Analysis of starch metabolism in South African pigeon pea (Cajanus cajan) varieties

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: Starch is a major storage polyglucan in plants that is composed of two fractions, amylose and amylopectin. The biosynthesis and degradation pathways of starch are well documented, with phosphoglucomutase (PGM) and ADP-glucose pyrophosphorylase (AGPase) catalysing the first two steps in its biosynthesis. This project examined starch in five pigeon pea (Cajanus cajan) varieties: uDhali, SEFA, Nondolo, Lari and India by measuring both total and resistant starches in the seeds and leaves, activities of PGM and AGPase as well as expression of the genes encoding these enzymes. The findings demonstrated that the seeds from these South African pigeon pea varieties are rich in starch, containing an average of 47% starch on a dry weight basis; however, one variety (SEFA) contained only 0.3% starch. The starch in the high- starch varieties contained a minimum of 50% resistant starch, with the India variety reaching 70%. Assessment of soluble sugars in seeds revealed sucrose to be the only sugar present in abundance in all varieties while amounts of galacto-oligosaccharides were low in all seeds. Starch in leaves was observed to be 10 fold less than that found in seeds and the amount of resistant starch in leaves was less than 2 mg/g fresh weight (7.6% of the total). The AGPase gDNA nucleotide sequence from one variety was identical to an already sequenced pigeon pea variety, whereas amplification PGM gDNA was unsuccessful. Amplification of coding sequences (CDSs) for both AGPase and PGM were also identified to be the same as the already sequenced AGPase and PGM genes from the pigeon pea genome resource database. Gene expression for both genes varied throughout a 24 h period and was at its peak during the day (light period). Activities of both AGPase and PGM were determined in seeds from all varieties whereas the AGPase enzyme activity was the same in leaves throughout the day while PGM activity varied between the day (light) and night (dark).
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Thesis (MScAgric)--Stellenbosch University, 2023.