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 119 (Marschall et al., 2000).High NPQ is suppressed by DTT. This suggests that high levels of xanthophyll-cycle-mediated photoprotection similar to that of higher plants, extra excitation energy dissipating as heat. PPFD response patterns in bryophytes having complex ventilated photosynthetic systems are similar to vascular plants (Figure 6). Relative electron flow rate (REFR) and C0

2-uptake curves for sunexposed Tortula ruralis show that C0

2-uptake accounts for ~ 60% of the low PPFD saturation value. This means the rest of the energy goes to other electron sinks (Figure 7). REFR responses for two contrasting species in various gas mixtures were the folio wings: the sun-exposed Schistidium apocarpum shows little difference in REFR between normal and C0

2-free air and N

2+l% C0

2. It means 0

2 and C0

2 are largely interchangeable as electron sinks. REFR is very low in pure N

2. 1-qP saturates at ~ 0.5 in the treatments that provide an electron sink, but rapidly rises to ~ 1.0 in pure N

2. NPQ quickly reaches a steady value of ~ 6.0 in pure N

2, but continues to rise with PPFD in the other treatments. The shade-adapted Plagiomnium undulatum appears less able to use C>2 as electron sink, or to generate high NPQ at high irradiance. The highest NPQ (~ 4.0) developed in N

2. REFR is markedly depressed in C0

2free air. 3.3 Desiccation tolerance, as an adaptive strategy Desiccation tolerance is a very widespread phenomenon among living organisms ((occurs among microorganisms, fungi, algae, lichens, bryophytes, vascular plants (it is uncommon in vegetative tissues, but characteristics in spores and seeds), in animal groups: invertebrates)). It presents independently from geological times in the plant kingdom, common and characteristics, but not universal in bryophytes. The origin of desiccation tolerance can be explained from the intermittent availability of water to the plant. Between two periods of precipitation, bryophytes can reach full turgor in many ways: storing sufficient water to extend to moist periods with the help of their morphological features; from dewfall, cloudmist, interception, precipitation. Bryophytes are much more tolerant of high (or very low) temperatures dry than wet. Species of constant moist and shade are the most sensitive to desiccation. The rate, the speed of desiccation and the light condition is very important in the recovery of photosynthesis upon rehydration. 3.4 UV-B-tolerance in bryophytes The effect of UV-B is heavier with desiccation. An effective antioxidant system, different anatomical and morphological features of the species and