Role of Ethylene in Senescence of Petals--Morphological and Taxonomical Relationships

Petal senescence in mature flowers was studied in 93 speciesfrom 22 families. The initial symptom of senescence was eitherwilting or abscission, but in some species the time span betweenwilting and abscission was very short. There was no apparent relationship between corolla form (choripetalousor sympetalous), ovary position (inferior or superior with respectto the corolla) and type of senescence (initial wilting or initialabscission). In monocots no initial abscission was found, whilein dicots the difference between the wilting type and the abscissiontype was generally at the family level. With respect to petalsenescence, sensitivity to exogenous ethylene (C₂H₄) was alsorelated to the family level. Except for a few families (all tested Campanulaceae, Caryophyllaceaeand Malvaceae, and most Orchidaceae), most of the flowers investigatedthat showed initial wilting were not sensitive to exogenousethylene, e.g. all tested Compositae, Iridaceae, and Liliaceae.Most of the flowers showing initial abscission were sensitiveto exogenous ethylene (Geraniaceae, Labiatae, Ranunculaceae,Rosaceae, Scrophulariaceae). Experiments with silver thiosulphate (STS) confirmed the effectsof exogenous ethylene, both in flowers showing initial wiltingand in flowers showing initial abscission. The data indicate,therefore, that ethylene is involved in the natural senescenceof only a minority of the wilting type of flowers and in a majority(if not all) of the abscising type of flowers. Key words: Abscission, ethylene, senescence, silver thiosulphate     

Histochemical and genetic analysis of host and non-host interactions of Arabidopsis with three Botrytis species: an important role for cell death control

Susceptibility was evaluated of host and non-host plants to three pathogenic Botrytis species: the generalist B. cinerea and the specialists B. elliptica (lily) and B. tulipae (tulip). B. tulipae was, unexpectedly, able to infect plant species other than tulip, and to a similar extent as B. cinerea. To study host and non-host interactions in more detail, the three Botrytis species were inoculated on Arabidopsis wild-types and 23 mutant genotypes. Disease development was monitored macroscopically by quantifying the lesion area and microscopically by bright-field and fluorescence microscopy following histochemical staining. B. cinerea and B. tulipae were very similar in their ability to infect the tested Arabidopsis genotypes, whereas B. elliptica caused disease only on a few Arabidopsis mutant genotypes. Arabidopsis mutants with a delayed or reduced cell death response were generally more resistant to Botrytis infection, whereas mutants in which cell death was accelerated were more susceptible. Differences in susceptibility between genotypes were generally gradual. Only the camalexin-deficient mutant pad 3 was fully susceptible to all three Botrytis species. Cellular changes were monitored during compatible and incompatible interactions. The formation of papillae, the presence of lysosome-like vesicles and the intracellular accumulation of H₂O₂ and nitric oxide were visualized in the infection zones using fluorescent probes. Based on histology and responses of Arabidopsis mutants, a model is proposed in which resistance against Botrytis , besides the production of camalexin, depends on the balance between cell death and survival.     

Role of Rostellum Desiccation in Emasculation-Induced Phenomena in Orchid Flowers

The effects of relative humidity (RH) and of treatment of therostellum with aminoethoxyvinylglycine (AVG), 1-aminocyclopropane-1-carboxylicacid (ACC) and water-insoluble vacuum grease on emasculation-inducedphenomena in Cymbidium and Phalaenopsis flowers were investigated.Under conditions of high RH and after treatment of the rostellumwith water-insoluble grease, the normal response to emasculation(i.e. increased ethylene production, lip coloration and wilting)was absent. However, under conditions of high RH this responsecould be restored by the addition of 2.0 nmol ACC on to therostellar surface. Under conditions of low RH the response wasinhibited by AVG; this inhibition was partially reversed byaddition of 2.0 nmol ACC. The data provide evidence that desiccation of the rostellumis responsible for post-emasculation phenomena in orchid flowers. Key words: Emasculation, ethylene, orchids, senescence     

Epigenetic regulation of trophic morphology through feeding behaviour in Arctic charr, Salvelinus alpinus

Several models of speciation suggest that in species that are phenotypically plastic, selection can act on phenotypic variation that is environmentally induced in the earliest stages of divergence. One trait that could be subject to this process is foraging behaviour, where discrete foraging strategies are common. One species which is highly plastic in the expression of phenotype, the Arctic charr, Salvelinus alpinus (L.), is characterized by discrete variation in the anatomy of the head and mouthparts. These traits have been shown to have a functional significance, but the expression of which is thought to be at least partly phenotypically plastic. Here we test the hypothesis that foraging behaviour may regulate the anatomy of the head and mouthparts in Arctic charr. In a dyad experiment, size‐matched pairs of fish from a mixed family group were fed a diet of either Mysis (a hard‐bodied shrimp) or Chironomid larvae. Nine morphometric measures of head dimensions that describe wild trophic morphs were measured at the start of the experiment and 24 weeks later. Principal component scores of size‐corrected morphometric measures showed highly significant differences between fish exposed to the two diets. Univariate ANOVA analysis of the head morphometric variables showed that fish fed on Chironomids developed longer, wider jaws, longer heads and a larger eye for a given body length than did those fish fed upon Mysis. We conclude that foraging anatomy in Arctic charr is phenotypically plastic and that variation in foraging behaviour that results in feeding specialization in the wild could induce variation in head anatomy. This in turn could reinforce foraging specialization. Very rapid epigenetic divergence into distinct feeding morphs (as demonstrated here) would allow selection to act at more than one mode and thus could promote rapid evolutionary divergence, initially prior to genetic segregation, in species which are highly plastic. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 43–49.     

Interrelationship between the Different Flower Parts during Emasculation-Induced Senescence in Cymbidium Flowers

In Cymbidium flowers emasculation by removal of the anther capand the pollinia, led to rapid colouration of the lip and advancedwilting of the petals and sepals. The ethylene production ofwhole flowers showed an emasculation-induced early peak in ethyleneevolution followed some days later by a second increase concomitantwith the wilting of the flower. In non-emasculated flowers theethylene production increased later and simultaneously withcolouration of the lip and wilting of the petals and sepals.At all stages of senescence, the contribution of the lip, petals,and sepals to the total amount of ethylene produced was negligible. Parallel to the increase in ethylene production of whole flowers,an increase in 1-aminocyclopropane-l-carboxylic acid (ACC) andmalonyl-ACC (MACC) in the central column and, to a lesser extent,in the ovary was observed. Also an increase in internal ethyleneconcentration was demonstrated and this, in contrast, was apparentin all the different flower parts. The activity of the ethylene-formingenzyme in lips, petals, and sepals showed an increase afteremasculation and such an effect could also be induced by treatmentof isolated lips with low concentrations of ethylene. The data indicate that senescence in Cymbidium flowers is regulatedby the central column and perhaps the ovary and that both ACCand ethylene may play a signalling role in inter-organ communication. Key words: 1-aminocyclopropane-l-carboxylic acid, ethylene, Cymbidium, senescence