THE ACTION OF GRAVITY IN AGRAVITROPIC ZEA PRIMARY ROOTS - EFFECT OF GRAVISTIMULATION ON THE EXTRACELLULAR FREE-CA2-MM APICAL ROOT-TIP IN THE DARK( CONTENT IN THE 1)

The action of gravity stimulation in darkness was examined in agravitr opic primary roots of Zea mays L. (cv. Golden Cross Bantam 70). Conten ts of diffusible and nitric-acid-extractable Ca2+ in 1-mm apical tips of roots gravistimulated in the dark were measured by flow-injection a nalysis as free Ca2+ and bound Ca2+, respectively. The free-Ca2+ conte nt increased transiently, reaching a maximum 0.5 h after gravistimulat ion. This transient increase was also observed when gravistimulation w as applied by changing the orientation of the roots back from horizont al to vertical again. On the other hand, the bound-Ca2+ Content decrea sed transiently following gravistimulation. Furthermore, when the root caps were treated with 10 mM 2-(N-morpholino) ethane-sulfonic acid bu ffer, the elevation of free Ca2+ following gravistimulation was preven ted. These results indicate that gravity perception and the initial tr ansduction steps proceed in the dark, and moreover that the elevation of free Ca2+ brought about by the interaction of Ca2+/H+ in the apopla st of root tips may be involved in transmission of the gravity signal.