Endogenous cytokinins in rose petals and the effect of exogenously applied cytokinins on flower senescence

In extracts from rose petals cytokinin activity was detected by Amaranthus bioassay in HPLC eluates corresponding to the standards: Z, ZR, 2iP and 2iPA; subsequently, the presence of two groups of endogenous cytokinins was confirmed by ELISA.Measurements of senesence indicators (cell sap osmolarity and conductivity) and observations of flower vase-life indicated that when the above cytokinins were applied as holding solutions they delayed flower senescence by 34–56% and prolonged rose longevity.Abbreviations B.H.T. 2.6-di-t-buytl-4-methyl phenol - ELISA Enzyme linked Immunosorbent Assay - HPLC High Performance Liquid Chromatography - 2iP isopentenyladenine - 2iPA isopentenyladenosine - Z trans-zeatin - ZR trans-zeatin riboside     

Distribution and transport of IAA in tomato plants

We determined as to indole-3-acetic acid (IAA), endogenous levels byliquid chromatography-mass spectrometry using ¹³C₆-IAA, diffusible levels byfluorometric detection using indole-propionic acid, and polar transportactivityby radioactive IAA in 3-month-old tomato plants (stems, leaves or roots). TheIAA concentration in the apoplast (AP) solution was higher than those in thesymplast (SP) solution in both the upper and lower parts of stems, showing thatIAA analysis of AP solution is important. Younger leaves exported much morediffusible IAA than older leaves. The IAA concentration in the main roots wasalmost at the same level as in the stems. The results suggested that thetransport capacity of IAA is probably the limiting factor for the amount of IAAtransported in stems and the amount of polar IAA transport might be only 19% ofthe endogenous IAA amount in stems.     

翠菊根系养分捕获形态塑性及其生理机制

为验证以下3个假设: 1) NO₃ ^-和NH₄ ⁺及其不同供给方式显著影响根系生长; 2) NO₃ ^-和NH₄ ⁺以及不同供给方式对根内激素含量影响显著; 3)根构型(1级根长、单位2级根上1级侧根密度(分枝强度)和1级根在2级根上的根间距)与根内激素(生长素(IAA)、脱落酸(ABA)和细胞分裂素(玉米素核苷+玉米素) (CK (ZR + Z))含量显著相关, 采用营养液培养方法, 使实验植物翠菊(Callistephus chinensis)在两种氮肥(NO₃ ^-和NH₄ ⁺)、不同施氮浓度(NO₃ ^-: 0.2、1.0和18.0 mmol·L ^-1; NH₄ ⁺: 0.2、4.0和20.0 mmol·L ^-1), 以及脉冲和稳定两种施用方式处理下生长。在处理35天后收获植物, 测定根系生物量、根系构型指标(根系1级根长、单位2级根上1级侧根数和1级根在2级根上的根间距)和根系中激素含量(IAA、ABA和CK (ZR + Z))。结果显示: 1)实验处理对根生物量和根系中IAA、ABA和CK (ZR + Z)含量均有不同程度的显著影响: 施用NH₄ ⁺使根生物量和根内IAA含量显著低于施用NO₃ ^-; 高浓度NO₃ ^-和NH₄ ⁺处理亦使根生物量和IAA降低; 相对于稳定处理, 脉冲施氮显著降低根生物量和根内IAA含量; NO₃ ^-使根内CK (ZR + Z)含量显著高于施用NH₄ ⁺, 且与施氮浓度及施氮方式无关; NO₃ ^-处理下, 高浓度使根内ABA含量提高, 且脉冲处理使ABA含量升高。NH₄ ⁺处理下, 高浓度使根内ABA含量降低, 而施氮方式对其没有显著影响。2)根构型因素与根内激素关系各异: 各激素与1级根间距无显著关系; IAA和CK (ZR + Z)与1级根长和侧根密度有显著回归关系。3)根构型因素与根生物量的关系是根生物量与1级根长和侧根密度有显著正回归关系, 与1级根间距无显著回归关系。实验结果表明翠菊根生长的 “反常”可能是由于其对脉冲高浓度NH₄ ⁺耐受阈值低所致。该研究通过实验建立了氮养分种类/供应方式通过改变激素、影响根构型而影响根生长的联系, 进一步探究了植物根养分捕获塑性机制。     

Sensitivity of oat leaf chlorophyll retention bioassay to natural and synthetic cytokinins

The cytokinin bioassay based on retention of chlorophyll in excised oat leaf pieces is more sensitive to the synthetic cytokinins (6-benzylaminopurine and kinetin) than to the natural cytokinins (trans-zeatin and N⁶-[Δ²isopentenyl]adenine). This difference in sensitivity decreases with increasing length of leaf pieces (from 2 to 10 cm) and with increasing volume of application (from 5 μ1 to 25 μl). Application of the cytokinin solution to the basal and apical part of the 8 cm pieces decreases the sensitivity of the bioassay but has no significant effect on the relative activities of trans-zeatin and 6-benzylaminopurine. Using 7 cm pieces and 20 μl of solution the trans-zeatin and N⁶-(Δ₂-isopentenyl)-adenine can be detected at concentrations of 10^-5 M and 5 x 10^-5 M, respectively.     

A trans-zeatin riboside in root xylem sap negatively regulates adventitious root formation on cucumber hypocotyls

Shoot cultures of cucumber were used to analyse the roles of root-derived substances in adventitious root formation on hypocotyl tissues. Xylem sap collected from the roots of squash had a strong inhibitory effect on the formation of hypocotyl adventitious roots. Double-solvent extraction followed by fractionation with both normal and reverse phase column chromatographies and analysis by liquid chromatography/tandem mass spectrometry identified trans-zeatin riboside (ZR) as the primary suppressor of adventitious root formation. ZR was the predominant cytokinin present in the xylem sap, occurring at a concentration of 2x10(-8 )M. Application of ZR at concentrations from 3.16x10(-9) M effected inhibition of adventitious root formation. These results suggest that ZR transported from roots via xylem sap may act as an endogenous suppressor of hypocotyl adventitious root formation in planta.     

UV-B辐射增强和O3浓度升高对大豆叶片内源激素和抗氧化能力的影响

揭示大豆叶片内源激素对UV-B和臭氧胁迫的代谢机制和响应方式,为从分子水平研究植物内源激素对UV-B(Ultraviolet-B)和O3(Ozone)胁迫的适应机制奠定基础。以大豆(Glycine max.)为试验材料,利用开顶式气室研究UV-B(0.32W/m2)和O3((110±10)nmol/mol)复合胁迫对大豆叶片内源激素含量及活性氧代谢系统的影响。结果表明:在大豆整个生育期内,与对照相比,UV-B胁迫使大豆叶片ABA(Abscisic acid)含量、ZR(Zeatin riboside)含量和IAA(Indoleacetic acid)含量显著降低,IAA/ABA、ZR/ABA、(IAA+ZR)/ABA比值升高,O·-2(Superoxide anion free radical,O·-2)产生速率和MDA(Malonaldehyde)含量升高,SOD(Superoxide dismutase)、CAT(Catalase)和POD(Peroxidase)活性显著降低;高浓度O3胁迫下,大豆叶片ABA和IAA含量显著下降、ZR含量显著增加,IAA/ABA、ZR/ABA、(IAA+ZR)/ABA值显著升高,O·-2产生速率和MDA含量增加,SOD、CAT和POD活性显著降低;UV-B和O3复合胁迫下,大豆叶片ABA含量、ZR含量和IAA含量降低,ZR/ABA、(IAA+ZR)/ABA值下降,而IAA/ABA值升高,O·-2产生速率和MDA含量显著增加,SOD、CAT和POD活性显著降低。UV-B辐射增强和O3浓度升高单一及复合作用使大豆叶片内源激素间平衡改变,进而影响大豆叶片的代谢水平。持续胁迫下,植株抗氧化能力下降,对大豆表现为伤害效应。UV-B和O3复合胁迫比单独胁迫时的影响有所加深,但是小于两者单独作用时影响的简单累加。     

Relationships between endogenous hormonal content and direct somatic embryogenesis in Prunus persica L. Batsch cotyledons

Cotyledons of peach (Prunus persica L. Batsch cv. ZiseMay^®) were cultured in vitro on medium deprived of plant growth regulators. Two different lines varying in their embryogenic capacity were studied after 90 days in culture media. Endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), trans-zeatin (Z), trans-zeatin riboside (ZR), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), salicylic acid (SA), and jasmonic acid (JA) were analyzed in embryogenic and non-embryogenic cotyledons. No significant differences were observed in total ABA, IAA, ZR, SA and JA concentrations between the embryogenic and non-embryogenic cotyledons. On the contrary, lower Z and ACC contents, and also a reduced balance between Z and IAA levels were related with the embryogenic capacity of the cotyledons. These results suggest that the difference in somatic embryo formation capacity observed between embryogenic and non-embryogenic cotyledons is related to their endogenous Z contents, and that the endogenous hormonal balance between Z and IAA is an important index defining the embryogenic potential in peach cotyledons.     

The effect of plant hormones on phosphate uptake and translocation in maize roots

In short-term (1 h) uptake experiments GA₃(10^-5M) stimulated P_i uptake into maize root cortex cells by 28.7 %, Ethrel (10^-3M) inhibited it by 18.5 % and BA, IAA, and ABA were inactive. In long-term (5 h) experiments ABA remained inactive, GA₃ lost its stimulatory effect, and BA (5. 10^-6M), IAA (10^-4 -10^-5M), and Ethrel (10^-3 -5. 10^-4M) decreased P_i uptake. When the hormones were present only during 3 h preincubation (“augmentation”) period ABA was inactive, GA₃ slightly raised and BA, IAA, and Ethrel slowed down subsequent P_i uptake. BA(10^-7 –10^-5M) decreased xylem sap volume flow and P_i translocation. ABA in all tested concentrations (10^-8 –10^-5M) reduced exudation rate and P_i translocation, its effect declining with time. IAA effect strongly depended on concentration used and on application time and varied from strong inhibition to moderate stimulation of both volume flow and P_i translocation. GA₃ (10^-7M) slightly stimulated xylem volume flow but inhibited phosphate translocation. Ethrel (10^-4 and 10^-5M) increased both parameters, but P_i transloeation much more than volume flow. IAA, BA, and ABA influenced volume flow and P transloeation to the same extent leaving P_i concentration in the xylem sap unchanged. GA₃ and Ethrel influence P_i concentration in the xylem sap and it is thus probable that these hormones regulate release of phosphate ions into the xylem sap.     

Response of Endogenous Hormone Concentrations to Two Floral Inductive Treatments,viz. KNO<Subscript>3</Subscript> and PBZ,in Mango cv. ‘Tommy Atkins’ Growing Under Tropical Conditions

Floral induction (FI) has been intensively studied in mango, more under sub-tropical than under tropical environments. Decreases in temperature below 20 °C, which is common in sub-tropical regions but seldom occurs in many tropical ones, has been considered a critical factor for FI in this species. Trying to understand the way by which two FI treatments, potassium nitrate (KNO₃) and paclobutrazol (PBZ), can regulate flowering by modulating the endogenous concentrations of plant hormones, the following compounds were analyzed in terminal buds, wood and bark sections of lateral branches from treated and untreated ‘Tommy Atkins’ mango trees growing under tropical conditions: indole-acetic acid (IAA), gibberellins (GAs), zeatin/zeatin riboside (Z/ZR) and N ⁶ (Δ²-isopentenyl) adenine/N ⁶ (Δ²-isopentenyl) adenosine. Behavior in the contents of these endogenous hormones was often irregular but their course was in general similar for all three treatments. However, levels of GAs were consistently lower in most evaluations of wood and bark sections of PBZ-treated trees compared to KNO₃-treated and control plants. In contrast, the endogenous levels of the presumably FI promoting Z/ZR raised considerably at the time close to FI in buds of KNO₃-treated trees. These KNO₃-treated trees flowered earlier and more profusely than those from other treatments. Although PBZ could be related in this work to a reduction in GA contents, no direct influence of this compound over FI could be established. KNO₃ might partially exert its promoting effect on mango FI by increasing Z/ZR contents.     

Reduced abscisic acid content is responsible for enhanced sucrose accumulation by potassium nutrition in vegetable soybean seeds

In order to understand the physiological mechanism of potassium (K) application in enhancing sugar content of vegetable soybean seeds, pot experiments were conducted in 2014 and 2015 with two vegetable soybean (Glycine max L. Merr.) cultivars (c.v. Zhongkemaodou 1 and c.v. 121) under normal rate of nitrogen and phosphorus application. Three potassium (K) fertilization treatments were imposed: No K application (K0), 120 kg K₂SO₄ ha^?1 at seeding (K1), and 120 kg K₂SO₄ ha^?1 at seedling?+?1% K₂SO₄ foliar application at flowering (K2). Contents of indole-3-acetic acid (IAA), gibberellins (GA), cytokinins (ZR) and abscisic acid (ABA) in seeds were determined from 4 to 8 weeks after flowering. K fertilization increased the contents of IAA, GA, ZR, soluble sugar, sucrose and fresh pod yield, but reduced ABA content consistently. When the contents of soluble sugar and sucrose reached the highest level at 7 weeks after flowering for the 2 cultivars, the contents of IAA、GA、ZR all reached the lowest level in general. The content of ABA in seed was negatively correlated with the sucrose content (P?<?0.01, r = ?0.749**, ?0.768** in 2014 and ?0.535**, ?0.791** in 2015 for c.v.121 and c.v. Zhongkemaodou 1 respectively). The changes in ratio of the ABA to (IAA?+?GA?+?ZR) from 4 to 8 weeks after flowering affected by K application were coincident to the changes of sucrose accumulation. The reduced ratio of ABA/(IAA?+?GA?+?ZR) affected by K nutrition particularly reduced abscisic acid content plays a critical role in enhancing sucrose content, which might be a partial mechanism involved in K nutrition to improve the quality of vegetable soybean.     

云南山楂中吲哚乙酸、脱落酸、玉米素和玉米素核苷的内源水平及其生根率

以云南山楂(Crataegus scabrifolia (Franch.)Rchd.)几个株系的成年树和实生苗的离体培养芽条为材料,用酶联免疫吸附测定法(ELISA)测定了它们的叶片中吲哚乙酸(IAA),脱落酸(ABA),玉米素和玉米素核苷(Z+ZR)的内源水平,探讨了这三种激素及其之间的平衡与生根率的相关性。结果发现:1.IAA内源水平之差异存在于株系间。2.内源(Z+ZR)在株系间无显著差异,而幼树发育至成年树的过程中,与IAA的平衡是多样的,同成年树的生根率似有以下相关性,当IAA水平降低,同时(Z+ZR)水平升高,有利于生根,反之则抑制生根。3.ABA内源水平无论成年或幼年树都呈低水平且无显著差异。     

Principal component analysis of hormone profiling data suggests an important role for cytokinins in regulating leaf growth and senescence of salinized tomato

High throughput analytical methods allow phytohormonal profiling, but the magnitude of the data generated makes it difficult to draw firm conclusions about the physiological roles of different compounds. Principal component analysis (PCA) was used as a mathematical tool to evaluate relationships between physiological and hormonal variables in two experiments with salinised tomato. When tomato plants (cv Boludo F1) were grafted onto a recombinant inbred line (RIL) population derived from a Solanum lycopersicum x S. cheesmaniae cross and grown under moderate salinity (75 mM NaCl) for 100 days under greenhouse conditions, PCA revealed an important role for leaf xylem cytokinins (CKs) in controlling leaf growth and photosystem II efficiency (Fv/Fm) and thus crop productivity under salinity. PCA analysis from a similar experiment, with ungrafted tomato grown under highly saline (100 mM NaCl) conditions, that evaluated the temporal sequence of leaf growth (as relative growth rate, LRGR) and senescence and hormone concentrations, revealed a similar influence of CKs on both processes, since Fv/Fm and LRGR were strongly loaded along the two principal components and placed in the same cluster as leaf trans-zeatin and/or related to other CK-related parameters. The conservative behaviour of the eigen vectors for Fv/Fm and the analyzed phytohormones in different compartments (xylem, leaf and root) between different experiments suggests an important role for CKs in regulating leaf senescence, while CKs and other hormones seem to regulate leaf growth under salinity.Key words: cytokinins, leaf growth, principal component analysis, salinity, senescence, tomatoAn important paradigm of plant growth regulation is that plant roots can sense their environment, alter their metabolism and transmit chemical signals via the xylem to the shoots to regulate shoot physiology.¹ Much work has aimed to substantiate this “chemical signaling hypothesis” by determining the production and distribution of various signals such as the plant hormones ABA, cytokinins, the ethylene precursor ACC and various nutrient ions.² Although this work has largely been “ABA-centric”, in part due to its relative ease of measurement, the advent of high-throughput, multi-analyte physicochemical techniques to quantify plant hormones^3,4 greatly amplifies the information available from analyses of long-distance signaling, and allows us to move away from a priori assumptions as to which hormone(s) might be physiologically relevant to particular processes. Ultimately, interpreting this information is necessary to provide a sound physiological basis to underpin efforts aimed at manipulating long-distance signaling in planta.Full spectrum hormone profiling can potentially assay more variables per sample than the typical number of samples assayed. Principal component analysis (PCA) is a mathematical algorithm that reduces the dimensionality of the data set while retaining most of the inherent variation.⁵ This is achieved by identifying directions, called principal components, along which the variation in the data is maximal. By using few components, each sample can be represented by relatively few numbers instead of values for many variables.⁶ PCA identifies new variables, the principal components, which are linear combinations of the original variables, and may be an appropriate technique to aid understanding of hormone profiling experiments.Recently, we grew a commercial tomato cultivar (cv Boludo F1) grafted onto 100 rootstocks from a population of recombinant inbred lines derived from a Solanum lycopersicum x S. cheesmaniae cross, and exposed the plants to moderate (75 mM NaCl) salinity for 100 days.⁷ The rootstock generated considerable variability in vegetative vigour (assessed as fresh weight of a fully expanded leaf, LFW) and leaf senescence (assessed by the chlorophyll fluorescence parameter Fv/Fm in that leaf). Ionic and hormonal factor(s) putatively regulating these processes (xylem concentrations of Na⁺ and K⁺ and ABA; the cytokinins trans-zeatin, Z, and the storage form trans-zeatin riboside, ZR; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, ACC) were analyzed in leaf xylem sap collected 50 days after salinisation in seven graft combinations of contrasting vigour. Since different xylem parameters showed a high degree of autocorrelation, PCA was performed in order to gain further insights about their real contribution to the physiological processes. Xylem K⁺, K⁺/Na⁺, the active cytokinins Z and ZR, its sum (Z + ZR) and ratio (Z/ZR), and especially the ratio between cytokinins and ACC (Z (ZR)/ACC and Z + ZR/ACC) were strong and positively loaded into the first principal component (PC1) determining both LFW and Fv/Fm (Fig. 1A⁷). Although other variables are included in the same cluster at the 95% of confidence level, their strength in PC1 was much weaker (e.g., Na⁺, Z/ABA, ACC). Does this PCA output provide generic information about the hormonal processes regulating leaf growth and Fv/Fm of salinized plants, or is it specific to the particular methodological conditions (duration of salinization, choice of genotypes or plant compartment) imposed by our experimental design?Open in a separate windowFigure 1Two axes of a principal components (PC1, PC2) analysis showing plant productivity trait vectors (leaf fresh weight, LFW or relative growth rate, LRGR, and Fv/Fm, indicated by arrows) and the position of various hormonal and ionic variables (denoted by abbreviations) for the long-term grafting experiment which analysed xylem variables (A), and the medium-term experiments with ungrafted plants that analyzed leaf (B) and root (C) variables. Arrows indicate eigen vectors representing the strength (given by the length of the vector) and direction of the trait correlation relative to the first two principal components (PC1, PC2). The circles enclose those variables that fall into the same cluster (95% confidence level). Abbreviations for the variables are given thus: ABA, abscisic acid; AC , 1-aminocyclopropane-1-carboxylic acid; IAA , indole-3-acetic acid; Z, trans-zeatin; ZR, trans-zeatin riboside.To answer this question, PCA was performed on data obtained from a similar experiment where a single genotype of tomato (cv Moneymaker) was exposed to high (100 mM NaCl) salinity for 22 days under hydroponic conditions in a controlled environment chamber.^8,9 Although the same ionic and hormonal variables (including the auxin indole-3-acetic acid, IAA) were assayed in both roots and leaves, xylem ion concentrations were not quantified. Therefore PCA was conducted using leaf relative growth rate (LRGR) as an indicator of vegetative vigour (due to the temporal variation of leaf fresh weight in young plants) and senescence (Fv/Fm), and hormonal and ionic variables measured in leaves (Fig. 1B) and roots (Fig. 1C).Both physiological variables (LRGR and Fv/Fm) were significantly loaded into the two major principal components (PC1 and PC2) explaining more than 90% of the variance, and in which most of the leaf and root ionic and hormonal parameters were strongly associated in three clusters (enclosed within the circles, Fig. 1B and C). As in the PCA from the grafting experiment (Fig. 1A), LRGR and Fv/Fm, were also placed in the same cluster as the cytokinin Z and the ionic variables K⁺ and K⁺/Na⁺ in the leaf (Fig. 1B), although some dissociation between them was observed, probably due to the temporal dynamics of these variables in the same plant organ. Moreover, most of the other CK-related variables (ZR, Z + ZR, Z + ZR/ACC, Z + ZR/ABA) were associated in a distinct cluster that was also strongly loaded along with Fv/Fm parameter in PC1 (Fig. 1B). When the root data were considered (Fig. 1C), all these CK-related (with the exception of Z) and ionic variables were placed in the same cluster as Fv/Fm and loaded into PC1 explaining 71% of variance.Interestingly, the position and value of the eigen vector defining Fv/Fm remained highly conservative and positively associated with hormonal (ZR, Z + ZR, Z + ZR/ACC) and ionic (K⁺, K⁺/Na⁺) variables independent of the experimental design and organ analyzed. However, the position of the vector for LRGR was more variable since its relationship with PC2 and some hormonal parameters (e.g., IAA, IAA/Z + ZR) was positive in the leaves and negative in the roots. Particular attention should be paid to leaf Z concentration since it was highly related to both Fv/Fm and leaf growth vectors in both experiments (Fig. 1A and B), while this hormone was placed in an opposite (to Fv/Fm) or orthogonal (to LRGR) vector in the roots (Fig. 1C). Only two of the hormones analyzed showed differential responses to salinity in leaves and roots suggesting an important role in biomass partitioning: Z and IAA decreased in leaves and increased in roots.⁸ Similar responses of both roots and leaves (for the other hormones) may indicate the importance of root-to-shoot signaling in maintaining hormone homeostasis in particular organs and integrating the whole plant response to the stress, but reciprocal grafting experiments with hormone-content or -sensitivity mutants are required to test this hypothesis for each compound.¹⁰ Additionally, PCA also revealed a conserved position for some hormonal parameters such as ACC and ABA tissue concentrations (Fig. 1B and C) and also the ratio ACC/ABA in both tissues and leaf xylem (Fig. 1A–C), which were always placed in clusters opposed to Fv/Fm (ACC, ABA) and leaf growth (ACC/ABA), supporting a role of these hormones in negatively regulating salt-induced leaf senescence⁹ and growth.⁷The relatively conservative geometric positions of some ionic and hormonal variables, and their co-occurrence with physiological variables of interest, suggest that PCA was relatively insensitive to methodological issues such as duration of salinisation, choice of genotypes or plant compartment. Moreover, similar PCAs for both tissue (Fig. 1B and C) and xylem (Fig. 1A) samples indicate the adequacy of the latter (with its considerably decreased sample preparation time) to infer physiological relationships. Particularly noteworthy was the clustering of cytokinin-related variables with the chlorophyll fluorescence parameter Fv/Fm in both experiments and organs, as well as the leaf Z concentration and growth, which highlighted the potential physiological importance of cytokinins in a way that was not so apparent from inspection of a typical correlation matrix which analyses two variables at a time. Accordingly, we have instigated experiments manipulating the cytokinin status of salinised plants by selectively overexpressing the ipt gene. That these plants grew better, and showed delayed senescence, under salinity (Ghanem ME, unpublished results) supports our use of PCA as a tool to explore temporal^8,9 and genetic⁷ correlations.     

Growth retardation induced by nutritional deficiency or abscisic acid in Lemna gibba: The relationship between growth rate and endogenous cytokinin content

The relationship between endogenous cytokinin content and relative growth rate (RGR) was studied in cultures of Lemna gibba L. G3 supplied with daily doses of mineral nutrients that were increased exponentially over time. At the optimal level of nutrient supply the RGR was 30–35% day^-1. The RGR was regulated by adjusting the rate of nitrogen supply, or it was restricted by addition of 0.5 M abscisic acid (ABA). Another approach used to investigate the specific roles of nitrogen (N) and phosphorus (P), was to transfer optimally growing plants to media without N or P but otherwise complete. The plants were harvested at regular intervals for determination of the RGR and levels of cytokinins of the isopentenyladenosine (iPA) and zeatinriboside (ZR) types with an enzyme-linked immunosorbent assay (ELISA). Levels of both iPA- and ZR-type cytokinins decreased when nitrogen was applied to cultures in growth limiting amounts. The cytokinin levels decreased more rapidly than the RGR when either N or P was lacking in the medium, suggesting an early influence of nutrient availability on cytokinin levels which in turn may induce adaptive response by the plant. RGR retardation induced by ABA did not affect cytokinin levels during the first 4 days of the treatment, and the later effects were small. The experiments gave no indication that ABA is involved in the adaptation response of Lemna plants to nutritional stress.Abbreviations ABA - abscisic acid - BAP - benzylaminopurine - ELISA - enzyme-linked-immunosorbent-assay - iP - isopentenyladenine - iPA - isopentenyladenosine - PBS - phosphate-buffered saline - PVP - polyvinylpyrrolidone - RGR - relative growth rate - R_N - relative nitrogen addition rate - Z - trans-zeatin - ZR - trans-zeatin riboside     

Squash xylem sap has activities that inhibit proliferation and promote the elongation of tobacco BY-2 cell protoplasts.

To elucidate the physiological functions of the substances in xylem sap, we analyzed the biological activities of xylem sap from squash (Cucurbita maxima Duch.) root using tobacco BY-2 (Nicotiana tabacum L. cv. Bright Yellow 2) cell protoplasts. When BY-2 cell protoplasts were cultivated with the total substance of squash xylem sap, the protoplasts elongated remarkably, and cell division was inhibited. Although trans-zeatin riboside (ZR), the most abundant cytokinin in squash xylem sap, had a concentration-dependent effect similar to that of total squash xylem sap, ZR concentrations several orders of magnitude greater than those found endogenously in squash xylem sap (i.e. 2 x 10(-8) M) were required to affect the growth of BY-2 cell protoplasts. The ability to stimulate cell elongation and inhibit cell division in BY-2 cell protoplasts was observed for the ethyl acetate phase fraction (pH 2) of squash xylem sap and an acetonitrile-eluate fraction from reverse-phase chromatography. The xylem sap also showed inhibitory activity for auxin-induced elongation of excised cucumber hypocotyls. These results suggest that an organic substance other than ZR is produced in the root and transported to above-ground organs through the xylem via the transpiration stream, where it is involved in regulating cell proliferation and elongation in the shoot, possibly as an auxin antagonist.     

Transport and metabolism of xylem cytokinins during lateral bud release in decapitated chickpea (Cicer arietinum) seedlings

Although cytokinins (CKs) are widely thought to have a role in promoting shoot branching, there is little data supporting a causative or even a correlative relationship between endogenous CKs and timing of bud outgrowth. We previously showed that lateral bud CK content increased rapidly following shoot decapitation. However, it is not known whether roots are the source of this CK. Here, we have used shoot decapitation to instantaneously induce lateral bud release in chickpea seedlings. This treatment rapidly alters rate and direction of solvent and solute (including CK) trafficking, which may be a passive signalling mechanism central to initiation of lateral bud release. To evaluate changes in xylem transport, intact and decapitated plants were infiltrated with [³H]zeatin riboside ([³H]ZR), a water‐soluble blue dye or [³H]H₂O by injection into the hypocotyl. All three tracers were recovered in virtually all parts of the shoot within 1 h of injection. In intact plants, solute accumulation in the lateral bud at node 1 was significantly less than in the adjacent stipule and nodal tissue. In decapitated plants, accumulation of [³H]ZR and of blue dye in the same bud position was increased 3‐ to 10‐fold relative to intact plants, whereas content of [³H]H₂O was greatly reduced indicating an increased solvent throughput. The stipule and cut stem, predicted to have high evapotranspiration rates, also showed increased solute content accompanied by enhanced depletion of [³H]H₂O. To assess whether metabolism modifies quantities of active CK reaching the buds, we followed the metabolic fate of [³H]ZR injected at physiological concentrations. Within 1 h, 80–95% of [³H]ZR was converted to other active CKs (mainly zeatin riboside‐5′phosphate (ZRMP) and zeatin (Z)), other significant, but unconfirmed metabolites some of which may be active (O‐acetylZR, O‐acetylZRMP and a compound correlated with sites of high CK‐concentrations) and inactive catabolites (adenosine, adenine, 5′AMP and water). Despite rapid metabolic degradation, the total active label, which was indicative of CK concentration in buds, increased rapidly following decapitation. It can be inferred that xylem sap CKs represent one source of active CKs appearing in lateral buds after shoot decapitation.     

光质和光周期对山白兰苗木生长、生理的影响

为筛选出山白兰(Michelia baillonii)苗木培育过程中适宜的光环境，该研究以一年生山白兰幼苗为试验材料，设置12、16 h·d^-1两个光周期，配合使用红蓝复合光(8R1B、6R1B)、红蓝紫绿复合光(8R1B1P1G、6R1B1P1G)4种光质和白光(W)对照，采用双因素随机区组试验设计和隶属函数法，探讨了山白兰苗木生长、光合色素、内源激素含量对不同光质和光周期处理的响应规律。结果表明：(1)光质、光周期及其交互作用对山白兰苗高增长量、叶面积、叶绿素a、玉米素(ZR)、脱落酸(ABA)的含量、内源激素比值[IAA/ABA、(IAA+GA₃+ZR)/ABA]等均有显著影响(P<0.05)。(2)16 h·d^-1光周期有利于苗高增长量、叶面积、苗木质量指数、生物量、叶绿素a、生长素(IAA)、ZR的含量、内源激素比值的提高。(3)当光周期为16 h·d^-1时，8R1B处理下的苗高增长量、叶面积和苗木质量指数均最大，分别为21.84 cm、158.39 cm²和2...     

不同成花量金花茶花果期果枝叶内源激素的变化

该研究采用ISSR分子标记,对黄枝油杉7个自然种群的遗传多样性进行了分析。结果表明：用12条ISSR引物对218个黄枝油杉个体进行扩增,共扩增出125个位点。在物种水平上,多态性位点百分数( PPL)为100.00％,Shannon信息多样性指数( I)为0.4177,Nei’ s基因多样性指数( H)为0.2666;在种群水平上,多态性位点百分数(PPL)在71.20％~92.00％之间,平均值为80.69％,Shannon信息多样性指数(I)在0.3273~0.3886之间,平均值为0.3548,Nei’ s基因多样性指数( H)在0.2139~0.2478之间,平均值为0.2291。这说明黄枝油杉在物种水平和种群水平上均显示出较高的遗传多样性。 Nei’ s遗传多样性分析( Gst＝0.1433)和AMOVA分析(Φst＝17.91％)表明,黄枝油杉的遗传变异主要存在于种群内,种群间的遗传分化程度较低,种群间保持一定的基因交流( Nm＝2.9890>1)。 Mantel分析显示,黄枝油杉种群间的遗传距离和地理距离之间不存在显著的相关关系( r＝0.4567, P＝0.0610>0.05)。     

Isolation of two cytokinin metabolites from the rhizosphere of Norway spruce seedlings (Picea abies L. Karst.)

Roots of young Norway spruce seedlings were incubated under hydroculture conditions in a synthetic nutrient medium containing either ³H-isopentenyladenosine, isopentenyladenosine or zeatin riboside. When feeding with ³H-isopentenyladenosine a new radiaolabelled metabolite was found in the feeding solution as well as in root extracts. Isopentenyladenosine and zeatin riboside were metabolised and for both compounds an unknown metabolite was detected in the feeding solution. The metabolites were purified by solid phase extraction, HPLC and partially characterised. A major characteristic of the metabolites is their reactivity in the presence of NH₄OH, which results in the formation of the cytokinin bases isopentenyladenine or zeatin, respectively. UV-spectra and the chemical characteristics indicate that the new metabolites are closely related. The GC-MS analysis revealed, that the metabolites are true derivatives of isopentenyladenine and zeatin. The biogenesis of the new metabolites is discussed with regard to plant microbial interactions.Abbreviations Ck(s) = cytokinin(s) - GC-MS = gas chromatography-mass spectrometry - iP = isopentenyladenine - [9R]iP = isopentenyladenosine - [9G]iP = isopentenyladenine-9-glucoside - [9R-MP]iP = isopentenyladenosine-5-monophosphate - Z = trans-zeatin - [9R]Z = trans-zeatin riboside     

Interactive effects of α-NAA and UV-B radiation on the endogenous hormone contents and growth of Trichosanthes kirilowii Maxim seedlings

The impact of UV-B radiation on endogenous hormones in plants has recently drawn attention from researchers. The mechanism for reduced stem elongation by UV-B might be due to changes in the phytohormone levels, especially IAA, which plays a role in stem elongation. In this study, effects of UV-B radiation on Trichosanthes kirilowii Maxim (T. kirilowii) seedlings in greenhouse-grown plants were investigated. The results indicated that: (1) In comparison to controls, exposure to 0.029 Jm^?2 s^?1. UV-B radiation led to accumulation of endogenous abscisic acid (ABA) and zeatinriboside (ZR) in the plant contents, and decreased contents of endogenous indole-3-acetic acid (IAA) and gibberellic acid (GA_1/3). Exposure to UV-B radiation reduced the height and leaf area of plants. As a result, total biomass (plant dry weight) was lower. (2) In comparison to controls, addition of 2 mg l^?1 α-naphthaleneacetic acid (α-NAA) slightly increased the contents of IAA, GA_1/3 and ZR, and decreased the content of ABA in leaves. This addition of α-NAA significantly increased plant height and leaf area, but only slightly increased total biomass. (3) Addition of α-NAA to UV-B-exposed plants: increased the content of endogenous IAA, GA_1/3 and ZR; decreased accumulation of endogenous ABA; and increased plant height and leaf area in comparison to plants that only were exposed to UV-B. Moreover, total biomass increased slightly. This suggests that addition of α-NAA may compensate to a certain extent for the lack of IAA resulting from UV-B radiation; it also increases the content of GA_1/3 and ZR, decreases the accumulation of ABA, and promotes the growth of plants.