Among the different mineral nutrients, potassium (K) is recognized as the macronutrient that most strongly affects the quality parameters of crops. An adequate K nutrition is in fact associated with increased fruit size, enhanced nutraceutical properties (e.g., content of sugar, organic acids, antioxidants), improved color and increased shelf life for many agricultural products. Previous studies have shown that, in controlled conditions, the foliar application of K-based fertilizers during the fruit development period could improve fruit quality; however, it is not clear whether such positive results can also be obtained in field-cultivated plants. For these reasons, the aim of the present study was to assess if the repeated applications of K-based fertilizers during the production period (mid-June to late August) might affect the quality parameters of strawberry (Fragaria × ananassa 'Murano') fruits. Frigoplants, transplanted in April, were cultivated in grow bags on cocopeat (8 plants per linear meter) and treated foliarly spraying K(2)SO(4) (6 g L(-1)) either once or twice a week. Control plants were sprayed with distilled water. As expected, foliar K-fertilization increased the K concentration by 8-11% in fruits and by 7-5% in leaves according to the frequency of application (once and twice a week, respectively). In addition, strawberry fruits exhibited an enhanced total soluble solids content (approximately 12%) and sweetness index (approximately 13%). Conversely, other nutraceutical compounds (e.g., phenolics, flavonoids and flavonols) as well as the fruit yield were not affected by K treatments, regardless the fertilization levels. In conclusion, results here presented show that at the field scale the foliar K-fertilization during the development of strawberries can enhance the quality and the nutraceutical value of fruits.

With the aim of developing an efficient protocol for protoplast isolation from leaf tissue of three cultivars of Rubus spp., the effect of different pretreatments and digestion solutions were tested in leaf tissue of 'Autumn Bliss' (2x-raspberry), 'Hull Thornless', and 'Chester' (4x-blackberry). The highest protoplast yields (21.6 x 10(5) protoplast x g fw(-1)), with 85% viability, were obtained using W5/2 (MENCZEL et al., 1981) salt solution supplemented with pectolyase Y23 Sigma (0.1%), cellulase R-10 Yakult (2.5%), macerozime-R10 Yakult (0.8%). Cell division and calli formation from leaf-derived protoplast of both blackberry varieties were obtained only when imbedded in agarose blocks and co-cultured with 'nurse cells' of the same varieties, harvested at the exponential phase of the culture on a medium containing macro-micro elements of Gamborg (1968) or KM (KAO and MICHAYLUK, 1975), vitamines and organic acid of KM, supplemented with 10.74 mu M alpha-naphthaleneacetic acid (NAA) and 1.78 mu M N-6 benzyladenine (BA). Under these conditions, up to 12% leaf-derived protoplasts of 'Hull Thornless' and 5% of 'Chester' showed the first division after 5-6 days and formed callus colonies after 6 weeks of culture. A much higher protoplast yield was obtained using cell suspensions of 'Autumn Bliss' and 'Hull Thornless', incubated 4-5 hrs in a solution containing driselase Sigma (2%), cellulase R-10 Yakult (0.25%), pectolyase Y-23 Sigma (0.025%) supplemented with 0.35M mannitol, 0.35M sorbitol, 15 mM CaCl2 . 2H(2)O, 1 mM NaH2PO4 and 5 mM MES. This result was also related to cell culture condition. Cell suspension from the 7th to 11(th) days of culture on liquid modified KM salts supplemented with 10.74 mu M NAA, 2.25 CIM 2,4-D, 1.7 yM BA, gave the highest release (3.9 x 10(6) protoplast x g fw(-1)). Callus lines obtained from both these sources of protoplasts were isolated and cultured. Treatments with different PGR combinations and also stress factors were tested for the induction of plant regeneration. Bur, at this stage root formation was the only type of differentiation observed.

The morphogenic response of somatic (leaf and petiole) and de-differentiated tissue (callus) of two blackberry (Rubus fruticosus) and one raspberry (Rubus idaeus) cultivars have been studied in vitro. With the aim to induce regeneration the effect of two sets of plant growth regulator (PGR) combinations (high cytokinin/auxin ratios and high auxin/cytokinin ratios) in Murashige and Skoog basal medium, were analysed. The three cultivars were characterised by a qualitatively different morphogenic response to the PGR combinations. Raspberry adventitious shoot regeneration from somatic tissue was improved by the 6-benzylaminopurine (BAP)/indol-3-butyric acid (IBA) combinations. On the contrary, shoot regeneration of both blackberry cultivars was reduced by high concentrations of BAP and completely inhibited by BAP/IBA combination. Media supplemented with high auxin/cytokinin ratios promoted callus production and root differentiation according to genotype and type of auxin. All the genotypes responded to media supplemented with IBA. 2,4-dichlorophenoxyacetic acid induced good callus formation in blackberry, but was toxic to raspberry. Indirect shoot formation was observed only in callus of blackberry cultivar Hull Thornless cultivated on medium with 10 µM BAP, the same concentration able to trigger efficient direct shoot regeneration from leaf explants of the same cultivar.

The effect of several inhibitors of polyamine synthesis on root growth and morphology and on polyamine titres in normal and Agrobacterium rhizogenes-transformed hairy root cultures of Hyoscyamus muticus was investigated. Five millimolar cyclohexylamine (CHA) and 1 mM methylglyoxal-bis-guanylhydrazone (MGBG) significantly inhibited both root growth and lateral root formation. One millimolar alpha-difluoromethylarginine (DFMA) significantly reduced while 1 mM alpha-difluoromethylornithine (DFMO) stimulated elongation growth of primary and lateral roots without affecting lateral root number. Both normal and hairy roots treated with DFMO, alone or in combination with DFMA, displayed a very evident lack of root hairs. Free polyamines constituted only a small part of the total polyamines present in hairy roots; of these, spermidine was the most abundant. A conspicuous accumulation of trichloracetic acid-soluble and -insoluble conjugated putrescine was also found. Although DFMO did not significantly alter total putrescine content, DFMA reduced it dramatically. This effect was further accentuated when DFMO and DFMA were supplied together. CHA and MGBG did not provoke the expected depletion in spermidine and/or spermine, but both inhibitors caused a marked accumulation in free and conjugated putrescine.