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Carbohydrates are an important regulator of canola seed oil content. However, understanding the physiological regulation by carbohydrates governing seed oil accumulation is fragmented. In the present study, activities of sucrose and starch catalytic enzymes, including neutral and alkaline invertase, sucrose synthase (SUS), and starch phosphorylase, and biosynthetic enzymes, including sucrose phosphate synthase and ADP-glucose pyrophosphorylase, were compared in developing silique and seed of high oil content and low oil content lines (HOCL and LOCL, respectively). The results showed that the HOCL had significantly higher total soluble sugar concentration in the developing silique wall and seed during the seed lipid accumulation stage. Strikingly, all the enzymes showed very strong activities at 20 days after anthesis in the silique wall of the HOCL, which was in agreement with the higher amounts of corresponding gene expression. The result indicated that the homeostasis of the high efficiency of cleavage and biosynthetic of carbohydrates in the HOCL was beneficial for the rapid volume expansion of silique and transportation of carbohydrates, i.e., sucrose and starch, to the seed for utilization. At seed deposition stage, all the enzymes exhibited significantly higher activities in the HOCL than in the LOCL, which was helpful for increased production of carbohydrates. The results of gene expression at seed oil deposition stages revealed that one of the SUS genes, SUS3, showed significantly higher transcript amount in the HOCL than in the LOCL at all stages while most of other genes showed no significant differences between two lines at developing stages. Therefore, SUS3 might be played vital roles in the sucrose cleavage.

Increasing seed oil content is one of the most important breeding targets for rapeseed (Brassica napus). In this study, we combined quantitative trait loci (QTL) mapping and marker-trait association analysis to dissect the genetic basis of seed oil content in rapeseed. A doubled haploid (DH) population with 261 lines was grown in two highly contrasting macro-environments, Germany with winter ecotype environment and China with semi-winter ecotype environment, to explore the effect of environment effect of on seed oil content. Notable macro-environment effect was found for seed oil content. 19 QTL for seed oil content were identified across the two macro-environments. For association analysis, a total of 142 rapeseed breeding lines with diverse oil contents were grow in China macro-environment. We identified 23 simple sequence repeat (SSR) markers that were significantly associated with the seed oil content. Comparative analysis revealed that five QTL identified in the DH population, located on chromosomes A03, A09, A10 and C09, were co-localized with 11 significantly associated SSR markers that were identified from the association mapping population. Of which, the QTL on chromosome A10 was found to be homeologous with the QTL on chromosome C09 by aligning QTL confidence intervals with the reference genomes B. napus. Those QTL associated with specific macro-environments provides valuable insight into the genetic regulation of seed oil content and will facilitate marker-assisted breeding of B. napus.

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. Electronic supplementary material The online version of this article (doi:10.1186/1999-3110-55-34) contains supplementary material, which is available to authorized users.

High temperature stress is an important abiotic stress during plant growth and development that can damage canola male reproductive organ development. In this present study, we characterized a canola genic male sterile line that its fertility can be restored after high temperature induction with heterozygous but not homozygous condition. Anther length and weight was elongated and increased 2 and 5.7 times at 9 days after high temperature treatment in heterozygous line. Furthermore, viable pollen grain was produced in the anther. Anther carbohydrate content was assayed. The result showed that fructose and sucrose contents were much more stable under heat stress both in hetero- or homozygous lines. However, glucose and starch content was considerably increased after high temperature treatment in heterozygous line. In particular, anther glucose content was twice as much as that of starch content after 5 days high temperature treatment. Activity of neutral invertase, acid invertase, and sucrose synthase were increased in the anther of heterozygous line under heat stress. But activity of neutral invertase was the highest among these three sucrose cleavage enzymes. Both activity of sucrose phosphate synthase and starch phosphorylase were decreased under heat stress in the anther of heterozygous line. Activity of ADP glucose pyrophosphorylase was greatly increased in the heterozygous line, which was beneficial for starch accumulation. Transcription level of carbohydrate related genes was analyzed. 27 and 34 of the carbohydrate related genes were identified for down- and up-regulated in the anther of heterozygous line, respectively. Their function involved in the regulation of heat tolerance of heterozygous line was also discussed. Key words: Canola, carbohydrate, gene.