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 115 Conflicting requirements of water conduction and storage and free gas exchange for photosynthesis (molecular diffusion is slower in water than in air by a factor of about 10

4) are achieved in various ways in bryophytes: — water-repellent cuticular material on leaf surfaces; — granular or crystalline epicuticular vax (glaucous-looking endohydric species) on surfaces; — shoots with closely overlapping concave leaves: inner faces for water storage, outer ones for free gas exchange (kept in dry); — papilla/mamilla covered leaf surfaces, apices remaining dry, interstices for water (interstices between them provide a countinuous network of water-conducting channels); — complex ventilated photosynthetic tissue (Polytrichales leaves, Marchantiales thalli); the leaves of Polytrichales and thalli of Marchantiales have complex ventilated photosynthetic tissues paralleling leaves of vascular plants (pores and chambers) with preventing water loss (surface vaxes, water-repellent edges of pores and stomatas); increased area for C02-uptake. Table 1. Comparison of characteristics are important in water relations in bryophytes and vascular plants Bryophytes Vascular plants lack of roots, rhizoids water uptake in roots ectohydry: external water movement in capillary spaces endohydry: some bryophytes have well-developed internal conducting structures (in a limited number of large acrocarpous mosses), that is not approaching vascular plant transpiration stream myxohydry: some combination of the two, balance between them, none of them is predominant poikilohydry, internal water conduction (xylem) ectohydry: external water movement in capillary spaces endohydry: some bryophytes have well-developed internal conducting structures (in a limited number of large acrocarpous mosses), that is not approaching vascular plant transpiration stream myxohydry: some combination of the two, balance between them, none of them is predominant poikilohydry, root pressure ectohydry: external water movement in capillary spaces endohydry: some bryophytes have well-developed internal conducting structures (in a limited number of large acrocarpous mosses), that is not approaching vascular plant transpiration stream myxohydry: some combination of the two, balance between them, none of them is predominant poikilohydry, waterproof and water-repellent cuticle in leaves and young stems lack of complex water movement, relatively diffuse water movement (there is no unified stream) cuticular and stomatal transpiration streams stomata in a few cases, their role is not relevant complex water movement