Growth irradiance affects the photoprotective mechanisms of the resurrection angiosperm Haberlea rhodopensis Friv. in response to desiccation and rehydration at morphological, physiological and biochemical levels

Abstract

In the present study, we examined the photoprotective mechanisms of the homoiochlorophyllous desiccation-tolerant (DT) Haberlea rhodopensis Friv. (Gesneriaceae) during the desiccation–rehydration cycle in its natural understory shaded and sunny habitats within drought prone regions. The integration of classical analysis of chlorophyll fluorescence with a detailed analysis of energy partitioning showed a re-adjustment in the function and extent of the different components of energy management in photosystem II (PSII) depending on the degree of dehydration. At mild dehydration, the non-photochemical quenching by active centres (NPQ) played a relevant role in preventing photoinhibition, while under the photoinhibitory conditions occurring when dehydration was severe, the light-dependent quenching by inactive centres provided strong photoprotection. These analyses of the photosynthetic and PSII functionality together with measurements of carotenoid changes showed that the photoprotective mechanisms of this resurrection species were also affected by growth irradiance. Plants growing in understory shaded habitats were mainly protected against dehydration by the mechanism of thermal re-emission by inactive PSII reaction centres together with the relevant contribution of an operative xanthophyll-cycle involved in a quenching process triggered by dehydration itself. Conversely, plants growing in sunny open environments relied more on the quenching mechanism in the light-harvesting antennae. One additional role of carotenoids, in particular of β-carotene, in dehydration tolerance of H. rhodopensis may well be quenching of ROS, a mechanism that could occur in homoiochlorophyllous resurrection plants as a consequence of the retained chlorophylls and photosynthetic apparatus, especially when plants grow in open sunny habitats.