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

Acta Acad. Paed. Agriensis, Sectio Biologiae XXV (2004) 113-126 Aspects of stress tolerance in bryophytes Marschall, M.

1 and Proctor, M. C. F.

2 ' Department of Plant Physiology, Eszterházy Károly College, H-3301 Eger, Leányka út 6-8, Hungary. 2 School of Biological Sciences, University of Exeter, Washington Singer Laboratories, Perry Road, Exeter, EX4 4QG, UK. Corresponding author, marschal@ektf.hu Abstract. To understand the various physiological processes and stress responses of bryophytes comparing with higher plants' reactions it is essential to know the actual water status of the bryophyte tissue. Cell water relations in bryophytes essentially are the same as those of other plant cells and can be described by the 'Höfler diagram'. Surface water amount can vary widely without affecting cell water status, which can result in difficulties in expressing precise actual water content (WC). The knowledge of WC at full turgor is principal to calculate RWC. The different adaptive types of bryophytes and higher plant cells respond similarly to water deficit. Bryophytes include but are not inherently shade plants. Shade-loving bryophytes saturate at a PPFD of 100-300 pmol m

2 s"

1, responses are similar to those of the shade-loving vascular plants. Sun-exposed bryophytes saturate at a PPFD of 1000 pmol m

2 s"

1. In this species REFR rises almost linearly with increasing irradiance and they show extraordinary high levels of NPQ, which can be suppressed by DTT. 1-qP generally stabilises at around 0.3 to 0.4. Responses of this kind are found in a taxonomically and ecologically diverse range of bryophytes. PPFD response patterns in bryophytes having complex ventilated photosynthetic systems are similar to vascular plants'ones. In sun-exposed bryophytes 0

2 and C0

2 are largely interchangeable as electron sinks and C0

2-uptake accounts for ~ 60% of the low PPFD saturation value. Shade-adapted species appears less able to use 0

2 as electron sink, or to generate high NPQ at high irradiance. In bryophytes the strongest limiting stress factors are desiccation and high temperature, and the last one can be lethal if the tissue is metabolically