The aim of this study was to develop an efficient in vitro propagation method of Pelargonium plant (seven cultivars) using axillary buds and shoot tips as explants. The influence of the time period in which the explants were collected and the influence of the growth regulators (BAP, meta-topolin, IBA) were studied.The explants taken in April had a higher regeneration ability than those isolated in July and September. The most efficient regeneration and axillary multiplication were achieved on the medium supplemented with meta-topolin. The application of BAP caused a lower regeneration potency of explants and resulted in a decrease of shoot quality with every subculture. Four of the six cultivars showed growth inhibition after three months of growth on BAP-medium. The highest multiplication rate (2.7-4.7 depending on genotype) and the high quality of shoots were noted on the medium supplemented with mT (0.5-1.0 mg l -1 ). It is also very important to note that mT had stimulating effect on organogenesis in P. × hederaefolium and P. × hortorum cultivars over the long term. Moreover, meta-topolin had no after-effect on the growth and inhibition of rooting. Only one cultivar (Sofie Cascade) rooted better on control medium without auxin. In case of the other cultivars, IBA added in concentrations of 0.01-0.1 mg l -1 had a stimulating effect on root production. The higher level of auxin inhibited root formation, stimulated senescence of shoots and had a negative after-effect on acclimatization in greenhouse conditions.

The ad ven ti tious shoot re gen er a tion from pet i ole explants of Pelargonium × hederaefolium 'Bonete' was achieved via a mixed path way i.e. organogenesis and so matic embryogenesis. The histological study of re gen er ated structures re vealed the pres ence of both shoot primordia and embryo-like struc tures. The ini tial growth in pet i ole explants occurred on me dia with BAP + auxin or TDZ alone. How ever, the most ef fec tive re gen er a tion (24 struc tures/explant) was noted in the pres ence of TDZ (2 mg·l -1 ) and IBA (0.1 or 0.2 mg·l -1 ). More over, the ap pli ca tion of TDZ in the in duc tion phase reduced the time needed for the for ma tion of ad ven ti tious structures and pos i tively in flu enced the fur ther shoot de vel op ment on the me dium con tain ing m-topolin and IBA. List of ab bre vi a tions:BAP -N 6 -benzylaminopurine; IAA -indole-3-ace tic acid; IBA -indole-3-bu tyric acid; MS -Murashige and Skoog me dium; mT -(meta-topolin)-N 6 -(3-hydroxybenzyl) ad e nine; TDZ -thidiazuron (N-phenyl-N'-1,2,3-thiadiazol --5-ylurea) In tro duc tionPelargonium is one of the most im por tant bed ding and pot plant in the world. Cur rently, the ma jor produc ers and dis trib u tors of pelargonium plants are North Amer ica and Eu rope. Out of four com mercially im por tant groups (Pelargonium × hortorum L. H. Bailey -P. zonale hort., P. × domesticum L. H. Bailey -P. × grandiflorum hort., P. × hederaefolium -P. peltatum hort. and scented ge rani ums) the most pop u lar in North Amer ica are cultivars of P. × hortorum, which are in high percent (50 %) prop a gated by seed (Lange and Horn 1996). In Eu rope, P. × hortorum and P. × hederaefolium, mostly prop a gated vege ta tively by cut ting, are bought in the same pro por tion. The basic fac tors be ing a req ui site of a prof it able mass pro duc tion are: breed ing, new cul ti va tion tech nology and, first of all, healthy star t ing ma te rial. The need for patho gen-free plants as the elite mother stock led to the de vel op ment of in vi tro prop a ga tion sys tem. How ever, be cause of the spe cific re quirements of dif fer ent ge no types for a me dium com posi tion (min er als, or ganic com pounds and growth reg u la tors) an op ti mal and uni ver sal method of Pelargonium sp. micropro pa ga tion has not been elab o rated yet. A suc cess ful re gen er a tion of plants from dif fer ent ini tial explants both via organogenesis or embryogenesis was widely reported for P. × hortorum cultivars (Abo El-Nil and 255 ACTA PHYSIOLOGIAE PLANTARUM

The aim of the study was to develop an efficient micropropagation system for Rosa ‘Konstancin’, an interspecific hybrid between R. rugosa and R. beggeriana, whose fruits have high pro-health value. Shoot cultures were initiated from shoot buds collected in May and August from 15-year-old field-grown Rosa ‘Konstancin’ shrubs. The effect and interaction of different concentrations of phytohormones, sucrose and iron sources on in vitro initiation, multiplication and rooting of shoots were studied. The time of collecting explants from donor plants significantly affected the initiation of shoot culture of Rosa ‘Konstancin’. Considerably higher frequency of bud break (100%) was obtained in explants isolated in August as compared to those collected at the end of May (30%). All buds developed into single shoots after 2-4 weeks of growing on the basal Murashige and Skoog medium containing 2.2 µM BAP, 0.3 µM GA3 and 88 mM of sucrose. The highest multiplication rate (4.8 shoots/explant) in a 5-week period was obtained on MS medium containing 50% of nitrogen salts, 3.1 µM BAP, 0.9 µM GA3 and 58 mM sucrose. High rooting frequency (100%) and quality of rooted plantlets was obtained on a medium containing 0.5 µM IBA, 138 µM Fe-EDDHA and 88 mM sucrose. Fe-EDDHA had a beneficial effect on the growth and photosynthetic activity of Rosa ‘Konstancin’ plantlets, which were successfully acclimatized ex vitro, with a more than 90% survival rate.

The total soluble sugar content and antioxidant enzyme activities were studied for the first time during axillary shoot formation in Magnolia × 'Spectrum' in vitro in response to BAP (0.3 mg l -1 ), different levels of gibberellic acid (GA 3 ; 0.0, 0.1, 0.5, 1.0 mg l -1 ), sucrose (20 and 30 g l -1 ) and nitrogen salts (KNO 3 /NH 4 NO 3 ; 100/100% and 75/50% relative to MS medium). Among various GA 3 and sucrose/nitrogen salts ratios, the most effective axillary multiplication (5.9 shoots/explant) and leaf formation (25.7 leaves per multiplied clumps) were obtained after addition of GA 3 at 0.1 mg l -1 to a BAP medium containing 20 g l -1 sucrose and reduced levels of nitrogen salts (75% KNO 3 and 50% NH 4 NO 3 ). The addition of GA 3 to the BAP medium enhanced shoot formation by 36% and leaf formation by 27%. The highest shoot formation capacity of M. × 'Spectrum' in vitro coincided with enhanced levels of soluble sugar and peroxidase (POD) activity. Increasing GA 3 concentration from 0.1 to 1.0 mg l -1 in the above medium resulted in inhibition of shoot and leaf formation and a decrease in the soluble sugar content. The influence of GA 3 on the activities of catalase (CAT) and POD depended on its concentration and the levels of sucrose and nitrogen salts in the medium. The highest increase in CAT and POD activities, that coincided with the enhanced shoot formation capacity of M. × 'Spectrum' in vitro, was observed after addition of GA 3 to the medium containing high levels of sucrose and nitrogen salts.

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