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PHOTOREGULATION OF LOGARITHMIC FLUENCE‐RESPONSE CURVES FOR PHYTOCHROME CONTROL OF CHLOROPHYLL FORMATION IN PISUM SATIVUM L *
Author(s) -
Raven C. W.,
Shropshire W.
Publication year - 1975
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.1751-1097.1975.tb06700.x
Subject(s) - etiolation , phytochrome , pisum , sativum , chlorophyll , botany , biology , far red , fluence , biophysics , red light , horticulture , physics , optics , biochemistry , laser , enzyme
— Logarithmic fluence‐response curves for red (660 nm) and far red (730 nm) light induction of rapid chlorophyll a (Chi a ) accumulation in pea seedlings ( Pisum sativum L. cv. Early Alaska) indicate extreme light sensitivity in dark‐grown seedlings. The energy requirement for onset of 660 nm light induction is less than 20 μJ m ‐2 and for 730 nm is about 1 mJ m ‐2 . De‐etiolation produced by a saturating exposure of red light (3–8 kJ m ‐2 ) 24 h prior to the construction of the logarithmic fluence‐response curves resulted in approximately a 3 fold increase in slope for 660 nm light, whereas the energy requirement for onset of induction shifted to about 100 mJ m ‐2 . In such de‐etiolated plant material, far red applied at low incident energies almost completely lost its inductive capacity. The inductive capacity of far red applied as high irradiance over a long period of time (16h) appeared not to be affected by the de‐etiolation treatment. Reciprocity failed for both dark‐grown and de‐etiolated seedlings upon exposures exceeding 1,000s. Nearly identical results were obtained for seedlings de‐etiolated by red exposures immediately followed by far red (4.8 kJ m ‐2 ), although this treatment did not lead to any significant decrease in spectrophotometrically measurable phytochrome. Therefore, no simple correlation was observed between the level of phytochrome present and the sensitivity of seedlings for induction of rapid Chl a accumulation. In order to explain this apparent phytochrome paradox the possibility was tested and ruled out for changes in the degree of synchronization of seedlings, or for induction of some sort of circadian rhythmicity in light sensitivity being involved. In addition, no correlation was observed between induction of morphogenic development and changing light sensitivity. These results formed, therefore, additional support for a model for phytochrome action involving its intracellular transport and local concentration during the process of seedling de‐etiolation.