Stefano Moscatello

Signaling Pathways Mediating the Induction of Apple Fruitlet Abscission

Apple (Malus × domestica) represents an interesting model tree crop for studying fruit abscission. The physiological fruitlet drop occurring in this species can be easily magnified by using thinning chemicals, such as benzyladenine (BA), to obtain fruits with improved quality and marketability. Despite the economic importance of this process, the molecular determinants of apple fruitlet abscission are still unknown. In this research, BA was used to obtain fruitlet populations with different abscission potentials to be analyzed by means of a newly released 30K oligonucleotide microarray. RNAs were extracted from cortex and seed of apple fruitlets sampled over a 4-d time course, during which BA triggers fruit drop, and used for microarray hybridization. Transcriptomic profiles of persisting and abscising fruitlets were tested for statistical association with abscission potential, allowing us to identify molecular signatures strictly related to fruit destiny. A hypothetical model for apple fruitlet abscission was obtained by putting together available transcriptomic and metabolomic data. According to this model, BA treatment would establish a nutritional stress within the tree that is primarily perceived by the fruitlet cortex whose growth is blocked by resembling the ovary growth inhibition found in other species. In weaker fruits, this stress is soon visible also at the seed level, likely transduced via reactive oxygen species/sugar and hormones signaling cross talk, and followed by a block of embryogenesis and the consequent activation of the abscission zone.

Influence of CPPU on carbohydrate accumulation and metabolism in fruits of Actinidia deliciosa (A. Chev.)

Abstract A trial was carried out to evaluate the influence of N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU), a diphenylurea derivative cytokinin, on kiwi productivity, on carbohydrate accumulation and metabolism and on post-harvest fruit performance. CPPU (20 ppm) was sprayed on fruitlets inside the canopy 2 weeks after full bloom (AFB). CPPU influenced fruit growth soon after treatment and, at harvest, treated fruit weight and, consequently, yield per vine were about 25% higher than the control. During fruit growth, soluble sugars (glucose, fructose and sucrose) were higher in treated fruits than in the control ones. In the first period of fruit development glucose was the most abundant carbohydrate and CPPU treatment increased the fruit glucose content significantly. During the period of starch accumulation, treated fruits showed a higher starch content and a higher ADP-glucose pyrophosphorylase activity. Starch accumulation started earlier in treated fruits than in the control ones. At the end of the growing season the degradation of starch in treated fruits started earlier and/or was faster than in the control ones, so that at harvest treated and control fruits contained the same amount of starch. As a consequence, treated fruits at harvest had higher contents of soluble sugars. This indicates that CPPU induced faster and/or advanced fruit ripening. The chlorophyll content was higher in CPPU treated fruits. During storage, the differences in carbohydrate content disappeared and treated fruits performed as well as control ones, maintaining good quality for up to 6 months.

Yield, water requirement, nutrient uptake and fruit quality of zucchini squash grown in soil and closed soilless culture

Summary The effects of soil and closed soilless systems (cocofibre, perlite and pumice culture) on precocity, productivity, water use, plant mineral composition and fruit quality were studied on zucchini plants (Cucurbita pepo L. ‘Afrodite’ grown in a greenhouse at Viterbo, central Italy. The plants grown in a soilless system exhibited higher yield (total, marketable and fruit number), harvest index, and water-use efficiency compared with those grown in soil. Among soilless treatments, pumice had the lowest water requirement and hence the highest water use efficiency. Use of cocofibre led to the earliest yield compared with the other substrates due probably to the higher minimal temperatures recorded on the organic substrate. Plants grown in soilless culture had a higher uptake of N, Mg, Na, Fe, Cu, Mn, Zn than those grown in soil. After 73 d of solution recycling in soilless treatments, N-NO3, K, P, Fe and Mn were depleted by 26, 16, 40, 92, and 25% respectively, while Ca, Mg, Na, Cu and Zn increased by 6, 69, 113, 360, and 981 % respectively. Carbohydrate concentration (glucose, fructose, sucrose and starch) increased in soilless over soil culture. No significant differences were observed in dry matter or total protein content. Nitrate concentration of fruits was lower in soil than in soilless treatments. The results demonstrated that the growers may improve water and nutrient control, yield and fruit quality by switching from soil to closed soilless culture.

Increase of ascorbic acid content and nutritional quality in spinach leaves during physiological acclimation to low temperature

The effect of acclimation to 10 degrees C on the leaf content of ascorbic and oxalic acids, was investigated in spinach (Spinacia oleracea L.). At 10 degrees C the content of ascorbic acid in leaves increased and after 7 days it was about 41% higher than in plants remaining under a 25 degrees C/20 degrees C day/night temperature regime. In contrast, the content of oxalate, remained unchanged. Transfer to 10 degrees C increased the ascorbic but not the oxalic acid content of the leaf intercellular washing fluid (IWF). Oxalate oxidase (OXO EC 1.2.3.4) activity was not detected in extracts of leaf blades. Therefore, oxalic acid degradation via OXO was not involved in the control of its content. Our results show that low temperature acclimation increases nutritional quality of spinach leaves via a physiological rise of ascorbic acid that does not feed-forward on the content of oxalic acid.

The effect of growing spinach (Spinacia oleracea L.) at two light intensities on the amounts of oxalate, ascorbate and nitrate in their leaves

Summary The effect of growing spinach at two light intensities on the content of oxalate, ascorbate and nitrate in their leaves was determined. Plants were grown for five weeks in a growth cabinet under a 10 h light/14 h dark photoperiod and a photon flux density of either 800 or 200 µmol quanta m–2 s–1. The content of oxalate, ascorbate and nitrate in the fourth and fifth fully expanded true leaves was then determined at three times during the photoperiod. Spinach plants grown at the lower light intensity showed decreased growth, a decreased leaf area per plant and an increased shoot to root ratio. Leaves from plants grown under low light contained less ascorbate but more oxalate and nitrate. Our data show that the nutritional quality of spinach is thereby decreased by growth in low light intensities and suggest that the content of oxalic acid in leaves may depend on the rate of its catabolism.

Seasonal and inter-annual dynamics of growth, non-structural carbohydrates and C stable isotopes in a Mediterranean beech forest.

Seasonal and inter-annual dynamics of growth, non-structural carbohydrates (NSC) and carbon isotope composition (δ(13)C) of NSC were studied in a beech forest of Central Italy over a 2-year period characterized by different environmental conditions. The net C assimilated by forest trees was mainly used to sustain growth early in the season and to accumulate storage carbohydrates in trunk and root wood in the later part of the season, before leaf shedding. Growth and NSC concentration dynamics were only slightly affected by the reduced soil water content (SWC) during the drier year. Conversely, the carbon isotope analysis on NSC revealed seasonal and inter-annual variations of photosynthetic and post-carboxylation fractionation processes, with a significant increase in δ(13)C of wood and leaf soluble sugars in the drier summer year than in the wetter one. The highly significant correlation between δ(13)C of leaf soluble sugars and SWC suggests a decrease of the canopy C isotope discrimination and, hence, an increased water-use efficiency with decreasing soil water availability. This may be a relevant trait for maintaining an acceptable plant water status and a relatively high C sink capacity during dry seasonal periods. Our results suggest a short- to medium-term homeostatic response of the Collelongo beech stand to variations in water availability and solar radiation, indicating that this Mediterranean forest was able to adjust carbon-water balance in order to prevent C depletion and to sustain plant growth and reserve accumulation during relatively dry seasons.

Soluble sugar and organic acid contents and the occurrence and potential role of phosphoenolpyruvate carboxykinase (PEPCK) in gooseberry (Ribes grossularia L.).

Summary Changes in carbohydrate and organic acid contents, and the occurrence and potential role of phosphoenolpyruvate carboxykinase (PEPCK) were investigated in gooseberry fruit (Ribes grossularia L., cv. White Smith), in 2006, in central Italy. The concentrations of glucose, fructose, and sucrose (mg g−1 FW) were relatively low up to 60 d after full bloom (DAFB), with glucose and fructose levels being higher than that of sucrose. All then increased up to harvest (approx. 110 DAFB), and sucrose became the most abundant soluble sugar. Malate and citrate concentrations (mg g−1 FW) and contents per fruit (mg fruit−1) increased up to 70 – 80 DAFB (malate up to approx. 70 DAFB and citrate up to approx. 80 DAFB) then decreased. The level of PEPCK was determined using both western blotting and enzyme activity measurements. PEPCK increased during fruit ripening and was most abundant when the malate and citrate contents decreased. The results are consistent with PEPCK playing a role in the catabolism of malate and citrate in gooseberry flesh during ripening.

Development and metabolism of the fruit and seed of the Japanese plum Ozark premier (Rosaceae).

The growth characteristics of some plums and their component parts have been previously studied, as have some aspects of their developmental anatomy and composition. However, little is known about either their metabolism or about the interactions between the metabolism of their component parts. In this study we investigated these aspects in the Japanese plum Ozark Premier. Throughout fruit and seed development, changes in sugar and organic acid contents, protein composition and abundance of selected enzymes were determined. In the stone, there was a transient accumulation of vegetative storage proteins. These were subsequently mobilized and this coincided with the onset of the lignification of the stone and the start of storage protein accumulation in the seed. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was present in the seeds, even though they lacked chlorophyll, and its presence may be related to limited gas exchange. In the flesh of some fruits, phosphoenolpyruvate carboxykinase (PEPCK) and NADP malic enzyme (NADP-ME) are thought to function in the dissimilation of malate and/or citrate during ripening. However, PEPCK and NADP-ME were present in plum flesh for most of its development, although there was no net dissimilation of malate until the latter stages of ripening. There is an interaction between the developing seed and endocarp with respect to the utilization of imported sugars and amino acids. An hypothesis is presented to account for the presence of PEPCK and NADP-ME enzyme in plum flesh when there was no net dissimilation of organic acids.

Phosphoenolpyruvate carboxykinase in cherry (Prunus avium L.) fruit during development

In this study the abundance and location of phosphoenolpyruvate carboxykinase (PEPCK) was determined in the flesh and skin of the sweet cherry (Prunus avium L.) cultivar Durone Nero II during development. PEPCK was not present in young fruit but appeared in both tissues as the fruit increased in size. In these there was no net dissimilation of malic acid, which accounts for the bulk of their organic acid contents when PEPCK was present. To assist in understanding the function of PEPCK, the abundance of a number of other enzymes was determined. These enzymes were aspartate aminotransferase (AspAT), glutamine synthetase (GS), phosphoenolpyruvate carboxylase (PEPC), pyruvate, orthophosphate dikinase (PPDK), and ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco). A potential role for PEPCK in the regulation of pH and the utilization of malate in gluconeogenesis in the flesh and skin of cherries is presented.

Is stored malate the quantitatively most important substrate utilised by respiration and ethanolic fermentation in grape berry pericarp during ripening

A widely held view is that in grape pericarp glycolysis is inhibited during ripening, and that stored malate rather than sugars become the major substrate for respiration. In this study we determined what contribution stored malate could make to the substrate requirements of respiration and ethanolic fermentation in the pericarp of Cabernet Sauvignon berries during ripening. At a number of time points through development the amount of malate in the pericarp was measured. The change in malate content between each time point was then calculated, having first allowed for dilution arising from expansion of the fruit. The amount of CO2 that was released by the berry in the interval between each pair of time points was measured. It was found that the contribution that stored malate could make to the substrate requirements of respiration and ethanolic fermentation of grape pericarp was dependent on the stage of ripening. At the beginning of ripening stored malate could provide a greater proportion of substrate than later in ripening, and during the latter its contribution was relatively low. Therefore, stored malate was not the quantitatively most important substrate utilised by respiration and ethanolic fermentation in the pericarp of grape berries during most of ripening. It is likely that sugars provide the bulk of the deficit in substrate. Further, the increase in the respiratory quotient during most of ripening does not arise from the use of malate as main respiratory substrate.