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).