Influence of alterations in the purine ring on biological activity of cytokinins

The 1-deaza-, 3-deaza-, 8-aza-1-deaza- and 8-aza-3-deaza-analogs of kinetin and 6-(3-methyl-2-butenylamino)purine and some of their ribosides were synthesized and their growth-promoting activities in the tobacco bioassay were determined and compared with those of the parent compounds. The replacement of nitrogen by carbon in the 1 -position of the purine ring decreases cytokinin activity 15-fold for kinetin and 2-fold for 6-(3-methyl-2-butenylamino)purine (IPA); however, the replacement of nitrogen by carbon in the 3-position decreases the activity 2000 times for kinetin and 1000 times for 6-(3-methyl-2-butenylamino)-purine. The activity of 8-aza-1-deaza-analogs appears to be of the same order of somewhat lower than the corresponding 1-deaza-analogs. The corresponding 8-aza-3-deaza-analogs are less active than kinetin (400 times and 6-(3-methyl-2-butenylamino)purine (40 times). However, they are more active than the corresponding 3-deaza-analogs. The concentration range in which the ribosides show activity is nearly the same as for the corresponding free bases, but the maximum yield of tobacco-callus for the riboside of the 3-deaza-analog of 6-(3-methyl-2-butenylamino)purine is very low.     

Development of auxin autotrophy in Nicotiana tabacum callus cultures

Changes of auxin and ethylene metabolism of Nicotiana tabacum var. Xanthi callus were investigated in relation to auxin-independent growth. During the habituation process, changes occur progressively in hormone metabolism in auxin-heterotrophic tissues: the potential for the destruction of indoleacetic acid (IAA) increases, the IAA level in the cultures rises slightly, and the auxin sensitivity of the callus becomes modified. Preceding the onset of habituation, ethylene production is enhanced although the tissues retain their ability to undergo regeneration.
Gradual changes in auxin metabolism and ethylene production confirm the epigenetic character of the habituation process.     

Differential growth dependency of normal and habituated sugarbeet cell lines upon endogenous ethylene production and exogenous ethylene application

A fully habituated (auxin‐ and cytokinin‐independent) nonorganogenic (HNO) sugarbeet ( Beta vulgaris ) callus produces very little ethylene as compared with a normal (N) hormone‐requiring callus of the same strain. Both callus types react by growth changes to application of inhibitors of ethylene biosynthesis and ethylene action, of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) as the immediate precursor of ethylene, to transfer from light to darkness, and also to application of exogenous ethylene or an ethylene trapper. This indicates their growth dependency upon their endogenously biosynthesized ethylene and also their sensitivity to exogenous gas. However, the sensitivity was generally higher for the HNO callus producing naturally less ethylene. The weaker reaction of the HNO callus to the exogenous ethylene was attributed to its hyperhydric status (a water layer surrounding the cells). Because low ethylene production appears as a general characteristic of habituated cell lines, the causal and/or consequential relationships of this low ethylene production with other characteristics of habituated tissues (absence of exogenous hormones in the culture media, deficiency of cell differentiation, accumulation of polyamines in neoplastic tissues) are discussed.     

The effect of cytokinin and thidiazuron on tomato inoculated with endomycorrhiza

Seeds of tomato (Lycopersicon lycopersicum var. Peto 86) were planted in soil inoculated with two vesicular-arbuscular mycorrhizal isolates (Glomus intraradices Schenck & Smith). After 7 weeks, plants were transplanted to the field and sprayed twice with cytokinin and thidiazuron, at 50% flowering and 3 weeks later. These treatments significantly increased the percentage of infected roots (30–43%) and chlorophyll content (8–13%). Mycorrhizal plants had less carbohydrates in the roots than in the leaves. Total protein and phenylalanine contents showed pronounced increases, while proline content decreased. Treatment of the mycorrhizal plants with thidiazuron or cytokinin significantly increased plant dry weight (51–54%), and the tomato yield significantly increasecd after inoculation with both isolates (18–35% and 14–32%).     

Signaling mechanism mediating the anti-senescence effect of low-concentration chemical stressors sprayed onto bean seedlings

The anti-senescence effect of low-concentrations of some stress-inducing compounds of different toxicity and chemical nature such as Cd and Pb salts or 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) was investigated in the primary leaves of bean seedlings. In these leaves treated by spraying, chlorophyll content and photosynthetic activity increased, the active cytokinin content of roots and leaves was also significantly higher as compared to the control. These symptoms of stimulation could be eliminated by the inhibitors Li and PD [2-(2′-amino-3′-methoxyphenyl)-oxanaphthalen-4-one] added to each agent, indicating the involvement of PIP₂-IP₃/DAG and MAPK signaling pathways, respectively, in the response.     

An improved micropropagation of <Emphasis Type="Italic">Eclipta alba</Emphasis> by in vitro priming with chlorocholine chloride

An efficient method of micropropagation for Eclipta alba from young nodal axils of shoot tip explants has been developed by giving special attention to ‘priming’ in vitro plantlets in view of increasing their hardening ability after transplantation ex vitro. Among 3 cytokinins—BAP, kinetin and TDZ, BAP was found most effective in inducing and proliferating adventitious shoots. The highest frequency of responding explants (100%) and maximum number of shoots (23.0) per explant were obtained after 60 days culture on MS medium containing 8.8 μM BAP. Cent percent shoots developed roots directly from shoot base when transferred to growth regulator-free MS medium. For priming E. alba microshoots, 6.3 μM of chlorocholine chloride (CCC) was found most effective. The major changes observed in 30 days old treated shoots were, production of increased number of root, elevation of chlorophyll level in leaves and increase in plant biomass. Furthermore, arrested undesirable shoot elongation made the plants sturdier and more suitable for acclimatization. The primed micropropagated E. alba plants were healthy and survived by higher frequency (100%) in soil in comparison to the non-treated plants (84% survival).     

Endogenous cortisol suppression with metyrapone enhances acoustic startle in healthy subjects

Previous human studies have shown that excess cortisol sufficient to fully occupy central nervous system (CNS) corticosteroid receptors may reduce startle eye blink. The present study tested whether cortisol depletion and the resulting reduction in activity of CNS corticosteroid receptors has the opposite effect. In a single-blind, placebo-controlled, randomized study, eye blink EMG responses to 105 dB acoustic startle stimuli were assessed in 25 healthy subjects who received oral metyrapone (1500 mg) to suppress endogenous cortisol production, while 24 controls received oral placebo. As expected, metyrapone significantly reduced salivary cortisol, indicating effective endogenous cortisol suppression. Startle eye blink responses were significantly increased in the metyrapone group. Short-term habituation of the startle reflex was not different between groups. Our results suggest that startle is enhanced during depletion of cortisol. This effect may be mediated by CNS mechanisms controlling cortisol feedback.     

Occurrence of plant hormones in cells of the phototrophic purple bacterium Rhodospirillum rubrum 1R

Abstract Plant hormones from biomass of the purple non-sulfur bacterium Rhodospiririllum rubrum were isolated for the first time. These compounds show high physiological activities (300–330%) in the cytokinin bioassay. All three detected cytokinins are adenine derivatives, according to spectral analysis. One of them was identified as 6-(4-hydroxy-3-methyl-2-trans-2-bytenylamino)-9-ß-D-ribofuranosylpurine (zeatinriboside) as shown by thin-layer chromatography and reversed-phase high-performance liquid chromatography. The possible functions of bacterial cytokinins are also discussed.