Suzy Y. Rogiers

Does night-time transpiration contribute to anisohydric behaviour in a Vitis vinifera cultivar?

The hypothesis that vines of the Semillon wine grape variety show anisohydric behaviour was tested, i.e. that tissue hydration is unstable under fluctuating environmental conditions. Stomatal conductance and transpiration rates from leaves were measured during the day and at night. Leaf water potential (Ψl) in Semillon was negatively correlated to vapour pressure deficit (VPD) both predawn and during the day. Furthermore, Ψl fell to significantly lower values than in any of the nine other varieties examined. Night-time values of stomatal conductance (gn) and transpiration (En) in Semillon were up to four times higher than in other varieties; plants enclosed in plastic bags overnight to reduce En resulted in better plant–soil equilibration so that predawn Ψl in Semillon was the same as in Grenache. These data indicate that the hypothesis is supported, and that night-time transpiration contributes significantly to the low Ψl values in Semillon during warm, dry nights. The other contributing factor is daytime stomatal conductance (gday), which in Semillon leaves was higher than in other varieties, although the decline in gday with increasing VPD was greater in Semillon than in Shiraz or Grenache. The high values of gday were associated with high rates of transpiration (Eday) by Semillon through a day when VPD reached 4.5 kPa. When compared to other varieties, Semillon was not unusual in terms of root length density, stomatal density, xylem sap abscisic acid, or leaf electrolyte leakage. Night-time and daytime water loss and insufficient stomatal regulation therefore account for the tendency to anisohydric behaviour shown by Semillon.

Stomatal response of an anisohydric grapevine cultivar to evaporative demand, available soil moisture and abscisic acid

Stomatal responsiveness to evaporative demand (air vapour pressure deficit (VPD)) ranges widely between species and cultivars, and mechanisms for stomatal control in response to VPD remain obscure. The interaction of irrigation and soil moisture with VPD on stomatal conductance is particularly difficult to predict, but nevertheless is critical to instantaneous transpiration and vulnerability to desiccation. Stomatal sensitivity to VPD and soil moisture was investigated in Semillon, an anisohydric Vitis vinifera L. variety whose leaf water potential (Ψ(l)) is frequently lower than that of other grapevine varieties grown under similar conditions in the warm grape-growing regions of Australia. A survey of Semillon vines across seven vineyards revealed that, regardless of irrigation treatment, midday Ψ(l) was dependent on not only soil moisture but VPD at the time of measurement. Predawn Ψ(l) was more closely correlated to not only soil moisture in dry vineyards but to night-time VPD in drip-irrigated vineyards, with incomplete rehydration during high night-time VPD. Daytime stomatal conductance was low only under severe plant water deficits, induced by extremes in dry soil. Stomatal response to VPD was inconsistent across irrigation regime; however, in an unirrigated vineyard, stomatal sensitivity to VPD-the magnitude of stomatal response to VPD-was heightened under dry soils. It was also found that stomatal sensitivity was proportional to the magnitude of stomatal conductance at a reference VPD of 1kPa. Exogenous abscisic acid (ABA) applied to roots of Semillon vines growing in a hydroponic system induced stomatal closure and, in field vines, petiole xylem sap ABA concentrations rose throughout the morning and were higher in vines with low Ψ(l). These data indicate that despite high stomatal conductance of this anisohydric variety when grown in medium to high soil moisture, increased concentrations of ABA as a result of very limited soil moisture may augment stomatal responsiveness to low VPD.

Nocturnal and daytime stomatal conductance respond to root-zone temperature in ‘Shiraz’ grapevines

Background and Aims Daytime root-zone temperature may be a significant factor regulating water flux through plants. Water flux can also occur during the night but nocturnal stomatal response to environmental drivers such as root-zone temperature remains largely unknown. Methods Here nocturnal and daytime leaf gas exchange was quantified in ‘Shiraz’ grapevines (Vitis vinifera) exposed to three root-zone temperatures from budburst to fruit-set, for a total of 8 weeks in spring. Key Results Despite lower stomatal density, night-time stomatal conductance and transpiration rates were greater for plants grown in warm root-zones. Elevated root-zone temperature resulted in higher daytime stomatal conductance, transpiration and net assimilation rates across a range of leaf-to-air vapour pressure deficits, air temperatures and light levels. Intrinsic water-use efficiency was, however, lowest in those plants with warm root-zones. CO2 response curves of foliar gas exchange indicated that the maximum rate of electron transport and the maximum rate of Rubisco activity did not differ between the root-zone treatments, and therefore it was likely that the lower photosynthesis in cool root-zones was predominantly the result of a stomatal limitation. One week after discontinuation of the temperature treatments, gas exchange was similar between the plants, indicating a reversible physiological response to soil temperature. Conclusions In this anisohydric grapevine variety both night-time and daytime stomatal conductance were responsive to root-zone temperature. Because nocturnal transpiration has implications for overall plant water status, predictive climate change models using stomatal conductance will need to factor in this root-zone variable.

Erratum to: Use of diffusion magnetic resonance imaging to correlate the developmental changes in grape berry tissue structure with water diffusion patterns[ Plant Methods (2014); 4(10),35. doi 10.1186/1746-4811-10-35.

[This corrects the article DOI: 10.1186/1746-4811-10-35.].

Soil temperature moderates grapevine carbohydrate reserves after bud break and conditions fruit set responses to photoassimilatory stress

In cultivated grapevines (Vitis vinifera L.), suboptimal photoassimilatory conditions during flowering can lead to inflorescence necrosis and shedding of flowers and young ovaries and, consequently, poor fruit set. However, before this study it was not known whether carbohydrate reserves augment fruit set when concurrent photoassimilation is limited. Carbohydrate reserves are most abundant in grapevine roots and soil temperature moderates their mobilisation. Accordingly, we grew potted Chardonnay grapevines in soil at 15°C (cool) or 26°C (warm) from bud break to the onset of flowering to manipulate root carbohydrate reserve status. Then to induce photoassimilatory responses we subjected the plants to low (94µmolmol-1) CO2 or ambient (336µmolmol-1) CO2 atmospheres during fruit setting. Analyses of photoassimilation and biomass and carbohydrate reserve distribution confirmed that fruit set was limited by concurrent photoassimilation. Furthermore, the availability of current photoassimilates for inflorescence development and fruit set was conditioned by the simultaneous demands for shoot and root growth, as well as the restoration of root carbohydrate reserves. Results indicate that great seasonal variability in grapevine fruit set is a likely response of cultivated grapevines to photoassimilatory stresses, such as shading, defoliation and air temperature and to variations in carbohydrate reserve status before flowering.

Effects of spray adjuvants on grape (Vitis vinifera) berry microflora, epicuticular wax and susceptibility to infection by Botrytis cinerea

Spray adjuvants were tested for their effects on epicuticular wax morphology, grape berry microflora and susceptibility of berries to Botrytis cinerea on Chardonnay, Shiraz and Cabernet Sauvignon cultivars. The four adjuvants used in this trial altered epicuticular wax morphology. Disintegration of the wax platelets was least for the wetter-spreader recommended for sensitive crops, and greatest for the crop oil concentrate and the activator-penetrant. Waxes did not regenerate over the season after treatment with the adjuvants. A cyprodinil/fludioxonil fungicide was effective at controlling B. cinerea infection, but when combined with an adjuvant, was less effective in the three grape cultivars. Irrespective of whether a fungicide was used, adjuvant application resulted in lower yeast and fungal populations on Chardonnay berries. There were no effects of the adjuvants on the microflora of Shiraz and Cabernet Sauvignon berries, except for the crop oil concentrate which resulted in higher bacterial populations on Cabernet Sauvignon berries. We hypothesise that spray adjuvants increased the susceptibility of grape berries to B. cinerea through epicuticular wax alteration and, in some circumstances, through the reduction of the indigenous microflora on the berry surface.

Changes in volatile composition and sensory attributes of wines during alcohol content reduction.

A desirable sensory profile is a major consumer driver for wine acceptability and should be considered during the production of reduced-alcohol wines. Although various viticultural practices and microbiological approaches show promising results, separation technologies such as membrane filtration, in particular reverse osmosis and evaporative perstraction, in addition to vacuum distillation, represent the most common commercial methods used to produce reduced-alcohol wine. However, ethanol removal from wine can result in a significant loss of volatile compounds such as esters (ethyl octanoate, ethyl acetate, isoamyl acetate) that contribute positively to the overall perceived aroma. These losses can potentially reduce the acceptability of the wine to consumers and decrease their willingness to purchase wines that have had their alcohol level reduced. The change in aroma as a result of the ethanol removal processes is influenced by a number of factors: the type of alcohol reduction process; the chemical-physical properties (volatility, hydrophobicity, steric hindrance) of the aroma compounds; the retention properties of the wine non-volatile matrix; and the ethanol level. This review identifies and summarises possible deleterious influences of the dealcoholisation process and describes best practice strategies to maintain the original wine composition.

Potassium in the Grape (Vitis vinifera L.) Berry: Transport and Function

K+ is the most abundant cation in the grape berry. Here we focus on the most recent information in the long distance transport and partitioning of K+ within the grapevine and postulate on the potential role of K+ in berry sugar accumulation, berry water relations, cellular growth, disease resistance, abiotic stress tolerance and mitigating senescence. By integrating information from several different plant systems we have been able to generate new hypotheses on the integral functions of this predominant cation and to improve our understanding of how these functions contribute to grape berry growth and ripening. Valuable contributions to the study of K+ in membrane stabilization, turgor maintenance and phloem transport have allowed us to propose a mechanistic model for the role of this cation in grape berry development.

Use of diffusion magnetic resonance imaging to correlate the developmental changes in grape berry tissue structure with water diffusion patterns.

BackgroundOver the course of grape berry development, the tissues of the berry undergo numerous morphological transformations in response to processes such as water and solute accumulation and cell division, growth and senescence. These transformations are expected to produce changes to the diffusion of water through these tissues detectable using diffusion magnetic resonance imaging (MRI). To assess this non-invasive technique diffusion was examined over the course of grape berry development, and in plant tissues with contrasting oil content.ResultsIn this study, the fruit of Vitis vinfera L. cv. Semillon at seven different stages of berry development, from four weeks post-anthesis to over-ripe, were imaged using diffusion tensor and transverse relaxation MRI acquisition protocols. Variations in diffusive motion between these stages of development were then linked to known events in the morphological development of the grape berry. Within the inner mesocarp of the berry, preferential directions of diffusion became increasingly apparent as immature berries increased in size and then declined as berries progressed through the ripening and senescence phases. Transverse relaxation images showed radial striation patterns throughout the sub-tissue, initiating at the septum and vascular systems located at the centre of the berry, and terminating at the boundary between the inner and outer mesocarp. This study confirms that these radial patterns are due to bands of cells of alternating width that extend across the inner mesocarp. Preferential directions of diffusion were also noted in young grape seed nucelli prior to their dehydration. These observations point towards a strong association between patterns of diffusion within grape berries and the underlying tissue structures across berry development. A diffusion tensor image of a post-harvest olive demonstrated that the technique is applicable to tissues with high oil content.ConclusionThis study demonstrates that diffusion MRI is a powerful and information rich technique for probing the internal microstructure of plant tissues. It was shown that macroscopic diffusion anisotropy patterns correlate with the microstructure of the major pericarp tissues of cv. Semillon grape berries, and that changes in grape berry tissue structure during berry development can be observed.

Efficacy of low O2 and high CO2 atmospheres in maintaining the postharvest quality of saskatoon fruit (Amelanchier alnifolia Nutt.)

Changes in fruit quality of saskatoon (cvs. Pembina, Smoky, Northline, and Thiessen) stored under three O2 levels (2, 10, and 21%) factorially combined with two CO2 concentrations (0.035% and 5%) were assessed during 56 d of storage at 0.5 °C. The 5% CO2 atmosphere combined with 21 or 10% O2 was most effective at minimizing losses in fruit soluble solids, anthocyanins, firmness, and fresh weight. Fungal colonization of fruit after 8 wk of storage was eliminated in 5% CO2 at all O2 concentrations. Storage of fruit in 0.035% CO2 and 21 or 10% O2 resulted in the highest titratable acidity and lowest ethanol concentrations. Ethanol did not exceed 0.03% in fruit stored in any of the atmospheres. While changes in some of the quality characteristics of fruit during storage were cultivar dependent, differences among cultivars were small, and all four cultivars benefited from controlled atmosphere storage. Key words:Amelanchier alnifolia, saskatoon fruit, controlled atmosphere, postharvest quality