Az Eszterházy Károly Tanárképző Főiskola Tudományos Közleményei. 2004. Sectio Biologiae. (Acta Academiae Paedagogicae Agriensis : Nova series ; Tom. 25)

Marschall, M. and Proctor M. C. F.: Aspects of stress tolerance in bryophytes

Aspects of Stress Tolerance in Bryophytes 121 3.6 Desiccation tolerance mechanisms in bryophytes What are the factors that enable a plant to be tolerant of desiccation? Cell structure that can lose most of its water without disruption, and membranes that retain the essentials of their structure in the dry state or are readily and quickly reconstituted on remoistening. In vascular plants under desiccation or/and extreme temperature macromolecules of cytoplasm stabilized by compatible solutes (carbohydrates, polyols, proteins) (= 'molecular packaging') producing a vitreous phase. Soluble carbohydrate pool, including sucrose, fructan and polyols, have a great importance in certain bryophyte genera, and a similar role has been proposed in desiccation tolerance (Marschall et al, 1998). The storage carbohydrates are 'membrane compatible' (Marschall et al.

, 1998). The soluble carbohydrates did not show large responses to changes in the environment suggesting that they are well-buffered and available to act as desiccation protectants. Photosynthetic apparatus is homoiochlorophyllous, does not disintegrate, recovery is quick and complete upon rehydration (Tuba et al., 1998). Protein synthesis also recover quickly (Oliver et al., 1998) in desiccation-tolerant species. Their antioxidant system protects them against ROS during desiccation and following rehydration. 4. Summary Intermittent availability of water keeps up photosynthesis and growing in bryophytes. The amount of external water can vary widely without affecting the water status of the cells. In dry period they are metabolically inactive. Their desiccation tolerance represents an 'escaping drought' strategy, based on moistly constitutive mechanisms. The preservation of photosynthetic system and chloroplast structure wholly during desiccation, instead of de novo synthesis, seems to be an effective mechanism with using repair systems as well. The newest research line focusing on the inducible mechanisms can enrich our knowledge on desiccation tolerance. It can be stated that bryophytes are not a primitive precursors of vascular plants, but the diverse and highly evolved representatives of an alternative adaptation strategy.