Spectrophotometric Quantification of Phytic Acid During Embryogenesis in Bambara groundnut (Vigna subterranea L.) Through Phosphomolybdenum Complex Formation

Abstract

In relation to seed vigour and hyperosmotic stress, phytic acid has implications in imparting drought tolerance and enrichment of seed mineral reserves respectively. The present study was undertaken to determine the variation in phytic acid during seed development and physiological maturity of 4 Bambara groundnut landraces. The landraces were grown in field during 2017–2018 rain season at Ukulinga, Pietermaritzburg. The phytate content was estimated indirectly from 14-65 days after flowering (DAF) by using a spectrophotometer, evaluating the total extractable phosphorus absorbance at 720 nm. An analysis is described for the rapid determination of phosphorus in developing seeds. The colour complex (phosphomolybdenum) formed under acidic conditions absorbs maximally at 720 nm in acidic (pH<4.5) solutions. Absorbance of the chromophore when measured spectrophotometrically at 720 nm, it obeys Beer’s law over the range of 0 to 75 ppm of standard phosphorus solution. There were significant differences (P<0.001) in total extractable phosphorus at 14, 21, 28, 35, 42 and 65 DAF. The highest and lowest extractable phosphorus was recorded in G340A and Kazai respectively. Pi seed content was between 1.51 and 5.69 mgkg-1 at 14 DAF, at physiological maturity (65 DAF) Pi was recorded between 21.73 and 32.23 mgkg-1. We drew conclusions that Bambara groundnut landraces may differ in both (1) phytic acid accumulation rate and (2) phytic acid content at physiological maturity. The results reported open the possibility of a specific seed selection criterion for improving the mineral element value of Bambara groundnut through the identification of landraces with high-Pi (phytic acid).