Strigolactones inhibit auxin feedback on PIN-dependent auxin transport canalization

Directional transport of the phytohormone auxin is a versatile, plant-specific mechanism regulating many aspects of plant development. The recently identified plant hormones, strigolactones (SLs), are implicated in many plant traits; among others, they modify the phenotypic output of PIN-FORMED (PIN) auxin transporters for fine-tuning of growth and developmental responses. Here, we show in pea and Arabidopsis that SLs target processes dependent on the canalization of auxin flow, which involves auxin feedback on PIN subcellular distribution. D14 receptor- and MAX2 F-box-mediated SL signaling inhibits the formation of auxin-conducting channels after wounding or from artificial auxin sources, during vasculature de novo formation and regeneration. At the cellular level, SLs interfere with auxin effects on PIN polar targeting, constitutive PIN trafficking as well as clathrin-mediated endocytosis. Our results identify a non-transcriptional mechanism of SL action, uncoupling auxin feedback on PIN polarity and trafficking, thereby regulating vascular tissue formation and regeneration.

Auxin flow-mediated competition between axillary buds to restore apical dominance

Apical dominance is one of the fundamental developmental phenomena in plant biology, which determines the overall architecture of aerial plant parts. Here we show apex decapitation activated competition for dominance in adjacent upper and lower axillary buds. A two-nodal-bud pea (Pisum sativum L.) was used as a model system to monitor and assess auxin flow, auxin transport channels, and dormancy and initiation status of axillary buds. Auxin flow was manipulated by lateral stem wounds or chemically by auxin efflux inhibitors 2,3,5-triiodobenzoic acid (TIBA), 1-N-naphtylphtalamic acid (NPA), or protein synthesis inhibitor cycloheximide (CHX) treatments, which served to interfere with axillary bud competition. Redirecting auxin flow to different points influenced which bud formed the outgrowing and dominant shoot. The obtained results proved that competition between upper and lower axillary buds as secondary auxin sources is based on the same auxin canalization principle that operates between the shoot apex and axillary bud.

Competitive canalization of PIN-dependent auxin flow from axillary buds controls pea bud outgrowth

Shoot branching is one of the major determinants of plant architecture. Polar auxin transport in stems is necessary for the control of bud outgrowth by a dominant apex. Here, we show that following decapitation in pea (Pisum sativum L.), the axillary buds establish directional auxin export by subcellular polarization of PIN auxin transporters. Apical auxin application on the decapitated stem prevents this PIN polarization and canalization of laterally applied auxin. These results support a model in which the apical and lateral auxin sources compete for primary channels of auxin transport in the stem to control the outgrowth of axillary buds.

Activation of caspase-like proteases and induction of apoptosis by isopentenyladenosine in tobacco BY-2 cells

The effects of isopentenyladenosine (iPA) on tobacco (Nicotiana tabacum L.) BY-2 cells were examined. The number of BY-2 cells decreased in a time- and concentration-dependent manner after being exposed to micromolar concentrations of iPA. This decrease was mainly due to a loss of cell viability, since no substantial changes in cell cycle progression were revealed by flow-cytometric analysis. Dying cells exhibited the typical morphological and biochemical hallmarks of apoptosis, including cell shrinkage, chromatin condensation, and degradation of nuclear DNA to nucleosomal size fragments. Caspase-1-like and caspase-3-like proteases also became activated, the former being dominant. Inhibitor-sensitivity studies revealed that although synthetic caspase inhibitors failed to prevent cell death they markedly reduced cell death in tobacco BY-2 cells, Nu-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, a specific inhibitor for caspase-1, being the most effective. Our results indicate that caspase-like proteases, and particularly caspase-1-like protease, might be critically implicated in iPA-induced apoptosis of BY-2 cells. Finally, the outcome of inhibiting adenosine kinase by 4-amino-3-iodo-1(beta- D-ribofuranosyl)pyrazolo[3,4-d]-pyrimidine revealed that intracellular phosphorylation of iPA is required for its cytotoxicity to develop.

Noncontact Er:YAG laser ablation: clinical evaluation

OBJECTIVE

The aim of this study is to evaluate the quality of laser ablation in comparison with the classical drilling preparation.

METHODS

For the experiment, the Er:YAG laser drilling machine was used. The system had a laser head, water cooler, and power supply with automatic control. Spot size of 300-350 microns was used for the preparation. Repetition rate of 1-4 Hz, and pulse energies of 100-400 mJ with water spray were chosen. Cavity shape in comparison with classical drill, time of preparation, and influence of cavity shape on filling materials retention in accordance with the U.S. Public Health Service System were used. The evaluation criteria for noncontact Er:YAG ablation were done.

RESULTS

The cavity shape is irregular, but spot surface has larger area and microretentive appearance. Caries of enamel and dentin were treated with a noncontact preparation. It was possible to remove the old insufficient fillings, except for amalgam or metal alloys. The average number of pulses was 111.22 (SE 67.57). Vibrations of microexplosions during preparation were felt by patients on 14 cavities; however, nobody felt unpleasant pain. The qualities of filling materials in laser cavities were very stable; however, cavo surface margin discoloration of 82-86% of Alfa rating could be a problem. Changes of the color and anatomic form of the tooth were observed in 4-8%.

CONCLUSIONS

In comparison with the classical treatment, it could be said that the retention and quality of filling materials is the same or very similar.

Dentin and pulp response to Erbium:YAG laser ablation: a preliminary evaluation of human teeth

OBJECTIVE

We determined the real effect of Erbium:YAG laser ablation on human teeth in vivo.

SUMMARY BACKGROUND DATA

We advocated the idea that overheating of teeth, specially pulp damage can be avoided if correct laser parameters are used.

METHODS

We evaluated human premolars scheduled for extraction during orthodontic treatment. Before tooth extraction, an oval cavity preparation was made with a pulsed Er:YAG laser. After extraction, the teeth were decalcified for 6 weeks. Routine staining with haematoxylin and eosin was performed on longitudinal section. One hundred seventy-two sections were prepared and examined in a light microscope.

RESULTS

Under Er:YAG laser application, reduction of the dentin layer was observed. Dentinal tubules had a radial course up to the surface. No cracks or structural injury were observed. Inflammatory reaction in the pulp was not found. The vascularity of the pulp was normal. The odontoblasts were of the usual spindle-like or star-like cell shape. The cementum and epithelial attachment were healthy. No changes of structure or indications of inflammation were observed.

CONCLUSIONS

The results of this in vivo experiment on human teeth confirm safety of Er:YAG laser ablation of enamel and dentin under the conditions described.

Transport of Benzyladenine and Gibberellin A(1) from Roots in Relation to the Dominance between the Axillary Buds of Pea (Pisum sativum L.) Cotyledons

In etiolated, 5-day-old pea (Pisum sativum L.) seedlings a significantly more intensive growth of buds situated in the axil of the excised cotyledons was observed as early as 4 hours after decapitation and excision of one cotyledon of each pair. If [8-(14)C]benzyladenine ([(14)C]BA) was applied to roots of intact plants 10 hours prior to such decapitation and excision, significantly higher both total and specific (14)C activities were observed in buds situated on the side of the excised cotyledons as early as 4 hours after decapitation and excision. Although the removal of a substantial part of the root system carried out simultaneously with decapitation and excision of one cotyledon resulted in a decrease in total (14)C activity of buds, nevertheless a higher accumulation of (14)C activity was maintained in buds situated on the side of excised cotyledon. If [(14)C]BA was applied to roots of seedlings after they were decapitated and deprived of one cotyledon, both total and specific (14)C activities of buds situated on the side of excised cotyledons were significantly higher as early as the end of uptake of [(14)C]BA by roots, i.e. after 10 hours. On the other hand, [1,2-(3)H]gibberellin A(1) applied to roots of intact and/or decapitated and one-cotyledon-deprived seedlings in the same way as [(14)C]BA did not appear in the buds until very much later and only in negligible amounts (i.e.(3)H activity). This indicates that the release of buds from apical dominance represents an active and selective process which can result from the ability of buds to utilize and/or synthesize only certain growth substances within a certain time interval.