THE PROTECTION STRATEGIES REALIZED IN A RESURRECTION PLANT UNDER DROUGHT STRESS

Hui Min Olivia Oung

The homoiochlorophyllous resurrection plants adapt unique capabilities against damage caused by reactive oxygen species (ROS) from photosynthesis during desiccation. Under severe drought stress, the plants can maintain most of the photosynthetic apparatus and chlorophylls while minimizing the ROS damage and recover efficiently after re-watering. This study aims to reveal the protection mechanisms under drought stress at different ages of the life cycle in the homoiochlorophyllous resurrection plant Craterostigma pumilum and provides comprehensive information on the regulation of photosynthesis. The investigations in younger (< four months) and older (> six months) C. pumilum plants included high energy quenching analyses, photosynthetic protein composition and functional analyses, as well as ultrastructure imaging of chloroplast alteration in the cause of de- and rehydration. Both younger and older C. pumilum show similar general responses to drought, including dehydration rate, sucrose accumulation, partial chlorophyll breakdown, and having the capability of swift recovery of the relative water content. The chlorophyll fluorescence analysis shows that high-energy quenching (qE) increases in younger plants for protection, but it decreases in older plants during dehydration. The difference in qE protection depends on the change of a proton motive force (pmf) between both plant types. Prominent photosynthetic protein degradation was observed in older C. pumilum. The specific degradation of the D1 subunit of photosystem II and in particular of the cytochrome b6f complex leads to lower linear electron transport (LET) in older plants than that in younger plants. Furthermore, ultrastructure analysis provides evidence that dehydrated older plants possess senescence-like chloroplast degradation with a significant increase in plastoglobuli accumulation and appearance of degradation vesicles. This chloroplast degradation is suppressed in younger plants. The results conclude that younger plants employ a photoprotection-based strategy and maintain a high capability of D1 subunit repair against drought stress which results in a faster recovery. In contrast, older plants employ a degradation-based protection strategy through a breakdown of D1 proteins and of subunits of the cyt b6f complex when dehydrated. It follows that the protection strategies depend on the ontogenetic state of C. pumilum. Both strategies are capable of protecting C. pumilum from severe drought stress.

THE PROTECTION STRATEGIES REALIZED IN A RESURRECTION PLANT UNDER DROUGHT STRESS

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