Cytokinin Glucosides Research Articles

Shared and genetically distinct Zea mays transcriptome responses to ongoing and past low temperature exposure

BackgroundCold temperatures and their alleviation affect many plant traits including the abundance of protein coding gene transcripts. Transcript level changes that occur in response to cold temperatures and their alleviation are shared or vary across genotypes. In this study we identify individual transcripts and groups of functionally related transcripts that consistently respond to cold and its alleviation. Genes that respond differently to temperature changes across genotypes may have limited functional importance. We investigate if these genes share functions, and if their genotype-specific gene expression levels change in magnitude or rank across temperatures.ResultsWe estimate transcript abundances from over 22,000 genes in two unrelated Zea mays inbred lines during and after cold temperature exposure. Genotype and temperature contribute to many genes’ abundances. Past cold exposure affects many fewer genes. Genes up-regulated in cold encode many cytokinin glucoside biosynthesis enzymes, transcription factors, signalling molecules, and proteins involved in diverse environmental responses. After cold exposure, protease inhibitors and cuticular wax genes are newly up-regulated, and environmentally responsive genes continue to be up-regulated. Genes down-regulated in response to cold include many photosynthesis, translation, and DNA replication associated genes. After cold exposure, DNA replication and translation genes are still preferentially downregulated. Lignin and suberin biosynthesis are newly down-regulated. DNA replication, reactive oxygen species response, and anthocyanin biosynthesis genes have strong, genotype-specific temperature responses. The ranks of genotypes’ transcript abundances often change across temperatures.ConclusionsWe report a large, core transcriptome response to cold and the alleviation of cold. In cold, many of the core suite of genes are up or downregulated to control plant growth and photosynthesis and limit cellular damage. In recovery, core responses are in part to prepare for future stress. Functionally related genes are consistently and greatly up-regulated in a single genotype in response to cold or its alleviation, suggesting positive selection has driven genotype-specific temperature responses in maize.

A Highly Selective Biosensor with Nanomolar Sensitivity Based on Cytokinin Dehydrogenase

We have developed a N 6-dimethylallyladenine (cytokinin) dehydrogenase-based microbiosensor for real-time determination of the family of hormones known as cytokinins. Cytokinin dehydrogenase from Zea mays (ZmCKX1) was immobilised concurrently with electrodeposition of a silica gel film on the surface of a Pt microelectrode, which was further functionalized by free electron mediator 2,6-dichlorophenolindophenol (DCPIP) in supporting electrolyte to give a bioactive film capable of selective oxidative cleavage of the N 6- side chain of cytokinins. The rapid electron shuffling between freely diffusible DCPIP and the FAD redox group in ZmCKX1 endowed the microbiosensor with a fast response time of less than 10 s. The immobilised ZmCKX1 retained a high affinity for its preferred substrate N 6-(Δ2-isopentenyl) adenine (iP), and gave the miniaturized biosensor a large linear dynamic range from 10 nM to 10 µM, a detection limit of 3.9 nM and a high sensitivity to iP of 603.3 µAmM−1cm−2 (n = 4, R2 = 0.9999). Excellent selectivity was displayed for several other aliphatic cytokinins and their ribosides, including N 6-(Δ2-isopentenyl) adenine, N 6-(Δ2-isopentenyl) adenosine, cis-zeatin, trans-zeatin and trans-zeatin riboside. Aromatic cytokinins and metabolites such as cytokinin glucosides were generally poor substrates. The microbiosensors exhibited excellent stability in terms of pH and long-term storage and have been used successfully to determine low nanomolar cytokinin concentrations in tomato xylem sap exudates.

Novel Cytokinin Derivatives Do Not Show Negative Effects on Root Growth and Proliferation in Submicromolar Range

BackgroundWhen applied to a nutrition solution or agar media, the non-substituted aromatic cytokinins caused thickening and shortening of the primary root, had an inhibitory effect on lateral root branching, and even showed some negative effects on development of the aerial part at as low as a 10 nanomolar concentration. Novel analogues of aromatic cytokinins ranking among topolins substituted on N9-atom of adenine by tetrahydropyranyl or 4-chlorobutyl group have been prepared and tested in standardized cytokinin bioassays [1]. Those showing comparable activities with N6-benzylaminopurine were further tested in planta.Methodology/Principal FindingsThe main aim of the study was to explain molecular mechanism of function of novel cytokinin derivatives on plant development. Precise quantification of cytokinin content and profiling of genes involved in cytokinin metabolism and perception in treated plants revealed several aspects of different action of m-methoxytopolin base and its substituted derivative on plant development. In contrast to standard cytokinins, N9- tetrahydropyranyl derivative of m-topolin and its methoxy-counterpart showed the negative effects on root development only at three orders of magnitude higher concentrations. Moreover, the methoxy-derivative demonstrates a positive effect on lateral root branching and leaf emerging in a nanomolar range of concentrations, in comparison with untreated plants.Conclusions/SignificanceTetrahydropyranyl substitution at N9-position of cytokinin purine ring significantly enhances acropetal transport of a given cytokinins. Together with the methoxy-substitution, impedes accumulation of non-active cytokinin glucoside forms in roots, allows gradual release of the active base, and has a significant effect on the distribution and amount of endogenous isoprenoid cytokinins in different plant tissues. The utilization of novel aromatic cytokinin derivatives can distinctively improve expected hormonal effects in plant propagation techniques in the future.

Corolla of the Large-flowered Petunia (Petunia hybrida Vilm.) Cultivars Exhibit Low Endogenous Cytokinin Concentration through Enhanced Expression of the Genes Encoding Cytokinin Oxidases

We previously reported that cytokinin (CK) application enlarged the corolla of petunia (Petunia hybrida Vilm.). In this paper, the effect of the large-flowered trait of petunia caused by the Grandiflora (G) allele to CK biosynthesis was investigated. Concentrations of endogenous CK nucleobases (i.e., N6-(Δ2-isopentenyl)adenine (iP) and trans-Zeatin (tZ)), CK nucleosides (iP riboside and tZ riboside), and a CK glucoside (iP-7-glucoside) in the developing corolla were markedly lower in large-flowered cultivars with a Gg genotype than small- and medium-flowered cultivars with a gg genotype. We isolated the cDNAs encoding CK biosynthesis enzymes expressed in the young corolla, i.e., cDNAs of an adenosine phosphate-isopentenyltransferase gene (SHO), a CK riboside 5'-monophosphate phosphoribohydrolase gene (PhLOG), and two CK oxidase/dehydrogenase genes (PhCKX1 and PhCKX2). Expression levels of SHO and PhLOG in the developing corolla were not markedly different among small-, medium-, and large-flowered cultivars. However, expression levels of PhCKX1 and PhCKX2, which catalyze CK degradation through removal of the isoprenoid side chain, were much higher in large-flowered cultivars than in small- and medium-flowered cultivars. Therefore, low CK concentrations in large-flowered cultivars are very probably induced by the promoted expressions of PhCKX1 and PhCKX2, which may partially repress corolla enlargement.

The etr1‐2 mutation in Arabidopsis thaliana affects the abscisic acid, auxin, cytokinin and gibberellin metabolic pathways during maintenance of seed dormancy, moist‐chilling and germination

In Arabidopsis thaliana, the etr1-2 mutation confers dominant ethylene insensitivity and results in a greater proportion of mature seeds that exhibit dormancy compared with mature seeds of the wild-type. We investigated the impact of the etr1-2 mutation on other plant hormones by analyzing the profiles of four classes of plant hormones and their metabolites by HPLC-ESI/MS/MS in mature seeds of wild-type and etr1-2 plants. Hormone metabolites were analyzed in seeds imbibed immediately under germination conditions, in seeds subjected to a 7-day moist-chilling (stratification) period, and during germination/early post-germinative growth. Higher than wild-type levels of abscisic acid (ABA) appeared to contribute, at least in part, to the greater incidence of dormancy in mature seeds of etr1-2. The lower levels of abscisic acid glucose ester (ABA-GE) in etr1-2 seeds compared with wild-type seeds under germination conditions (with and without moist-chilling treatments) suggest that reduced metabolism of ABA to ABA-GE likely contributed to the accumulation of ABA during germination in the mutant. The mutant seeds exhibited generally higher auxin levels and a large build-up of indole-3-aspartate when placed in germination conditions following moist-chilling. The mutant manifested increased levels of cytokinin glucosides through zeatin-O-glucosylation (Z-O-Glu). The resulting increase in Z-O-Glu was the largest and most consistent change associated with the ETR1 gene mutation. There were more gibberellins (GA) and at higher concentrations in the mutant than in wild-type. Our results suggest that ethylene signaling modulates the metabolism of all the other plant hormone pathways in seeds. Additionally, the hormone profiles of etr1-2 seed during germination suggest a requirement for higher than wild-type levels of GA to promote germination in the absence of a functional ethylene signaling pathway.

Purification, crystallization and preliminary X-ray analysis of a maize cytokinin glucoside specific beta-glucosidase.

Zm-p60.1, a cytokinin glucoside specific beta-glucosidase from maize, is a key enzyme involved in plant development and growth. It has been overexpressed in soluble form from Escherichia coli with a His tag at its N-terminus. The recombinant protein has been purified and crystallized at room temperature using PEG 4000 as the main precipitant. At least three crystal forms have been observed from very similar growth conditions. A flash-annealed monoclinic crystal diffracted to high resolution (beyond 2 A) with space group P2(1) and unit-cell parameters a = 55.66, b = 110.72, c = 72.94 A, beta = 92.10 degrees. The asymmetric unit is estimated and confirmed by molecular-replacement solution to contain one Zm-p60.1 dimer, giving a crystal volume per protein mass (V(M)) of 1.89 A(3) Da(-1) and a solvent content of 35%.

Comparison of cytokinin and cytokinin-O-glucoside cleaving β-glucosidase productionin vitrobyVenturia inaequalisand other phytopathogenic fungi with differing modes of nutritionin planta

Early symptoms of apple scab caused byVenturia inaequalisinclude leaf curl and green island formation, both of which are indicative of an imbalance of plant growth regulators. To test whetherV. inaequalishas the potential to contribute to this phenomenon, cytokinin productionin vitrowas analysed quantitatively by high performance liquid chromatography followed by enzyme linked immunosorbant assay. Both zeatin riboside and isopentenyl adenosine type cytokinins were detected in extracts from mycelia and culture filtrates. The highest amounts of cytokinins were recovered from mycelium grown in Murashige and Skoog glucose vitamins medium (MSGV). These were five-fold greater than those recovered from malt extract salts medium (MES).To ascertain whether cleavage of biologically inactive cytokinin glucosides into free cytokinins by fungal β-glucosidases contributed to this phenomenon, the production of cytokinin-glucoside cleaving β-glucosidasesin vitrobyV. inaequaliswas compared with a range of other phytopathogenic fungi, with differing modes of nutritionin planta. All of the fungi tested apart fromBotrytis cinerea, produced β-glucosidase which specifically cleaved the substrate, Zeatin-O-glucoside ((OG)Z). The levels of (OG)Z cleaving β-glucosidase from mycelia of the hemibiotrophsV. inaequalisandLeptosphaeria maculans, grown in MSGV were 12-fold and seven-fold higher, respectively than when grown in MES. In comparison, mycelia (OG)Z cleaving β-glucosidase activity in mycelium of the biotrophCladosporium fulvumgrown in MSGV was over four-fold higher than MES. Spore washes from the obligate biotrophErysiphe graminisshowed no detectable (OG)Z cleaving β-glucosidase activity. No significant difference in (OG)Z cleaving β-glucosidase activity was seen between mycelium grown in MES and MSGV for the hemibiotroph,Pyrenopeziza brassicae. For the necrotrophic fungi,Penicillium expansum, Monilinia fructicola, B. cinerea, Alternaria brassicaeandAlternaria brassicicolaeither no (OG)Z activity was detectable or no significant difference in levels of (OG)Z cleaving β-glucosidase activity were found between the nutrient rich and growth limiting media. These results are discussed in relation to factors that may contribute to the biotrophic nutrition of fungal phytopathogens.

Cytokinins from terminal buds of Euphoria longana during different growth stages

The presence of endogenous cytokinins were detected in the terminal buds of longan (Euphoria longana Lam.) after purification by ion exchange and Sephadex LH‐20 chromatography, and bioassay, enzymic degradation, high‐performance liquid chromatography and gas chromatography‐mass spectrometry. Permethylated derivatives of two highly active cytokinin glucoside compounds from dormant buds were: 6‐(4‐O‐β‐D‐glucosyl‐3‐methyl‐but‐2‐enylamino) purine (zeatin‐O‐glucoside) and 9‐β‐D‐ribofuranosyl‐6‐(4‐hydroxy‐3‐methyl‐but‐2‐enylamino) purine (zeatin riboside‐O‐glucoside). Simultaneously, four active cytokinins from buds at the stages of leaf flush and flower bud initiation were identified as 6‐(4‐hydroxy‐3‐methyl‐but‐trans‐2‐enylamino) purine (zeatin), zeatin‐9‐β‐D‐ribofuranosylpurine (zeatin riboside), 6‐(3‐methyl‐2‐butenyl) aminopurine (isopentenyladenosine, 2iPA) and N‐(3‐methyl‐2‐butenyl) adenine (isopentenyladenine, 2iP). The total cytokinin levels were low at leaf flush, with the zeatin and zeatin riboside in the buds about 70% of the total. In the transition of the terminal bud from leaf flush to dormancy, the principal cytokinins were zeatin‐O‐glucoside and zeatin riboside‐O‐glucoside. However, significant decreases in the levels of zeatin‐O‐glucoside and zeatin riboside‐O‐glucoside and increases in those of zeatin, zeatin riboside, 2iPA and 2iP were observed at flower bud initiation. It is suggested that in longan, the cytokinins that are translocated to the shoots are accumulated in the buds at the dormant stage, and that later there is a considerable increase in free cytokinins during flower bud initiation, leading to the promotion of flower bud development.

Are cytokinin glucosides exported from mature deciduous leaves?

In an attempt to find proof that cytokinin glucosides are exported from senescing leaves prior to abscission, [ 3 H](OG)DHZ was applied to mature senescing leaves of Salix babylonica. Within the leaf, radioactivity was redistributed mainly acropetally towards the leaf tip. Only 8% of the radioactivity moved basipetally and very low levels of radioactivity were detected in stem sections. The export of cytokinin glucosides may well occur but apparently it is not a major event occurring from mature leaves. Whether the process can be accelerated during the senescence stages of the leaf needs to be established.

Chemically induced expression of the rolC‐encoded β‐glucosidase in transgenic tobacco plants and analysis of cytokinin metabolism: rolC does not hydrolyze endogenous cytokinin glucosides in planta

SummaryThe rolC gene of Agrobacterium rhizogenes T‐DNA plays an essential role in the establishment of hairy root disease and its overexpression in transgenic plants causes pleiotropic developmental alterations. This study investigated whether the biological activity of the rolC β‐glucosidase is due to an alteration of the cytokinin balance in planta. HPLC radiocounting assays of [3H]‐labeled cytokinin glucosides fed exogenously to tobacco leaf disks, to rolC expressing Escherichia coli cells or cell‐free extracts showed that cytokinin N3‐ and O‐glucosides are the preferred substrate of the rolC protein. Hydrolysis of N7‐ and N9‐glucosides was not detected at substrate concentrations close to physiological levels. Furthermore, these conjugates were also not active as cytokinins in biotests when fed to rolC‐expressing tissues. For analysis of the rolC activity on endogenous cytokinin conjugates the gene was expressed under the transcriptional control of a modified tetracycline‐inducible 35S promoter. This was done to avoid possible interference with secondary effects or plant homeostatic mechanisms which could mask primary in planta events when transgenes are expressed constitutively. No changes in the endogenous pool of different cytokinin glucosides, as determined by a newly developed electrospray tandem mass spectroscopy directly coupled to high performance liquid chromatography, were found following chemical induction of the rolC gene. Also the levels of free cytokinins remained unchanged after gene induction. Hybrid tobacco plants expressing the cytokinin‐synthezising ipt gene and the rolC gene showed added phenotypes indicating that the rolC phenotype is mediated on a signalling pathway different from those of cytokinins. RolC/ipt hybrids also accumulated high levels of cytokinin O‐glucosides. It is concluded that the phenotypic alterations caused by the rolC gene product are not due to a release of free cytokinins from inactive conjugates, most likely because of subcellular compartmentation of the putative substrate.

Release of active cytokinin by a beta-glucosidase localized to the maize root meristem.

A beta-glucoside encoded by a cloned Zea mays complementary DNA (Zm-p60.1) cleaved the biologically inactive hormone conjugates cytokinin-O-glucosides and kinetin-N3-glucoside, releasing active cytokinin. Tobacco protoplasts that transiently expressed Zm-p60.1 could use the inactive cytokinin glucosides to initiate cell division. The ability of protoplasts to sustain growth in response to cytokinin glucosides persisted indefinitely after the likely disappearance of the expression vector. In the roots of maize seedlings, Zm-p60.1 was localized to the meristematic cells and may function in vivo to supply the developing maize embryo with active cytokinin.

Quantification of Intact Cytokinin Glucosides in Datura innoxia Crown Gall Tissue by Desorption Chemical Ionisation Mass Spectrometry

Cytokinin glucosides are routinely quantified as their aglycones produced by enzymic or chemical hydrolysis. It is, however, important to be able to measure their levels per se. The present paper illustrates the use of desorption chemical ionisation mass spectrometry coupled with stable isotope dilution for the determination of intact, underivatized N- and O- glucosyl conjugates of cytokinins in Datura innoxia crown gall tissue. A total of six glucosyl conjugates were determined; the two N-glucosides, zeatin-7-glucoside and zeatin-9-glucoside, were present in higher quantities than the O-glucosyl derivatives of zeatin, dihydrozeatin and their ribosides.

The stability and metabolism of benzyladenine glucosides in soybean callus

Summary Using cytokinin dependent soybean callus the 3-, 7- and 9-glucosides of BA were investigated with respect to biological activity and metabolic stability. [3G]BA was the most, and the [7G]BA the least active in the soybean callus bioassay. This order was also established with respect to the rates of metabolism, and is apparently the reason for the differential rates of cell division observed with the three BA-glucosides investigated. The rapid metabolism of [3G]BA resulted in the release of a biologically active compound that had a similar retention time to that of BA. As this hydrolysis and release of BA resulted in substantially better growth it provides further circumstantial evidence that the free base is the active cytokinin. Although all three glucosides have N-C bonds, [3G]BA is hydrolyzed more readily by acid. In addition it can be enzymatically hydrolyzed by R-glucosidase. We propose that the term «storage» compound must be applied more rigorously with respect to cytokinin glucosides. In the case of [7G]BA and [9G]BA this term is clearly inappropriate and the terms «detoxification, inactivation» and/or «bound» seem more correct. As [3G]BA can be utilized readily and appears to serve as a ready source of BA (slow release compound) following application to plant tissues the use of the term «storage» compound appears in order. From the present results it would not seem as if there is reversible sequestration between BA and [3G]BA. During the 24 h of the experiment [7G]BA and [9G]BA but not [3G]BA were formed following BA application to soybean callus.

The plant oncogene rolC is responsible for the release of cytokinins from glucoside conjugates.

The rolC gene of Agrobacterium rhizogenes, which drastically affects growth and development of transgenic plants, codes for a cytokinin-beta-glucosidase. Indeed, rolC protein expressed in Escherichia coli as a fusion protein hydrolyses cytokinin glucosides, thus liberating free cytokinins. Furthermore, beta-glucosidase activity present in E. coli extracts expressing the rolC protein was inhibited by affinity-purified antibodies specific for the rolC protein. Finally, rolC proteins expressed in transgenic plants were shown to be responsible for cytokinin-beta-glucosidase activity. Morphological and phytohormonal analysis, performed on transgenic plants that are somatic mosaics for the expression of the rolC gene, extend and confirm our interpretation that the developmental, physiological and morphological alterations caused by rolC expression in transgenic plants are primarily due to a modification of the cytokinin balance. These observations shed new light on the control of growth and differentiation in plants by growth factors.

Effect of systemic tobacco mosaic virus infection on endogenous cytokinin concentration in tobacco ( Nicotiana tabacum L.) leaves: consequences for the control of resistance and symptom development

Capillary gas chromatography (GC) with nitrogen-specific detection was used to measure cytokinin concentration in White Burley tobacco ( Nicotiana tabacum L.) systemically-infected with tobacco mosaic virus (TMV). Infected plants developed a mosaic of distinct light-green and darkgreen areas in syslemically-infected leaves. Virus infection reduced the concentration of zeatin (Z) in dark-green areas of infected leaves. Zeatin riboside (ZR) concentration was unchanged by infection. Both healthy and TMV-infected leaves contained the cytokinin glycosides, zeatin-O-glucoside (ZOG) and zeatin-O-glucoside riboside (ZROG). The concentration of ZOG in uninfected leaves was typically 1·7 to 2·4 times that of Z on a molar basis while ZROG occurred at approximately the same level as ZR. Virus infection increased the concentration of ZOG and ZROG by up to 1·7 and 4·5-fold respectively in dark-green areas of infected leaves while glucosioe concentration in light-green areas of leaves was largely unchanged. Treatment with exogenous abscisic acid (ABA) stimulated cytokinin catabolism in both healthy control and infected plants, reducing the concentration of Z and increasing markedly the concentration of cytokinin glucosides. The role of the observed changes in cytokinin concentration and their interaction with ABA metabolism in control of symptom development and resistance are discussed.

Evidence of cytokinin bases, ribosides and glucosides in roots of Douglas-fir, Pseudotsuga menziesii.

Concentrations of cytokinin-like compounds were measured in root tips of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) collected in spring. Cytokinin bases and ribosides were estimated by radioimmunoassay after purification by immunoaffinity (zeatin riboside and isopentenyladenosine antibodies coupled to cellulose gel) and high performance liquid chromatography. Cytokinin glucosides were similarly analyzed in root extracts treated with beta-glucosidase and octadecyl-silica column chromatography in conjunction with immunoaffinity purification. The identity of predominant cytokinins obtained after enzymatic degradation was confirmed by gas chromatography-mass spectrometry. Each of the observed cytokinin bases and ribosides seemed to have a corresponding hexose conjugate form. Total quantity of cytokinin glucosides was twice that of cytokinin bases and ribosides, and the major compound was isopentenyladenosine hexose conjugate.

Identification of cytokinin glucosides in a seaweed extract

Zeatin-O-glucoside, its dihydro derivative, and dihydrozeatin riboside-O-glucoside have been identified as the main cytokinin-O-glucosides in Seasol, a commercial preparation from Tasmanian giant bull kelp marketed as a liquid organic fertilizer. The analysis, which also indicated the presence of zeatin riboside-O-glucoside, was carried out by gas chromatography-mass spectrometry of the aglucones using the stable isotope dilution method.

Tuberization in Cassava ( Manihot esculenta): Cytokinin and Abscisic Acid Activity in Tuberous Roots

The nature and distribution of cytokinins and abscisic acid in tuberous roots of cassava (Manihot esculenta Crantz) was studied. Trans-ribosylzeatin, dihydrozeatin and trans-zeatin were tentatively identified as the major cytokinins in tuberous root extracts. Cytokinin activity was concentrated in the meristematic region of the secondary xylem and in the phloem. This suggests a role for cytokinins in the regulation of meristematic activity which is responsible for the growth of the tuberous roots. Some cytokinin activity which co-eluted with cytokinin glucosides was found in extracts from the phloem. Inhibitor activity which was tentatively identified as cis-abscisic acid was present in tuberous root extracts. The activity of this hormone did not vary greatly between the different tissues analysed.

Changes in cytokinin activity during flower development in Cosmos sulphureus Cav

Endogenous cytokinin activity was determined in the flowers of Cosmos sulphureus Cav. from bud emergence to full bloom using the soybean callus bioassay. Cytokinin activity was low early in flower development but increased prior to full bloom. In Sephadex LH-20 column chromatography of flower extracts, the cytokinins present co-eluted with zeatin, zeatin riboside and glucoside cytokinin. While the former two predominated prior to full bloom, cytokinin glucoside activity appeared to be at a maximum at full bloom. The possible relevance of these findings is discussed in relation to flower development.

The effect of seaweed concentrate and fertilizer on growth and the endogenous cytokinin content of Phaseolus vulgaris

The effect of foliar applications of a commercially available seaweed concentrate (Kelpak 66) on the growth and cytokinin content of Phaseolus vulgaris L. plants was investigated. Kelpak 66 at a dilution of 1:500 improved the growth of bean plants significantly irrespective of whether it was applied on its own as a foliar spray, or together with soil applications of a chemical fertilizer. Significant differences were also detected in the levels of endogenous cytokinins present in such treated plants. The cytokinin-like activity present in plants treated with seaweed concentrate was higher than in the control plants. Cytokinin glucosides were detected only in the fruits. The levels of these compounds were greatest in the fruits of plants which received both seaweed concentrate and fertilizer applications. The significance of these findings is discussed.