| Oilseed rape (Brassica napus) is one of the important oil crops on the world. To elevate oil yield has always been a important target for rapeseed breeding and cultivation. As a strategy to promote seed oil production, many efforts have been made in promoting seed lipid biosynthesis efficiency. However, little has been done to prevent seed lipid breakdown. As a matter of fact, the process of seed lipid accumulation is a dynamic balance between seed lipid synthesis and decomposition. Recently, we discovered in model plant Arabidopsis that Seed Fatty Acid Reducers (SFARs), a group of GDSL lipase genes upregulated by GA signaling, play an important role in seed fatty acid breakdown. It becomes interesting to know if the blockage of GA synthesis could also cause a higher oil output in rapeseed production. With this in mind, we designed and carried through a multiple-year and multiple-location field experiment with randomly-arranged-blocks design. We aim to understand the effect of paclobutrazol (PAC), a kind of reagent blocking GA biosynthesis, on oil yield and the constituting agronomic traits, seed fatty acid composition, seed tocopehrol content and composition, seed storage protein and soluble sugars, etc. in oilseed rape. The major findings are as the following.1. GA signal significantly affect oil output per unit of landGA signal significantly affects seed yield, seed oil content and oil output per unit land. The application of PAC resulted in an increase of65.60kg oil output per hector (6.96%) and an increase of92.42kg oil output per hector (10.10%) compared with water control (CK) and the GA3treatment, respectively. The PAC application led to an217.12kg (9.451%) and293.40kg (13.16%) increases of grain yield in comparison with CK and the GA3treatment, respectively. The increases were statistically significant. On the other hand, the PGRs didn’t give rise to significant changes in oil content per unit of seeds.RT-q-PCR experiment was carried to investigate the responses of a group of genes, which are either key transcriptional factors regulating seed development or encoding essential enzymes catalyzing fatty acid biosynthesis, to the application of PGRs. The experiment indicated that the reduction of GA synthesis downregulated the expressions of transcriptional factors and the enzymes, indicating rather the blockage of lipid decomposition than more lipid synthesis were likely the cause of increase oil output from the plants treated with PAC.We further investigate three components essentially constituting seed yield, namely number of seeds pods (NSP), thousand-seed-weight (TSW) and number of seeds per pod (NSP). The application of PAC gave rise to an increase of96.42(31.65%) and an increase of100.35pods (33.38%) compared to the CK and GA3treatment, respectively. On the other hand, PAC caused a significant reduction of0.23g (5.45%) and0.32g (7.42%) in TSW, compared with the CK and the GA3treatment, respectively. Notably, the effect of PRGs on NSP was insignificant. Overall, the effect of SNP increases were much greater than the effect of TSW decreases, therefore, the grain yield per unit land was increased.2. GA signal significantly affect other agronomic traitsThe application of PGRs significantly affect the number of first branches (NFB), number of second branches (NSB), number of total effective branches (NTEB), plant height (PH) and pod length (PL). The application of PAC resulted in NFB increases of of0.92(11.33%) and0.86(10.51%), NSB increases of2.99(57.28%) and3.38(69.98) and NTEB increases of3.91(29.31%) and4.24(32.59%) in comparison with the CK and GA3treatment, respectively. The significant increase of NTEB can be a reason accounting for a NSP increase.The application of PAC significantly reduced plant height. The PH of the plant treated with PAC was7.32cm (4.93%) and9.74cm (6.45%) lower than those of the CK and the plants treated with GA3.The situation of PL was similar to that of PH. The moderate PH reduction of the PAC treated plants can be a reason partly accounting for their higher grains yield, due to less yield loss caused by lodging.3. GA signal significantly affect seed total tocopherol (total-Toe) and tocopherol compositionWe investigated the effects of PRGS on Toc biosynthesis and also explored the interactive effects between the two plant growth regulators (PGRs) and other factors, such as PGR treatment duration, genotype, and growing location on the total Toe yield and composition in oilseed rape seed. GA3significantly enhanced the production of Toe and elevated the a-/y-Toc ratio in a time-dependent and genotype-development manner. By contrast, PAC significantly reduced Toe yield. Genotypic differences were observed in the effects of GA3on Toe yield and composition in the seeds. GA3significantly increased the Toe yield and a-/y-Toc ratio in Zheyou-50, a genotype with a low proportion of very long chain fatty acids (VLCFA). However, GA3did not significantly influence these parameters in Jiu-Er-13Xi, a genotype with a high VLCFA proportion. The increased Toe yield induced by GA3was mediated by the upregulation of genes (BnPDSl and BnVTEl) that catalyze the production of Toe precursors. Therefore, applying GA3can improve rapeseed quality by increasing the yield and improving the composition of Toe4. GA signal significantly affect the content of storage protein (CSP) and fatty acid composition (FAC)The application of PAC caused an reduction of storage protein at a rate of6.06%in comparison with CK. On the other hand, GA3gave rise to relative increases of the FAs such as C20:0, C20:1and decrease of the FAs such as C22:0. In contrast, PAC led to higher C22:1, but lower C18:1, C18:3, C20:0and C20:1.Taken together, the reduction of endogenous GA synthesis caused by exogenous PAC can lead to a significant increase of oil production per unit land but a down-grade seed nutritional value by reducing total-Toe, α-/γ-Toc ratio, and desirable fatty acids. These findings are an enrichment to our knowledge about the role of GA in seed maturity and oil accumulation in oilseed rape. |
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