Radomíra Vaňková

Distribution, biological activities, metabolism, and the conceivable function of cis-zeatin-type cytokinins in plants

Cytokinins (CKs) are plant hormones affecting numerous developmental processes. Zeatin and its derivatives are the most important group of isoprenoid CKs. Zeatin occurs as two isomers: while trans-zeatin (transZ) was found to be a bioactive substance, cis-zeatin (cisZ) was reported to have a weak biological impact. Even though cisZ derivatives are abundant in various plant materials their biological role is still unknown. The comprehensive screen of land plants presented here suggests that cisZ-type CKs occur ubiquitously in the plant kingdom but their abundance might correlate with a strategy of life rather than with evolutionary complexity. Changing levels of transZ and cisZ during Arabidopsis ontogenesis show that levels of the two zeatin isomers can differ significantly during the life span of the plant, with cisZ-type CKs prevalent in the developmental stages associated with limited growth. A survey of the bioassays employed illustrates mild activity of cisZ and its derivatives. No cis↔trans isomerization, which would account for the effects of cisZ, was observed in tobacco cells and oat leaves. Differences in uptake between the two isomers resulting in distinct bioactivity have not been detected. In contrast, cisZ and transZ have a different metabolic fate in oat and tobacco. Analysis of a CK-degrading enzyme, cytokinin oxidase/dehydrogenase (CKX), reveals that Arabidopsis possesses two isoforms, AtCKX1 expressed in stages of active growth, and AtCKX7, both of which have the highest affinity for the cisZ isomer. Based on the present results, the conceivable function of cisZ-type CKs as delicate regulators of CK responses in plants under growth-limiting conditions is hypothesized.

Accumulation of heavy metals using Sorghum sp.

The essential requirement for the effective phytoremediation is selection of a plant species which should be metal tolerant, with high biomass production and known agronomic techniques. The above mentioned criteria are met by crop plant sorghum (Sorghum bicolor). The response of hydroponically grown S. bicolor plants to cadmium and zinc stress was followed. The impact of metal application on physiological parameters, including changes in chlorophylls contents and antioxidative enzymes activities, was followed during the stress progression. Cadmium and zinc were accumulated primarily in the roots of sorghum plants. However, elevation of metal concentrations in the media promoted their transfer to the shoots. Toxic effects of metals applied at lower concentrations were less serious in the shoots in comparison with their influence to the roots. When applied at higher concentrations, transfer of the metals into the leaves increased, causing growth reduction and leading to Chl loss and metal-induced chlorosis. Moreover, higher metal levels in the roots overcame the quenching capacity of peroxidase and glutathione transferase, which was associated with reduction of their activities. Fortification of antioxidant system by addition of glutathione significantly increased the accumulation of cadmium in the roots as well as in the shoots at the highest cadmium concentration applied.

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.

Study of soil-plant transfer of 226Ra under greenhouse conditions.

A soil-plant transfer study was performed using soil from a former uranium ore processing factory in South Bohemia. We present the results from greenhouse experiments which include estimates of the time required for phytoremediation. The accumulation of (226)Ra by different plant species from a mixture of garden soil and contaminated substrate was extremely variable, ranging from 0.03 to 2.20 Bq (226)Ra/g DW. We found differences in accumulation of (226)Ra between plants from the same genus and between cultivars of the same plant species. The results of (226)Ra accumulation showed a linear relation between concentration of (226)Ra in plants and concentration of (226)Ra in soil mixtures. On the basis of these results we estimated the time required for phytoremediation, but this appears to be too long for practical purposes.

Biotransformation of (−)-limonene using Solanum aviculare and Dioscorea deltoidea immobilized plant cells

The biotransformation course of S-(−)-limonene by Solanum aviculare and Dioscorea deltoidea plant cells was studied using 5 different immobilization methods (entrapment into alginate, carrageenan and pectate gels, binding to polyphenyleneoxide and permeation into polyurethane foam). All techniques, with exception of permeation into pre-formed matrix, affected the product ratio. The main products were cis- and trans-carveol and carvone.

Two-dimensional fluorescence spectroscopy – a new tool for the determination of plant cell viability

Abstract Two-dimensional fluorescence spectroscopy (2D-FS) has been used as a new method for determining the viability of tobacco cells (Nicotiana tabacum L.). Both horizontal beam geometry and a vertical set-up achieved with bifurcated fibres were tested. The latter arrangement enabled us to avoid the negative effect of cell sedimentation. Incubation of a tobacco BY-2 cell suspension with dimethylsulfoxide (DMSO) (0–10% v/v) resulted in cell samples differing in their viability – from fully viable (0–2% DMSO) to totally non-viable (8–10%DMSO). The validity of determining viability by means of measuring cell esterase activity by 2D-FS using fluorescein diacetate as a fluorogenic substrate was verified by comparison with microscopic evaluation of fluorescein fluorescence as well as with the routinely adopted trypan blue exclusion test.

Auxins and Cytokinins in Plant Development … and Interactions with Other Phytohormones 2014

From June 29 to July 4, 2014, the 4th International Symposium on ‘‘Auxins and Cytokinins in Plant Development ... and Interactions with Other Phytohormones’’ (ACPD 2014) was held in Prague, Czech Republic. These symposia have traditionally provided a platform for the presentation of the current state of knowledge and discussion of progressing research on the fascinating cooperative roles of these two major classes of plant hormones in the control of plant development and plant responses to environmental factors. There is a long-lasting tradition of conferences and symposia devoted to plant growth substances organized by the Institute of Experimental Botany of the Academy of Sciences of the Czech Republic. The first conference in this series took place as early as 1974 in the baroque castle Liblice near Prague. Since then, three other meetings have been held in Liblice and subsequently four in Prague— starting in 1999 and already named ‘‘Auxins and Cytokinins in Plant Development’’ (ACPD). In addition, another Prague meeting, organized as the U.S.A.—Czech Regional Workshop on Cytokinins, was a satellite to the 17th International Conference on Plant Growth Substances held in Brno in 2001. A great number of distinguished founders of auxin and cytokinin research like Kenneth V. Thimann (CALTECH, California, USA), Folke Skoog (University of Wisconsin, Madison, USA), Carlos O. Miller (University of Indiana, USA), Philip F. Wareing (University College of Wales, UK), Robert E. Cleland (University of Washington, USA), and others participated in these symposia and contributed to their success. Last but not least, before 1989, such meetings and their participants helped scientists beyond the ‘‘iron curtain’’ to stay in contact with colleagues from the free part of the world. These meetings have always been very open and some of the recent break-through discoveries in auxin and cytokinin research were presented there already in the year of their publishing. For example, the previously predicted polar localization of PIN auxin efflux carriers was visualized in Arabidopsis roots and shown for the first time there (ACPD 1999), and the talks about the discovery of TIR1 as the gene-expression-related auxin receptor were given by both groups that found it independently (ACPD 2005). In the case of cytokinins, the identification of a family of plant DMAPP:ATP/ADP isopentenyltransferase genes encoding enzymes catalyzing cytokinin biosynthesis and the identification of histidine kinase two-component systems involved in cytokinin perception and signaling should be mentioned (U.S.A.—Czech Regional Workshop on Cytokinins 2001). In the sequence of these meetings, one can easily trace the stepwise development in both auxin and cytokinin fields, and in many cases in each meeting one group of hormones showed more progress and the other group got ‘‘inspired’’ and ‘‘counterbalanced’’ this in the following one. The current ACPD Symposium (2014) was deliberately given a subtitle ‘‘... and Interactions with Other Phytohormones’’ reflecting the wide cross-talk not only between auxins and cytokinins but also intensive interrelations with other plant hormones. The 2014 meeting was the most R. Vaňková J. Petrášek E. Zažı́malová M. Kamı́nek V. Motyka Institute of Experimental Botany AS CR, Rozvojová 263, 165 02 Prague 6, Czech Republic

Thorium impact on tobacco root transcriptome

Thorium is natural actinide metal with potential use in nuclear energetics. Contamination by thorium, originated from mining activities or spills, represents environmental risk due to its radioactivity and chemical toxicity. A promising approach for cleaning of contaminated areas is phytoremediation, which need to be based, however, on detail understanding of the thorium effects on plants. In this study we investigated transcriptomic response of tobacco roots exposed to 200μM thorium for one week. Thorium application resulted in up-regulation of 152 and down-regulation of 100 genes (p-value <0.01, fold change ≥2). The stimulated genes were involved in components of jasmonic acid and salicylic acid signaling pathways and various abiotic (e.g. oxidative stress) and biotic stress (e.g. pathogens, wounding) responsive genes. Further, up-regulation of phosphate starvation genes and down-regulation of genes involved in phytic acid biosynthesis indicated that thorium disturbed phosphate uptake or signaling. Also expression of iron responsive genes was influenced. Negative regulation of several aquaporins indicated disturbance of water homeostasis. Genes potentially involved in thorium transport could be zinc-induced facilitator ZIF2, plant cadmium resistance PCR2, and ABC transporter ABCG40. This study provides the first insight at the processes in plants exposed to thorium.

Auxins and Cytokinins in Plant Development 2005

The International Symposium ‘‘Auxins and Cytokinins in Plant Development 2005’’ (ACPD 2005), held in Prague, Czech Republic, July 7–12, 2005, was well timed to reflect the current enormous progress in research of the two classes of phytohormones. The symposium was a continuation of a long tradition of conferences devoted to plant growth substances organized by the Institute of Experimental Botany of the Academy of Sciences of the Czech Republic. Five international symposia have already been held in the baroque chateau at Liblice near Prague, and the sixth and last one, ‘‘Auxins and Cytokinins in Plant Development 1999’’ was held in Prague itself. The ACPD 2005 meeting provided a platform for discussions on recent achievements and future directions in and prospects for research on the two hormones for controlling plant development. The meeting fulfilled expectations and highlighted the very recent advances in molecular biology, biochemistry, and physiology of both phytohormones, as well as some aspects of their applications in biotechnology. The scientific program consisted of two opening lectures and seven sessions, which always included both hormones: (1) Biosynthesis and metabolism, (2) Transport, (3) Signaling, (4) Pattern formation and development, (5) Auxin-cytokinin crosstalk and interaction with other hormones, (6) Responses to environment, and (7) Novel methods. The interplay of these processes during plant development is shown in Figure 1. The conference attracted 180 participants from 28 countries in Europe, North America, Asia, Africa, and Australia. Abstracts of oral and poster presentations were published in Biologia Plantarum 49 (Suppl.) 2005 (and are also available on the Web at http://acpd. cas.cz). A comparison between the proportion of contributions to the topics selected for the 1999 conference with that in 2005 revealed that most of the topics selected in 2005 received even attention by the participants, reflecting the attractive program of the meeting (Figure 2). Most noticeable was the increase in contributions in the transport session in 2005 compared to 1999. In the first plenary lecture which he dedicated to Prof. Milan Kutacek, Athanasios Theologis (Plant Gene Expression Center, Albany, NY, USA) focused on the native auxin, indole-3-acetic acid, as a ‘‘simple *Authors are listed alphabetically Received 17 October 2005; accepted 18 October 2005; Online publication 28 February 2006 *Corresponding author ; e-mail: eva.zazim@ueb.cas.cz J Plant Growth Regul (2006) 25:89–97 DOI: 10.1007/s00344-005-0120-0