Daniela Farinelli

Stomatal closure is induced by hydraulic signals and maintained by ABA in drought-stressed grapevine

Water saving under drought stress is assured by stomatal closure driven by active (ABA-mediated) and/or passive (hydraulic-mediated) mechanisms. There is currently no comprehensive model nor any general consensus about the actual contribution and relative importance of each of the above factors in modulating stomatal closure in planta. In the present study, we assessed the contribution of passive (hydraulic) vs active (ABA mediated) mechanisms of stomatal closure in V. vinifera plants facing drought stress. Leaf gas exchange decreased progressively to zero during drought, and embolism-induced loss of hydraulic conductance in petioles peaked to ~50% in correspondence with strong daily limitation of stomatal conductance. Foliar ABA significantly increased only after complete stomatal closure had already occurred. Rewatering plants after complete stomatal closure and after foliar ABA reached maximum values did not induced stomatal re-opening, despite embolism recovery and water potential rise. Our data suggest that in grapevine stomatal conductance is primarily regulated by passive hydraulic mechanisms. Foliar ABA apparently limits leaf gas exchange over long-term, also preventing recovery of stomatal aperture upon rewatering, suggesting the occurrence of a mechanism of long-term down-regulation of transpiration to favor embolism repair and preserve water under conditions of fluctuating water availability and repeated drought events.

Relationships between stomatal behavior, xylem vulnerability to cavitation and leaf water relations in two cultivars of Vitis vinifera

Current understanding of physiological mechanisms governing stomatal behavior under water stress conditions is still incomplete and controversial. It has been proposed that coordination of stomatal kinetics with xylem vulnerability to cavitation [vulnerability curve (VC)] leads to different levels of isohydry/anisohydry in different plant species/cultivars. In this study, this hypothesis is tested in Vitis vinifera cultivars displaying contrasting stomatal behavior under drought stress. The cv Montepulciano (MP, near-isohydric) and Sangiovese (SG, anisohydric) were compared in terms of stomatal response to leaf and stem water potential, as possibly correlated to different petiole hydraulic conductivity (k(petiole)) and VC, as well as to leaf water relations parameters. MP leaves showed almost complete stomatal closure at higher leaf and stem water potentials than SG leaves. Moreover, MP petioles had higher maximum k(petiole) and were more vulnerable to cavitation than SG. Water potential at the turgor loss point was higher in MP than in SG. In SG, the percentage reduction of stomatal conductance (PLg(s)) under water stress was almost linearly correlated with corresponding percentage loss of k(petiole) (PLC), while in MP PLg(s) was less influenced by PLC. Our results suggest that V. vinifera near-isohydric and anisohydric genotypes differ in terms of xylem vulnerability to cavitation as well as in terms of k(petiole) and that the coordination of these traits leads to their different stomatal responses under water stress conditions.

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.

The contribution of stored malate and citrate to the substrate requirements of metabolism of ripening peach (Prunus persica L. Batsch) flesh is negligible. Implications for the occurrence of phosphoenolpyruvate carboxykinase and gluconeogenesis.

The first aim of this study was to determine the contribution of stored malate and citrate to the substrate requirements of metabolism in the ripening flesh of the peach (Prunus persica L. Batsch) cultivar Adriatica. In the flesh, stored malate accumulated before ripening could contribute little or nothing to the net substrate requirements of metabolism. This was because there was synthesis and not dissimilation of malate throughout ripening. Stored citrate could potentially contribute a very small amount (about 5.8%) of the substrate required by metabolism when the whole ripening period was considered, and a maximum of about 7.5% over the latter part of ripening. The second aim of this study was to investigate why phosphoenolpyruvate carboxykinase (PEPCK) an enzyme utilised in gluconeogenesis from malate and citrate is present in peach flesh. The occurrence and localisation of enzymes utilised in the metabolism of malate, citrate and amino acids were determined in peach flesh throughout its development. Phosphoenolpyruvate carboxylase (essential for the synthesis of malate and citrate) was present in the same cells and at the same time as PEPCK and NADP-malic enzyme (both utilised in the dissimilation of malate and citrate). A hypothesis is presented to explain the presence of these enzymes and to account for the likely occurrence of gluconeogenesis.

Malate as substrate for catabolism and gluconeogenesis during ripening in the pericarp of different grape cultivars

Malate is accumulated in grape pericarp until the start of ripening and then it is dissimilated. One aim of this study was to determine if the potential contribution of stored malate to the substrate requirements of metabolism in ripening grape pericarp is dependent on the cultivar. Two Vitis vinifera L. cultivars which accumulated different amounts of malate and had ripening periods of a different length were compared. The potential contribution of stored malate over the whole period of ripening was around 20 % in the cv. Sagrantino and 29 % in the cv. Pinot Noir. The contribution was higher in Pinot Noir because it contained more malate and had a shorter ripening period. A second aim of this study was to evaluate the contribution of gluconeogenesis to the amount of sugar accumulated in the pericarp. If all the dissimilated malate was utilized by gluconeogenesis, then the maximum contribution of stored malate to the total amount of sugar accumulated in the pericarp over the whole period of ripening was around 2.4 % in Sagrantino and 2.9 % in Pinot Noir. However, the actual contribution was only about 0.1–0.6 % in both cultivars because the majority of stored malate was not utilized by gluconeogenesis. However, it is likely that the actual contribution is much lower. This suggests that the function of gluconeogenesis is not to support accumulation of sugars in the fruits, but probably it plays other roles.

A model based on S-allele dominance relationships to explain pseudo self-fertility of varieties in the olive tree

Self-fertility is largely decreased and even prevented by various mechanisms because, broadly, it causes inbreeding depression, although some species have retained self-reproduction regimes. Species of plants that display the self-incompatible sporophytic type of self-incompatibility may rarely self-pollinate. It is only possible in the absence of foreign compatible pollen. In the olive tree with a sporophytic mechanism, we will show that three co-dominant S-alleles R1, R3 and R5 do not lead to the same level of self-fertility. All varieties that carry R1 are less self-fertile than those that carry R5, whatever the other S-alleles, while those carrying R3 are intermediate. S-allele pair-wise combinations that differ by two or three levels of dominance, and not the other combinations allow self-fertility, and moreover each S-allele R1, R3 and R5 decreases, maintains and enhances the self-fertility rate, respectively.

Influence of light and shoot development stage on leaf photosynthesis and carbohydrate status during the adventitious root formation in cuttings of Corylus avellana L.

Adventitious root formation in plant cuttings is influenced by many endogenous and environmental factors. Leaf photosynthesis during rooting of leafy cuttings in hard to root species can contribute to supply carbohydrates to the intensive metabolic processes related to adventious root formation. Light intensity during rooting is artificially kept low to decrease potential cutting desiccation, but can be limiting for photosynthetic activity. Furthermore, leafy cuttings collected from different part of the shoot can have a different ability to fuel adventitious root formation in cutting stem. The aim of this work was to determine the role of leaf photosynthesis on adventitious root formation in hazelnut (Corylus avellana L) (a hard-to-root specie) leafy cuttings and to investigate the possible influence of the shoot developmental stage on cutting rooting and survival in the post-rooting phase. Cutting rooting was closely related to carbohydrate content in cutting stems during the rooting process. Cutting carbohydrate status was positively influenced by leaf photosynthesis during rooting. Non-saturating light exposure of leafy cuttings can contribute to improve photosynthetic activity of leafy cuttings. Collection of cuttings from different part of the mother shoots influenced rooting percentage and this appear related to the different capability to concentrate soluble sugars in the cutting stem during rooting. Adventitious root formation depend on the carbohydrate accumulation at the base of the cutting. Mother shoot developmental stage and leaf photosynthesis appear pivotal factors for adventitious roots formation.

Impact of climate change on the possible expansion of almond cultivation area pole-ward: a case study of Abruzzo, Italy

ABSTRACT Climate warming is causing an advance of the latest spring frosts and a consequent decrease of spring freeze risk during flowering. Cultivation areas of early blooming tree crops, such as almond, could be shifted pole-ward as consequence of global warming. On the other hand, warming winters and springs can cause an advance of the flowering period. The aim of the present work was to estimate which was the impact of climate change in the past six decades on the spring freeze damage risk during the almond blooming period in the Abruzzo region of Italy. According to our analysis a reduction of spring freeze risk due to the mitigation of springtime temperatures was counterbalanced by advanced almond blooming leaving the risk of spring freeze damage unchanged. These results suggest that the adaptation of almond phenology to changing climates could continue to limit the northward expansion of almond in Italy. Finally, these results may suggest that the loss of suitable areas due to loss of chilling units in the warmest climate areas cannot be compensated for by a pole-ward shift of almond plantings.

Reply to Saumitou-Laprade et al. (2017) “Controlling for genetic identity of varieties, pollen contamination and stigma receptivity is essential to characterize the self-incompatibility system of Olea europaea L.”. Eva:https://doi.org/10.1111/eva.12498

This study was carried out to examine the validity of previous studies on the intercompatibility of olive and to compare the approach and techniques used for proposing the diallelic self‐incompatibility system and the sporophytic self‐incompatibility system. Analysis of the literature indicates that the mating system of the olive tree is a controversial issue and requires further studies to clearly and fully comprehend it. All possible approaches should be used to maximize reliability of the final conclusions on the olive mating system.