Adaptation processes enable phototropism of Phycomyces to operate over a 10‐decade range of blue‐light intensity (1 nW m−2‐10 W m‐2). To investigate the influence of calcium on dark adaptation, the phototropic latency method was employed with the modification that sporangiophores were temporarily immersed in solutions containing CaCI2 or LaCI3 Following such treatment, the time course of bending was found to have two components with distinct latencies and bending rates. After immersion in darkness for 30 min in LaCI3 solution or 1 h in a solution of CaCI2 MgCI2, or the calcium chelator EGTA, each sporangiophore was adapted to a blue light beam (1 W m‐2) for 45 min by rotation around its vertical axis. Cessation of rotation defined the onset of the phototropic stimulus, at which time the intensity was reduced by as much as 103‐fold. For a 102‐fold reduction (to 10−2 W m−2), immersion in CaCl2 (10–100 μM) reduces the latency 13 min for the early bending component and 18 min for the late component, whereas treatment with the calcium‐channel blocker lanthanum (0.1–11 μM LaCI3) increases the latency 12 min for the early component and 13 min for the late component. EGTA (10 μM) also had an inhibitory effect, increasing the latency of the first and the second components by 7 and 10 min, respectively. In experiments performed similarly, but without the light adaptation treatment after immersion, no differences between calcium‐treated and control sporangiophores were found. The bending rates of both components show only a weak dependence on calcium. Finally, experiments with MgCI2 (10–100 μM) were indistinguishable from control experiments, indicating that the divalent cation Mg+2, unlike Ca+2, had no effect on latency or bending rate. The results show that calcium affects the phototropic latency, and may function in the adaptation processes for Phycomyces phototropism.
|Original language||English (US)|
|Number of pages||9|
|Journal||Photochemistry and Photobiology|
|State||Published - Nov 1992|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry