Studies Of Structure And Function Of Conducting Tissues In Two Mosses

Water moves down a water potential gradient, hydration is essential to cellmetabolism. Plant cell walls are a porous weave that act much like a wick,evaporation creates capillary suction within the cell wall pores, causing tension to betransmitted down the water column in the tracheary element, it is the evaporation thatdrives water movement. The frictional resistance to water transport is significantlyreduced when water travels through hollow tracheary element rather than thepathways that characterize symplastic water movement. Ectohydric water transport iscommon in bryophytes. Bryophyte plants represent transition from aquatic toterrestrial. Gametophyte is dominant generation in the life cycle and can liveindependently, sporophyte can only be parasitic on the gametophyte. Waterconduction of Bryophyte plants can be divided into three types：endohydric，ectohydric and mixohydric. Endohydric mosses possess a well-developed internalwater-conducting tissues (conducting strands), these conducting strands are composedof specialized hydroids. Polytrichaceae is typical endohydric mosses. Waterconduction of most mosses are ectohydric. Specialized internal water-conductingstrands are absent in ectohydric mosses, these mosses rely primarily on externaltransport of water and can absorb water over almost the entire plant surface.Ectohydric mosses mainly utilize capillary conduction systems to absorb water, retainhydration and conduct water, capillary conduction systems display many forms, suchas the gaps between the leaves.The structure of conducting tissues in Pogonatum inflexum（Lindb.）Lac. andPhyscomitrella patens ( Hedw. ) B. S. G. were studied by using light microscope andScanning electron microscope（SEM），the rate of ascent of water in water conductingtissues of two mosses were measured by tracing the distribution of dyes. Hydroidswalls and cortex cells walls of P. inflexum are investigated by using FourierTransform Infrared Microspectroscopy (FTIR) , the effects of 1-naphthlcetic acid（NAA）and 6-Benzylaminopurine（6-BA）on the development of P. patens are studied too. The results show as follows : (1) In P. inflexum stem，thewater-conducting tissues are consist of hydroids，the thick sidewalls of hydroidscontain polyphenolic compounds, the oblique thin end walls have smooth imperforatesurface; (2) In P. patens stem, the central conducting tissues show low degree ofdifferentiation and contain chloroplasts, these tissues are composed of cells with smalldiameters, plasmodesma-derived pores perforate the end walls of these central cellswith thin sidewalls; (3) The rate of conduction of the acid fuchsin solution in P.inflexum is 21 times faster than that in P. patens approximately. P. inflexumrepresents endohydric mosses, while P. patens is an ectohydric moss; (4) Hydroidswalls of P. inflexum contain hemicellulose, and probably contain cellulose and pectin;cortex cells walls contain hemicellulose and probably contain cellulose and pectin; (5)NAA can promote the growth of P. patens protonema; the higher the concentration ofNAA is, the stronger inhibition of plant growth is. 0.1mg/l 6-BA can induce P. patenscallus significantly. three NAA tests and three 6-BA tests have faint effects on thedevelopment of P. patens conducting tissues.