The role of storage reserves and their mobilization during seed germination under drought stress conditions of rapeseed cultivars with high and low oli contents

Seed germination is one of the complex traits in the plant life cycle, which is accomplished by the interaction of various complex processes including seed reserve mobilization and utilization under various environmental conditions. Since seed reserves can influence seed germination, the quantitative and qualitative differences in seed reserves may relate to the germination characteristics of rapeseed seeds. Therefore, we hypothesized the positive relationship between seed germination and mobilization process of seed reserves during the seed imbibition of two rapeseed cultivars with high and low oil contents under normal and drought stress conditions. Herein, we measured the initial absorption of water and seed microstructure during seed imbibition, besides, we also determined seed germination parameters, osmolytes, enzymatic activity, lipid peroxidation, and fatty acid composition in both rapeseed cultivars. Our results displayed that the high oil content cultivar (QY1) showed a higher germination percentage with higher water absorption during the seed imbibition under drought stress conditions. Moreover, seed microstructural analysis indicated that oil bodies (OBs) were surrounding the protein storage vacuoles (PBs) compartment and cell periphery, the gap between OBs was increased to some extent, and boundaries became blurred in QY1 under drought stress conditions. Besides, the number of oil bodies was higher, while their area was lower, which might provide more energy for the germination process. Furthermore, the active metabolism of protein, sugar, and proline in QY1 was higher than ZYZ108 under normal and drought stress conditions, which might be closely related to the accretion of osmoregulatory substances that improved water uptake, thereby improving seed germination. Additionally, unsaturated fatty acids were higher in QY1 than ZYZ108, which provide greater protection against drought stress damages. Besides, QY1 exhibited high efficiency of defense system, which reduced malonaldehyde (MDA) content, hence ameliorating the oxidative damage due to drought stress. Taken together, this investigation provides new insight into the role of seed reserves as energy resources in the germination process in high oil content seeds of rapeseed cultivars, especially under drought stress conditions.