Identification of genes involved in the ACC-mediated control of root cell elongation in Arabidopsis thaliana.

BACKGROUND: Along the root axis of Arabidopsis thaliana, cells pass through different developmental stages. In the apical meristem repeated cycles of division increase the numbers of cells. Upon leaving the meristem, these cells pass the transition zone where they are physiologically and mechanically prepared to undergo subsequent rapid elongation. During the process of elongation epidermal cells increase their length by 300% in a couple of hours. When elongation ceases, the cells acquire their final size, shape and functions (in the differentiation zone). Ethylene administered as its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is capable of inhibiting elongation in a concentration-dependent way. Using a microarray analysis, genes and/or processes involved in this elongation arrest are identified. RESULTS: Using a CATMA-microarray analysis performed on control and 3h ACC-treated roots, 240 differentially expressed genes were identified. Quantitative Real-Time RT-PCR analysis of the 10 most up and down regulated genes combined with literature search confirmed the accurateness of the analysis. This revealed that inhibition of cell elongation is, at least partly, caused by restricting the events that under normal growth conditions initiate elongation and by increasing the processes that normally stop cellular elongation at the end of the elongation/onset of differentiation zone. CONCLUSIONS: ACC interferes with cell elongation in the Arabidopsis thaliana roots by inhibiting cells from entering the elongation process and by immediately stimulating the formation of cross-links in cell wall components, diminishing the remaining elongation capacity. From the analysis of the differentially expressed genes, it becomes clear that many genes identified in this response, are also involved in several other kind of stress responses. This suggests that many responses originate from individual elicitors, but that somewhere in the downstream signaling cascade, these are converged to a 'common pathway'. Furthermore, several potential keyplayers, such as transcription factors and auxin-responsive genes, were identified by the microarray analysis. They await further analysis to reveal their exact role in the control of cell elongation.

First study of oral Artenimol-R in advanced cervical cancer: clinical benefit, tolerability and tumor markers.

BACKGROUND/AIM: Artenimol-R is cytotoxic in transformed cervical cells and safety in humans is yet to be established. The present study investigates the clinical benefits, safety and the tumor marker effect of orally administered Artenimol-R in patients with advanced cervix carcinoma. PATIENTS AND METHODS: Ten patients were treated with Artenimol-R for 28 days. Clinical symptoms, vaginal discharge and pain were followed-up. Adverse events were recorded. Biopsy samples were analyzed by immunohistochemistry for the expression of relevant tumor markers. RESULTS: Artenimol-R treatment induced clinical remission with a median time for the disappearance of the symptoms being 7 days. No adverse events of grade 3 or 4 occurred. The expression of p53, Epidermal growth factor receptor (EGFR), and antigen Ki-67 as a cellular marker of proliferation, as well as the number of blood vessels stained by the CD31 antibody decreased, whereas the expression of transferrin receptor protein 1 (CD71) increased. CONCLUSION: The current pilot study provides evidence on the improvement of the clinical symptoms and the good tolerability of Artenimol-R in patients with advanced carcinoma of the cervix uteri. A survival trial with Artenimol-R in advanced patients is warranted.

Apoplastic alkalinization is instrumental for the inhibition of cell elongation in the Arabidopsis root by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid.

In Arabidopsis (Arabidopsis thaliana; Columbia-0) roots, the so-called zone of cell elongation comprises two clearly different domains: the transition zone, a postmeristematic region (approximately 200-450 µm proximal of the root tip) with a low rate of elongation, and a fast elongation zone, the adjacent proximal region (450 µm away from the root tip up to the first root hair) with a high rate of elongation. In this study, the surface pH was measured in both zones using the microelectrode ion flux estimation technique. The surface pH is highest in the apical part of the transition zone and is lowest at the basal part of the fast elongation zone. Fast cell elongation is inhibited within minutes by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid; concomitantly, apoplastic alkalinization occurs in the affected root zone. Fusicoccin, an activator of the plasma membrane H(+)-ATPase, can partially rescue this inhibition of cell elongation, whereas the inhibitor N,N'-dicyclohexylcarbodiimide does not further reduce the maximal cell length. Microelectrode ion flux estimation experiments with auxin mutants lead to the final conclusion that control of the activity state of plasma membrane H(+)-ATPases is one of the mechanisms by which ethylene, via auxin, affects the final cell length in the root.

The Root Apex of Arabidopsis thaliana Consists of Four Distinct Zones of Growth Activities: Meristematic Zone, Transition Zone, Fast Elongation Zone and Growth Terminating Zone.

In the growing apex of Arabidopsis thaliana primary roots, cells proceed through four distinct phases of cellular activities. These zones and their boundaries can be well defined based on their characteristic cellular activities. The meristematic zone comprises, and is limited to, all cells that undergo mitotic divisions. Detailed in vivo analysis of transgenic lines reveals that, in the Columbia-0 ecotype, the meristem stretches up to 200 microm away from the junction between root and root cap (RCJ). In the transition zone, 200 to about 520 microm away from the RCJ, cells undergo physiological changes as they prepare for their fast elongation. Upon entering the transition zone, they progressively develop a central vacuole, polarize the cytoskeleton and remodel their cell walls. Cells grow slowly during this transition: it takes ten hours to triplicate cell length from 8.5 to about 35 microm in the trichoblast cell files. In the fast elongation zone, which covers the zone from 520 to about 850 microm from the RCJ, cell length quadruplicates to about 140 microm in only two hours. This is accompanied by drastic and specific cell wall alterations. Finally, root hairs fully develop in the growth terminating zone, where root cells undergo a minor elongation to reach their mature lengths.