genotypes can be categorized into very fine, fine and small diameter classes. Some wild lentil genotypes had significantly higher TRL in the B and C soil horizons when grown under severe or moderate drought and therefore, could act as resources for the transfer of root traits to cultivated lentil genotypes. Further evaluations focused on the root systems of interspecific recombinant inbred lines under drought conditions will be required to determine whether these traits are heritable.

Dry seeding is a resource-saving rice establishment method. With an equivalent yield, dry seeded flooded rice (DSR) has been considered as a replacement for traditional transplanted flooded rice (TFR). However, the differences in leaf and root senescence during grain filling between DSR and TFR were seldom identified. In this study, the root length, root tip number and leaf senescence of rice varieties Huanghuazhan and Yangliangyou 6 during ripening were compared between DSR and TFR. Results showed that top three leaves in DSR had the characteristics of relatively lower SPAD value, lower N content and premature leaf senescence. In addition, both the total root length and total root tip number of DSR were significantly lower than those of TFR. In conclusion, premature and quick leaf senescence was related with inadequate root length and root tip number during ripening, which might result from the deficiency of nitrogen supply in DSR. Techniques on improving leaf nitrogen status and delaying the leaf senescence during grain-filling in DSR should be developed in future researches. Keywords: dry seeded rice, transplanted flooded rice, SPAD value, leaf senescence, root length, root tip number

Phosphorous (P) deficiency induces root cortical aerenchyma (RCA) formation in Chinese fir seedlings with marked genotypic variation, and the adaptive role of RCA is mainly related to root P reduction. Root cortical aerenchyma (RCA) formation in response to phosphorus (P) deficiency and its adaptive role are largely unexplored in trees. We hypothesized that RCA formation in response to P deficiency varies with its severity and genotype, and that P-stressed seedlings maintain similar seedling growth to non-stressed seedlings by reducing the P requirements of roots and metabolic cost of soil exploration. Seedlings of two half-sib families (nos. 25 and 36) of Cunninghamia lanceolata (Chinese fir) were grown in pots with three levels of P supply for 3 months. Significant differences in RCA formation in 40–45 mm root segments from the root tip were observed between families and P supply levels. Severe P deficiency induced more RCA formation in family no. 36 than in family no. 25, whereas moderate P deficiency induced RCA formation in family no. 36 only. Family no. 36 had significantly higher height increment, needle biomass, and P concentration in stems and needles, but lower root biomass and root P concentration, than family 25. A significantly negative relationship was found between RCA and root P concentration, increments in average root diameter, and root surface area, whereas significantly positive correlations were observed between some root morphological traits and biomass and P concentration in the organs of P-stressed seedlings of family 36. In conclusion, severe P deficiency induces formation of RCA in Chinese fir seedlings with marked genotypic variation, and the adaptive role of RCA formation during P deficiency is mainly related to the reduction of root P concentration.

Exposure of barley roots to mM concentrations of L-NAME for 30 min caused a considerable root growth inhibition in a dose-dependent manner. The inhibition of root growth was higher in seedlings co-treated with Cd and L-NAME, compared with roots treated with Cd alone, despite the fact that L-NAME markedly reduced the uptake of Cd by roots. Treatment of roots with L-NAME evoked a decrease in NO level in both control and Cd-treated root tips only after a relatively long lag period, which overlaps with an increase in superoxide and H2O2 levels and peroxynitrite generation. L-NAME-induced root growth inhibition is alleviated not only by the application of the NO donor SNP but also by the ROS and peroxynitrite scavengers. Our results indicate that L-NAME, a NOS inhibitor in the animal kingdom, indeed evokes NO depletion also in the plant tissues; however, it does not occur due to the action of L-NAME as an inhibitor of NOS or NOS-like activity, but as a consequence of L-NAME-induced enhanced superoxide generation, leading to increased peroxynitrite level in the root tips due to the reaction between superoxide and NO.

Regulation of flowering is one of the key issues in crop yield. The Flowering Locus T ( FT ) gene is a well-known florigen, which integrates various signals from multiple flowering-regulation pathways to initiate flowering. We previously reported that there are at least six FT genes ( GmFTL1 – 6 ) in soybean displaying flowering activity. However, the individual functions of genes GmFTL1 – 6 remain to be identified. In this study, we cloned the GmFTL2 promoter ( GmFTL pro ) from soybean ( Glycine max ) cultivar Tianlong 1 and analyzed its motifs bioinformatically and its expression patterns using both a transgenic approach and quantitative RT-PCR (qRT-PCR). In GmFTL pro :: GUS transgenic lines, GUS signals were enriched in cotyledons, hypocotyledons, pollen, embryos, and root tips in a photoperiod-independent manner. qRT-PCR confirmed the GUS reporter results. Our results suggest that GmFTL2 expression is regulated by developmental and tissue-specific clues and plays roles in seedling establishment and the development of microgametophytes, embryos, and roots.

Transient exposure of roots to Cd, Pb, Hg or Cu for 30 min reduced root growth in a concentration-dependent manner. While the lower concentrations of metals evoked a marked root growth inhibition accompanied by a visible radial root expansion, the higher concentrations caused root growth arrest without the radial expansion of root cells. At lower metal concentrations, evoking mild stress, the amount of reactive oxygen species (ROS) increased linearly after the treatments. They probably function in both stress signalization and metabolic adaptation processes without damaging the root cells. In turn, at high metal concentrations, causing moderate or severe stress, their production has a biphasic character. The amount of ROS, mainly superoxide, increased rapidly in a metal dose-dependent manner, causing a marked cell death at the site of their generation in the root tips. After this transient burst, ROS generation increased again, together with highly ROS, during the destructive processes associated with cell death in the root tips. Our results show that despite the different origin of ROS induced by these heavy metals, the rate of their generation, depending on the metal concentration, determines the development of typical mild stress-activated morphogenic changes or severe stress-caused cell death within a few minutes after the exposure of roots to toxic level of metals.

Premise of research. The Australian members of the genus Craspedia (Asteraceae: Gnaphalieae) are known to contain polyploids, but only a very limited number of chromosome counts are available, and a systematic overview of ploidy levels and genome sizes is lacking. In the present study, we aimed to document chromosome number variation across the genus in Australia, test whether polyploids occur more often in alpine than in lowland environments, and test whether there is a proportional increase in genome size with polyploidy that would enable the use of flow cytometry as a proxy for chromosome counts in future studies.Methodology. We used flow cytometry to measure genome sizes (2C values) of 59 individual plants and obtained 45 chromosome counts from root tip squashes.Pivotal results. We found polyploidy to be common and documented intraspecific ploidy variation in several species, indicating multiple independent origins of polyploidy within the genus. Polyploidy was not more prevalent in high-elevation spe...

This unit presents a highly reliable protocol to produce and screen metaphase chromosome spreads from root tip cell suspensions of soybean (Glycine max), or other legumes. The procedures represent soybean-optimized versions of protocols developed for maize. The use of pressurized nitrous oxide to reliably generate metaphase-arrested chromosomes is crucial to overcoming one of the challenges of working with tiny and numerous soybean chromosomes. © 2017 by John Wiley & Sons, Inc.

Conditioning small groups of root pericycle cells for future lateral root formation has a major impact on overall plant root architecture. This priming of lateral roots occurs rhythmically, involving temporal oscillations in auxin response in the root tip. During growth, this process generates a spatial pattern of prebranch sites, an early stage in lateral root formation characterized by a stably maintained high auxin response. To date, the molecular mechanism behind this rhythmicity has remained elusive. Some data implicate a cell-autonomous oscillation in gene expression, while others strongly support the importance of tissue-level modulations in auxin fluxes. Here, we summarize the experimental data on periodic lateral root priming. We present a theoretical framework that distinguishes between a priming signal and its subsequent memorization and show how major roles for auxin fluxes and gene expression naturally emerge from this framework. We then discuss three mechanisms that could potentially induce oscillations of auxin response: cell-autonomous oscillations, Turing-type patterning, and tissue-level oscillations in auxin fluxes, along with specific properties of lateral root priming that may be used to discern which type of mechanism is most likely to drive lateral root patterning. We conclude with suggestions for future experiments and modeling studies.

Duckweed is considered to be one of the most attractive higher plants to provide the life support requirements of the crew in long-duration space missions. Two species of duckweed, Lemna aequinoctialis and Wolffia globosa, were comparatively studied with focus on the effects of simulated microgravity conditions. A significant enhancement of plant relative growth rate (RGR) was observed under simulated microgravity conditions. The mean RGR of L. aequinoctialis was 32% increased, and W. globosa was 12% increased compared to control. Light and electron microscope analyses showed that the mesophyll cells of duckweed fronds were loosely arranged and many intercellular air spaces enclosed by mesophyll cells were observed in reaction to simulated microgravity, and few starch grains were detected in root tip cells in L. aequinoctialis under simulated microgravity conditions. For L. aequinoctialis, the starch content was significantly increased under simulated microgravity conditions. Thus, the starch content of W. globosa under simulated microgravity conditions was kept stable during all growth periods. This pattern might be associated with the different expression change of the rate-limiting gene APL in regulating starch levels. Taking into consideration of the duckweed growth, ultra-structure and starch content changes, we considered that simulated microgravity conditions do not have a significant adversely affect on the duckweed growth.

It has long been considered that mechanical impedance on root will restrict root elongation and consequently promote radial growth. When seedlings grew in sands, we did observe radial expansion of roots and it, however, arose before elongation restriction. Mechanical impedance of sands can be classified into frontal- and lateral-type based on the interaction site of root. Therefore, we suspected that radial expansion might be mainly stimulated by lateral- rather than frontal-impedance. To verify our speculation, roots were exposed to frontal- and lateral-impedance separately. Small plastic caps were used to provide pure frontal impedance on root tips and cylindrical plastic containers were used to provide pure lateral impedance. Root elongation was remarkably suppressed under the frontal impedance of plastic caps, and more than that in sand-condition. However, the radial expansion of the plastic-cap-fitted roots was far inferior to that of the sand-cultured roots. Microstructural analysis revealed that sand-condition thickened root largely dependents on cortical expansion, whereas plastic cap did it mainly by thickening stele. In cylindrical plastic containers, mechanical impedance came only from the lateral direction and promoted the expansion of cortex like sand-condition. Thus, we proposed that the expansion of cortex and the consequent radial growth of roots were mainly due to lateral impedance when seedlings grew in sands.

Rehmannia glutinosa L. (R. glutinosa) is one of the most common traditional Chinese medicines, whose productivity and quality, however, are seriously impacted by replanting disease, also known as consecutive monoculture obstacle. Little is known about R. glutinosa’s critical responsive stage to consecutive monoculture. There were two parts to this study: first, we analyzed different gene expression profiles in root of R. glutinosa between first-year planting (FP) and second-year replanting (SP) in five development stages (stage I to V) using Illumina sequencing to interpret the stage that most dramatically responding to consecutive monoculture; second, applying tissue culture technique, the harm of consecutive monoculture in a sterile condition was simulated and the medium was added with the soil extracts from FP and SP soil. The results showed that a significant difference in gene expression appeared at stage I under consecutive monoculture. Using a calcium indicator, the fluo-3 fluorescence to detect calcium distribution in the root tip of seedlings cultured in medium, the results revealed that after being cultured for 10 days, the SP fluorescence intensity of the seedlings was significantly higher than that of FP while crown position was particularly prominent. The evidence from gene expression profiling and tissue culture reached agreement that early stage of R. glutinosa growth was the critical stage to perceive consecutive monoculture stress. The results are of great significance to study the molecular mechanism of consecutive monoculture, which is expected to await a quick and accurate evaluation of land feasibility to plant R. glutinosa.

Gibberellic acid (GA) is a natural plant growth regulator (PGR) which stimulates germination, vegetative growth, flowering, and fruit formation. However, when high concentrations of GA are used, it inhibits plant growth and development and causes abnormalities in the plant tissue. In our study, we determined the effects of different concentrations of GA on Allium cepa L. var. cepa roots. Increasing concentrations of GA (50 - 5 000 mg dm-3) were used in A. cepa root growth inhibition tests. Further, random amplified polymorphic DNA technique was used for determination of possible genotoxic effects of 600 - 1200 mg dm-3 GA on A. cepa root tips. Our findings show cytotoxic and genotoxic effects of these concentrations of GA and indicate that the difference among control and treatment groups were statistically significant.

Highlights • Cell ablation mimics wounding on a single cell level. • Calcium, ROS, and hormone dynamics were described. • Local, regional, and systemic responses can be distinguished., Plants as sessile organisms are constantly under attack by herbivores, rough environmental situations, or mechanical pressure. These challenges often lead to the induction of wounds or destruction of already specified and developed tissues. Additionally, wounding makes plants vulnerable to invasion by pathogens, which is why wound signalling often triggers specific defence responses. To stay competitive or, eventually, survive under these circumstances, plants need to regenerate efficiently, which in rigid, tissue migration-incompatible plant tissues requires post-embryonic patterning and organogenesis. Now, several studies used laser-assisted single cell ablation in the Arabidopsis root tip as a minimal wounding proxy. Here, we discuss their findings and put them into context of a broader spectrum of wound signalling, pathogen responses and tissue as well as organ regeneration.

How the body plan is established and maintained in multicellular organisms is a central question in developmental biology. Thanks to its simple and symmetric structure, the root represents a powerful tool to study the molecular mechanisms underlying the establishment and maintenance of developmental axes. Plant roots show two main axes along which cells pass through different developmental stages and acquire different fates: the root proximodistal axis spans longitudinally from the hypocotyl junction (proximal) to the root tip (distal), whereas the radial axis spans transversely from the vasculature tissue (centre) to the epidermis (outer). Both axes are generated by stereotypical divisions occurring during embryogenesis and are maintained post-embryonically. Here, we review the latest scientific advances on how the correct formation of root proximodistal and radial axes is achieved.

The aim of this study was to investigate the effect of 4-phenoxyphenylboronic acid (PPBo), an effective inhibitor of YUCCA enzyme on mild, moderate and severe Cd stress-induced responses in the root tips of young barley seedlings. While mild and moderate Cd stresses increased, severe Cd stress decreased the root IAA level. PPBo post-treatment strongly inhibited the Cd-induced IAA accumulation without affecting the Cd level in roots and mitigated the mild Cd stress-induced root growth inhibition, root swelling and lipoxygenase and glutathione peroxidase activity. In addition, PPBo reduced the H2O2 and NO generation under mild but had no effect under severe Cd stress, indicating that both H2O2 and NO act downstream of IAA in root responses to mild Cd stress. In turn, moderate or severe Cd stress strongly reduced the expression of IAA synthesis and cell cycle genes in the barley root tip. Therefore, we can conclude that IAA accumulation in the barley root tips is a distinctive feature of mild and moderate Cd stresses, which is involved in both root growth reorientation and defense response activation. PPBo completely reversed this Cd-induced IAA accumulation and stress responses, indicating that Cd induces IAA synthesis via indole-3-pyruvic acid biosynthesis pathway. On the contrary, severe Cd stress reduced IAA level was coupled with high ROS in the root tips and root growth arrest.

Root tip is capable of sensing and adjusting its growth direction in response to gravity, a phenomenon known as root gravitropism. Previously, we have shown that negative gravitropic response of roots (NGR) is essential for the positive gravitropic response of roots. Here, we show that NGR, a plasma membrane protein specifically expressed in root columella and lateral root cap cells, controls the positive root gravitropic response by regulating auxin efflux carrier localization in columella cells and the direction of lateral auxin flow in response to gravity. Pharmacological and genetic studies show that the negative root gravitropic response of the ngr mutants depends on polar auxin transport in the root elongation zone. Cell biology studies further demonstrate that polar localization of the auxin efflux carrier PIN3 in root columella cells and asymmetric lateral auxin flow in the root tip in response to gravistimulation is reversed in the atngr1;2;3 triple mutant. Furthermore, simultaneous mutations of three PIN genes expressed in root columella cells impaired the negative root gravitropic response of the atngr1;2;3 triple mutant. Our work revealed a critical role of NGR in root gravitropic response and provided an insight of the early events and molecular basis of the positive root gravitropism.

Premise of the study Lead (Pb) is a contaminant whose removal from soil remains a challenge. In a previous study, border cells released from root tips were found to trap Pb, alter its chemistry, and prevent root uptake. Rhodizonic acid (RA) is a forensic tool used to reveal gunshot residue, and also to detect Pb within plant tissues. Here we report preliminary observations to assess the potential application of RA in exploring the dynamics of Pb accumulation at the root tip surface. Methods and results Corn root tips were immersed in Pb solution, stained with RA, and observed microscopically. Pb trapping by border cells was evident within minutes. The role of extracellular DNA was revealed when addition of nucleases resulted in dispersal of RA-stained Pb particles. Conclusions RA is an efficient tool to monitor Pb-root interactions. Trapping by border cells may control Pb levels and chemistry at the root tip surface. Understanding how plants influence Pb distribution in soil may facilitate its remediation.

Callus formation in tissue culture follows the rooting pathway, and newly formed callus seems to be a group of root primordium-like cells. However, it is not clear whether there are multiple mechanisms of callus initiation in different species and in different organs. Here we show that the OsIAA11-mediated pathway is specifically and strictly required for callus initiation in the lateral root (LR) formation region of the primary root (PR) but not for callus initiation at the root tip or the stem base in rice. OsIAA11 and its Arabidopsis homolog AtIAA14 are key players in lateral rooting. However, the AtIAA14-mediated pathway is not strictly required for callus initiation in the LR formation region in Arabidopsis. LRs can be initiated through either the AtIAA14-mediated or AtWOX11-mediated pathway in the Arabidopsis PR, therefore providing optional pathways for callus initiation. In contrast, OsIAA11 is strictly required for lateral rooting in the rice PR, meaning that the OsIAA11 pathway is the only choice for callus initiation. Our study suggests that multiple pathways may converge to WOX5 activation during callus formation in different organs and different species.

In this study, wheat (Triticum aestivum L.) roots were treated with hypoxic water. The staining of cell preparations with DAPI revealed morphological changes of the cells such as nuclear condensation, deformation and fragmentation. Under TEM, cellular membrane shrinkage and breakage, chromatin condensation and apoptotic-like bodies were displayed. The number of mitochondria increased dramatically; their cristae were damaged; the interior became a cavitation and only some flocculent materials were distributed. Indirect immunofluorescence staining indicated that cytochrome C diffused from mitochondria to nucleoplasm and cytoplasm. TUNEL positive nuclei indicated double strand breaks of DNA. DAB staining was used for the identification of hydrogen peroxide and examination showed that the longer the treating time, the darker the staining of the meristematic zones of the roots which suggested the increased accumulation of these Reactive Oxygen Species (ROS). The elevation of hydrogen peroxide production was paralleled with the increase of SOD and POD activities. A negative correlation between the exposure time under hypoxia and the contents of soluble proteins was found. No obvious effect of hypoxia on MDA was established. The obtained results demonstrate that hypoxia causes programmed cell death in the root-tip meristematic cells of Triticum aestivum L. which is most probably attributed to the accumulation of large amounts of ROS.

Texas bluegrass (Poa arachnifera Torr.) is a dioecious, perennial, cool-season grass native to southern Kansas, Oklahoma, western Arkansas and most of Texas. Its major use has been for forage on rangelands in Texas and Oklahoma. More recently, interspecific hybrids between Texas bluegrass and Kentucky bluegrass (P. pratensis L.) have been developed and commercially released as heat tolerant turfgrass. Currently, the 2C nuclear DNA content of Texas bluegrass is unknown. Therefore, flow cytometry was performed on an assortment of male and female Texas bluegrass genotypes (n = 24) collected from fourteen locations in Texas and Oklahoma to estimate DNA content in picograms (pg). The DNA content of Texas bluegrass fell into two groups based on collection location. Plants collected from northwest Oklahoma and five other locations west of 33.75, −98.39 (latitude, longitude) ranged from 9.64 ± 0.04 to 10.07 ± 0.09 pg. Plants collected from four sites in Texas, east of 33.20, −98.16 contained a DNA content that ranged from 14.02 ± 0.04 to 14.75 ± 0.13 pg. Based on a root tip chromosome count, a male Texas bluegrass plant estimated to be 9.96 pg, appeared to contain 56 chromosomes, indicating the smaller DNA content plants may be octaploids (2n = 8x = 56). Significant differences were not detected between male and female plants based on DNA content. Knowledge of the DNA content in Texas bluegrass should be useful in a breeding program for characterizing germplasm and identifying desired DNA content levels among parental genotypes.

Morphogenic responses, ROS generation and changes in enzymes activity induced by the short-term exposure of barley roots to Cd were very similar to those of triiodobenzoic acid (TIBA) treatment. Both Cd and TIBA markedly increased the amount of IAA in root apex. In addition, the treatment of roots with TIBA before Cd treatment had an additive effect on morphogenic responses, changes in enzymes activity and ROS generation. In turn, the application of auxin efflux/influx inhibitor 1-naphthoxyacetic acid (1-NOA) before Cd treatment significantly reduced the Cd-induced ROS generation, root growth inhibition and enzymes activity in spite of the elevated level of IAA in the root apex. The auxin signalling inhibitor p-chlorophenoxyisobutyric acid (PCIB) nearly fully eliminated some of these Cd-induced responses. These results indicated that the short-term Cd treatment-induced ROS generation, morphogenic responses and activity of some enzymes can be attributed to the disturbance of IAA homeostasis in root apex. While auxin efflux inhibitor TIBA evoked similar response to Cd, auxin efflux/influx inhibitor 1-NOA attenuated and auxin signalling inhibitor PCIB blocked these Cd-induced responses suggesting that apart from the elevated level of IAA in root apex its enter and accumulation inside of until closely undetermined cells or tissues is a prerequisite for the induction of characteristic root responses to short-term Cd exposure.

Cd (cadmium) stress always alters the homeostasis of ROS (reactive oxygen species) including H2O2 (hydrogen sulfide) and O2•– (superoxide radical), leading to the oxidative injury and growth inhibition in plants. In addition to triggering oxidative injury, ROS has been suggested as important regulators modulating root elongation. However, whether and how Cd stress induces the inhibition of root elongation by differentially regulating endogenous H2O2 and O2•–, rather than by inducing oxidative injury, remains elusive. To address these gaps, histochemical, physiological, and biochemical approaches were applied to investigate the mechanism for Cd to fine-tune the balance between H2O2 and O2•– in the root tip of Brassica rapa. Treatment with Cd at 4 and 16 μM significantly inhibited root elongation, while only 16 μM but not 4 μM of Cd induced oxidative injury and cell death in root tip. Fluorescent and pharmaceutical tests suggested that H2O2 and O2•– played negative and positive roles, respectively, in the regulation of root elongation in the presence of Cd (4 μM) or not. Treatment with Cd at 4 μM led to the increase in H2O2 and the decrease in O2•– in root tip, which may be attributed to the up-regulation of Br_UPB1s and the down-regulation of their predicted targets (four peroxidase genes). Cd at 4 μM resulted in the increase in endogenous H2S in root tip by inducing the up-regulation of LCDs and DCDs. Treatment with H2S biosynthesis inhibitor or H2S scavenger significantly blocked Cd (4 μM)-induced increase in endogenous H2S level, coinciding with the recovery of root elongation, the altered balance between H2O2 and O2•–, and the expression of Br_UPB1s and two peroxidase genes. Taken together, it can be proposed that endogenous H2S mediated the phytotoxicity of Cd at low concentration by regulating Br_UPB1s-modulated balance between H2O2 and O2•– in root tip. Such findings shed new light on the regulatory role of endogenous H2S in plant adaptions to Cd stress.

Roots respond to changes in environmental nitrate with a localized stimulation of ABA levels in the root tip. This rise in ABA levels is due to the action of ER-localized β-GLUCOSIDASE 1, which releases bioactive ABA from the inactive ABA-glucose ester. The slow rise in root tip ABA levels stimulates expression of nitrate metabolic enzymes and simultaneously activates a negative feedback loop involving the protein phosphatase, ABI2, which reduces nitrate influx via the AtNPF6.3 transceptor. The rise in root-tip localized ABA also negatively regulates expression of the SCARECROW transcription factor, thus providing a sensitive mechanism for modulating root growth in response to environmental changes.

Phosphite is used to control Oomycetes in a wide range of horticultural and native plant species worldwide. However, phosphite can be phytotoxic, and some pathogens have exhibited a reduction in the effectiveness of phosphite due to prolonged use. In this study, salicylic acid (SA) was investigated as an alternative, or supplementary, treatment to be used to protect plant species. With the use of aeroponics chambers, foliar application of phosphite, SA, and phosphite/SA to Lupinus augustifolius was assessed in relation to root tip damage, in planta phosphite and SA concentration and lesion development. Both phosphite and SA were measurable at the root tip within 24 h of application, and all treatments significantly (P ≤ 0.05) reduced the lesion length at 7 days. However, while phosphite and SA application increased the in planta SA concentration, phosphite caused significantly more damage to the root tip by reducing root cap layers and length than the SA, or phosphite/SA application. This study supports the notion that phosphite-induced sensitivity may be SA-dependent, as both phosphite and SA were found to control P. cinnamomi and stimulate SA accumulation. A combination of phosphite and SA may be more beneficial to plants if it can reduce phytotoxic effects and reduce the chance of pathogen sensitivity to phosphite.

Plants rapidly release photoassimilated carbon (C) to the soil via direct root exudation and associated mycorrhizal fungi, with both pathways promoting plant nutrient availability. This study aimed to explore these pathways from the root's vascular bundle to soil microbial communities. Using nanoscale secondary ion mass spectrometry (NanoSIMS) imaging and (13) C-phospho- and neutral lipid fatty acids, we traced in-situ flows of recently photoassimilated C of (13) CO2 -exposed wheat (Triticum aestivum) through arbuscular mycorrhiza (AM) into root- and hyphae-associated soil microbial communities. Intraradical hyphae of AM fungi were significantly (13) C-enriched compared to other root-cortex areas after 8 h of labelling. Immature fine root areas close to the root tip, where AM features were absent, showed signs of passive C loss and co-location of photoassimilates with nitrogen taken up from the soil solution. A significant and exclusively fresh proportion of (13) C-photosynthates was delivered through the AM pathway and was utilised by different microbial groups compared to C directly released by roots. Our results indicate that a major release of recent photosynthates into soil leave plant roots via AM intraradical hyphae already upstream of passive root exudations. AM fungi may act as a rapid hub for translocating fresh plant C to soil microbes.

Short-term exposure (15 min) of barley roots to different chemical elements revealed that Cd, Cu, Hg and Pb were the most toxic ones causing a marked root growth inhibition even at µM concentrations. Gd, La, Al, Cr, As, Zn, Ni and Se inhibited root growth to a similar extent only at mM concentrations. Despite the high 20 mM concentration, Co caused only a slight, while Mn, Mg or Ca did not evoke any root growth inhibition. Elements at concentrations inhibiting root growth caused a considerable accumulation of indole-3-acetic acid in the root apex. While Cr, As and Zn inhibited, Cd, Cu, Hg, Pb, Gd, La and Al markedly stimulated the generation of reactive oxygen species in the beginning of differentiation zone. Auxin signalling inhibitor alleviated or prevented root growth inhibition, reactive oxygen species generation and the stimulation of lipoxygenase and glutathione peroxidase activity by various elements, indicating a key role of auxin signalling in the stress response of barley root tip. On the other hand, it did not affect or even had an additive effect on dehydroascorbate reductase and ascorbic acid oxidase activity in combination with different elements. Our results indicate that the primary response of barley roots to the presence of various chemical elements during the short-term treatment is not a specific but rather a general adaptive stress response enabling the plant to survive adverse conditions.

Gymnosperm root protophloem is not well understood. There is a question as to whether root protophloem cells mature as phloem parenchyma, or as sieve elements, or if within the protophloem there is an anatomical and evolutionary gradient having characteristics of both cell types. This question is relevant to understanding anatomical and physiological mechanisms that supply nutrients to the root tip. Anatomical data from a broad range of species show that gymnosperms have one to three layers of parenchymatous protophloem cells located at the vascular cylinder periphery between the pericyle and the metaphloem. In some species, these cells are associated with secretory idioblasts. Near the root apex, protophloem cells develop a large central vacuole and, in transverse sections, their radial walls tend to be radially elongated. When mature, these cells are highly longitudinally elongated. Only these cells exhibit surging toward the root apex during chemical fixation. These data indicate that protophloem of gymnosperm roots lacks sieve elements. Because of its distinctive anatomical characteristics and the absence of sieve elements, gymnosperm root protophloem is a vegetative synapomorphy among extant species. The restriction of this tissue type to gymnosperms supports the hypothesis that it originated in a progenitor of that clade.

Despite the critical role of EMF in nutrient and carbon (C) dynamics, combined effects of global atmospheric pollutants on ectomycorrhizal fungi (EMF) are unclear. Here, we present research on EMF root-level community responses to elevated CO2 and O3. We discovered that belowground EMF community richness and similarity were both negatively affected by CO2 and O3, but the effects of CO2 and O3 on EMF communities were contingent on a site soil pH and cation availability gradient. These results contrast with our previous work showing a strong direct effect of CO2 and O3 on sporocarp community dynamics and production. We discuss the possible role of carbon demand and allocation by EMF taxa in the discrepancy of these results. EMF communities were structured by a legacy of spatially defined soil properties, changing atmospheric chemistry and temporal dynamics. It is therefore necessary to understand global change impacts across multiple environmental gradients and spatiotemporal scales.

Changes caused by lead, supplied in the form of Pb(NO3)2, in roots and hypocotyls of 4 day old yellow lupin (Lupinus luteus L. cv. ventus) seedlings have been analyzed using a transmission electron microscope and polyacrylamide gel electrophoresis (PAGE). The cells of all examined parts of the roots growing in the presence of Pb2+ contained many lead deposits (mainly in the cell walls and vacuoles) and the increased amount of polypeptides of molecular weight close to 16 kDa have been observed. Similar changes were detected in the area of hypocotyl adjoining the root. However, in upper regions of the hypocotyl only a slight amount of lead deposits was visible and the 16 kDa polypeptide content was comparable to the control cells. The obtained results indicate a relationship between the presence of lead deposits in cells and accumulation of polypeptides of - 16 kDa. The results seem also to indicate that in the analyzed parts of the seedlings, both the amount of accumulated polypeptides of MW - 16 kDa and the amount of lead decreased from root tip to hypocotyl.

This paper is a brief review of the problem of lead-in the environment, particularly constitutional tolerance to lead about which little is known. Taking Allium cepa L. roots as a model it has been shown that after an initial phase in which lead is toxic to cells, defence processes appear with the results that lead is no longer poisonous. The lead which penetrates into the root symplast is detoxified in vacuoles, cell walls and dictiosomal vesicles. Initial cells of the meristem (quescent centre) which play a basic role in the root regeneration processes are protected against lead penetration. This surprising result is in agreement with the absence of any symptoms of lead poisoning in plants growing in natural conditions, and suggests that there is a defence mechanism specific only for plant cells.

Observations were carried out to define the place of lead absorption within three regions of the poplar adventitious root tip (Populus nigra "Italica" Moench.) after 24-hour exposure to a solution of Pb(N03)2 (25 mg dm-3 Pb). Deposits of lead were not observed in certain cells of the apical part of the meristem. In other cells, lead deposits were first observed in the lumen of several endomembrane compartments - the endoplasmic reticulum, dictyosomal stacks and nuclear envelope. Certain differences were noted in the amount of deposits in protoplasts with varied electron density. In the cells with greater deposits, lead was also observed in the cytoplasm, the mitochondria and the paramural bodies. Practically no lead precipitated in the cell wall. The presence of lead in the form of small deposit granules in the plasmodesmata may suggest transfer from cell to cell.