Exploring the disease resistance response (chitinase, lysozyme, acid phosphatase and total phenolic content) of Kowhai (Sophora microphylla x S. chathamica) to hormones (salicylic acid and ethylene)
The aim of this research is to find out if the disease resistance of kowhai (New Zealand native Sophora species) is induced by hormones. Kowhai is an indigenous legume belonging to the Sophora genus. Disease resistance in this case is represented by an increase in the level of plant defensive enzymes and total phenolic content for phenylpropanoid phytoalexins. The Kowhai species used in the study was identified using DNA amplified from the chloroplast rbcL, matK and atpB-rbcL genes. The nucleotide sequence results of the rbcL and matK genes were used to perform a DNA barcode search using a Basic Local Alignment Search Tool (BLAST) and the sequence result of the atpb-rbcL gene was used for a neighbour joining phylogenetic analysis. Combining the result of the DNA barcode, phylogenetic analysis and morphological analysis, the sample used in the study was a S. microphylla x S. chathamica hybrid, and hence, it is New Zealand native kowhai. The kowhai was treated with 20 μg g-1 of 2,6 dichloroisonicotinic acid (INA) and 1000ppm of ethephon. Chitinase, lysozyme and acid phosphatase activities and total phenolic content (phenylpropanoids) were tested by fluorometric and colormetric assays to determine if these hormone sources induced increases in enzyme and total phenolic content in kowhai. Total protein content was also measured by the Bradford method to minimize the experimental error. The result was analyzed by two sample t-test. Acid phosphatase activity and total phenolic content was significantly (p<0.05) induced by 1.77 times and 1.24 times by INA and chitinase and acid phosphatase activities were significantly (p<0.05) induced by 1.92 times and 1.76 times by ethephon. These results indicate that Kowhai has a response to ethylene of a similar order of magnitude to Eurasian legumes such as Pisum sativum (Pea). In contrast, the response to INA differed from other legumes and was very weak. This may be related to it being a woody perennial legume rather than a herbaceous annual legume on which most previous hormone research has been based.