K:Mg impact on rubisco activity and sugar metabolism in legume plants: challenges of NADH-linked microtiter plate-based and 14C-based assays

Abstract

Magnesium (Mg) is part of the chlorophyll molecule and plays an important physiological role as an enzymatic activator of rubisco. However, Mg is known as a forgotten element due to the scarcity of research regarding the nutritional and physiological role of Mg in plants. In addition, Mg is found at low concentrations in the soil of tropical areas, possibly resulting from anthropogenic activities, such as the inadequate oversupply of potassium (K) fertilizers. Potassium is an essential element for plants; however, high K concentration soil application can induce antagonism with Mg uptake by plants causing an imbalance in the K:Mg ratio dramatically decreasing crop yield. This study hypothesizes that K:Mg ratio drastically affect rubisco activation sites in cowpea and soybean plants, leading to lower synthesis and translocation of sugars (sucrose, glucose, fructose, mannitol, and sorbitol) from the source (leaves) to the drains (roots and nodules), negatively affecting nodulation and biological nitrogen fixation. Therefore, this study aims to evaluate the effect of K:Mg combination on rubisco activity using different techniques like NADH-linked microtiter plate-based and 14C-based assays to precisely determine the activation state of rubisco. Relations with biological nitrogen fixation (nitrogen compounds), photosynthetic metabolism and productivity of legume plants will also be analyzed. (AU)