Cytokinin activity of disubstituted aminopurines in Amaranthus

Cytokinin (CK) receptors have different affinities for certain ligands, and consequently, studies of the plant's response to CK analogues constitute a good approach to identify active compounds that trigger specific plant responses. In this study, N⁶ and N⁶,N⁶-substituted CK analogues were synthesized and their CK-like activity was examined in the Amaranthus betacyanin and the bacterial receptor assay. The compounds showed CK-like activities that were not always associated with their binding affinity to the Arabidopsis receptors AHK3 and CRE1/AHK4. The highest level of activity in both bioassays was obtained for the N⁶-alkylaminopurines, which showed an especially high binding affinity to AHK3. In contrast to previously published data, we found remarkable activity of N⁶,N⁶-alkylbenzylaminopurines in the Amaranthus betacyanin bioassay, which was not associated with their binding affinity to the tested receptors. The N⁶,N⁶-substituted CK that showed the highest activity at the lowest concentration, N⁶,N⁶-methylbenzylaminopurine (BAP-C1), was studied to determine its effect on different leaf parameters of whole Amaranthus plants, with benzylaminopurine (BAP) used as standard compound. The interaction with ethylene was examined in plants supplied with the ethylene-synthesis inhibitor aminooxiacetic acid (AOA). After 3 d, the CKs supplied in the solution culture exerted effects on leaf dry weight and gas-exchange parameters. These effects of exogenous CKs are suggested to be ethylene-synthesis dependent.     

Auto‐phosphorylation of a voltage‐gated K+ channel controls non‐associative learning

Here, we characterize a new K⁺ channel–kinase complex that operates in the metazoan Caenorhabditis elegans to control learning behaviour. This channel is composed of a pore‐forming subunit, dubbed KHT‐1 (73% homology to human Kv3.1), and the accessory subunit MPS‐1, which shows kinase activity. Genetic, biochemical and electrophysiological evidence show that KHT‐1 and MPS‐1 form a complex in vitro and in native mechanosensory PLM neurons, and that KHT‐1 is a substrate for the kinase activity of MPS‐1. Behavioural analysis further shows that the kinase activity of MPS‐1 is specifically required for habituation to repetitive mechanical stimulation. Thus, worms bearing an inactive MPS‐1 variant (D178N) respond normally to touch on the body but do not habituate to repetitive mechanical stimulation such as tapping on the side of the Petri dish. Hence, the phosphorylation status of KHT‐1–MPS‐1 seems to be linked to distinct behavioural responses. In the non‐phosphorylated state the channel is necessary for the normal function of the touch neurons. In the auto‐phosphorylated state the channel acts to induce neuronal adaptation to mechanical stimulation. Taken together, these data establish a new mechanism of dynamic regulation of electrical signalling in the nervous system.     

The effect of cytokinins on growth and sexual organ development in the gametophyte of <Emphasis Type="Italic">Blechnum spicant</Emphasis> L.

In this study, we report the role of exogenous and endogenous cytokinins on growth and sexual organ development in the fern Blechnum spicant L. Spore-derived gametophytes (SG) were cultured in full-strength Murashige and Skoog (1962) liquid medium supplemented with (a) 4.44 μMN⁶-benzyladenine (BAP), (b) a crude extract from mature female gametophytes, and (c) 4.44 μM BAP in combination with the crude extract from mature gametophytes, respectively. Both BAP and the crude extract delayed the gametophyte development, and this effect was increased when they were added together. With respect to sexual organ development, BAP inhibited the sexual organ formation, while the crude extract favored antheridia formation; however, when added together, the percentage of antheridia decreased. The endogenous level of the cytokinins cis-zeatin (cZ), cis-zeatin-riboside (cZR), dihydrozeatin (DHZ), dihydrozeatin riboside (DHZR), isopentenyl adenine (iP), isopentenyl adenosine (iPR), isopentenyl-9-glucoside (iP9G), trans-zeatin (tZ), and trans-zeatin riboside (tZR) were analyzed in female and male gametophytes of B. spicant L. The endogenous levels of cytokinins tZ, cZ, DHZ, cZR, iP, and iPR were higher in female gametophytes than in male gametophytes, with the endogenous iP and iPR content being increased more than 300 and 400 times, respectively.     

Cytokinin Profiles in the Conifer Tree <Emphasis Type="Italic">Abies nordmanniana</Emphasis>: Whole-Plant Relations in Year-Round Perspective

Conifer trees are routinely manipulated hormonally to increase flowering, branching, or adjust crown shape for production purposes. This survey of internal cytokinin levels provides a background for such treatments in Abies nordmanniana, a tree of great economic interest. Reference points in the crown and root system were sampled destructively in 4- and 6-year-old trees and analyzed for a range of cytokinins by LC-MS/MS. No seasonal patterns were detected in the root samples, and a major portion of cytokinin was in conjugated forms. Dramatic and consistent seasonal changes occurred in the crown, at levels 17–65 times higher than in the root. Predominant among crown cytokinins was ZR, except in the needles where IPR was also prominent. Within the crown, cytokinin profiles in different organs differed consistently. The leader bud showed a pronounced mid-June minimum, and a maximum later in summer. Subapical buds showed the same June minimum but peaked in mid autumn at a much lower level. Maxima in these buds were preceded by peaks in the subapical stem. Parallel patterns were observed in homologous tissues on branches.This pattern is consistent with two surges beginning in the uppermost stem tissues leading to subsequent accumulation or stimulated production within the buds. Strong differential hormonal profiles between adjacent buds with different fates agree with recent evidence of localized cytokinin production. The data suggest a reduced role of root-derived cytokinins in crown development. Practical cytokinin treatments for crown-shape regulation require close attention to dosage as well as precise timing and positioning.     

The Effect of Human Presence and Human Activity on Risk Assessment and Flight Initiation Distance in Skinks

Antipredator behavior and risk assessment of many species are affected by the presence of humans and their activities. Previous studies have largely been conducted on birds and mammals and relatively less is known about human impacts on reptiles. We used flight initiation distance (FID) as a measure of risk assessment in inland blue‐tailed skinks (Emoia impar) and tested the direct and indirect effects of humans on risk assessment. We first examined the effects of varying levels and types of human disturbance and activity on skink FID. We found that skinks flushed at significantly longer distances in areas with the least human activity. We then tested the degree to which skinks are able to discriminate different numbers of humans by comparing FID across three different types of approaches. Skinks did not significantly differentiate between a single approacher and a single approacher coming from a group of two other people, but did flush at greater distances when approached by three people simultaneously. Although skinks are not directly harvested or harassed by humans, they have refined human discrimination abilities. Overall, skinks habituate to a variety of human activities and perceive a larger threat when the number of human approachers is greater.     

Rapid habituation by mosquito larvae to predator kairomones

Larvae of some species of mosquitoes have been shown to respond to water‐borne kairomones from predators by reducing bottom‐feeding and replacing it with surface filter‐feeding, which uses less movement and is thus less likely to attract a predator. However, if no predator attack takes place, then it would be more efficient to use a risk allocation strategy of habituating their response depending on the predator and the overall risk. The larvae of Culiseta longiareolata Macquart live in temporary rain‐filled pools, where they are exposed to a high level of predation. Within one hour, they responded to kairomones from dragonfly or damselfly nymphs, or to the fish Aphanius, by significantly reducing bottom‐feeding activity. Continued exposure to the predator kairomones resulted in habituation of their response to damselflies, a slower habituation to fish, but no habituation to dragonflies even after 30 h. In contrast, the larvae of Culex quinquefasciatus Say normally live in highly polluted and thus anaerobic water, where the predation risk will be much lower. They also showed a significant reduction in bottom‐feeding after 1 h of exposure to predator kairomones but had completely habituated this response within 6 h of continuous exposure. Some species of mosquito larvae can thus show a very rapid habituation to predator kairomones, while others only habituate slowly depending on the predator and overall predation risk.     

Regulation of source/sink relations by cytokinins

Many physiological effects of cytokinins are well established and are known to be involved in various aspects of the plant life cycle. In contrast, little is known about how these effects are evoked at the molecular level. Since cytokinins have been shown to play a major role in the regulation of various processes associated with active growth and thus an enhanced demand for carbohydrates, a link to the regulation of assimilate partitioning has been suggested. This review discusses the current knowledge of the role of cytokinins in the regulation of source-sink relations, based on the finding of the co-ordinated cytokinin induction of an extracellular invertase and a hexose transporter. The induction of these key enzymes of an apoplastic unloading mechanism may be one important molecular prerequisite for different cytokinin-mediated effects.     

Cytokinin synthesis is higher in the Arabidopsis amp1 mutant

Cytokinins are involved in plant cell proliferation leading to plant growth and morphogenesis. Earlier we described a mutant of Arabidopsis thaliana, amp1, that had five times higher levels of cytokinin and had a number of pleiotropic phenotypes, including increased cell proliferation and de-etiolated growth in the dark. While these phenotypes were correlated with higher levels of cytokinin, the actual mechanism of how cytokinin is elevated was not elucidated before. In order to understand if the increased cytokinin is a result of increased biosynthesis or decreased degradation we have compared the synthesis of cytokinins from radiolabelled adenine and the degradation of zeatin ribosides and other cytokinins between amp1 and wild type plants. The degradation of the hormone is not affected in the mutant but there is a 4 to 6 fold increase in cytokinin synthesis compared to the wild type. Because the amp1 mutant is recessive we hypothesise that the AMP1 product negatively regulates cytokinin production.     

Organogenesis of Phaseolus angularis L.: high efficiency of adventitious shoot regeneration from etiolated seedlings in the presence of N6-benzylaminopurine and thidiazuron

A step-wise procedure for the regeneration of fertile plants by organogenesis from cultures of the economically important Phaseolus angularis L., cultivars: KS-6, KS-7 and KS-8 using etiolated seedlings was established. Pre-culture of 5-day old seedling explants with MS (Murashige and Skoog (1962) Physiol Plant 15:473–493) + B₅-vitamins (Gamborg et al. (1968) Exp Cell Res 50:151–158) liquid medium containing either 5.0 μM TDZ or 5.0 μM BAP under dark condition was essential for organogenesis. Bud growth and shoot multiplication were stimulated by reducing the BAP concentrations from 5.0 to 2.5 μM after 3 weeks. The maximum frequency of shoot induction was 65.2% (33.8 ± 2.54 shoots/explant) in cultivar KS-8 followed by KS-7 34.6% (23.4 ± 1.91 shoots/explant) and KS-6 30.6% (21.2 ± 2.28 shoots/explant). The multiplied buds elongated after transferring to solid MSB₅ medium supplemented with 4.0 μM GA₃, 12.5 μM AgNO₃ and 0.4 μM IBA. Up to 98% rooting efficiency of was obtained when the shoots were pulse-treated with liquid medium containing 4.5 μM IBA for 10 min. The rooted plantlets were transferred to pots in the greenhouse, where they grew, mature, flowered and bared pod normally. The efficient shoot bud induction capability was found to be cultivar dependent. All the three cultivars tested formed multiple shoots. This efficient and rapid regeneration system may also be helpful for Agrobacterium- or particle gun-mediated transformation for this important legume crop.     

玉米素核苷的酶标免疫测定法

牛血清白蛋白-玉米素核苷(BSA-ZR)的兔抗血清对玉米素核苷具有很高的亲和性,而且专一性强,除了玉米素外,对其它一些细胞分裂素如激动素(KT)的交叉反应甚微。用辣根过氧化物酶(HRP)作为标记物的酶标免疫法,由于它的灵敏度高,相当于几十毫克量的样品就可以测出细胞分裂素的含量。测定范围在0.25—50pmol之间,测定范围较广。由于该方法专一性高,植物组织的粗提取物可以直接用于测定。避免了提取分离的繁琐程序,使得测定方法较简便、快速,可成批进行,适用于一般实验室。用该方法测得风信子(Hyacinthus orientalis L.)各部分的细胞分裂含量(以玉米素核苷计)在10—60×10~(-9)克/克鲜重,即10—60ng/g F.W.。