Glycinebetaine as a means of frost protection in Grapevines (Vitis vinifera L.): A dissertation submitted in partial fulfillment of the requirements for the Degree of Bachelor of Horticultural Science with Honours at Lincoln University

Abstract

Freezing causes osmotic stress and to cope with this plants can synthesize 'compatible solutes' that either help retain water within the cell or protect cellular components from dehydration induced injury. Quaternary ammonium compounds (QACs) including glycinebetaine (GB) are solutes that can act in both capacities. The current studies were undertaken to firstly measure naturally occurring QACs in different grapevine cultivars, and secondly to evaluate the efficiency of different methods of GB application on GB accumulation in order to examine the effect on frost tolerance. In the seven grapevine (Vitis vinifera L.) cultivars surveyed,low foliar levels of total naturally occurring QACs (ca. 1 μmol.gFW⁻¹ ) were detected using mass spectrometry analysis. GB was found to be in foliar concentrations from 0.26 to 0.39 μmol.gFW⁻¹ Exogenous application of 100 mM GB by spraying onto mature leaves in the field resulted in variable uptake (1.0 - 9.6 μmol.gFW⁻¹). To determine an efficient method of uptake, further experiments involved applying GB by 'vacuum infiltration', 'floating', and 'spraying'. Floating of leaf discs on buffered 25 mM GB solution resulted in the most efficient uptake, with foliar GB concentration of 4.12 μmol.gFW⁻¹ Frosting damages cellular membranes resulting in electrolyte leakage. After application of different concentrations of GB the frost tolerance of grapevine leaves was determined using the electrolyte leakage assay. The accumulated levels of GB achieved in these experiments did not protect against frosting. The effect of exogenously applied GB on some physiological parameters of young shoots were assessed. Under control conditions applications of 50 mM GB inhibited the leaf expansion rate of young grapevine shoots (0.51 mm day⁻¹) compared to controls (0.83 mm day⁻¹). However, application of 25 mM GB did increase net C0₂ assimilation from 8.6 μmol.m⁻²s⁻¹ (control) to 11.5 μmol·m⁻²s⁻¹ and facilitated maintenance of net C0₂ assimilation after frost treatment.