Antioxidant Defense during Recovery of Resurrection Plant Haberlea rhodopensis from Drought- and Freezing-Induced Desiccation

In this study, the contribution of nonenzymatic (ascorbate, glutathione) and enzymatic antioxidants (superoxide dismutase, catalase, glutathione reductase, glutathione S-transferase) in the first hours of recovery of the resurrection plant Haberlea rhodopensis from drought- and freezing-induced desiccation was assessed. The initial stage of recovery after desiccation is critical for plants, but less investigated. To better understand the alterations in the activity of antioxidant enzymes, their isoenzyme patterns were determined. Our results showed that ascorbate content remained high during the first 9 h of rehydration of desiccated plants and declined when the leaves′ water content significantly increased. The glutathione content remained high at the first hour of rehydration and then strongly decreased. The changes in ascorbate and glutathione content during recovery from drought- and freezing-induced desiccation showed great similarity. At the beginning of rehydration (1–5 h), the activities of antioxidant enzymes were significantly increased or remained as in dry plants. During 7–24 h of rehydration, certain differences in the enzymatic responses between the two plant groups were registered. The maintenance of a high antioxidant activity and upregulation of individual enzyme isoforms indicated their essential role in protecting plants from oxidative damage during the onset of recovery.

Analysis of the complete mitochondrial genome sequence of the resurrection plant Haberlea rhodopensis

Haberlea rhodopensis is a paleolithic tertiary relict species that belongs to the unique group of resurrection plants sharing remarkable tolerance to desiccation. When exposed to severe drought stress, this species shows an ability to maintain structural integrity of its deactivated photosynthetic apparatus, which easily reactivates upon rehydration. In addition to its homoiochlorophyllous nature, the resurrection capability of H. rhodopensis is of particular importance to the global climate change mitigation. In this study, we sequenced, assembled, and analyzed the mitochondrial (mt) genome of H. rhodopensis for the first time. The master circle has a typical circular structure of 484 138 bp in length with a 44.1% GC content in total. The mt genome of H. rhodopensis contains 59 genes in total, including 35 protein-coding, 21 tRNAs, and 3 rRNAs genes. 7 tandem repeats and 85 simple sequence repeats (SSRs) are distributed throughout the mt genome. The alignment of 20 plant mt genomes confirms the phylogenetic position of H. rhodopensis in the Lamiales order. Our comprehensive analysis of the complete mt genome of H. rhodopensis is a significant addition to the limited database of organelle genomes of resurrection species. Comparative and phylogenetic analysis provides valuable information for a better understanding of mitochondrial molecular evolution in plants.

QUANTITATIVE ASSESSMENT OF ANISOCOTYLY IN HABERLEA RHODOPENSIS AND RAMONDA MYCONI

Anisocotyly, the unequal development of cotyledons post germination, is a unique trait observed only in Old World Gesneriaceae (Lamiales). New World Gesneriaceae have isocotylous seedlings. In both Old and New World Gesneriaceae, cotyledons initially grow equally for a short period just after germination. In the New World species, both cotyledons cease their growth at the same time early on, whereas in Old World species one cotyledon continues to expand to become a macrocotyledon while the other withers away. In this study, cotyledon growth was observed in two European Old World Gesneriaceae: Haberlea rhodopensis and Ramonda myconi. The results were compared with those for the typical anisocotylous species Streptocarpus rexii and the typical isocotylous species Corytoplectus speciosus. We found that the cotyledon growth patterns in Haberlea rhodopensis and Ramonda myconi were intermediate between the typical anisocotylous or isocotylous species. Haberlea rhodopensis and Ramonda myconi showed irregular growth patterns, with some plants being slightly anisocotylous but most being isocotylous. The developmental basis for the residual anisocotyly, the extended basal meristem activity in the macrocotyledon, appeared to be identical in the European species to that in the typical Old World Streptocarpus rexii but weakly expressed, rare and terminated early. In conclusion, European Gesneriaceae retain a reduced anisocotylous growth that may be linked to their early plumule development.