A. Minnocci

Variation in mesophyll anatomy and photosynthetic capacity during leaf development in a deciduous mesophyte fruit tree (Prunus persica) and an evergreen sclerophyllous Mediterranean shrub (Olea europaea)

The relative importance that biomechanical and biochemical leaf traits have on photosynthetic capacity would depend on a complex interaction of internal architecture and physiological differences. Changes in photosynthetic capacity on a leaf area basis and anatomical properties during leaf development were studied in a deciduous tree, Prunus persica, and an evergreen shrub, Olea europaea. Photosynthetic capacity increased as leaves approached full expansion. Internal CO2 transfer conductance (gi) correlated with photosynthetic capacity, although, differences between species were only partially explained through structural and anatomical traits of leaves. Expanding leaves preserved a close functional balance in the allocation of resources of photosynthetic component processes. Stomata developed more rapidly in olive than in peach. Mesophyll thickness doubled from initial through final stages of development when it was twice as thick in olive as in peach. The surface area of mesophyll cells exposed to intercellular air spaces per unit leaf area tended to decrease with increasing leaf expansion, whereas, the fraction of mesophyll volume occupied by the intercellular air spaces increased strongly. In the sclerophyllous olive, structural protection of mesophyll cells had priority over efficiency of photochemical mechanisms with respect to the broad-leaved peach. The photosynthetic capacity of these woody plants during leaf development relied greatly on mesophyll properties, more than on leaf mass per area ratio (LMA) or nitrogen (N) allocation. Age-dependent changes in diffusion conductance and photosynthetic capacity affected photosynthetic relationships of peach versus olive foliage, evergreen leaves maturing functionally and structurally a bit earlier than deciduous leaves in the course of adaptation for xeromorphy.

Flash Thermal Conditioning of Olive Pastes during the Olive Oil Mechanical Extraction Process: Impact on the Structural Modifications of Pastes and Oil Quality

The quality of virgin olive oil (VOO) is strictly related to the concentrations of phenolic and volatile compounds, which are strongly affected by the operative conditions of the VOO mechanical extraction process. The aim of this work is to study the impact of a new technology such as flash thermal conditioning (FTC) on olive paste structural modification and on VOO quality. The evaluation of olive paste structure modification by cryo-scanning electron microscopy (cryo-SEM) showed that the application of FTC after crushing produces significant differences in terms of the breaking of the parenchyma cells and aggregation of oil droplets in comparison to the crushed pastes. The virgin olive oil flash thermal conditioning (VOO-FTC) featured a higher concentration of volatile compounds compared to that in the control, particularly of all saturated and unsaturated aldehydes and esters, whereas the phenolic concentration was higher in VOO obtained from the traditional process (VOO-C).

Responses of two olive tree (Olea europaea L.) cultivars to elevated CO2 concentration in the field

Five-year-old plants of two olive cultivars (Frantoio and Moraiolo) grown in large pots were exposed for 7 to 8 months to ambient (AC) or elevated (EC) CO2 concentration in a free-air CO2 enrichment (FACE) facility. Exposure to EC enhanced net photosynthetic rate (PN) and decreased stomatal conductance, leading to greater instantaneous transpiration efficiency. Stomata density also decreased under EC, while the ratio of intercellular (Ci) to atmospheric CO2 concentration and chlorophyll content did not differ, except for the cv. Moraiolo after seven months of exposure to EC. Analysis of the relationship between photosynthesis and Ci indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase after five months of exposure to EC. Based on estimates derived from the PN-Ci relationship, there were no apparent treatment differences in daytime respiration, CO2 compensation concentration, CO2-saturated photosynthetic rate, or photosynthetic rate at the mean Ci, but there was a reduction in stomata limitation to PN at EC. Thus 5-year-old olive trees did not exhibit down regulation of leaf-level photosynthesis in their response to EC, though some indication of adjustment was evident for the cv. Frantoio with respect to the cv. Moraiolo.

Compositional and Tissue Modifications Induced by the Natural Fermentation Process in Table Olives

Olive fruits contain high concentrations of phenols that include phenolic acids, phenolic alcohols, flavonoids, and secoiridoids. The final concentration of phenols is strongly affected by brine conditions. The factors involved in modification by brine are still partially unknown and can include hydrolysis of secoiridoid glucosides and the release of hydrolyzed products. In this study olives from various Italian cultivars were processed by natural fermentation (e.g., without a preliminary treatment of olives with NaOH) using a selected Lactobacillus strain. Processed olives are characterized by a low phenolic concentration of phenols, consisting mainly of phenyl alcohols, verbascoside, and the dialdehydic form of decarboxymethylelenolic acid linked to (3,4-dihydroxyphenyl)ethanol (3,4-DHPEA-EDA), whereas a high level of phenols occurs in olive brine from all the cultivars studied. Olives of the Coratina cultivar, control and with fermentation by Lactobacillus pentosus 1MO, were analyzed in a frozen hydrated state by cryo scanning electron microscopy and energy-dispersive X-ray microanalysis, on both surface and transversal freeze-fracture planes. Structural modifications, found in olives after fermentation, may explain the phenol release in brine.

Leaf structural modifications in Populus × euramericana subjected to Zn excess

In previous experiments elevated but sub-symptomatic applications of Zn (0.1 mM and 1 mM) caused impairments in growth parameters and photosynthetic performance of Populus × euramericana (Dode) Guinier clone I-214. The aim of this work was to evaluate leaf morphological and anatomical traits in this clone in response to the same Zn concentrations. The results showed that Zn treatments induced variations in leaf dry mass, area, mesophyll thickness, intercellular spaces, stomatal density and size. Stronger modifications, especially concerning stomata characteristics induced by 1 mM Zn, were consistent with physiological impairments while those induced by 0.1 mM Zn suggested a compensatory strategy for maintaining functional integrity.

Anatomical differences of poplar (Populus × euramericana clone I-214) roots exposed to zinc excess

Poplar is one of the suitable candidates for phytoremediation due to extensive root system, fast growth rate, easy propagation and high biomass production. Zinc (Zn) is an essential element, but at high concentration becomes toxic to plants, similarly like cadmium (Cd). In order to evaluate the effect of Zn on root tissue development we conducted experiments with poplar (Populus × euramericana clone I-214) grown in hydroponics. Plants were treated with low (control) and excess level of Zn (1 mM). Changes in the development of apoplasmic barriers — Casparian bands and suberin lamellae in endodermis, as well as lignification of xylem vessels have been investigated. We found that both apoplasmic barriers developed closer to the root apex in higher Zn-treated root when compared with control root. Similar changes were observed in lignification of xylem vessels. For localization of Zn within root tissues, cryo-SEM/EDXMA analyses were used. Most of Zn was localized in the cortical tissues and four-time less Zn was determined in the inner part of the root below the endodermis. This indicates that endodermis serves as efficient barrier of apoplasmic Zn transport across the poplar root.

Changes in the structure of the skin of kiwifruit in relation to water loss

Summary Fruit water loss and calcium inflow decrease in kiwifruit (Actinidia deliciosa ‘Hayward’) after the first few weeks of growth, but the relationship between fruit transpiration and the structure of the skin is not clear. Changes in skin structure during fruit development were studied using cryo-scanning electron microscopy and the concentrations and types of waxes present in the skin were measured. Young fruit were covered in turgid unicellular and multicellular hairs, which grew on an amorphous and continuous layer of wax platelets. However, 5 weeks after fruit set, the hairs began to collapse and the wax layer began to crack. The epidermal cells dehydrated and suberised to form a peridermlike layer. The degeneration of the hairs and the wax layer continued as the fruit matured. Fruit surface area increased from 6.9 cm2 at 4 weeks after fruit set, to 98.2 cm2 at 20 weeks after fruit set (i.e., at harvest), while the total wax content increased from 0.33 to 2.40 mg per fruit. Total wax density peaked at 91 µg cm−2 5 weeks after fruit set, then decreased to 24 µg cm−2 at harvest.Alkyl alkanoates were the main waxes [approx. 70% (w/w)] in young fruit, while hydrocarbons and alkyl alkanoates (approx. 50% each) were the main waxes in mature fruit. The decline in fruit water loss in kiwifruit was consistent with degeneration of the hairs on the skin, the evolution of the suberised outer layers, and the death of outer cells associated with wax biosynthesis.

In vitro olive (Olea europaea L.) cvs Frantoio and Moraiolo microshoot tolerance to NaCl

Abstract In vitro culture of rooted and unrooted olive microshoots, established from seed lines of free-pollinated “Frantoio” and “Moraiolo” cultivars, were evaluated for NaCl tolerance. The aim was to use growth and physiological parameters in order to identify salt-adapted genotypes. Leaf tissue elemental distribution of Na, Cl and K was also investigated in unrooted plantlets by cryo-scanning electron microscopy and energy-dispersive X-ray microanalysis. Both in unrooted and rooted plantlets, increased concentrations of NaCl reduced shoot growth, whereas plant survival was not affected. However, no significant interactions between line and NaCl concentration were found. Elemental distribution showed that Moraiolo J and Frantoio Z accumulated more Na and Cl inside leaves, and that these elements followed a tissue-dependent pattern. Rooting capacity was reduced at the higher levels of NaCl. Significant interactions between seed line and salt treatment were found. Seed lines showed different abilities to develop roots at different salt levels. In particular, Frantoio Z showed a significant and different behaviour relative to the other seed lines at 50 mM NaCl with regard to both length and dry weight of roots. The results obtained suggest that rooting parameters are the most useful tools in the evaluation and screening of salt-tolerant olive genotypes through in vitro shoot culture.

Heavy Metals Stress on Poplar: Molecular and Anatomical Modifications

Heavy metal stress responses vary from plant to plant depending on the type of heavy metals and require a coordinated interplay of complex physiological and biochemical processes, gene expression, protein modification and changes in metabolites compositions leading to proper stress signal and tolerance.

Genotypic differences in the response to elevated CO2 concentration of one-year-old olive cuttings (Olea europaea L. cv. Frantoio and Moraiolo)

ABSTRACT One-year-old olive (Olea europaea L) cuttings of two cultivars (Frantoio and Moraiolo) were exposed for five months to ambient (360 ± 16 μmol mol-1) or elevated (560 ± 52 μmol mol-1) CO2 concentration in a free-air CO2 enrichment facility. Current-year leaves were used for gas exchange measurements, chlorophyll and nutrient determinations. Stomatal density was measured on frozen hydrated current-year leaves by low temperature scanning electron microscopy. Above-ground dry mass (stem and leaves) and leaf area were determined, and leaf mass ratio and specific leaf area calculated. Results showed that exposure to elevated CO2 enhanced rates of net photosynthesis and decreased stomatal conductance, leading to higher water use efficiency; this was not translated in increased growth rates (particularly in the cultivar Frantoio, which showed reductions in above-ground plant dry mass compared with the cultivar Moraiolo). Chlorophyll concentrations (chlorophyll content per unit leaf area) decreased only in Frantoio leaves of plants grown in elevated CO2. Stomatal density and leaf nutrients did not differ between treatments and cultivars. Some adjustment to elevated CO2 was observed for the cultivar Frantoio, which showed strong reductions in leaf area, thus counterbalancing increased photosynthetic rates per unit leaf area (but also decreased stem dry mass). The decrease in total leaf dry mass in response to elevated CO2 was accompanied by a decrease in the fraction of aerial plant dry mass belonging to leaves (elevated CO2 changed dry mass allocation by decreasing leaf mass ratio), suggesting that canopy-level adjustment in carbon assimilation may occur in both cultivars.