A mathematical model for the growth kinetics and synthesis of phenolics in oregano (Origanum vulgare) shoot cultures inoculated with Pseudomonas species

Abstract

Elicitation with Pseudomonas sp. reduced hyperhydricity in clonally propagated shoot cultures of oregano under in vitro conditions and over many subcultures without re-inoculation. This was characterized by changes in the growth kinetics, total chlorophyll, total phenolics and moisture content. Total chlorophyll in the inoculant-containing shoot cultures was higher than the control throughout the growth cycle of all subcultures. Moisture content (wb) of the inoculated shoot cultures was 8% lower than the control. The pattern of total phenolics synthesis in the inoculated shoot cultures showing characteristics of a periodic response and significant differences when compared to control was observed. A Leudking-Piret’s logistic model was used to study the growth kinetics of the control and inoculated shoot cultures to describe quantitatively the differences in the growth kinetics. There was a fourfold reduction in the biomass by fresh weight and a twofold reduction by dry weight due to inoculation. The specific growth rate remained unchanged, but the length of the growth cycle was reduced by 6 days for the inoculated shoot cultures. It appeared that the growth reduction was linked to the stress-related response mediated by the elicitation from Pseudomonas sp. to stimulate the synthesis of secondary metabolites. In spite of the growth reduction, the inoculated shoot cultures, however, had similar numbers of shoot node explants for subsequent propagation and all the shoot node explants were unhyperhydrated.