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Type: Thesis
Title: Hypoxia and cell death in grape berries (Vitis vinifera L.)
Author: Xiao, Zeyu
Issue Date: 2018
School/Discipline: School of Agriculture, Food and Wine
Abstract: Cell death in the mesocarp of berries occurs late in the ripening process, and may influence berry sensory attributes and water retention. There are cultivar-dependent correlations between mesocarp cell death and berry shrivel. Cell death is likely to be associated with yield losses of up to 30% for Shiraz due to berry shrivel, which concentrates sugars and potentially leads to high alcohol content in wine. The main objective of this thesis was to investigate the association between berry internal oxygen concentrations and berry cell death. Experiments were carried out at the Waite vineyards and at the SARDI research vineyard in Nuriootpa. Firstly, in Chapter 2, internal oxygen concentration ([O₂]) across the mesocarp was measured in berries from Chardonnay and Shiraz, both seeded, and Ruby Seedless, from the Waite vineyards, using an oxygen micro-sensor. Change of berry and seed respiration was investigated in Chardonnay. The lenticel density of Chardonnay and Shiraz berry pedicels (stem and receptacle) was assessed. We then tested the long-term effect of blocking pedicel lenticels on berry internal [O₂] profiles and cell death. Air spaces within the Chardonnay berries at different developmental stages were visualized using x-ray micro-CT. Second, in Chapter 3, a factorial trial of two irrigation regimes was applied in season 2014/2015 and a factorial trial of two irrigation regimes and two temperatures was applied in season 2015/2016, in Nuriootpa. Midday stem water potential, stomatal conductance and photosynthetic rate were measured to examine the efficiency of drought and canopy heating treatments. The oxygen micro-sensor was used to measure oxygen concentration in grapes and their respiration rate. Lastly, in Chapter 4, we tested the effects of overhead shading (2014/2015), rootstocks and kaolin application (both in 2016/2017), on Shiraz berry cell death and berry shrivel. In Chardonnay, Shiraz and Ruby Seedless grapes, steep [O₂] gradients were observed across the skin and [O₂] decreased toward the middle of the mesocarp. As ripening progressed, the minimum [O₂] approached zero in the seeded cultivars and correlated to the profile of cell death across the mesocarp. Seed respiration declined during ripening, from a large proportion of total berry respiration early to negligible at latter stages. [O₂] increased towards the central axis corresponding to the presence of air spaces visualised using x-ray micro-CT. These air spaces connect to the pedicel where lenticels are located that are critical for berry O₂ uptake as a function of temperature, and when blocked caused hypoxia in Chardonnay berries, ethanol accumulation and cell death. This work has been published in the Journal of Experimental Botany in February 2018. In Chapter 3, the results of a factorial field experiment comprising two thermal regimes (ambient and heated) and two irrigation regimes (irrigated and non-irrigated) are reported. Non-irrigation, in the first season, increased the rate of cell death relative to control irrigated Shiraz vines. In the second season, non-irrigation advanced the onset of cell death relative to the irrigated treatments independent of temperature. Non-irrigation treatments in the second season also decreased [O₂] within the berry mesocarp relative to the irrigated treatments. An association was established between mesocarp [O₂] and berry cell death. Berry respiration and total berry porosity were also found to decrease during berry ripening. This work has been submitted to the Australian Journal of Grape and Wine Research in February 2018. In Chapter 4, three preliminary trials were undertaken to investigate possible mitigation strategies for berry cell death and dehydration. Trial 1 tested the effect of overhead shading on berry dehydration, cell death and internal oxygen concentrations [O₂]. Trial 2 tested the effect of rootstocks having different drought tolerance on berry dehydration and cell death. Trial 3 tested the effect of kaolin spray, which has been proposed to reduce leaf and cluster temperature and transpiration. Overhead shading reduced the rate of increase in cell death and berry dehydration in Shiraz. This treatment also affected the progression of hypoxia in the berry. Shiraz on the drought tolerant 140 Ruggeri had significantly less cell death and berry dehydration than the less drought tolerant rootstocks (420 A and Schwarzmann). Kaolin spray application reduced berry shrinkage independently of either mesocarp cell death or cluster and leaf temperature. In summary, grape internal [O₂] declined during fruit development and was correlated with the profile of mesocarp cell death. Lenticels on the pedicel provided a pathway for O₂ diffusion into the berry and when covered to restrict O2 diffusion into the berry caused a large reduction in [O₂] in the centre of the berry, an increase in ethanol concentration and cell death. Differences in internal O₂ availability of berries between cultivars could be associated with seed development and differences in lenticel surface area. Higher rates of mesocarp cell death caused by water stress was also associated with hypoxia within grape berries. Rootstocks with different drought resistance properties can affect Shiraz berry dehydration and cell death. Kaolin can effectively reduce Shiraz dehydration after the peak berry mass was reached. The data generated in this study provides the basis for further research into the role of berry gas exchange on berry quality and cultivar selection for adapting viticulture to a warming climate. Understanding the association between berry internal oxygen status and berry shrivel and cell death, as well as the effect of strategies to mitigate cell death and berry shrivel, will provide researchers and growers with new insights in berry ripening and is the basis for future research on berry flavour development and yield optimization.
Advisor: Tyerman, Steve
Sadras, Victor
Rogiers, Suzy
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2018
Keywords: Grape berry
oxygen sensor
programmed cell death
Vitis vinifera
water stress
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