Conclusion
Our study analyzed the effects of repeated high temperature events at the onset of seed maturation on seed nutritional and physiological quality under induced thermotolerance. Our results pinpointed three aspects of thermo-sensitization for further investigation: (i) the synchronization between the expected thermopriming event and the underlying biosynthesis and maturation processes specific to the targeted storage compound, (ii) the optimal temperature to promote a targeted process and (iii) the non-additive effects of repeated stressing events as a result of positive stress memory or cumulative negative impacts of successive events. Our experiments were also designed to observe whether S nutrition (which is essential to Brassica species) interfered with expected priming effects. Nevertheless, we could only verify this hypothesis in a few priming effects that were observed via an indicator of desiccation tolerance ([raffinose+stachyose:sucrose]), which slightly diminished under S restriction. This raises the question of the direct role of S in the cascade of events leading to these sugars biosynthesis and the indirect role of S in stress memory mediated by epigenetic regulation. In contrast, S restriction optimized seed oil concentrations in stress-exposed maturing seeds, especially when the stress was delayed, thus highlighting the need to satisfy S requirements in certain climatic contexts.
Overall, we foresee the need for trade-offs to optimize quality criteria that are dependent on features of temperature such as intensity, frequency and timing of application. They should consider S supply which limitation or at least adjusted levels can either improve seed quality criteria (e.g. oil contents, UFAs) in temperature-stressed maturing seed, lessen the positive effects of a priming event (e.g. desiccation tolerance) or amplify the negative effects of high temperature stress when applied at sensitive stages during the maturation process (e.g. indicator of seed dormancy).