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INVOLVEMENT OF PHYTOCHROME IN LIGHT CONTROL OF STEM ELONGATION IN CUCUMBER ( Cucumis sativus L.) SEEDLINGS
Author(s) -
DRUMMHERREL H.,
MOHR H.
Publication year - 1991
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1991.tb03667.x
Subject(s) - phytochrome , etiolation , hypocotyl , cucumis , elongation , seedling , darkness , far red , botany , biology , blue light , photomorphogenesis , biophysics , red light , horticulture , physics , mutant , biochemistry , optics , enzyme , arabidopsis , gene , materials science , ultimate tensile strength , metallurgy
— Stem growth in cucumber ( Cucumis sativus L.) is strongly affected by blue light (B). The pending problem has been to what extent the action of B is related to phytochrome action. Hypocotyl growth in the etiolated cucumber seedling responds weakly to 5 min red (R) and B pulses whereas far‐red (FR) and long wavelength far‐red (RG9) light pulses have no effect. Blue and RG9‐light pulses were given in sequence or 5 min B was applied simultaneously with high fluence rate R (phytochrome photoequilibrium, Pfr/Ptot =∼ 0.8) or RG9‐light (? 0.01) to maintain a high or low during application of the B pulse. The results show that there is no expression of a B effect if the level of Pfr is kept low. A specific effect of B probably occurs but cannot be expressed in the absence of Pfr. Hypocotyl elongation is strongly affected by continuous R, FR and B. Light ← dark transfer experiments suggest that growth in darkness of seedlings de‐etiolated by R or B is controlled by phytochrome through a threshold mechanism. The results of dichromatic experiments (long wavelength far‐red light, 756 nm, applied simultaneously with B or R) show that the action of B on axis elongation is related to the level of Pfr, even in long‐term light. When > 0.01, the action of B is largely abolished. The residual B effect may not be attributed to a phytochrome‐independent action of B on axis elongation, because a small residual effect is also observed with dichromatic R/756 nm‐light.