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Positive and Negative Tropic Curvature Induced by Microbeam Irradiation of Protonemal Tip Cells of the Moss Ceratodon purpureus
Author(s) -
Lamparter T.,
Kagawa T.,
Brücker G.,
Wada M.
Publication year - 2004
Publication title -
plant biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 1435-8603
DOI - 10.1055/s-2003-44719
Subject(s) - biology , moss , microbeam , botany , physics , optics
The photoreceptor phytochrome mediates tropic responses in protonemata of the moss Ceratodon purpureus. Under standard conditions the tip cells grow towards unilateral red light, or perpendicular to the electrical vector of polarized light. In this study the response of tip cells to partial irradiation of the apical region was analysed using a microbeam apparatus. The fluence response curve gave an unexpected pattern: whereas a 15‐min microbeam with light intensities around 3 μmol m ‐2 s ‐1 induced a growth curvature towards the irradiated side, higher light intensities around 100 μmol m ‐2 s ‐1 caused a negative response, the cells grew away from the irradiated side. This avoidance response is explained by two effects: the light intensity is high enough to induce photoconversion into the active Pfr form of phytochrome, not only on the irradiated but also on the non‐irradiated side by stray light. At the same time, the strong light on the irradiated side acts antagonistically to Pfr. As a result of this inhibition, the growth direction is moved to the light‐avoiding side. Such a Pfr‐independent mechanism might be important for the phototropic response to distinguish between the light‐directed and light‐avoiding side under unilateral light.