Pyruvate kinase activity as a bioind1cator of cations in grafted watermelon plants

Abstract

Three cultivars of Cucurbita pepo L. were used as rootstocks (Brava, Shintoza and Kamel), and as scion part, four cultivars of Citrullus lanatus (Trumb) Mansfield (Sugar King, Early Star, Dulce Maravilla, and Sugar Bell) were grafted and subjected to the determination of calcium (Ca), potassium (K), sodium (Na), and magnesium (Mg), and pyruvate kinase activity in leaves. Control plants (not grafted) gave the highest level of total K with respect to the other cultivars. The cross Brava x Sugar Bell showed the higher K level, while the lowest was found with the cross Brava x Sugar King. Total sodium (Na) content did not show differences within the experimented crosses as 0.77 mg Na/g d.w. was obtained for all cultivars, while control plants gave levels of Na five times higher (3.49 mg/g d.w.). The cultivar Sugar King had the highest Ca integration capacity, whereas Dulce Maravilla showed a decrease, both with respect to the control plants. The results of soluble Mg were lower than those obtained in the control plants, the higher concentration of this cation was observed in Kamel x Dulce Maravilla, while Shintoza x Dulce Maravilla and Sugar Bell had the lower level of Mg with respect to the control. The endogenous activity of pyruvate kinase (PK) was higher in the grafted plants than the control plants. The essays in the presence of Mg or K induced an increase in the PK activity over the endogenous one. The results of the PK essay in the presence of Ca were higher with respect to the previous essays. It seems that grafted plants have a physiological deficiency, especially for Mg and K, whereas Ca had excessive concentrations, but some crosses showed a physiological demand for active Ca.