The small group of resurrection plants is a unique model which could help us in further understanding of abiotic stress tolerance. The most frequently used approach for investigations on gene functions in plant systems is genetic transformation. In this respect, the establishment of in vitro systems for regeneration and micro propagation is necessary. On the other hand, in vitro cultures of such rare plants could preserve their natural populations. Here, we present our procedure for in vitro regeneration and propagation of Haberlea rhodopensis -a resurrection plant species, endemic for the Balkan region.Numerous physiological and biochemical mechanisms allow plants to inhabit a wide range of arid environments, but in most cases, they are not able to protect them against prolonged water deficit. However, there is a small group of higher plants known as poikilohydric or resurrection plants, possessing unique desiccation tolerance of the vegetative tissues. Their fully mature leaves can lose up to 95% of the water content and then, upon re-watering, they become very fast rehydrated and fully photosynthetically active within several hours. In recent years, studies with these plants have contributed significantly in broadening our knowledge of the molecular regulation and physiology of dehydration tolerance in mature leaf tissue. Among them, the South-African plant species Craterostigma plantagineum is well recognized as a model system (Ingram and Bartels, 1996;Bartels and Salamini, 2001).As would be expected, most resurrection plant species are native to arid climates in the world such as southern Africa, southern America, and western Australia (Gaff, 1971). There, they inhabit ecological niches that are subjected to long periods of drought and are with shallow, sandy soils.Earlier in Bulgaria (Ganchev, 1950) it was shown that such habitats are not an obligatory prerequisite for the resurrection behavior. The Balkan region endemite Haberlea rhodopensis is a world record-holder in desiccation tolerance. It was established that, being dried for 31 months, this plant resumes its normal growth within hours after re-watering.There are no data for in vitro culture of Haberlea rhodopensis so far. Here, we present a simple and efficient procedure for regeneration and micropropagation.Plant material was collected from one of the natural habitats of the plant. We used various plant organs as explants for establishing of aseptic cultures. There were great problems with obtaining such cultures due to the morphology of Habelrea leaves and roots. Finally, we were able to develop in vitro cultures using seeds The seeds were surface sterilized with 70% ethanol for 1 min, followed by 6-10 min treatment with commercial bleach and 3-5 min with 0.1% HgCl 2 with subsequent three times washing with sterile distilled water.The seeds were germinated on MS (Murashige and Skoog, 1962) basal medium. The germination Plant Cell, Tissue and Organ Culture (2005) 80: 115-118 Ó Springer 2005

In 2008, a series of experiments were performed at the Institute of Ornamental Plants -Sofia in greenhouse conditions that tested the influence of salt stress on species of annual plants -Tagetes patula and Ageratum mexicanum. The plants were cultivated in pots under normal soil conditions and salt stress was induced by adding solutions with different concentrations of NaCl (0.4%, 1.2% and 2.0%). The following results were obtained:• The suppression of plant growth increases with the increase of NaCl concentration.• The plants, treated with NaCl, have earlier and shorter blooming period than non-treated plants.

A B S T R A C TNative populations of endemic, rare and threatened Limonium species (L. meyeri, L. bulgaricum, L. latifolium, L. vulgare, L. asterotrichum and L. gmelinii) in Bulgaria were monitored and found seriously declined. To preserve these wild genotypes, an approach involving in vitro propagation of explants isolated from immature inflorescence stems was applied at the Institute of Ornamental Plants, Sofia. The rooted plantlets produced were acclimated and grown outdoors under an optimized cultivation regime, which resulted in the establishment of an ex situ plantation. Plant performance ex situ (determined by leaf rosette diameter, plant height and the number of flower stems) was substantially improved and the variation in the biometric indices was found remarkably lower than in natural environment. The developmental stages of ex situ plants appeared with a delay in relation to their onset in the native environment, but occurred synchronously within each species. Analysis of germination of seeds harvested from ex situ and in situ grown plants showed species-specific behaviour, but in general, seed vitality remained relatively low in laboratory conditions, in the soil and in vitro. In order to assess the potential for protecting the native Limonium species from uncontrolled harvesting, the possibility for the production of cut flowers in ex situ conditions was studied. High yield of cut flowers from ex situ plants in comparison with the potential yield from the wild plants and extended vase life in comparison with commercially produced Limonium sinuatum were obtained. The results demonstrated that the applied micropropagation and agrotechnique for protected cultivation are reliable tools for ex situ conservation of the endangered Limonium genotypes in the Bulgarian flora. In addition to its advantage as a rescue measure, the developed system was shown to be suitable for obtaining cut flowers of competitive market quality.

In 2008, at the Institute of Ornamental Plants-Sofia, were performed series of experiments under greenhouse conditions that tested the influence of heavy metals (Pb, Cu, Zn) on species of Salvia. The plants were cultivated in pots under normal soil conditions and the stress was inducted by adding solutions with different concentrations of heavy metals: The following results were obtained: • The height of the plants is most affected by the solutions of CuSO 4 followed by the combined solutions and the solutions with ZnSO 4 • The branching of the plants is again most affected by the solutions of CuSO 4 , followed by the combined solutions and the solutions with ZnSO 4. • The blooming of the plants is also suppressed. The flowers are small and damaged.

Drought stress is one of the most important environmental factors in reduction of growth, development and production of plants. In our study, in order to simulate water deficit induced by osmotic stress, different concentrations of polyethylene glycol (PEG) 6000 were used: 10 %, 20 % and 40 %. The goal of the investigation is to establish the growth and physiological response of annual flowers (Callistephus chinensis L. and Helichrysum bracteatum) to drought. Seedlings from Callistephus chinensis L. and Helichrysum bracteatum react individually on the simulated drought stress, using PEG in controlled (in vivo) conditions-the detected water deficit varies between 49.9 % to 63.12 %-at 40 % PEG. Changes were identified in the seedling growth, cell membrane stability and the RWC in plant tissues, corresponding to the stress duration and increase of the PEG concentration. The usage of 40 % for 6 days was the maximum admissible for the seedlings from Callistephus chinensis L. and Helichrysum bracteatum, based on the low percentage of plants which regained their development.