Chlorophyll and carbohydrate metabolism in developing silique and seed are prerequisite to seed oil content of Brassica napus L

Abstract

Background: Although the seed oil content in canola is a crucial quality determining trait, the regulatory mechanisms of its formation are not fully discovered. This study compared the silique and seed physiological characteristics including fresh and dry weight, seed oil content, chlorophyll content, and carbohydrate content in a high oil content line (HOCL) and a low oil content line (LOCL) of canola derived from a recombinant inbred line in 2010, 2011, and 2012. The aim of the investigation is to uncover the physiological regulation of silique and seed developmental events on seed oil content in canola.

Results: On average, 83% and 86% of silique matter while 69% and 63% of seed matter was produced before 30 days after anthesis (DAA) in HOCL and LOCL, respectively, over three years. Furthermore, HOCL exhibited significantly higher fresh and dry matter at most developmental stages of siliques and seeds. From 20 DAA, lipids were deposited in the seed of HOCL significantly faster than that of LOCL, which was validated by transmission electron microscopy, showing that HOCL accumulates considerable more oil bodies in the seed cells. Markedly higher silique chlorophyll content was observed in HOCL consistently over the three consecutive years, implying a higher potential of photosynthetic capacity in siliques of HOCL. As a consequence, HOCL exhibited significantly higher content of fructose, glucose, sucrose, and starch mainly at 20 to 45 DAA, a key stage of seed lipid deposition. Moreover, seed sugar content was usually higher than silique indicating the importance of sugar transportation from siliques to seeds as substrate for lipid biosynthesis. The much lower silique cellulose content in HOCL was beneficial for lipid synthesis rather than consuming excessive carbohydrate for cell wall.

Conclusions: Superior physiological characteristics of siliques in HOCL showed advantage to produce more photosynthetic assimilates, which were highly correlated to seed oil contents.

Keywords: Biomass; Brassica napus L; Carbohydrate; Chlorophyll content; Seed oil content.

Figure 1

Dynamic of silique fresh weight in 2010, 2011, and dry weight in 2012 (A) and seed fresh weight in 2010, 2011, and dry weight in 2012 (B) of canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval. Each value is the mean of 15 main-inflorescence siliques of five plants from each of three replicate plots. Error bars represent standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.

Figure 2

Dynamic of seed oil content based on fresh weight in 2010, 2011, and that on dry weight in 2012 in canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval. Each value is the mean of 15 siliques from main inflorescence, five from each of three replicate plots in 2010 and 2011. Bars in the open and solid squares are standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.

Figure 3

Ultrastructure of silique (right panel) and seed (left panel) at 30 (A), 40 (B), and 50 (C) DAA by transmission electron microscopy (TEM). The circle in (A) is a magnification of chloroplast in the seed and silique. Cp, chloroplast; ImS, immature starch grain; MS, matured starch grain; N, nucleolus; O, oil body; P, protein; V, vacuole. Images are one representative out of 10 captured in 2012.

Figure 4

Dynamic chlorophyll content in developing silique of canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval in 2010, 2011, and 2012. Each value is the mean of 15 main-inflorescence siliques of five plants from each of three replicate plots. Error bars represent standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.

Figure 5

Dynamic of silique fructose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (A) and seed fructose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (B) of canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval. Each value is the mean of 15 siliques from main inflorescence, five from each of three replicate plots. Bars in the open and solid squares are standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.

Figure 6

Dynamic of silique glucose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (A) and seed glucose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (B) of canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval. Each value is the mean of 15 siliques from main inflorescence, five from each of three replicate plots. Bars in the open and solid squares are standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.

Figure 7

Dynamic of silique sucrose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (A) and seed sucrose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (B) of canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval. Each value is the mean of 15 siliques from main inflorescence, five from each of three replicate plots. Bars in the open and solid squares are standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.

Figure 8

Dynamic of starch content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (A) and seed starch content based on fresh weight in 2010, 2011, and that on 2012 (B) of canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval. Each value is the mean of 15 siliques from main inflorescence, five from each of three replicate plots. Bars in the open and solid squares are standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.

Figure 9

Dynamic of cellulose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (A) and seed cellulose content based on fresh weight in 2010, 2011, and that on dry weight in 2012 (B) of canola high oil content line (HOCL) and low oil content line (LOCL) from 10 to 65 days after anthesis (DAA) at a 5-day interval. Each value is the mean of 15 siliques from main inflorescence, five from each of three replicate plots. Bars in the open and solid squares are standard errors. “*” at each developmental stage indicates a significant difference at 5% probability between HOCL and LOCL in both years.