Brassica napus L. is a vital plant oil resource worldwide. The fatty acid biosynthesis and oil accumulation in its seeds are controlled by several genetic and environmental factors, including daytime and nighttime temperatures. We analyzed changes in oleic and erucic acid content in two double haploid (DH) lines, DH0729, a weakly temperature-sensitive line, and DH0815, a strongly temperature-sensitive line, derived from B. napus plants grown at different altitudes (1600, 1800, 2000, 2200, and 2400 m a.s.l., 28.85° N, 112.35° E) and nighttime temperatures (20/18, 20/16, 20/13 and 20/10 °C, daytime/nighttime temperature). Based on medium- and long-chain fatty acid metabolites, the total oleic acid content 35 and 43 days after flowering was significantly lower in low nighttime temperature (LNT, 20/13 °C) plants than in high nighttime temperature (HNT, 20/18 °C) plants (HNT: 58–62%; LNT: 49–54%; an average decrease of 9%), and the total erucic acid content was significantly lower in HNT than in LNT plants (HNT: 1–2%; LNT: 8–13%; an average increase of 10%). An RNA-seq analysis showed that the expression levels of SAD (LOC106366808), ECR (LOC106396280), KCS (LOC106419344), KAR (LOC106367337), HB1(LOC106430193), and DOF5 (LOC111211868) in STSL seeds increased under LNT conditions. In STSL seeds, a base mutation in the cis-acting element involved in low-temperature responsiveness (LTR), the HB1 and KCS promoter caused loss of sensitivity to low temperatures, whereas that of the KCS promoter caused increased sensitivity to low temperatures.
Winter rapeseed (Brassica rapa L.) can well‐adapt to environmental conditions such as barrenness, water deficit and low temperature in arid and semi‐arid planting regions and is the preferred rapeseed type. In this study, we analysed changes of root system morphology, antioxidant enzyme activity, endogenous hormone contents and differentially expressed proteins (DEPs) under control (CK), slight water deficit (SWD, 50–55% of maximum field water capacity), moderate water deficit (MWD, 40–45% of maximum field water capacity) and high water deficit (HWD, 30–35% of maximum field water capacity) conditions. Winter rapeseed experienced taproot elongation, decreased taproot diameter and increased lateral root number, under water deficit stress. The accumulation of reactive oxygen species (ROS) can cause membrane system peroxidation, and antioxidant enzyme activity increases to remove ROS. Changes in jasmonic acid (JA), salicylic acid (SA), cytokinin (CTK), auxin (IAA) and gibberellin (GA) levels promote the absorption of water and minerals by driving changes in the root system architecture to resist water deficit stress. A proteomic analysis has shown that DEPs are involved in energy metabolism, antioxidation response, osmotic regulation, hormone signal transduction, protein metabolism and the stress response, and these proteins are located in the peroxisome, chloroplast, mitochondrion, cell wall, vacuole, cytoplasm, extracellular space and cell membrane. In this study, multiple DEPs (malate dehydrogenase cytoplasmic 1 OS, 14‐3‐3‐like protein GF14 Psi, GA 3‐beta‐dioxygenase, glutathione reductase and jasmonate‐inducible protein) were involved in the root system architecture, revealing the complexity of the root response to water deficit. Significant/extremely significant synergistic relationships were observed between antioxidant enzyme activity and endogenous hormone contents. In conclusion, ROS, endogenous hormones and stress‐related proteins work synergistically to control the root system architecture of winter rapeseed roots in response to water deficit stress.
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