Memorizing of Gravistimulus in apical protonemal cells of the moss Ceratodon purpureus

Moss protonemata sense and realize gravity by apical cells of stolones, the function of gravisensors being performed by amyloplasts which sediment on lower side of the cell wall. The pattern of amyloplasts distribution and dynamics of their sedimentation were described in detail in different moss species (Sack, 1991; 1997; Young, Sack, 1992; Chaban et al., 1998; Schwuchow et al., 2002). The pathways of gravity transduction to growth process remain, however, still-uncleared (Sack, 1997; Kern et al., 2001; Schwuchow et al., 2002). The processes of the perception and transduction of the gravistimulus in the apical cells were uncoupled experimentally. It has been shown in our experiments that susception of gravistimulus takes place under conditions of low temperature, while the growth of apical cells is blocked. Being, however, transferred into usual conditions gravistimulated protonemata realize their gravitropic bend. To receive such effect gravistimulation of different duration, from 15 min to 24 h, was conducted at 2⁰C and the gravistimulated protonemata were then clinorotating for 8-20 h. Gravistimulus manifested itself in bending of tip zone of the stolons only in case of 8-20 h gravistimulation. 15-30 min was found to be uneffective, the stolons bends were not formed. Gravistimulation for 1 h and more proportionally the increased the bend angle. Probably, the gravistimulus may retain in cells for comparatively long time under low temperature being realized only under favourable conditions. The participation of growth substances, in particular that of IAA, in realization of gravistimulus in tip growing protonemal cells remains not quite clear. It has been established that realization of gravistimulus can be experimentally blocked by the inhibitors of calcium channels and pumps, respectively by 0.1--1.0 μ M of verapamil and 1.0--10.0 μ M of sodium orthovanadate. 0.1--1.0 μ M of exogenous IAA and α -NAA did not significantly influence the growth and gravi-bending of apical protonemata cells. 3,0 -- 30.0 μ M of phytotropin, however, strongly inhibited gravity dependent bending and only insignificantly influence the growth rate of apical protonema cells. Cytochalazin was observed to delay strongly the gravitropic bending not affecting the protonemata growth. On the grounds of conducted investigations it was concluded that the apical cells could retain gravistimulus rather long, right up to arising of proper intracellular conditions. Realization of gravistimulus is caused by apical-basal gradient of Ca²⁺ and IAA polarizing the processes of cell growth as well as by cytoskeleton signal system (Fidman et al., 2003).