Cold storage to overcome dormancy affects the carbohydrate status and photosynthetic capacity of Rhododendron simsii

Global warming leads to increasing irregular and unexpected warm spells during autumn, and therefore natural chilling requirements to break dormancy are at risk. Controlled cold treatment can provide an answer to this problem. Nevertheless, artificial cold treatment will have its consequences on carbon reserves and photosynthesis. In this paper the effect of dark cold storage at 7°C to break flower bud dormancy in the evergreen Rhododendron simsii has been quantified. Carbohydrate and starch content in leaves and flower buds of an early (‘Nordlicht’), semi-early (‘M. Marie’) and late (‘Mw. G. Kint’) flowering cultivar showed that carbon loss due to respiration was lowest for ‘M. Marie’, while ‘Mw. G. Kint’ was completely depleted in starch reserves at the end of cold treatment. The gene isolation resulted in a candidate gene for SUS (RsSus) which appears to be homologous to AtSus3 and had a clear increase in expression in leaves during cold treatment. Photosynthetic measurements on ‘Nordlicht’ and the late flowering cultivar ‘Thesla’ showed that during cold treatment dark respiration decreased by 58% and 63%, respectively. Immediately after cold treatment dark respiration increased and stabilized after 3 days. The light compensation point followed the same trend as dark respiration. The quantum efficiency showed no significant changes during the first days after cold treatment, but was significantly higher than in plants with dormant flower buds, at the start of cold treatment. In conclusion, photosynthesis stabilized 3 days after cold treatment and was improved compared to the level before cold treatment.