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Abstract. Shoots and roots can be regenerated through organogenesis in tissue culture by subjecting plant explants to the appropriate regime of hormone treatments. In an effort to understand the control of shoot organogenesis, we screened for mutants in Arabidopsis thaliana (L.) Heynh. Columbia ecotype for enhanced shoot development at sub-optimal concentrations of cytokinin. Mutants in four different...
Abstract. The expression of the mitotic cyclin Arath;CYCB1;1 and of the cyclin-dependent kinase Arath;CDC2a was located by -glucuronidase histochemical detection and in situ hybridization, and was quantified by 4-methylumbelliferyl -D-glucuronide assay in tobacco stem tissues during both in vivo differentiation and in vitro dedifferentiation. The changes in localization of endogenous cytokinins were...
Abstract. Mesophyll cells of Zinnia elegans L., cultured in the presence of phytohormones, will transdifferentiate and undergo programmed cell death to become tracheary elements, thick-walled cells of the xylem. This system is a model system for study of plant cell development and differentiation. We report that a high concentration of extracellular Ca2+ is necessary during the first 6h of culturing...
Abstract. The possible regulation of senescence-initiated remobilization of carbon reserves in rice (Oryza sativa L.) by abscisic acid (ABA) and cytokinins was studied using two rice cultivars with high lodging resistance and slow remobilization. The plants were grown in pots and either well-watered (WW, soil water potential = 0MPa) or water-stressed (WS, soil water potential = 0.05MPa) from 9days...
Abstract. Floral organs have been successfully induced from the regenerated floral buds of Hyacinthus orientalis L. by precisely controlling exogenous hormones in the medium. Under high concentrations of cytokinin and auxin, the regenerated floral bud produces only tepals. However, at reduced levels of the hormones, the regenerated floral bud can produce stamens and/or carpels with ovules. To understand...
Cytokinins inhibit hypocotyl elongation in darkness but have no obvious effect on hypocotyl length in the light. However, we found that cytokinins do promote hypocotyl elongation in the light when ethylene action is blocked. A 50% increase in Arabidopsis thaliana (L.) Heynh. hypocotyl length was observed in response to N6-benzyladenine (BA) treatment in the presence of Ag+. The level of the ethylene...
Senescence and reserve mobilization are integral components of plant development, are basic strategles 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 PSAG12 promoter (PSAG12-IPT) on seed germination...
A single application of cytokinin benzyladenine causes a threefold increase in the frequency of plasmodesmata in the vegetative shoot apical meristem (SAM) of Sinapisalba plants. This increase is observed 20 h after application within all cell layers (L1, L2, L3) as well as at the interfaces between these layers. Evidence is presented indicating that cytokinin promotes mainly the formation of new...
Mammalian sulfotransferases (EC 2.8.2) are involved in many important facets of steroid hormone activity and metabolism. In this study, Arabidopsis AtST4a and AtST1 were identified and characterized as brassinosteroid sulfotransferases that appear to be involved in different aspects of hormone regulation. The two proteins share 44% identity in amino acid sequence, and belong to different plant sulfotransferase...
Long-sized oligogalacturonides (OGs) are cell wall fragments that induce defence and developmental responses. The Ca2+-dependent “egg-box” conformation is required for their activity, and polyamines may prevent them from adopting this conformation. Although OGs are known to inhibit auxin-induced growth processes, their effect on cytokinin-induced ones requires investigation. In the present work OGs...
The PHO1 protein is involved in loading inorganic phosphate (Pi) to the root xylem. Ten genes homologous to AtPHO1 are present in the Arabidopsis thaliana (L.) Heyn genome. From this gene family, transcript levels of only AtPHO1, AtPHO1;H1 and AtPHO1;H10 were increased by Pi-deficiency. While the up-regulation of AtPHO1;H1 and AtPHO1;H10 by Pi deficiency followed the same rapid kinetics and was dependent...
S-adenosyl-l-homocysteine hydrolase (SAHH) is a key enzyme for maintenance of cellular transmethylation potential. Although a cytokinin-binding activity had been hypothesized for SAHH, the relation between cytokinin and transmethylation reactions has not been elucidated. Here we show that, of the two Arabidopsis thalianaSAHH genes, AtSAHH1 has a much higher expression level than AtSAHH2. A T-DNA...
In contrast to auxin, relatively little is known about the molecular mechanism of cytokinin (CTK) inhibition of lateral root initiation. Previous studies demonstrated that BREVIS RADIX (BRX), a protein of unknown biochemical function, maintains a rate-limiting brassinosteroid biosynthesis enzyme expression to keep brassinosteroid biosynthesis above a critical threshold. Here, we show that the brx-2...
The metabolism of vegetative organs in plants changes during the development of the reproductive organs. The regulation of this metabolism is important in the control of crop productivity. However, the complexity of the regulatory systems makes it difficult to elucidate their mechanisms. To examine these mechanisms, we constructed model experiments using Arabidopsis to analyze metabolic and gene expression...
Towards an understanding of the interacting nature of the CLAVATA (CLV) complex, we predicted the 3D structures of CLV3/ESR-related (CLE) peptides and the ectodomain of their potential receptor proteins/kinases, and docking models of these molecules. The results show that the ectodomain of CLV1 can form homodimers and that the 12-/13-amino-acid CLV3 peptide fits into the binding clefts of the CLV1...
Grapevine bud fruitfulness is determined by the differentiation of uncommitted meristem (UCM) into either tendril or inflorescence. Since tendril and inflorescence differentiation have long been considered sequential steps in inflorescence development, factors that control the progression of floral meristem development may regulate the final outcome of UCM differentiation, and thus affect fruitfulness...
Trans-zeatin is a kind of cytokinins that plays a crucial role in plant growth and development. The master trans-zeatin O-glucosyltransferase of Arabidopsis thaliana, UGT85A1, has been previously identified through biochemical approach. To determine the in planta role of UGT85A1 gene, the characterization of transgenic Arabidopsis plants overexpressing UGT85A1 was carried out. Under normal...
Plant root architecture is regulated by the initiation and modulation of cell division in regions containing pluripotent stem cells known as meristems. In roots, meristems are formed early in embryogenesis, in the case of the root apical meristem (RAM), and during organogenesis at the site of lateral root or, in legumes, nodule formation. Root meristems can also be generated in vitro from leaf explants...
Main conclusionsExogenously applied GR24 affected somatic embryo formation and morphogenesis of strigolactone-deficient tomato mutant through cross-talk with auxins and cytokinins indicating involvement of SLs in the embryogenic process.Strigolactones (SLs) mediate the regulation of plant responses to the environment through cross-talk with other plant hormones, especially auxins. Auxins play a crucial...
Main conclusion Isoprenoid and aromatic cytokinins occur in poplar as free compounds and constituents of tRNA, poplar isopentenyltransferases are involved in the production of isoprenoid cytokinins, while biosynthesis of their aromatic counterparts remains unsolved.Cytokinins are phytohormones with a fundamental role in the regulation of plant growth and development. They occur naturally either as...
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