The elongation of rice shoots(Oryza salivaL.) exposed to various light conditions was measured using angular movement transducers. Plants growing in continuous light responded to a sudden increase in light fluence rate with a pronounced decrease in the rate of elongation. The growth rate returned to the initial steady state within 15-60 min, depending on the difference in fluence rate between the continuous and the supplemental light. When the fluence rate was reduced to its original level, the elongation rate rose transiently before returning to the initial value. The inhibition of elongation was fluence dependent, and blue and red light were more effective in reducing the elongation rate than was green or infrared irradiation. Irradiation of a single tiller affected also other tillers of the same plant which were shielded from the light. Measurements of transpiration and water uptake by whole plants and of leaf temperatures indicated that the transient changes in growth rates were caused by perturbations in the water balance of the plant.
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