Exogenous supply of pantoyl lactone to excised leaves increases their pantothenate levels

Abstract

Background and aims: All plants synthesize pantothenate but its synthesis and regulation are not well understood. The aim of this work is to study the effect of exogenous supply of precursor compounds on pantothenate levels in leaves.

Methods: Precursor compounds were supplied in solution to excised leaves and the pantothenate content was measured using a microbial method.

Key results: Pantothenate levels in excised leaves of Limonium latifolium, tomato (Lycopersicon esculentum), bean (Phaseolus vulgaris) and grapefruit (Citrus x paradisi) were examined following an exogenous supply of the precursor compounds pantoyl lactone or beta-alanine. Significantly higher levels of extractable pantothenate were found when pantoyl lactone was supplied, but not when beta-alanine was supplied despite a measurable uptake of beta-alanine into the leaf.

Conclusions: The results suggested that the pantoate supply may be rate-limiting or regulating pantothenate synthesis in leaves.

Fig. 1.

Biosynthesis of pantothenate in plants (after Jones et al., 1994). Steps numbered are catalysed by the following enzymes: 1, ketopantoate hydroxymethyltransferase; 2, ketopantoate reductase; and 3, pantothenate synthetase.

Fig. 2.

Pantothenate levels in tomato leaflets supplied with nutrient medium alone (control) or nutrient medium supplemented with 0·1 or 1·0 mm of pantoyllactone or 1 mm β-alanine for periods of time up to 24 h. Each point represents mean and standard error of three replicates.

Fig. 3.

Uptake of exogenously supplied β-alanine by excised tomato leaflets over a period of time up to 24 h. Each point represents the mean and standard error of four replicates. Uptake was monitored by using [¹⁴C]β-alanine as described in Materials and methods.