Zeatin Riboside Research Articles

ВПЛИВ БІОЛОГІЧНО АКТИВНИХ ЕКСТРАКТІВ З ВИСОКИМ ВМІСТОМ ЦИТОКІНІНІВ З МІЦЕЛІАЛЬНОЇ БІОМАСИ HERICIUM CORALLOIDES ТА FOMITOPSIS OFFICINALIS НА ПУХЛИННІ КЛІТИНИ IN VITRO

Phytohormones cytokinins are known to promote cell division in plants. Contrary, in animal's and human's tissues they induce apoptosis and block the cell cycle of a wide spectrum of tumour cells. Therapeutic effects of cytokinins, specifically their anticancer and immunomodulatory actions are similar to those of medicinal mushrooms. We detected cytokinins in mycelial biomass of two species of medicinal mushrooms growing in vitro (Fomitopsis officinalis strain 5004 and Hericium coralloides strain 2332) using HPLC-MS. Trans-zeatin, zeatin riboside, zeatin-O-glucoside and isopentenyladenine were found. Crude extracts and purified cytokinin fractions from mycelial biomass were tested on the growth and development of cultures of tumor cells lines: Hela (MTT-assay), T24/83 (viability and level apoptotic cells) and HepG2 (consumption of glucose). The effect of cytokinin fraction from mycelial biomass of Fomitopsis officinalis on pathogenic cells was higher compared to Hericium coralloides one. The data obtained revealed a higher cytotoxic/cytostatic effect of the purified cytokinin fractions in comparison with crude methanolic extracts; also higher apoptotic index was found. Under the influence of the test agents the intensification of glucose uptake into cells was observed. This indicator was higher for crude mushroom mycelium extracts, whereas under the action of purified fractions the glucose uptake rate was lower, thus decreased glycolysis level was recorded. Also, the effect of both crude extract and purified fraction from H. coralloides mycelial biomass on glucose uptake in the conditioned medium was lower against F. officinalis.These results confirm the assumption that biologically active substances of medicinal mushrooms with high pharmacological potential include cytokinins.

Engineered nanomaterials inhibit Podosphaera pannosa infection on rose leaves by regulating phytohormones

In the present study, we investigated the antifungal effects of engineered nanomaterials (ENMs) against Podosphaera pannosa (P. pannosa), a fungal pathogen that causes powdery mildew on plants in the rose family. Four commercial ENMs, including multi-wall carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), copper oxide (CuO) nanoparticles (NPs) and titanium dioxide (TiO2) NPs, were used to prepare 50 or 200 mg/L NP suspensions in deionized water. Rose leaves in water-agar plates were sprayed by different ENM suspensions mixed with P. pannosa conidia. After a 19-day standard infection test, the growth of P. pannosa on rose leaves was evaluated. All four ENMs inhibited infection by P. pannosa at the concentration 200 mg/L, whereas only CuO NPs decreased fungal growth at 50 mg/L. The phytohormone content of the leaves was measured across all treatments to investigate potential ENMs antifungal mechanisms. The results suggest that ENMs increased plant resistance to fungal infection by altering the content of endogenous hormones, particularly zeatin riboside (ZR). Our study demonstrates that ENMs exhibited distinctly antifungal effects against P. pannosa on roses, and could be utilized as a novel plant protection strategy after a comprehensive assessment of potential environmental risk.

Alleviation of drought stress in grapevine by foliar-applied strigolactones

Drought is one of the major abiotic stress factors that affect grape growth and yield, which in turn negatively affects the grape and wine production industry. Developing effective approaches to improve grapevine tolerance to drought stress is a priority for viticulture. Strigolactones, a newly discovered class of carotenoid-derived phytohormones, have been found to participate in various physiological processes. Herein, the effect of strigolactones (SLs) on grape seedlings under drought stress was investigated. Two-year-old grape seedlings (Vitis vinifera L.) were sprayed with 3 doses of rac-GR24 (1 μM, 3 μM and 5 μM), a synthesized strigolactone, and then were subjected to 7% (w/v) polyethylene glycol (PEG-6000) to simulate the drought conditions. Synthetic GR24 treated plants showed higher tolerance to drought stress with regard to lower electrolyte leakage, stomatal opening, reactive oxygen species (ROS), and higher relative water content, chlorophyll content, photosynthesis rate and malondialdehyde (MDA) content. GR24 application also decreased the levels of indoleacetic acid (IAA) and zeatin riboside (ZR), while increasing the level of abscisic acid (ABA), both in the roots and leaves under drought stress. These results suggested that foliar application of GR24 could ameliorate the adverse effects of drought due to its regulation of stomatal closure through ABA or ROS, and modulation of chlorophyll components and photosynthesis, as well as activation of the antioxidant defense capacity. Cross-talk with other hormones, especially ABA, was also suggested to be one of the important mechanism during this process. This study contributes to our current understanding of GR24-induced drought tolerance in grapevines.

Effect of brassinolide application on antioxidant characteristics and endogenous hormones of Leymus chinensis (Trin.) Tzvelev under different light intensity regimes

Different light and shade intensities are the main constraints to achieve potential biomass accumulation in Leymus chinensis (Trin.) Tzvelev. An experiment was conducted to explain the physiochemical and morphological adversity triggered by various light intensities. Adverse impacts were lessened with exogenous brassinolide (BR). Treatments consisted of 100% natural light (T0), 100% natural light + 0.1 mg L-1 BR (BT0), light shade (70% natural light) (T1), light shade + BR (70% natural light + 0.1 mg L-1 BR) (BT1), moderate shade (50% natural light) (T2), and moderate shade + BR (50% natural light + 0.1 mg L-1 BR) (BT2). These were completely randomized design treatments with five replicates. Results showed that dry biomass production and endogenous hormone levels (abscisic acid [ABA], zeatin riboside [ZR], gibberellic acid [GA], and indole acetic acid [IAA]) increased, while osmolyte accumulation (soluble sugars and proteins, free amino acids, and proline), antioxidant activity (peroxidase [POD], superoxide dismutase [SOD], and catalase [CAT]), and lipid peroxidation decreased under shade at T0. Treatment T1 depicted the most promising results for these attributes. However, biomass accumulation (33%-56%), osmotic substances (soluble sugars,13%-38%; soluble proteins, 9%-41%; free amino acids, 8%-16%; proline, 11%-41%), and antioxidant enzyme activities (POD, 11%-14%; SOD, 3%-33%; CAT, 4%-23%) increased. On the other hand, lipid peroxidation was reduced by BR application, as indicated by decreased malondialdehyde (MDA) content (7%-31%) and relative conductivity (7%-19%) under both natural and shade conditions. Likewise, the biosynthesis of ABA (2%-22%), ZR (11%-24%), and GA (30%-50%) improved under exogenous BR compared with the control. The IAA contents (22%-28%) decreased under foliar-applied BR compared with the control. Results suggested that light to moderate shade improved the biomass production and physiological performance of L. chinensis, while BR application exhibited further improvement

A filter paper-based liquid culture system for citrus shoot organogenesis—a mixture-amount plant growth regulator experiment

This study determined the effects of a static liquid culture system on shoot regeneration from citrus epicotyl explants. A mixture-amount experiment was used to determine the effects of zeatin riboside (ZR), 6-benzylaminopurine (BA), and indole-3-acetic acid (IAA) on two citrus types—citrange (Citrus sinensis ‘Washington’ L. Osbeck. × Poncirus trifoliata L. Raf var. Carrizo) and sweet orange (Citrus sinensis L. Osbeck var. ‘Ridge Pineapple’). A liquid culture system comprising a Petri dish, cellulose filter paper, and liquid culture medium was used. Shoot regeneration experiments were conducted over 6 wk that included 2 wk in the dark followed by 4 wk in the light. Three responses were measured: (1) number of explants forming buds and/or shoots, (2) number of explants with shoots > 2 mm, and (3) overall explant and shoot quality. The effects of paper disc number, liquid medium volume, and explant size on shoot regeneration were determined. High-quality shoots were produced from explants cultured in 5.25 to 12 mL medium volume and explant sizes ranging from 2 to 15 mm. The effects of the plant growth regulators were similar for the two citrus types and were as follows: (1) use of ZR or BA resulted in high-quality shoot production; (2) ZR and BA were not synergistic; (3) culture in 20 μM ZR resulted in the highest shoot production; (4) BA and IAA were strongly synergistic, with the greatest production with BA when IAA was included in the mixture; and (5) ZR and IAA were antagonistic, particularly with Ridge Pineapple.

Expression of genes in the potential regulatory pathways controlling alternate bearing in ‘Fuji’ (Malus domestica Borkh.) apple trees during flower induction

Most perennial fruit trees have an alternate bearing problem where a heavy fruit load is produced one year (ON year) but few flowers and fruits produced the next year (OFF year), resulting in a significant fluctuation in production. In the present study, comparative transcriptome analysis of terminal buds of apple (Malus domestica Borkh., cv. Nagafu No. 2) trees was conducted during the floral induction period in the ON and OFF years to identify the potential regulatory pathways controlling alternate bearing. A total of 1027 differentially expressed genes (DEGs), most of which were involved in secondary metabolism, sugar metabolism, plant hormone pathways, were identified. The analysis focused on differences in sugar content and hormone levels between the ON and OFF trees. Sucrose content, zeatin-riboside (ZR), and abscisic acid (ABA) levels were lower in ON-year buds than in OFF-year buds. ON buds also had elevated levels of gibberellins (GAs), with a higher expression of GA20 oxidase (GA20ox) and a significant lower level of RGA-like2 (RGL2). Expression analyses also revealed a significantly higher level of SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE genes (MdSPL1, MdSPL6 and MdSPL12) transcripts levels in buds of OFF trees at 45 days after full bloom (DAFB). LEAFY (LFY) expression increased significantly prior to flower induction in OFF buds. These findings provide new information of the role of hormones in alternate bearing, as well as other processes, and provide new insights into the molecular mechanisms regulating alternate bearing in perennial fruit trees.

Seed filling in maize and hormones crosstalk regulated by exogenous application of uniconazole in semiarid regions.

In semiarid regions, deficit and unpredictable precipitation results in yield losses. Uniconazole is a plant growth regulator and its application is beneficial in water saving agriculture and improves maize production in semiarid regions. In order to determine the effects of uniconazole application on seed filling and hormonal changes of maize, a field study was conducted in the summer of 2015 and 2016. Seeds were soaked in uniconazole at concentration of 0 (SCK), 25 (S25), 50 (S50), and 75 (S75) mgkg-1, while in the second experiment, uniconazole was applied to the foliage at concentration of 0 (FCK), 25 (F25), 50 (F50), and 75 (F75) mgL-1 at the eight-leaf. Uniconazole application significantly improves the seed filling rates by regulating the endogenous hormones contents. Uniconazole seed soaking treatments improved significantly the seed filling rate of superior, middle, and inferior seeds compared with foliar application treatments. Uniconazole improved significantly the zeatin (Z) + zeatin riboside (ZR) and abscisic acid (ABA) contents while reducing the gibberellic acid (GA) content in the seeds during the process of seed filling. The Z + ZR and ABA contents were significantly positively correlated while the GA content was negatively correlated with maximum seed weight, maximum seed filling rates, and mean seed filling rates. Treatments S25 and F25 significantly improved the above dry matter accumulation plant-1, seed filling rates, ABA, Z + ZR contents, characters of ear, and grain yield while reduced the GA content. It is concluded from our results that the uniconazole application at concentration of 25mgkg-1 as seed soaking or 25mgL-1 foliar applied at the eight-leaf stage is beneficial to improve the seed filling rates and grain yield of maize in semiarid regions.

Grain development and endogenous hormones in summer maize (Zea mays L.) submitted to different light conditions.

Low light is a type of abiotic stress that seriously affects plant growth and production efficiency. We investigated the response mechanisms of summer maize to low light by measuring the changes in endogenous hormones in the grains and during grain filling in summer maize at different light intensities to provide a theoretical basis for the production and management of summer maize under light stress. We applied different light treatments in a field experiment as follows: S, shading from tassel stage (VT) to maturity stage (R6); CK, natural lighting in the field; and L, increasing light from VT to R6. The shading level was 60%, and the maximum illumination intensity of the increasing light treatment on cloudy days was 1600-1800μmolm-2s-1. Compared with the control, shading significantly increased the grain abscisic acid (ABA) content at 5-20days after pollination and decreased the indole acetic acid (IAA), zeatin riboside (ZR), and gibberellin (GA) contents (P < 0.05). The grain-filling rate decreased under shading conditions. Meanwhile, the grain volume, grain weight, and yield all decreased; the yields in 2013 and 2014 decreased by 61 and 60%, respectively. The grain IAA, ZR, and GA contents were increased by increasing light. The grain ABA content at 5-20days after pollination did not significantly differ from that of CK (P < 0.05). After 20days after pollination, the ABA content decreased, the grain-filling rate and the filling duration increased, and the yield increased. However, shading after anthesis increased the grain ABA content and reduced the IAA, ZR, and GA contents. Grain growth and development were inhibited, and the yield decreased. The grain ABA content decreased; the IAA, ZR, and GA contents increased; and the yield increased after increasing light. The results indicate that different light intensities regulated the levels of grains endogenous hormones, which influenced the grain-filling rate and duration, and consequently, regulated grain weight and yield.

Influence of Two Nitrogen Forms on Hormone Metabolism in Potential Storage Roots and Storage Root Number of Sweetpotato

In this study, we investigated the effects of two N forms on sweetpotato [Ipomoea batatas (L.) Lam.] root growth and development, zeatin riboside (ZR) and indole‐3‐acetic acid (IAA) concentrations in potential storage roots, and storage root number per plant. During the period 2015 to 2016, field experiments were performed using the sweetpotato cultivars ‘Shangshu 19’ and ‘Jixu 23’, which involved the following three treatments: no application of N fertilizer, application of 60 kg N hm−2 ammonium N, and application of 60 kg N hm−2 amide N. Our results indicated that during storage root formation, compared with the control treatment, the ammonium N treatment led to a significantly higher number of thick roots. However, the ammonium N treatment significantly reduced the average diameter of thick roots during early storage root formation and increased the average diameter during late storage root formation. Compared with the control treatment, ammonium N treatment inhibited the expression of Ibkn1, Ibkn2, and SRD1 genes during the early stage of storage root formation and also reduced the activities of IAA oxidase, peroxidase, and polyphenol oxidase enzymes, thereby ultimately reducing the ZR and IAA concentrations in potential storage roots. The opposite pattern was observed during the late stage of storage root formation. During the canopy closure period, compared with the control treatment, ammonium N treatment significantly increased the number of storage roots with diameters of 0.5 to 5.0 cm but decreased the number of storage roots with diameters &gt;5.0 cm. At harvest, the ammonium N treatment had resulted in the highest storage root yield and storage root number per plant.

Appropriate ultra-low seed moisture content stabilizes the seed longevity of Calocedrus macrolepis, associated with changes in endogenous hormones, antioxidant enzymes, soluble sugars and unsaturated fatty acids

Calocedrus macrolepis Kurz is a relic and endangered woody plant, which is naturally distributed in southwestern China and adjacent regions, and is known for its valuable timber. There is a serious bottleneck in C. macrolepis conservation: its seed vigor is lost rapidly after harvesting. To explore the feasibility of ultra-dry storage of the seeds of this species, seeds were dehydrated to five different moisture contents (MCs, 1–5%), and stored at ambient temperature for 5 years. Seeds stored at 2.1% or 3.0% had higher percentage germination than those stored than the non-dehydrated seeds. Furthermore, we measured quantitative changes in metabolic products, namely endogenous hormones, soluble sugars and fatty acids, and activities of antioxidant enzymes. Among four endogenous hormones investigated, the concentration of the auxin indole-3-acetic acid was not significantly different at different MCs, while there was a negative relationship between percentage germination and both gibberellic acid and cytokinin zeatin riboside concentrations, and a positive relationship between abscisic acid concentration and percentage germination. Seeds with MCs of 2.1 or 3.0% contained higher activities of the antioxidant enzymes glutathione reductase, ascorbate peroxidase, superoxide dismutase and catalase, corresponding to lower concentrations of malondialdehyde. Compared with seeds at other MCs, higher concentrations of sucrose, glucose, trehalose (but not fructose) and unsaturated fatty acids were maintained in seeds at 2.1% and 3.0% MCs. Therefore, we suggest that levels of certain endogenous hormones, antioxidant enzymes, soluble sugars and unsaturated fatty acids may help stabilize longevity of seed at ultra-low seed moisture content. Storage of seed of C. macrolepis at 2–3% MC at room temperature may be a useful method for conserving germplasm of this species and in facilitating nursery operations.

Reduction of Tomato-Plant Chilling Tolerance by CRISPR-Cas9-Mediated SlCBF1 Mutagenesis.

Chilling stress is the main constraint in tomato ( Solanum lycopersicum) production, as this is a chilling-sensitive horticultural crop. The highly conserved C-repeat binding factors (CBFs) are cold-response-system components found in many species. In this study, we generated slcbf1 mutants using the CRISPR-Cas9 system and investigated the role of SlCBF1 in tomato-plant chilling tolerances. The slcbf1 mutants exhibited more severe chilling-injury symptoms with higher electrolyte leakage and malondialdehyde levels than wild-type (WT) plants. Additionally, slcbf1 mutants showed lower proline and protein contents and higher hydrogen peroxide contents and activities of antioxidant enzymes than WT plants. Knockout of SlCBF1 significantly increased indole acetic acid contents but decreased methyl jasmonate, abscisic acid, and zeatin riboside contents. The reduced chilling tolerance of the slcbf1 mutants was further reflected by the down-regulation of CBF-related genes. These results contribute to a better understanding of the molecular basis underlying SlCBF1 mediation of tomato chilling sensitivity.

Chemical priming of seed alters cotton floral bud differentiation by inducing changes in hormones, metabolites and gene expression

Fruiting branches and floral buds are forming well before squares are visible and determine cotton (Gossypium hirsutum L.) productivity. Pre-soaking with plant growth regulators (PGRs) affects the quantity of floral buds. However, studies illustrating the physiological mechanism of floral bud differentiation in response to PGRs are lacking. To address this, cotton seeds were primed with water (control), 5 mg L−1 gibberellic acid (GA3), 25 mg L−1 N6-benzyladenine (6-BA), and 150 mg L−1 dimethyl piperidinium chloride (DPC) respectively. Results showed that plants from seed pre-treated with GA3 and 6-BA differentiated more floral buds relative to control, while DPC application initiated less floral buds than control. GA3 and 6-BA application significantly increased the levels of zeatin riboside (ZR) by up-regulating IPT expression and gibberellic acid (GA3) but decreased the indole-3-acetic acid (IAA) content. Consequently, the ZR/IAA and GA3/IAA ratios were markedly increased, contributing to higher floral bud numbers. Contrasting results were observed for DPC treatment. Additionally, GA3 and 6-BA treatments up-regulated GhSOC1, GhMADS13 and GhAGL24 expression, which was associated with higher sucrose contents mainly attributed to higher endogenous ZR levels, inducing floral initiation. Whereas the GhMADS13 was down-regulated to suppress floral bud differentiation under DPC application. Surprisingly, the floral-associated genes were more sensitive to GA3 than 6-BA, which induced the differences in bud numbers at the beginning of flower bud differentiation. Thus, we conclude that seed pre-treated with PGRs affected hormone content, induced sugar accumulation in apical buds and regulated genes involved in floral induction, which impacted floral bud differentiation.

Virus infection reduces shoot proliferation of in vitro stock cultures and ability of cryopreserved shoot tips to regenerate into normal shoots in ‘Gala’ apple (Malus × domestica)

Plant cryopreservation has provide secure back-ups of germplasm collections of vegetatively propagated crops. Often, recovery levels vary among laboratories when the same cryogenic procedures are used for the same genotypes. The present study investigated the effects of Apple stem grooving virus (ASGV) on shoot proliferation of in vitro stock cultures and recovery of cryopreserved shoot tips of ‘Gala’ apple. Results showed that virus infection reduced shoot proliferation of in vitro stock cultures and cell ability to regenerate normal shoots in cryopreserved shoot tips. Virus infection increased total soluble protein, total soluble sugar and free proline levels and altered endogenous levels of indoleacetic acid (IAA) and zeatin riboside (ZR), but induced severe cell membrane damage and caused alternation in mitochondria shape of the in vitro stock shoots. The altered levels of IAA and ZR were most likely to be responsible for the reduced shoot proliferation of in vitro stock culture. Cell damage and alternations in mitochondria shape in ASGV-infected shoot tips were most likely responsible for the reduced cell ability to regenerate normal shoots following cryopreservation. To the best of our knowledge, this is the first study on effects of virus infection on recovery of cryopreserved shoot tips. Results reported here emphasize that healthy in vitro stock cultures should be used for cryopreservation.

Temperature and Hormones Associated with Bacterial Etiolation Symptoms of Creeping Bentgrass and Annual Bluegrass

Bacterial etiolation, caused by Acidovorax avenae or Xanthomonas translucens pv. poae, is a problematic disease of creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua) turfgrass stands. The objective of this study was to determine whether temperature may play a role in phytohormone production by these bacteria and to determine if there is any change in phytohormones specifically in etiolated plant tissues. In vitro, A. avenae and X. translucens were cultured at 25, 30, 35 and 40 °C for 14 days. Bacterial cultures were sampled for gibberellic acid isoforms (GA1, GA3, GA4, and GA20), jasmonic acid, salicylic acid (SA), indole-3-acetic acid (IAA), zeatin riboside, and abscisic acid (ABA). No phytohormones were detected in pure cultures of X. translucens, whereas A. avenae produced GA1, GA3, GA4, and IAA. Acidovorax avenae isolate MSU-13 produced significantly higher GA1 and GA3 at 35 and 40 °C on most days measured. In the field study, etiolated stem and leaf tissues of creeping bentgrass and annual bluegrass were evaluated for bacterial identification, etiolation ratings, and phytohormone quantification. Significantly more etiolation symptoms were observed in both annual bluegrass and creeping bentgrass on days with higher temperatures. In annual bluegrass, etiolated stems and leaves showed significantly higher GA1, GA3, etiolated leaves showed significantly higher GA20, ABA, and lower IAA compared to normal turf tissues on most experimental dates. In creeping bentgrass, higher GA1, GA4, SA, ABA, and lower IAA were detected in etiolated turf tissues than normal tissues on most experimental dates. Plant hormone regulation due to the presence of bacteria may be altered differentially in response to different bacteria species eliciting similar plant symptoms.

Interactions between cytokinin and nitrogen contribute to grain mass in wheat cultivars by regulating the flag leaf senescence process

Premature senescence after anthesis reduces crop yields. Delaying leaf senescence could maintain photosynthetic activity for a longer period and lead to a higher photosynthetic rate. Recent studies have provided some insights into the interaction between cytokinin and nitrogen (N) in the regulation of plant development. In the present study, foliar application of exogenous 6-benzylaminopurine (6-BA) and lovastatin, an inhibitor of cytokinin synthesis, was combined with three N rates [0 kg ha−1 (low nitrogen, LN), 240 kg ha−1 (normal nitrogen, NN), and 360 kg ha−1 (high nitrogen, HN)] in two wheat cultivars, Wennong 6 (with a staygreen phenotype) and Jimai 20 (with a non-staygreen phenotype). Flag leaf senescence was assessed using a Gompertz growth curve. Grain mass, dry matter accumulation and distribution, total N of flag leaf, and concentrations of zeatin riboside (ZR) and abscisic acid (ABA) were also used to evaluate the functional characteristics of flag leaves. Grain mass was negatively correlated with initial senescence rate (r0) and duration of rapid chlorophyll loss (Chlloss), whereas it was positively correlated with maximum senescence rate (rmax), average senescence rate (raver), persistence phase (Chlper), total duration of flag leaf (Chltotal) and inflection point cumulative temperature (M). Compared to Jimai 20, Wennong 6 had larger raver, Chlper, and Chltotal. The concentration of ZR was highest under the 6-BA × NN treatment, followed by the 6-BA × HN and 6-BA × LN treatments. However, the concentration of ABA showed the opposite trend. It was concluded that the staygreen phenotype Wennong 6 was associated with greater grain mass and altered cytokinin metabolism and could be classified as a functional staygreen type. Foliar application of 6-BA interacting with N at the NN level (240 kg ha−1) may be a beneficial strategy for improving grain yield of wheat by regulating endogenous hormones and the flag leaf senescence process. Increasing endogenous cytokinin promoted the transport of dry matter to grain.

The effect of the graft union on hormonal and ionic signalling between rootstocks and scions of grafted apple (Malus pumila L. Mill.)

The transport of chemical signals between rootstocks and grafted scions is implicated in the dwarfing capacity of apple (Malus pumila) rootstocks. This study investigated whether the intensity of putative ionic and hormonal signals between a dwarfing rootstock (M.9) and a semi-invigorating rootstock (MM.106) grafted with ‘Queen Cox’ scions was altered by the graft union. The capacity of rootstocks with different dwarfing potential for polar auxin transport (PAT) was also compared. Split-top pressure chambers were used to collect xylem sap samples at a range of flow rates from above and below the graft union in composite M.9 and MM.106 trees. Concentrations of hormones, anions and cations were quantified in expressed xylem sap. The effects of the graft union, flow rate and rootstock on xylem sap solute concentrations and deliveries were compared. Rootstocks of different dwarfing capacities maintained in micro-propagation were used to estimate and compare acropetal auxin transport; the velocity and intensity of PAT were determined using radiolabelled auxin. Sap osmolality and Ca+ + concentrations were reduced by passage through the M.9 graft union at very low flow rates. At transpirational flow rates, Ca++ and Mg++ concentrations were increased, and those of Na+ and NO3− decreased, by passage through the graft union. Deliveries of anions and cations from roots into shoots of M.9 composite trees were always similar or greater than those of MM.106 composite trees. Sap zeatin and zeatin riboside concentrations were reduced above the graft in both rootstocks. No evidence was found that a sub-optimal supply of essential mineral ions was involved in the dwarfing effect of M.9. Root- and shoot- specific deliveries of ABA in M.9 composite trees were significantly higher compared to MM.106 trees, and the greater import of ABA correlated temporarily with earlier shoot growth termination in M.9 composite trees. Intensity of PAT through micro-propagated stem tissue was lower in the dwarfing rootstock compared to more invigorating rootstocks.

Using rootstock to increase watermelon fruit yield and quality at low potassium supply: A comprehensive analysis from agronomic, physiological and transcriptional perspective

Abstract Grafting is a widely used technique in watermelon production. How grafting affects watermelon fruit yield and quality at low potassium supply and the mechanism remains unclear. This study addresses the question from agronomic, physiological and transcriptional perspective. Watermelon plants [Citrullus lanatus (Thunb.) Matsum. and Nakai, cv. Zaojia 8424], either self-grafted or grafted onto the rootstock ‘Yongshi’ (Citrullus lanatus sp.), ‘Jingxinzhen No.1’ (Lagenaria siceraria Standl.), and ‘Qingyanzhen No.1’ (Cucurbita maxima × C. moschata). Plants were subjected to 6.0 mM K (normal K) and 0.1 mM K (low K). Compared with plants treated with 6.0 mM K, those supplied with 0.1 mM K produced less fruit yield as indicated by the decrease in single fruit weight of all plants; however, a smaller decrease was observed in plants grafted onto ‘Yongshi’ (10%), ‘Jingxinzhen No.1’ (15%) and ‘Qingyanzhen No.1’ (19%) than the self- grafted watermelon (38%). The K+ concentration of stem, leaf, fruit peel and flesh were obviously higher in the rootstock- grafted plants than in the self- grafted ones under 0.1 mM K. In addition, rootstock- grafted plant had significantly higher leaf zeatin riboside and chlorophyll content. Fruit quality, including contents of total soluble solid, sucrose, vitamin C, lycopene, β-carotene, were significantly decreased in the self- grafted plants under 0.1 mM K. However, 0.1 mM K treatment did not result in an obvious decrease in most of the measured fruit quality parameters in the rootstock- grafted plants. Fruit transcriptome analysis showed that there were 670, 27, 16 and 15 differential expressed genes (DGEs) responded to 0.1 mM K in the self- grafted, ‘Yongshi’, ‘Jingxinzhen No.1’ and ‘Qingyanzhen No.1’- grafted plants, respectively, indicating that rootstock grafting decrease the sensitivity of watermelon fruit to 0.1 mM K at the transcriptome level, GO and KEGG analysis showed that most of the DGEs were enriched in cellular metabolic process and metabolic pathways. Low K (0.1 mM K) significantly increased the gene expression of potassium channel (Cla020934), but decreased the gene expression of phytoene synthase (Cla009122- responsible for lycopene synthesis) in the fruit flesh of self-grafted watermelon. Taken together, the above results suggested that compared with self- grafted plants, watermelon grafted onto rootstock can enhance plant fruit yield, quality and decrease the sensitivity of fruit flesh transcriptome to low K. The mechanism of improved performance under low potassium is discussed.

Effects of Root Cutting on Cytokinin Content in the Shoot Apex Cells of Arabidopsis Plants

The dependence of cytokinin accumulation in the shoot apexes of Arabidopsis plants on the delivery of these hormones from the roots was studied. For the estimation of cytokinin content in the cells, the immunohistochemical localization method using antibodies against zeatin riboside was used. Differential conjugation of free cytokinin bases and their ribosides was used to prevent washing of cytokinins during the dehydration process. Root cutting decreased the immunostaining of zeatin in the cells of the shoot apical meristem, thereby supporting the hypothesis about dependence of cytokinin accumulation in these cells on the hormone delivery from the roots. The level of cytokinins in the cells of the shoot apex decreased under the effect of protonophore, indicating the important role of the secondary-active transmembrane transport process of cytokinins in the maintenance of their level in the cells of the shoot apex.

Effects of plant population density and root-induced cytokinin on the corn compensatory growth during post-drought rewatering

The effect of plant population density (PPD) and root-induced leaf cytokinin on the compensatory growth of potted corn seedlings during post-drought rewatering was investigated. The study design comprised four treatments: (1) wetness with low PPD, (2) wetness with high PPD, (3) rewatering with low PPD, and (4) rewatering with high PPD. Results showed that drought stress restrained the growth of corns. By contrast, rewatering enhanced the net photosynthetic rate and growth of corns. During the 8 days of rewatering, compensatory growth during post-drought rewatering occurred in corns with high PPD; however, such compensatory growth did not occur in corns with low PPD. Zeatin riboside concentrations in leaves and xylem saps were significantly higher under rewatering treatment than those under wet treatment. High leaf cytokinin concentration accelerated corn growth. The coefficients of variation and Gini-coefficient of wet treatment were significantly higher than those of rewatering treatment under high PPD, demonstrating that intense intraspecific competition occurred in the wet treatment. Extreme intraspecific competition negatively affected net photosynthetic rate. In brief, the interactions between root-induced leaf cytokinin and weak intraspecific competition promoted the compensatory growth under high PPD.

Improving biomass and starch accumulation of bioenergy crop duckweed (Landoltia punctata) by abscisic acid application

Duckweed is a valuable feedstock for bioethanol production due to its high biomass and starch accumulation. In our preliminary experiment, we found that abscisic acid (ABA) could simultaneously increase starch and biomass accumulation of duckweed, but the mechanisms are still unclear. The results showed that the biomass production of duckweed reached up to 59.70 and 63.93 g m−2 in 6 days, respectively, with an increase of 7% (P < 0.05) compared to the control. The starch percentage increased from 2.29% up to 46.18% after 14 days of treatment, with a total of starch level 2.6-fold higher than that of the control. Moreover, the level of endogenous ABA, zeatin-riboside (ZR) and indole-3-acetic acid (IAA) increased, while gibberellins (GAs) decreased. Notably, ABA content in treated samples reached 336.5 mg/kg (fresh weight), which was 7.5-fold greater than that of the control. Importantly, the enzyme activities involved in starch biosynthesis increased while those catalyzing starch degradation decreased after ABA application. Taken together, these results indicated that ABA can promote biomass and starch accumulation by regulating endogenous hormone levels and the activity of starch metabolism related key enzymes. These results will provide an operable method for high starch accumulation in duckweed for biofuels production.