Reversible in vivo cellular changes occur during desiccation and recovery: Desiccation tolerance of the resurrection filmy fern Hymenophyllum dentatum Cav.

Resumo

The present work explores in vivo physiological, morphological and chemical features during full hydration, desiccation and rehydration of the filmy fern Hymenophyllum dentatum with two main objectives: 1) to get further insight about the mechanisms underlying its desiccation tolerance, and 2) to understand how this plant manages mechanical stress induced by water loss and recovery. With these purposes, physiological (relative water content and Fv/Fm chlorophyll fluorescence parameter), morphological (Confocal Laser Scanning Microscopy and 3D reconstruction) and chemical (FTIR microspectroscopy) data were obtained and compared between fully hydrated, desiccated and rehydrated tissues of H. dentatum. Remarkable changes in cell architecture and chemical composition were observed in vivo in desiccated leaves. Cells were smaller, showed a collapsed general appearance, and were delimitated by apparently folded cell walls. Marked changes in chloroplasts location and decrease in the number of active chloroplasts were also evidenced. Chemical experiments showed that changes in the secondary structure of proteins and in the polysaccharide composition of the cell wall occur in desiccated cells. All changes were rapidly reversed upon rehydration. This study shows that H. dentatum presents an extreme case of desiccation tolerance, able to withdraw severe, rapid and consecutive dehydration/rehydration induced stress by the function of constitutive systems of protection and reparation, in which cell wall folding plays a relevant role as a protective system against mechanical and oxidative stress. Besides, H. dentatum is proposed as an excellent plant model for the study of dissection tolerance such as one cell layer fern, auto-fluorescence of cellular compartments, and simple long term storage under laboratory conditions, among others.