An Investigation of Factors that Contribute to Dihydroxyacetone Variation Observed in New Zealand Leptospermum scoparium

Honey derived from Leptospermum scoparium (commonly known as mānuka) is known to have anti-bacterial activity that is not entirely accounted for by the presence of hydrogen peroxide.1 This is known as non-peroxide activity (NPA). The discovery of this medical benefit has led to mānuka honey being a major export for New Zealand. In order to assure supply, mānuka trees are being investigated to determine why certain specimens yield honeys with a greater NPA than others. This might result in plantations of L. scoparium that would yield honey with a consistently high NPA. &#13;\nThe compound responsible for the NPA is a 1,2-dicarbonyl known as methylglyoxal (MGO).2 The precursor to this molecule was found in nectar of the mānuka flowers and was identified as dihydroxyacetone (DHA).3 An investigation of DHA in the nectar of L. scoparium across different regions of New Zealand was carried out by Williams (2012).4 It was confirmed that trees vary within and between regions across New Zealand. &#13;\nThis thesis describes different investigations into why the variation of DHA observed in various mānuka flowers is so great. Flowers were collected during flowering periods from 2011-2013 and were frozen prior to processing. The extraction method used ten flowers (10F) and samples were analysed by gas chromatography with flame ionisation detection (GC-FID). The DHA quantity was expressed with respect to the total sugar (Tsugar) in the nectar (DHA/Tsugar) in order to allow for comparison between samples.&#13;\nThe study by Williams (2012) was extended to include the Northland region.4 Wild L. scoparium var. incanum specimens were collected from this region and it was determined that these trees only produced a low to moderate amount of DHA/Tsugar. Williams (2012) also investigated the DHA variability of trees in close proximity to each other as these are supposed to be genetically similar.4 This study was repeated in a different region and the findings were the same; that is trees that were in close proximity to each other can have different DHA/Tsugar. &#13;\nOne possibility of why DHA is observed in mānuka flowers is that it is used to combat stress as a compatible osmolyte. This was tested using chemical additives and it was found that the DHA/Tsugar varied as a result of the Tsugar as opposed to the amount of DHA. This response was cultivar dependent.&#13;\nDifferent flower physiologies were also investigated. This included the andromonoecious nature of mānuka and the specific colour change in the hypanthium of the flower. Male flowers were found to have a larger amount of DHA/Tsugar as a result of a higher level of DHA than hermaphrodite flowers. This could suggest that DHA is being used in the hermaphrodite flowers for processes such as seed production. The DHA/Tsugar of flowers with different hypanthium colour was shown to be dependent on the variety type. The source and reason for DHA still remains unclear and therefore further study is required.

Topic: Botany, Ecology, and Taxonomy Studies
Subfield: Plant Science
Field: Agricultural and Biological Sciences
Domain: Life Sciences