Abdul Wahab, Nurniwalis
(2017)
Physiological, biochemical and molecular analyses of fruit development in oil palm (Elaeis guineensis Jacq.).
PhD thesis, University of Nottingham Malaysia Campus.
Abstract
In Malaysia, oil palm is the main commodity crop and has strongly contributed to the country’s economic development. However, the industry is facing several challenges including diminishing land resource for expansion. One of the targets to ensure oil palm sustainability is to increase yield per unit area without affecting its quality and with minimal impact to the environment. The non-synchronized ripening process and shedding of the fruits is among the factors that limit yield improvement and affect oil quality. Thus, the present study was conducted to deepen our understanding of the changes that occur within the fresh fruit bunch (FFB) during fruit development. This work also takes into account the various fruit positions (inner, middle and outer) and locations (apical, central and basal) within the bunch.
In the present study, physiological, biochemical and molecular analyses were performed using fruits from various stages of fruit development. Physiological and biochemical analyses included measurements of carotenoid, FAC (fatty acid composition) and ethylene production. UV-Vis spectrophotometer, gas chromatography mass spectrophotometry (GCMS) and GC equipped with flame ionization detector (FID) were used to estimate and quantify the β-carotene content, FAC and ethylene production from the fruit mesocarp from young until the ripening stages. Results showed that changes in the β-carotene content, FAC and ethylene production throughout the fruit developmental stages from young until ripening were significant (p<0.001). Both accumulation of the β-carotene and ethylene production increased as the fruits developed and reached the maximum at the ripest stage used in this study. Similarly, changes in the FAC was observed especially in palmitic, oleic, stearic and linoleic acid throughout the fruit developmental process where the level of oleic acid was found to be the highest in the ripest fruit stage used in this study, surpassing that of palmitic acid.
In the present study, it was also observed that fruit positioned within the spikelets throughout the bunch at the various fruit developmental stage from young until ripening showed significant changes (p<0.001) in the β-carotene content and FAC. For β-carotene, the outer fruits have the highest content while the inner fruits have the least. For FAC, palmitic and stearic acids were higher in the outer fruits as compared to the inner fruits while the levels of oleic and linoleic acids were in contrast to that of palmitic and stearic. The inner fruits also recorded higher iodine value (IV) than the outer fruits.
Ethylene production in the ripe bunch was not influenced by the fruit location or position within the bunch. Thus, the molecular mechanism of ethylene perception during fruit developmental processes, including ripening and abscission were investigated. In the present study, with the use of the oil palm genome sequence data, the oil palm ethylene receptor family which comprised of seven putative ethylene receptors including three splice variants were identified. In addition, combination of in silico bioinformatics tools and laboratory bench work also resulted in the successful isolation and characterisation of the putative ethylene receptor genes and their corresponding promoters. The putative regulatory motifs in the promoters provide a means to understand the possible mechanisms that drive the expression of the ethylene receptor genes. Expression analyses of the ethylene receptors in various oil palm tissues suggest multiple roles of the ethylene receptors in regulating many processes in oil palm which includes fruit development and fruit abscission.
Subsequently, the effect of gene(s) that influence oil quality was also investigated in this study. The full-length FLL1 gene encoding a lipase class 3 and its corresponding promoter were successfully isolated and characterised. FLL1 was expressed highly in the mesocarp tissues and at various developmental stages and at a much higher expression in the cold induced ripe fruits. Promoter analysis via transient expression assay using GUS as the reporter gene showed that the GUS expression in the mesocarp slices was targeted especially to the vascular bundles. Southern analysis of the FLL1 gene revealed the gene to belong to a multigene family. With the availability of the oil palm genome sequence data, sixty-two predicted proteins with identities ranging from 26 to 83% to FLL1 were identified indicating that there may be more lipase class 3 genes involved in the breakdown of TAGs in the oil palm thus affecting the oil quality.
From this study, it can be concluded that fruit development in oil palm is a complex process involving physiological, biochemical and molecular changes within the bunch throughout the ripening process and is affected by the position of the fruits within the spikelets. Since changes within the bunch were not influenced by the fruit location within the bunch, this may provide a simpler method for bunch analysis where changes within the whole bunch can just be represented by the fruits from a mix of all fruits positioned within the spikelet from the apical region of the bunch.
The molecular studies on the identification, isolation and characterisation of the genes and promoter of the ethylene receptors and lipase class 3 gene families also would be useful for genetic manipulation of oil palm especially for modifying oil composition and production of higher value products.
Actions (Archive Staff Only)
 |
Edit View |
Tools
Tools
![[img]](/style/images/fileicons/application_pdf.png)