PLANT PHYSIOLOGY , Vol 102, Issue 2 339-344, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
The Altered Gravitropic Response of the lazy-2 Mutant of Tomato Is Phytochrome Regulated
J. C. Gaiser and T. L. Lomax
Department of Botany and Plant Pathology and The Center for Gene Research and Biotechnology, Oregon State University, Corvallis, Oregon 97331-2902
Shoots of the lazy-2 (lz-2) gravitropic mutant of tomato (Lycopersicon
esculentum Mill.) have a normal gravitropic response when grown in the
dark, but grow downward in response to gravity when grown in the light.
Experiments were undertaken to investigate the nature of the light
induction of the downward growth of lz-2 shoots. Red light was effective at
causing downward growth of hypocotyls of lz-2 seedlings, whereas treatment
with blue light did not alter the dark-grown (wild-type) gravity response.
Downward growth of lz-2 seedlings is greatest 16 h after a 1-h red light
irradiation, after which the seedlings begin to revert to the dark-grown
phenotype. lz-2 seedlings irradiated with a far-red light pulse immediately
after a red light pulse exhibited no downward growth. However, continuous
red or far-red light both resulted in downward growth of lz-2 seedlings.
Thus, the light induction of downward growth of lz-2 appears to involve the
photoreceptor phytochrome. Fluence-response experiments indicate that the
induction of downward growth of lz-2 by red light is a low-fluence
phytochrome response, with a possible high-irradiance response component.
