Polynomial regressions reveal that levels of chlorophyll a, carotenoids, soluble phenolics and aldehydes modify mathematically sugarcane shoot multiplication rate in temporary immersion bioreactors under salt stress

Abstract

Polynomial regression analysis is a powerful statistical tool used to describe non-linear relationships. The goodness-of-fit of this model is assessed by evaluating the coefficient of determination (R2). An R2 value closer to 1 is indicative of a strong correlation between the two under consideration. While polynomial regression analysis has been widely used in studies of plant stress responses to stress, to the best of our knowledge, this represents the first report on the application of this method to study the response of sugarcane plants to salt stress in Temporary Immersion Bioreactors (TIBs). In this context, sugarcane plants were exposed to salt stress while undergoing multiplication in TIBs. At the end of the multiplication cycle, the levels of biochemical metabolites (i.e. chlorophylls, carotenoids, phenolics and aldehydes) were evaluated. Polynomial regression analysis was subsequently used to elucidate the relationships between shoots multiplied under high salt stress conditions and consequent metabolite levels. The results indicated that the levels of chlorophyll a had a strong positive relationship (in mathematical terms) with shoot multiplication rate (R2 = 0.7063) with a corresponding high determination coefficient. In contrast, shoot multiplication rate was decreased in response to increased levels of carotenoids, soluble phenolics in shoots, and other aldehydes. Changes in levels of chlorophyll b, cell wall-linked phenolics, soluble phenolics excreted to the culture medium and malondialdehyde did not seem to (mathematically) influence sugarcane shoot multiplication in TIBs under salinity stress. The results from the present investigation provides evidence for the application of polynomial regression analysis as a tool to elucidate relationships between plant metabolites as markers for stress and shoot multiplication (as an indicator of growth) in in vitro systems. It is recommended that this statistical tool would be useful in an overall in vitro screening approach to investigate the stress response of other plant species in similar systems.