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To determine whether the major influence of high salinity is caused by the osmotic component or by salinity-induced specific ion toxicity, we compared the effects of mannitol, sorbitol, NaCl and KCl (all in concentratuions corresponded to osmotic potential -1.0 MPa) on the antioxidant and anatomical responses of the apple rootstock MM 106 explants grown in the Murashige and Skoog (MS) medium. All the compounds had a significant influence on explant's mineral composition and reduced the leaf water content, whereas mannitol and salts decreased chlorophyll (Chl) content and increased proline content. Superoxide dismutase (SOD), peroxidase (POD) and non-enzymatic antioxidant activities as well as H 2 O 2 content were increased in the leaves and stems. In addition, in the leaves of explants exposed to NaCl an additional Mn-SOD isoform was revealed, while specific POD isoforms were detected in the leaves and stems treated with NaCl or KCl. However, catalase activity was depressed in the salt-treated leaves. At the ultrastructural level, the NaCl-treated leaves had the thickest lamina, due to an extensive increase of the size of epidermal and mesophyll cells. Also, an increase of the relative volume of the intercellular spaces in response to NaCl was observed. The results suggest that Na accumulation is the first candidate for the distinct antioxidant and anatomical responses between saline and osmotically generated stress in the MM 106 explants.

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Regulated deficit irrigation (RDI) involves inducing water stress during specific fruit growth phases by irrigating at less than full evapotranspiration. The objectives of this research were to study the effects of RDI perfomed at stage II of fruit growth and postharvest, on productivity of clingstone peaches, fruit quality as well as photosynthetic rate and midday leaf water potential. The research was conducted in a commercial clingstone peach (Prunus persica L. Batch cv. A-37) orchard in Greece. Trees were irrigated by means of microsprinklers and their frequency was determined using local meteorological station data and the FAO 56 Pennman-Monteith method. Photosynthetic rate was measured by a portable infrared gas analyzer. Midday leaf water potential was measured by the pressure chamber technique. During the years 2005 and 2006, the treatment RDII with irrigation applied at growth stage II of the peach tree did not affect productivity, fresh and dry mass of fruits. RDII reduced preharvest fruit drop in comparison to the control. RDII as well as the combined treatment RDII plus RDIP with irrigation applied at postharvest, at both years reduced shoot length of the vigorous shoots inside the canopy. RDII in comparison to the control increased the soluble solids content of the fruits and the ratio soluble solids/acidity. However it did not affect fruit acidity and fruit firmness. RDII as well as RDII plus RDIP in 2006 increased 'double' fruits and fruits with open cavity in comparison to the control and RDIP. Water savings were considerable and associated with the climatic conditions of each year. Key words: fruit drop, leaf water potential, photosynthetic rate, water savings Resposta de um cultivar de pêssego com caroço aderente à irrigação por défice regulado RESUMO: A irrigação por défice regulado (RDI) envolve a indução de défice de água durante fases específicas do crescimento das frutas, irrigando a taxas menores que a evapotranspiração. Os objetivos desse estudo foram verificar os efeitos da RDI no estágio II do crescimento das frutas e no periodo pós-colheita, avaliando a produtividade de pêssegos, a qualidade dos frutos, bem como a taxa fotossintética e o potencial da água na folha. A pesquisa foi desenvolvida em um pomar comercial de pêssegos com caroço aderente (Prunus persica L. Batch cv. A-37) da Grécia. As árvores foram irrigadas por meio de microaspersores e sua frequência foi determinada por meio de dados meteorológicos obtidos em estação automática e o método FAO 56 Pennman-Monteith para determinação de evepotranspiração. A taxa de fotossíntese foi medida por analisador de gás na faixa do infravermelho. O potencial da água na folha foi medido ao meio-dia usando a técnica da câmara de pressão.

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The apple (Malus domestica Borkh) rootstock M 4 shoots were grown in vitro for 4 weeks on Murashige and Skoog (MS) medium containing three NaCl concentrations (35, 100 and 200 mM) in combination with two CaCl 2 concentrations (5 and 10 mM). Inclusion of 10 mM CaCl 2 in the medium, in the presence of 35 mM NaCl, significantly increased the number of shoots and the fresh mass compared to 5 mM CaCl 2. The number of shoots, length of shoots, and the fresh mass of cultures were very low in the presence of 100 and 200 mM NaCl, independently of CaCl 2 concentration of the medium. By increasing NaCl and CaCl 2 concentrations in the culture medium, contents of N, Na, Cl, proline and soluble sugars in plantlets increased, whereas K, Mg, Β, Zn and chlorophyll content decreased in comparison to the control.

The effects of boron and NaCl induced salinity on growth and mineral composition of the pear (Pyrus communis L.) rootstock OH × F 333 shoots cultured in vitro were investigated. Shoots were grown in vitro for seven weeks on a Murashige and Skoog medium containing two B concentrations (0.1 and 2 mM) combined with five NaCl concentrations (0, 10, 20, 40, and 80 mM). Τhe longest shoots were produced at 0.1 mM B and 80 mM NaCl, but highest number of shoots were produced at 0.1 mM B and 0 -20 mM NaCl. Inclusion of 20 and 40 mM NaCl in the culture medium significantly increased fresh mass of cultures compared to 0 mM NaCl for all B concentrations tested. The concentrations of P, K, Ca, Mg, Na, Fe, Mn and Zn of plants were affected by B and NaCl concentration of the medium.