Immunoaffinity co-purification of cytokinins and analysis by high-performance liquid chromatography with ultraviolet-spectrum detection

Quantification of six types of cytokinins: Integration of an ultra-performance liquid chromatographic-electrospray tandem mass spectrometric method with antibody based immunoaffinity columns equally recognizing cytokinins in free base and nucleoside forms

Cytokinins (CTKs) exist in various types in plants. The accurate quantification of free base and nucleoside types of cytokinins are helpful for better understanding their physiological role. In the present study, antibodies against trans-zeatin riboside (tZR) and N⁶-isopentenyladenine riboside (iPR) antibodies with equal recognition to free base and nucleoside cytokinins were developed. The cross-reactivity of tZR mAb 3G101G7 with tZR, trans-zeatin (tZ), dihydrozeatin riboside (DHZR), dihydrozeatin (DHZ), iPR, and N⁶-isopentenyladenine (iP) was 100.0%, 95.7%, 19.1%, 18.0%, 1.1%, and 0.7%, and that of iPR mAb 5C82F1 with above-mentioned 6 types of cytokinins was 1.5%, 1.4%, 5.7%, 3.1%, 100.0% and 92.6%, respectively. The obtained antibodies were used to prepare two immunoaffinity columns (IAC). The elution efficiencies of tZR 3G101G7-IAC for tZ and tZR, DHZ and DHZR and of iPR 5C82F1-IAC for iP and iPR were almost no difference with the same loading amount on their corresponding IACs. Subsequently, six types of cytokinins in mepiquat chloride (MC)-treated cotton (Gossypium hirsutum L.) roots were determined by IACs combined with ultra-performance liquid chromatography-electrospray tandem mass spectrometry (UPLC-ESI-MS/MS). The contents of tZR, iPR and DHZR were increased by 9.3∼38.5%, 6.6∼23.5%, and 30.1∼110.0%, respectively, whereas those of tZ and iP were reduced by 5.3∼20.0% and 27.7∼32.1%, respectively. The decreased tZ and iP levels led to the ratio of auxin-to-active cytokinins increase to promote lateral root initiation in MC-treated cotton seeding. Integration of the IACs equally recognizing cytokinins in their free base and nucleoside forms with UPLC-ESI-MS/MS can accurately quantify different cytokinins in plant tissues.

5-Aminolevulinic Acid and 24-Epibrassinolide Improve the Drought Stress Resilience and Productivity of Banana Plants

Plant growth, development, and productivity are adversely affected under drought conditions. Previous findings indicated that 5-aminolevulinic acid (ALA) and 24-epibrassinolide (EBL) play an important role in the plant response to adverse environmental conditions. This study demonstrated the role of ALA and EBL on oxidative stress and photosynthetic capacity of drought-stressed 'Williams' banana grown under the Egyptian semi-arid conditions. Exogenous application of either ALA or EBL at concentrations of 15, 30, and 45 mg·L-1 significantly restored plant photosynthetic activity and increased productivity under reduced irrigation; this was equivalent to 75% of the plant's total water requirements. Both compounds significantly reduced drought-induced oxidative damages by increasing antioxidant enzyme activities (superoxide dismutase 'SOD', catalase 'CAT', and peroxidase 'POD') and preserving chloroplast structure. Lipid peroxidation, electrolyte loss and free non-radical H2O2 formation in the chloroplast were noticeably reduced compared to the control, but chlorophyll content and photosynthetic oxygen evolution were increased. Nutrient uptake, auxin and cytokinin levels were also improved with the reduced abscisic acid levels. The results indicated that ALA and EBL could reduce the accumulation of reactive oxygen species and maintain the stability of the chloroplast membrane structure under drought stress. This study suggests that the use of ALA or EBL at 30 mg·L-1 can promote the growth, productivity and fruit quality of drought-stressed banana plants.

Impacts of Effective Microorganisms, Compost Tea, Fulvic Acid, Yeast Extract, and Foliar Spray with Seaweed Extract on Sweet Pepper Plants under Greenhouse Conditions

Sweet pepperincludes several vitamins and is regarded as a great source of bioactive nutrients, such as carotenoids and phenolic compounds, for human growth and activities. This work aimed to investigate the effects of the soil addition of growth stimulants, namely, effective microorganisms (EM), compost tea, fulvic acid, and yeast extract, and foliar applications of seaweed extract, on the vegetative growth, enzyme activity, phytohormones content, chemical constituents of plant foliage, fruit yield, and fruit quality of sweet pepper plants (Capsicum annuum L. cv. Zidenka) growing under greenhouse conditions. The results showed that the tallest plant, largest leaf area/plant, and heaviest plant fresh and dry weights were recorded after combining a soil addition of yeast extract and foliar spray with seaweed extracts at 3 g/L in two growing seasons. The highest number of fruit/plant, fruit yield/m², fruit values of vitamin C (VC), total sugars, total soluble solids (TSS), and carotenoids, along with the highest leaf of cytokines, P, K, Fe, and total carbohydrates values, were obtained using a soil addition of fulvic acid and spray with seaweed extract at 3 g/L in the two seasons of study. These treatments also provided the lowest abscisic acid, peroxidase, and super oxidase dismutase values in the same conditions. Sweet pepper plants supplemented with compost tea and seaweed extract foliar spray at 3 g/L were the most promising for inducing the highest values of fruit fresh and dry weights, fruit length and diameter, and the leavesrichest in N, Zn, and Mn; inversely, it induced the lowest catalase levels in both seasons. The applications of EM, yeast extract, and seaweed extract could be applied for high growth, mineral levels, enzymatic activity, fruit yield, and nutritional value of sweet pepper fruit and minimizing environmental pollution.

Regulation and physiological role of silicon in alleviating drought stress of mango

Improvement of drought stress of mango plants requires intensive research that focuses on physiological processes. In three successive seasons (2014, 2015and 2016) field experiments with four different strains of mango were subjected to two water regimes. The growth and physiological parameters of possible relevance for drought stress tolerances in mango were investigated. Yield and its components were also evaluated. The data showed that all growth and physiological parameters were increased under K₂SiO₃ (Si) supplement and were followed by the interaction treatment (Si treatment and its combination with drought stress) compared to that of the controlled condition. Drought stress decreased the concentration of auxins (IAA), gibberellins (GA) and cytokinins (CK) in the three mango cultivars leaves, whereas, it increased the concentration of abscisic acid (ABA). On the contrary, IAA, GA, and CK (promoters) endogenous levels were improved by supplementing Si, in contrary ABA was decreased. Drought stress increased the activity of peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD) in the leaves of all mango cultivars grown during three experimental seasons. However, Si supplementation reduced the levels of all these antioxidative enzymes, especially the concentration of SOD when compared to that of control leaves. Fruit quality was improved in three successive seasons when Si was applied. Our results clearly show that the increment in drought tolerance was associated with an increase in antioxidative enzyme activity, allowing mango plants to cope better with drought stress. Si possesses an efficient system for scavenging reactive oxygen species, which protects the plant against destructive oxidative reactions, thereby improving the ability of the mango trees to withstand environmental stress in arid regions.

The role of cis-zeatin-type cytokinins in plant growth regulation and mediating responses to environmental interactions

Cytokinins (CKs) are well-established as important phytohormonal regulators of plant growth and development. An increasing number of studies have also revealed the function of these hormones in plant responses to biotic and abiotic stresses. While the function of certain CK classes, including trans-zeatin and isopentenyladenine-type CKs, have been studied in detail, the role of cis-zeatin-type CKs (cZs) in plant development and in mediating environmental interactions is less well defined. Here we provide a comprehensive summary of the current knowledge about abundance, metabolism and activities of cZs in plants. We outline the history of their analysis and the metabolic routes comprising cZ biosynthesis and degradation. Further we provide an overview of changes in the pools of cZs during plant development and environmental interactions. We summarize studies that investigate the role of cZs in regulating plant development and defence responses to pathogen and herbivore attack and highlight their potential role as 'novel' stress-response markers. Since the functional roles of cZs remain largely based on correlative data and genetic manipulations of their biosynthesis, inactivation and degradation are few, we suggest experimental approaches using transgenic plants altered in cZ levels to further uncover their roles in plant growth and environmental interactions and their potential for crop improvement.

Quo vadis plant hormone analysis?

Plant hormones act as chemical messengers in the regulation of myriads of physiological processes that occur in plants. To date, nine groups of plant hormones have been identified and more will probably be discovered. Furthermore, members of each group may participate in the regulation of physiological responses in planta both alone and in concert with members of either the same group or other groups. The ideal way to study biochemical processes involving these signalling molecules is 'hormone profiling', i.e. quantification of not only the hormones themselves, but also their biosynthetic precursors and metabolites in plant tissues. However, this is highly challenging since trace amounts of all of these substances are present in highly complex plant matrices. Here, we review advances, current trends and future perspectives in the analysis of all currently known plant hormones and the associated problems of extracting them from plant tissues and separating them from the numerous potentially interfering compounds.

A simple sample preparation approach based on hydrophilic solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry for determination of endogenous cytokinins

Cytokinins (CKs), a vital family of phytohormones, play important roles in the regulation of shoot and root development. However, the quantification of CKs in plant samples is frequently affected by the complex plant matrix. In the current study, we developed a simple, rapid and efficient hydrophilic interaction chromatography-solid phase extraction (HILIC-SPE) method for CKs purification. CKs were extracted by acetonitrile (ACN) followed by HILIC-SPE (silica as sorbents) purification. The extraction solution of plant samples could be directly applied to HILIC-SPE without solvent evaporation step, which simplified the analysis process. Moreover, with HILIC chromatographic retention mechanism, the hydrophobic co-extracted impurities were efficiently removed. Subsequently, CKs were separated by RPLC, orthogonal to the HILIC pretreatment process, and detected by tandem mass spectrometry. The method exhibits high specificity and recovery yield (>77.0%). Good linearities were obtained for all eight CKs ranging from 0.002 to 100ngmL(-1) with correlation coefficients (r) higher than 0.9927. The limits of detection (LODs, signal/noise=5) for the CKs were between 1.0 and 12.4pgmL(-1). Reproducibility of the method was evaluated by intra-day and inter-day measurements and the results showed that relative standard deviations (RSDs) were less than 10.5%. Employing this method, we successfully quantified six CKs in 20mg Oryza sativa leaves and the method was also successfully applied to Brassica napus (flower and leaves).

Profiling ABA metabolites in Nicotiana tabacum L. leaves by ultra-performance liquid chromatography-electrospray tandem mass spectrometry

We have developed a simple method for extracting and purifying (+)-abscisic acid (ABA) and eight ABA metabolites--phaseic acid (PA), dihydrophaseic acid (DPA), neophaseic acid (neoPA), ABA-glucose ester (ABAGE), 7'-hydroxy-ABA (7'-OH-ABA), 9'-hydroxy-ABA (9'-OH-ABA), ABAaldehyde, and ABAalcohol--before analysis by a novel technique for these substances, ultra-performance liquid chromatography-electrospray ionisation tandem mass spectrometry (UPLC-ESI-MS/MS). The procedure includes addition of deuterium-labelled standards, extraction with methanol-water-acetic acid (10:89:1, v/v), simple purification by Oasis((R)) HLB cartridges, rapid chromatographic separation by UPLC, and sensitive, accurate quantification by MS/MS in multiple reaction monitoring modes. The detection limits of the technique ranged between 0.1 and 1 pmol for ABAGE and ABA acids in negative ion mode, and 0.01-0.50 pmol for ABAGE, ABAaldehyde, ABAalcohol and the methylated acids in positive ion mode. The fast liquid chromatographic separation and analysis of ABA and its eight measured derivatives by UPLC-ESI-MS/MS provide rapid, accurate and robust quantification of most of the substances, and the low detection limits allow small amounts of tissue (1-5mg) to be used in quantitative analysis. To demonstrate the potential of the technique, we isolated ABA and its metabolites from control and water-stressed tobacco leaf tissues then analysed them by UPLC-ESI-MS/MS. Only ABA, PA, DPA, neoPA, and ABAGE were detected in the samples. PA was the most abundant analyte (ca. 1000 pmol/g f.w.) in both the control and water-stressed tissues, followed by ABAGE and DPA, which were both present at levels ca. 5-fold lower. ABA levels were at least 100-fold lower than PA concentrations, but they increased following the water stress treatment, while ABAGE, PA, and DPA levels decreased. Overall, the technique offers substantial improvements over previously described methods, enabling the detailed, direct study of diverse ABA metabolites in small amounts of plant tissue.

Mechanisms of salinity tolerance

The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na(+) or Cl() exclusion, and the tolerance of tissue to accumulated Na(+) or Cl(). Our understanding of the role of the HKT gene family in Na(+) exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na(+) accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability.

Immunoaffinity chromatography of abscisic acid combined with electrospray liquid chromatography-mass spectrometry

Polyclonal antibodies with high specificity for C1-immobilised (+)-cis,trans-abscisic acid (ABA) were raised, characterised by enzyme-linked immunosorbent assay (ELISA) and used for preparation of an immunoaffinity chromatography (IAC) gel. The detection limit of the ELISA was approximately 4.6x10(-10)mol/L. Sensitive electrospray liquid chromatography-mass spectrometry (LC-ESI-MS) methods were also developed with detection limits below 0.1x10(-12)mol. The IAC allowed quick, single-step processing of samples prior to the analyses. The LC-ESI-MS and LC-ELISA techniques were used for comparative estimation of endogenous ABA levels in immunoaffinity purified extracts of normal and water-stressed Nicotiana tabacum L. leaves. The analytical approaches were validated using deuterium- and tritium-labelled internal standards, respectively. The IAC method was found to be highly effective, sensitive and convenient for isolating the target analyte from plant material.

Batch immunoextraction method for efficient purification of aromatic cytokinins

A range of benzylaminopurines naturally occur in plants and exhibit high biological activity. Others have been synthesized, such as 6-(2-hydroxy-3-methoxybenzylamino)purine riboside (2OH3MeOBAPR), which has shown interesting anti-cancer activity under in vitro conditions. In order to study the biological activity of this interesting compound in more detail, a rapid and highly efficient method for its purification from complex samples (e.g. blood and plant extracts) is needed. Therefore, we prepared monoclonal antibodies against 2OH3MeOBAPR. The antibody had undetectable cross-reactivity with all natural isoprenoid cytokinins, but relatively high cross-reactivity with aromatic cytokinins as well as some synthetic di- and tri-substituted 6-benzylaminopurines and the corresponding ribosides. The antibody also showed strong responses and specificity in enzyme-linked immunoassays (ELISAs). In addition, it was used to prepare, for the first time, an immunoaffinity sorbent with high specificity and capacity for aromatic cytokinins. A batch immunoextraction method was then developed and optimized for the purification of 2OH3MeOBAPR from murine blood samples. The high efficacy and simplicity of this method (in off-line combination with HPLC-MS) for the isolation of target analytes from biological material is demonstrated in this study.

Effects of senescence-induced alteration in cytokinin metabolism on source-sink relationships and ontogenic and stress-induced transitions in tobacco

Senescence and reserve mobilization are integral components of plant development, are basic strategies in stress mitigation, and regulated at least in part by cytokinin. In the present study the effect of altered cytokinin metabolism caused by senescence-specific autoregulated expression of the Agrobacterium tumefaciens IPT gene under control of the P(SAG12) promoter (P(SAG12)-IPT) on seed germination and the response to a water-deficit stress was studied in tobacco (Nicotiana tabacum L.). Cytokinin levels, sugar content and composition of the leaf strata within the canopy of wild-type and P(SAG12)-IPT plants confirmed the reported altered source-sink relations. No measurable difference in sugar and pigment content of discs harvested from apical and basal leaves was evident 72 h after incubation with (+)-ABA or in darkness, indicating that expression of the transgene was not restricted to senescing leaves. No difference in quantum efficiency, photosynthetic activity, accumulation of ABA, and stomatal conductance was apparent in apical, middle and basal leaves of either wild-type or P(SAG12)-IPT plants after imposition of a mild water stress. However, compared to wild-type plants, P(SAG12)-IPT plants were slower to adjust biomass allocation. A stress-induced increase in root:shoot ratio and specific leaf area (SLA) occurred more rapidly in wild-type than in P(SAG12)-IPT plants reflecting delayed remobilization of leaf reserves to sink organs in the transformant. P(SAG12)-IPT seeds germinated more slowly even though abscisic acid (ABA) content was 50% that of the wild-type seeds confirming cytokinin-induced alterations in reserve remobilization. Thus, senescence is integral to plant growth and development and an increased endogenous cytokinin content impacts source-sink relations to delay ontogenic transitions wherein senescence in a necessary process.

Distinct isoprenoid origins of cis- and trans-zeatin biosyntheses in Arabidopsis

Plants produce the common isoprenoid precursors isopentenyl diphosphate and dimethylallyl diphosphate (DMAPP) through the methylerythritol phosphate (MEP) pathway in plastids and the mevalonate (MVA) pathway in the cytosol. To assess which pathways contribute DMAPP for cytokinin biosynthesis, metabolites from each isoprenoid pathway were selectively labeled with (13)C in Arabidopsis seedlings. Efficient (13)C labeling was achieved by blocking the endogenous pathway genetically or chemically during the feed of a (13)C labeled precursor specific to the MEP or MVA pathways. Liquid chromatography-mass spectrometry analysis demonstrated that the prenyl group of trans-zeatin (tZ) and isopentenyladenine is mainly produced through the MEP pathway. In comparison, a large fraction of the prenyl group of cis-zeatin (cZ) derivatives was provided by the MVA pathway. When expressed as fusion proteins with green fluorescent protein in Arabidopsis cells, four adenosine phosphate-isopentenyltransferases (AtIPT1, AtIPT3, AtIPT5, and AtIPT8) were found in plastids, in agreement with the idea that the MEP pathway primarily provides DMAPP to tZ and isopentenyladenine. On the other hand, AtIPT2, a tRNA isopentenyltransferase, was detected in the cytosol. Because the prenylated adenine moiety of tRNA is usually of the cZ type, the formation of cZ in Arabidopsis seedlings might involve the transfer of DMAPP from the MVA pathway to tRNA. Distinct origins of large proportions of DMAPP for tZ and cZ biosynthesis suggest that plants are able to separately modulate the level of these cytokinin species.

Cytokinin oxidase gene expression in maize is localized to the vasculature, and is induced by cytokinins, abscisic acid, and abiotic stress

Cytokinins are hormones that play an essential role in plant growth and development. The irreversible degradation of cytokinins, catalyzed by cytokinin oxidase, is an important mechanism by which plants modulate their cytokinin levels. Cytokinin oxidase has been well characterized biochemically, but its regulation at the molecular level is not well understood. We isolated a cytokinin oxidase open reading frame from maize (Zea mays), called Ckx1, and we used it as a probe in northern and in situ hybridization experiments. We found that the gene is expressed in a developmental manner in the kernel, which correlates with cytokinin levels and cytokinin oxidase activity. In situ hybridization with Ckx1 and transgenic expression of a transcriptional fusion of the Ckx1 promoter to the Escherichia coli beta-glucuronidase reporter gene revealed that the gene is expressed in the vascular bundles of kernels, seedling roots, and coleoptiles. We show that Ckx1 gene expression is inducible in various organs by synthetic and natural cytokinins. Ckx1 is also induced by abscisic acid, which may control cytokinin oxidase expression in the kernel under abiotic stress. We hypothesize that under non-stress conditions, cytokinin oxidase in maize plays a role in controlling growth and development via regulation of cytokinin levels transiting in the xylem. In addition, we suggest that under environmental stress conditions, cytokinin oxidase gene induction by abscisic acid results in aberrant degradation of cytokinins therefore impairing normal development.

Novel cytokinins: The predominant forms in mature buds of Pinus radiata

To elicit the roles of cytokinins in the regulation of maturation of Pinus radiata D. Don, the spectrum of endogenous cytokinins and their concentration in the mature buds were analysed using double-solvent extraction, column complex purification and separation, a novel immunoaffinity purification method, normal and reverse phase high-pressure liquid chromatography, enzymatic treatment, radioimmunoassay and electrospray MS/MS spectrometry. We have isolated two novel cytokinin glycosides whose proposed structures are isopentenyladenine-9-(glucopyranosyl riboside), dihydrozeatin-9-(glucopyranosyl riboside) and confirmed the presence of zeatin-9-(glucopyranosyl riboside). We have also found the presence of novel phosphorylated forms of these 3 cytokinin ribosyl-linked glycosides. Quantitative analyses revealed that the cytokinin ribosyl-linked glycosides predominate in P. radiata mature buds. Although cytokinin free base, riboside and nucleotide forms are also present, we could find no evidence of the traditional cytokinin O- or N-glucosides in the conifer buds. Thus, cytokinin metabolism in mature buds of P. radiata is very different from other species previously examined.

Nitrogen-dependent accumulation of cytokinins in root and the translocation to leaf: implication of cytokinin species that induces gene expression of maize response regulator

We have described the spatial and temporal accumulation pattern of various cytokinin species in roots, xylem sap and leaves during the resupply of nitrogen in maize. Upon addition of nitrate to nitrogen-depleted maize plants, isopentenyladenosine-5'-monophosphate (iPMP) started to accumulate in roots within 1 h preceding accumulation of trans-zeatin riboside-5'-monophosphate (ZMP), trans-zeatin riboside (ZR) and trans-zeatin (Z). In the xylem flow, both exudation rate of xylem sap and the concentration of the cytokinins increased, and ZR was the dominant species in the sap. In leaf tissue, the accumulation level of Z, which was the dominant form, started to increase 4 h after nitrate resupply to plants and the level was maintained for at least 24 h. Administration of a near physiological concentration of Z, ZR or ZMP (Z-type cytokinins) to detached leaves induced the accumulation of ZmRR1 transcript, that encode maize response regulators, but administration of isopentenyladenine, isopentenyladenosine or iPMP did not. These results strongly suggest that cytokinins are transported across the roots to shoots in response to nitrogen availability, and that, most probably, Z-type cytokinin(s), trigger the induction of ZmRR1.

Comparison of oriented and random antibody immobilization in immunoaffinity chromatography of cytokinins

Immunosorbents for the plant hormones cytokinins prepared by random antibody immobilization (to Affi-Gel 10) and by oriented approach via oxidized carbohydrate moieties on the Fc region (to Affi-Gel Hz or hydrazide derivative of Perloza MT 200) have been compared. Both approaches yielded immunosorbents with high dynamic capacity (ca. 5-10 nmol ml gel-1). Oriented antibody immobilization did not exhibit crucial effects in the case of low-molecular-mass cytokinins. Antibodies immobilized via a spacer to Affi-Gel 10 have probably enough conformational freedom to enable good accessibility to cytokinins. The sorbents were used in analysis of endogenous cytokinins in maize seeds. In phosphatase treated samples trans-zeatin and its riboside were predominant.

A response-regulator homologue possibly involved in nitrogen signal transduction mediated by cytokinin in maize

A cDNA clone, pZmCip1, encoding a maize (Zea mays) cytokinin-inducible protein 1 was isolated utilizing the differential display technique, and studied using the expression of ZmCip1 in nitrogen-starved maize plants. The cloned cDNA contained an open reading frame consisting of 157 amino acids with a predicted molecular mass of 16.7 kDa, which possesses similarity with the response-regulators of bacterial two-component signalling systems. In detached leaves, accumulation of ZmCip1 transcript by t-zeatin was dose-dependent in a range of 10(-9) M to 10(-7) M, and occurred within 30 min after treatment. The effect of t-zeatin was replaceable by isopentenyl-adenosine or isopentenyl-adenosine-5'-monophosphate. Pretreatment of detached leaves with cycloheximide did not inhibit the accumulation of the transcript. In whole plants, ZmCip1 transcript was transiently accumulated exclusively in leaves by supply of nitrate or ammonium ions to the roots, whereas the transcript was not accumulated in detached leaves by supply of the nitrogen nutrients. Both the cytokinin- and nitrate-responsive accumulations of ZmCip1 transcript were accompanied by an increase in the immunotitratable protein. Isopentenyladenosine and/or its phosphorylated form(s) accumulated in roots 2 h after supply of nitrate to plants. These results, taken together, suggest that ZmCip1 is a primary response gene to cytokinins, and that it involves, at least in part, the nitrogen-signal transduction mediated by cytokinin in maize.

Expression of early nodulin genes in alfalfa mycorrhizae indicates that signal transduction pathways used in forming arbuscular mycorrhizae and Rhizobium-induced nodules may be conserved

Transcripts for two genes expressed early in alfalfa nodule development (MsENOD40 and MsENOD2) are found in mycorrhizal roots, but not in noncolonized roots or in roots infected with the fungal pathogen Rhizoctonia solani. These same two early nodulin genes are expressed in uninoculated roots upon application of the cytokinin 6-benzylaminopurine. Correlated with the expression of the two early nodulin genes, we found that mycorrhizal roots contain higher levels of trans-zeatin riboside than nonmycorrhizal roots. These data suggest that there may be conservation of signal transduction pathways between the two symbioses-nitrogen-fixing nodules and phosphate-acquiring mycorrhizae.

The metabolism of benzyladenine in Spathiphyllum floribundum 'Schott Petite' in relation to acclimatisation problems

In Spathiphyllum floribundum 'Petite', which was cultured on medium containing benzyladenine (BA), uptake of this cytokinin and its conversion to 9-ß-D-ribofuranosyl-benzyladenine (9R-BA) or 9-ß-glucopyranosyl-benzyladenine (9G-BA) was monitored. BA and extremely large quantities of 9G-BA were exclusively located in the basal part of the plant (callus and meristems). 9R-BA was found in the basal part, the petioles and the leaf blades. After an acclimatisation period of 9 weeks the plants still contained high levels of 9G-BA, but BA and 9R-BA could no longer be detected after one week. The possible role of BA and its derivatives on inhibition of root initiation or irreversible chloroplast deficiency is discussed.