The nutrient distribution in the continuum of the pericarp, seed coat, and kernel during Styrax tonkinensis fruit development

Abstract

BackgroundStyrax tonkinensis is a great potential biofuel as the species contains seeds with a particularly high oil content. Understanding the nutrient distribution in different parts of the fruit is imperative for the development and enhancement of S. tonkinensis as a biodiesel feedstock.MethodsFrom 30 to 140 days after flowering (DAF), the development of S. tonkinensis fruit was tracked. The morphology change, nutrient content, and activity of associated enzymes in the continuum of the pericarp, seed coat, and kernel were analyzed.ResultsBetween 30 and 70 DAF, the main locus of dry matter deposition shifted from the seed coat to the kernel. The water content within the pericarp remained high throughout development, but at the end (130 DAF later) decreased rapidly. The water content within both the seed coat and the kernel consistently declined over the course of the fruit development (30–110 DAF). Between 70 and 80 DAF, the deposition centers for sugar, starch, protein, potassium, and magnesium was transferred to the kernel from either the pericarp or the seed coat. The calcium deposition center was transferred first from pericarp to the seed coat and then to the kernel before it was returned to the pericarp. The sucrose to hexose ratio in the seed coat increased between 30 and 80 DAF, correlating with the accumulation of total soluble sugar, starch, and protein. In the pericarp, the sucrose to hexose ratio peaked at 40 and 100 DAF, correlating with the reserve deposition in the following 20–30 days. After 30 DAF, the chlorophyll concentration of both the pericarp and the seed coat dropped. The maternal unit (the pericarp and the seed coat) in fruit showed a significant positive linear relationship between chlorophyll b/a and the concentration of total soluble sugar. The potassium content had significant positive correlation with starch (ρ = 0.673, p = 0.0164), oil (ρ = 0.915, p = 0.000203), and protein content (ρ = 0.814, p = 0.00128), respectively. The concentration of magnesium had significant positive correlation with starch (ρ = 0.705, p = 0.0104), oil (ρ = 0.913, p = 0.000228), and protein content (ρ = 0.896, p = 0.0000786), respectively. Calcium content had a significant correlation with soluble sugar content (ρ = 0.585, p = 0.0457).ConclusionsDuring the fruit development of S. tonkinensis, the maternal unit, that is, the pericarp and seed coat, may act a nutrient buffer storage area between the mother tree and the kernel. The stage of 70–80 DAF is an important time in the nutrient distribution in the continuum of the pericarp, seed coat, and kernel. Our results described the metabolic dynamics of the continuum of the pericarp, seed coat, and kernel and the contribution that a seed with high oil content offers to biofuel.

Proteomic analysis of metabolic mechanisms associated with fatty acid biosynthesis during Styrax tonkinensis kernel development

“…31,32 All DEPs were grouped into nine clusters using Mfuzz based on their patterns of expression. Consistent with gene change trends analyzed by transcriptomics in developing S. tonkinensis kernels, 10 most DEPs showed higher relative protein abundance at early stages, as kernels begin to increase in volume and accumulate biomass, 9 and the deposition centers for major storage materials transfer to the kernel from either the seed coat or the pericarp. 10 Overall, 70 DAF was identified to be an important time point during S. tonkinensis kernel development, as this is when the major nutritional components begin to rapidly accumulate.…”

“…9 The samples from 100 and 130 DAF were clustered closely in the PCA analysis, similar to the HCA analysis, indicating that S. tonkinensis fruits undergo maturation without much further physiological change occurring in kernels after 100 DAF, while the size and structure of kernels stabilize. 10 A total of 2338 proteins were identified and 1472 of them expressed differentially between different time points. Many DEPs were down-regulated during S. tonkinensis kernel development, showing similar results to developing A. hypogaea kernels, 24 which may be related to the large increase of stored protein in kernels.…”

“…Based on our previously published data 10,17 for observed changes in oil concentration which showed an up-down-up trend, and on transcriptome analysis of developing S. tonkinensis kernels, we defined four time points for sampling to investigate changes in the proteome:…”

“…After searching the S. tonkinensis transcriptome database, 10 42 proteins involved in carbohydrate metabolism and oil accumulation processes during kernel development were selected for close examination (Table 1), including four proteins for starch and sucrose metabolism, 12 for glycolysis/gluconeogenesis, three for the PPP, six for the TCA cycle, 13 for FA biosynthesis, three for FA metabolism and one for an oil body membrane protein.…”

“…sugars and starch, lipid and soluble protein) begin to accumulate about 60 days after flowering (DAF), as the seed volume and surface area increase. 10 The major unsaturated FAs (C18:1 and C18:2) account for 40% of the oil content initially and then increase to 87% as the kernels mature, while major saturated FAs (palmitic acid (C16:0) and stearic acid (18:0)) are abundant early on and then drop from 50% to 12% during kernel development. 9,11 A series of enzymes catalyze the process of FA biosynthesis, 12,13 including the acetyl-CoA carboxylase complex (ACC), the pyruvate dehydrogenase complex (PDC), the fatty acid synthase (FAS) complex and acyl-CoA:DAG acyltransferase (DGAT).…”