Auxin and cytokinin signaling participates in regulating a large spectrum of developmental and physiological processes in plants. The shoots and roots of plants have specific and sometimes even contrary responses to these hormones. Recent studies have clearly shown that establishing the spatiotemporal distribution of auxin and cytokinin response signals is central for the control of shoot apica...

The architecture of a plant's root system, established postembryonically, results from both coordinated root growth and lateral root branching. The plant hormones auxin and cytokinin are central endogenous signaling molecules that regulate lateral root organogenesis positively and negatively, respectively. Tight control and mutual balance of their antagonistic activities are particularly import...

Cytokinin is required for the initiation of leguminous nitrogen fixation nodules elicited by rhizobia and the delay of the leaf senescence induced by drought stress. A few free-living rhizobia have been found to produce cytokinin. However, the effects of engineered rhizobia capable of synthesizing cytokinin on host tolerance to abiotic stresses have not yet been described. In this study, two en...

Despite the crucial roles of phytohormones in plant development, comparison of the exact distribution profiles of different hormones within plant meristems has thus far remained scarce. Vascular cambium, a wide lateral meristem with an extensive developmental zonation, provides an optimal system for hormonal and genetic profiling. By taking advantage of this spatial resolution, we show here tha...

Cytokinins are a structurally diverse group of N 6 -substituted purine derivatives capable of inducing plant cell division. The discovery of cytokinins by Folke Skoog and colleagues in the 1950s initially focused on kinetin, a synthetic compound derived from autoclaved salmon sperm DNA (Miller et al., 1955). Miller, Skoog, and others subsequently found that cytokinins are naturally occurring pl...

The ability of N,N'-diphenylurea (Ph(2)urea) to substitute for cytokinin-active adenine derivatives in promoting callus growth of Phaseolus lunatus has been examined. In general, Ph(2)urea stimulated callus growth at high concentrations, although the growth of most callus tissues was irregular. Variability in the sensitivity and uniformity of the growth response to Ph(2)urea was found among dif...

CKX (cytokinin dehydrogenase) is a flavoprotein that cleaves cytokinins to adenine and the corresponding side-chain aldehyde using a quinone-type electron acceptor. In the present study, reactions of maize (Zea mays) CKX with five different substrates (N6-isopentenyladenine, trans-zeatin, kinetin, p-topolin and N-methyl-isopentenyladenine) were studied. By using stopped-flow analysis of the red...

Key steps in a plant's development and adaptation to the environment are the initiation and development of lateral roots (LRs). LR development is regulated by auxin, the major plant hormone promoting LR formation, its counteracting hormones cytokinin, and abscisic acid (ABA). Here, we show that mutating ABSCISIC ACID INSENSITIVE4 (ABI4), which encodes an ABA-regulated AP2 domain transcription f...

The natural occurrence of free cytokinins was examined in relation to the growth of serially propagated pea-root callus tissue cultures. The relatively slow-growing pea-root callus was harvested at regular intervals throughout a 12-week period and fresh weight, dry weight, cell number, and cytokinin activity were determined. At the end of the culture period the fresh weight had increased about ...

In Arabidopsis thaliana, lateral roots (LRs) initiate from anticlinal cell divisions of pericycle founder cells. The formation of LR primordia is regulated antagonistically by the phytohormones cytokinin and auxin. It has previously been shown that cytokinin has an inhibitory effect on the patterning events occurring during LR formation. However, the molecular players involved in cytokinin repr...