High temperature patterns during seed maturation determine seed yield and quality in oilseed rape (Brassica napus L.) in relation to sulfur nutrition

High temperatures (HTs) during the crop reproductive stage impact seed yield and quality. The changing climate will require consideration of the effects of repeated HT events following evidence for non-additive effects due to beneficial stress memory or amplification of individual event effects. Maturing seeds of the sulfur (S)-demanding crop, oilseed rape, were exposed to several HT sequences that varied in intensity, duration and frequency at the onset of seed maturation. The effects of these sequences in combination with two contrasting S supplies are reported. The results indicated that (i) as the number of HT days in a sequence increased, fatty acid (FA) concentrations decreased, the proportion of unsaturated FAs decreased, seed membranes were damaged, desiccation tolerance was lost, and dormancy increased, regardless of event intensity and (ii) a mild stress event prior to heat peaks had a priming effect on desiccation tolerance and the phytohormones involved in HT-induced thermoinhibition. Low S nutrition amplified or alleviated the effects of the HT sequences due the requirement for S in enhancing seed storage synthesis or inducing stress memory-associated mechanisms. This work provides insights to define thermopriming protocols in relation to the timing of quality building processes and their respective optimal temperature.