Miltiadis Vasilakakis

Physiological and proteomic approaches to address the active role of ozone in kiwifruit post-harvest ripening

Post-harvest ozone application has recently been shown to inhibit the onset of senescence symptoms on fleshy fruit and vegetables; however, the exact mechanism of action is yet unknown. To characterize the impact of ozone on the post-harvest performance of kiwifruit (Actinidia deliciosa cv. ‘Hayward’), fruits were cold stored (0 °C, 95% relative humidity) in a commercial ethylene-free room for 1, 3, or 5 months in the absence (control) or presence of ozone (0.3 μl l−1) and subsequently were allowed to ripen at a higher temperature (20 °C), herein defined as the shelf-life period, for up to 12 days. Ozone blocked ethylene production, delayed ripening, and stimulated antioxidant and anti-radical activities of fruits. Proteomic analysis using 1D-SDS-PAGE and mass spectrometry identified 102 kiwifruit proteins during ripening, which are mainly involved in energy, protein metabolism, defence, and cell structure. Ripening induced protein carbonylation in kiwifruit but this effect was depressed by ozone. A set of candidate kiwifruit proteins that are sensitive to carbonylation was also discovered. Overall, the present data indicate that ozone improved kiwifruit post-harvest behaviour, thus providing a first step towards understanding the active role of this molecule in fruit ripening.

Nitrosative responses in citrus plants exposed to six abiotic stress conditions

Nitrosative status has emerged as a key component in plant response to abiotic stress; however, knowledge on its regulation by different environmental conditions remains unclear. The current study focused on nitrosative responses in citrus plants exposed to various abiotic stresses, including continuous light, continuous dark, heat, cold, drought and salinity. Morphological observations and physiological analysis showed that abiotic stress treatments were sensed by citrus plants. Furthermore, it was revealed that nitrosative networks are activated by environmental stress factors in citrus leaves as evidenced by increased nitrite (NO) content along with the release of NO and superoxide anion (O₂⁻) in the vascular tissues. The expression of genes potentially involved in NO production, such as NR, AOX, NADHox, NADHde, PAO and DAO, was affected by the abiotic stress treatments demonstrating that NO-derived nitrosative responses could be regulated by various pathways. In addition, S-nitrosoglutathione reductase (GSNOR) and nitrate reductase (NR) gene expression and enzymatic activity displayed significant changes in response to adverse environmental conditions, particularly cold stress. Peroxynitrite (ONOO⁻) scavenging ability of citrus plants was elicited by continuous light, dark or drought but was suppressed by salinity. In contrast, nitration levels were elevated by salinity and suppressed by continuous light or dark. Finally, S-nitrosylation patterns were enhanced by heat, cold or drought but were suppressed by dark or salinity. These results suggest that the nitrosative response of citrus plants is differentially regulated depending on the stress type and underscore the importance of nitrosative status in plant stress physiology.

Arbutin oxidation by pear (Pyrus communis L.) peroxidases

The oxidation of arbutin (hydroquinone--D-glucopyranoside) by soluble and ionically bound to cell wall peroxidases (EC. 1.11.1.7) from pear (Pyrus communis L.) shoots is described for the first time. Following the initiation of the reaction with hydrogen peroxide, arbutin was transformed to a product that was detected by UV spectrophotometry. The stoichiometry of the oxidized product formation versus hydrogen peroxide was nearly 2:1 suggesting that arbutin oxidation is a one-electron process. Higher oxidation rates were observed in a narrow pH zone and ionically bound peroxidases showed lower apparent Km for arbutin than soluble ones. Arbutin is considered to be an antioxidant and peroxidases from pear may influence the pro- or antioxidant properties of this compound.

Ultraviolet-B radiation or heat cause changes in photosynthesis, antioxidant enzyme activities and pollen performance in olive tree

The present study attempts to determine how some physiological and reproductive functions of olive tree (Olea europaea L., cv. Koroneiki) respond to enhanced UV-B radiation or heat. Enhanced UV-B radiation was applied to (1) three-year-old potted plants in an open nursery (corresponded to ca. 16% ozone depletion), and (2) in vitro cultured pollen samples (220 μmol m−2 s−1, PAR = 400−700 nm + UV-B at 7.5, 15.0, or 22.5 kJ m−2 d−1). Potted olive plants were also subjected to high temperature (38 ± 4°C) for 28 h to mimic heat levels regularly measured in olive growing areas. A significant effect of UV-B on photosynthetic rate was observed. However, enhanced UV-B radiation did affect neither chlorophyll nor carotenoid content, supporting previous reports on hardiness of the photosynthetic apparatus in olive. Increased superoxide dismutase activity was observed in UV-B-treated olive plants (+ 225%), whereas no effect was found in the plants under heat stress. Neither UV-B and nor heat did affect H2O2 accumulation in the plant tissues. However, the same treatments resulted in enhanced lipid peroxidation (+ 18% for UV-B and + 15% for heat), which is likely linked to other reactive oxygen species. The increased guaiacol peroxidase activity observed in both treatments (+ 32% for UV-B and + 49% for heat) is related to the defense against oxidative membrane damage. The observed reduction in pollen germination (20–39%) and tube length (11–44%) could have serious implications on olive yields, especially for low fruit-setting cultivars or in years and environments with additional unfavorable conditions. UV-B and heat effects described here support the hypothesis that plant response to a given stressor is affected by the overall context and that a holistic approach is necessary to determine plant strategies for climate change adaptation.

Influence of cross-pollination on the development of parthenocarpic olive (Olea Europaea) fruits (shotberries)

The impact of three different pollination treatments (self-, cross-, free-) on the degree of shotberry (seedless fruit) formation of the olive tree cultivars (cvs) Koroneiki, Kalamata, Mastoidis and Amigdalolia was studied for three consecutive years. Controlled crosses were made for the cross-pollination treatments, while for the free pollination treatment flowers were allowed to receive pollen from more than 40 cultivars present in the field. Significant differences were recorded between treatments, cultivars and years. The lowest degree of shotberry formation was observed in free-pollinated trees while the highest was in self-pollinated trees of all cultivars. Low air temperature incidents during the flowering period increased shotberry formation. Cultivars Koroneiki and Mastoidis were reciprocally the most effective pollinator varieties in reducing shotberries. Cultivar Koroneiki could be considered as the most suitable pollinator to reduce shotberries in Kalamata. When cv. Amigdalolia was cross-pollinated by cvs Koroneiki and Mastoidis the degree of shotberry formation was lower when compared to cross-pollination by cv. Kalamata.

Effect of bumble bee pollination on greenhouse strawberry production

Summary In this study, bumble bees (Bombus terrestris) were used as pollinators in the hydroponic cultivation of strawberries in a greenhouse during winter. We supplied IN Hoagland nutrient solution three times per day to 160 strawberry plants (var. Selva) growing in two 10 cm diameter pipes filled with perlite. One row (control) of the strawberry plants was covered with a fine mesh in order to prevent bee visitation whilst other was open to pollinators. The fruit was collected and weighed weekly during the harvest period. Deformed fruit was counted separately. The results showed that the row pollinated by the bumble bees produced more well-shaped fruit and the total marketable fruit production was double compared to the control row.

Cell Wall Physicochemical Properties as Indicators of Peach Quality During Fruit Ripening after Cold Storage

A comparative study between melting flesh peach fruit (Prunus persica L. Batsch cvs. Royal Glory and Morettini No 2) with contrasting tissue firmness during their on-tree ripening was conducted. Such fruit were cold stored (0 °C) for 4 and 6 weeks, and subsequently transferred at 25 °C (shelf life) for up to 5 days and evaluated for quality attributes and cell wall physicochemical properties. Data were partly unexpected, since fruit of the soft cultivar (Morettini No 2) were characterized by lower exo- and endo-PG activity, lower amounts of ethylene evolution, as well as higher amounts of endogenous calcium bound in the cell wall compared to fruit of the firmer cultivar (Royal Glory). These differences may be attributed to the incidence of chilling injury symptoms, evident as loss of juiciness in Morettini No 2 fruit, while Royal Glory fruit were characterized by acceptable appearance and eating quality even after 6 weeks cold storage plus 5 days shelf life, as the fruit softened gradually without cell rupture. Overall results showed that no direct relationship between cell wall physicochemical properties and sensory attributes can be established, indicating the complexity of peach fruit ripening. Since fruit of both cultivars presented similar tissue firmness after 5 days shelf life an attempt to distinguish normal peach fruit softening from cell rupture-chilling injury also has been made in the current study.

Experimental use of a novel temporary immersion system for liquid culture of olive microshoots

A novel temporary immersion system (TIS), designed at the laboratory of VITRO HELLAS S.A., was used for the liquid culture of olive microshoots during their proliferation phase. The results were compared with those obtained in agar solidified medium, which was used as control, and with other bioreactor systems including the LifeReactor ©, liquid culture in Erlenmeyer flasks under agitation and liquid culture on filter paper bridges. After 30 days of culture, results derived from the novel TIS (1.93 new microshoots per explant, 0.95 cm shoot length) were statistically the same as the control (1.75 microshoots per explant, 1.22 cm shoot length respectively). Equally high results were obtained with the agitated Erlenmeyer flasks, while LifeReactor

Growing Red Raspberry in Soilless Culture Under Different Chilling Treatments for Early Summer Production

Abstract Tissue culture plants (8-10 weeks old) of ‘Autumn Bliss’, a primocane-fruiting red raspberry (Rubus idaeus L.) cultivar, produced in Haberli, Switzerland, were sent to the Agricultural Research Institute of Cyprus on 10 October 2002. The plant material was divided into four groups with each group consisting of 24 plants. The first group was planted in the greenhouse (non-chilling) and the remaining three groups were held at 4°C cooler as follows: (a) 21 days (continuous-chilling), (b) alternating 7 days in and 7 days out of the cooler for a total of 14 days of chilling (alternating-chilling), and (c) 21 days after the 2.5 months of growth in the greenhouse (post-chilling). Following chilling, plant material was removed from the cooler and placed in a media-based soilless plant bed system, under natural (unheated and without supplemental lighting) greenhouse conditions (32°E long., 35°N lat.). Chilling treatments did not affect vegetative growth and fruit quality of primocane-fruiting ‘Autumn Bliss’, but it did advance flowering and fruiting to yield an acceptable early summer crop. The continuous-chilling for 21 days advanced flowering by 3 weeks compared to the other chilling-treatments and the plants flowered after 6 months in the greenhouse.

Effects of Boron and Salinity on Red Raspberry in Vitro

ABSTRACT Raspberry (Rubus idaeus L.) explants were cultured in vitro under two boron concentrations (0.1 and 0.5 mM) and three levels of NaCl salinity (0, 5, and 10 mM) on an MS medium. The high boron and salt treatment (0.5 mM B and 10 mM NaCl) diminished mean shoot length and fresh and dry weights of the explants; however, fresh-to-dry weight ratio was positively affected. When B increased in the medium, leaf chlorophyll content and fluorescence were reduced under saline conditions. The absorption of boron, chloride, and sodium was enhanced by increased concentrations of boron and NaCl in the medium. Moreover, B enhanced the uptake and accumulation of chloride and sodium in the explants, but the reverse was not true. Finally, the relative growth rate and relative performance of the explants, under the combined effect of B and NaCl, showed a rapid decline at high boron and salt treatment.