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Coleoptile Growth: Variation in Elongation Patterns of Individual Coleoptiles

A. LIPTAY and D. DAVIDSON
Annals of Botany
New Series, Vol. 35, No. 143 (November 1971), pp. 991-1002
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/42751986
Page Count: 12
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Coleoptile Growth: Variation in Elongation Patterns of Individual Coleoptiles
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Abstract

Etiolated coleoptiles of barley differ in rate of growth and the time during germination when most rapid growth occurs. The final heights of coleoptiles fall into these classes: (1) short,~10mm, (2) medium,~20mm, and (3) tall, > 30 mm. Tall coleoptiles are produced by coleoptiles that show rapid growth,~800 µ/h, in one of three periods, i.e. around 33 h, or 45 h or 70 h. The time when rapid growth occurs is, therefore, a critical characteristic by which we can distinguish three types of coleoptiles. Medium-height coleoptiles result from fairly rapid growth,~400 µ/h, around either 45 h or 70 h. Small coleoptiles form a class that grows very slowly throughout the whole period of germination. Coleoptiles of uniform height at any time do not have identical growth-rates; we suggest they are in different physiological states. Variation in growth-rate parallels the variation in response of coleoptile segments to IAA. When coleoptiles of similar growth-rate and height are selected, segments show a repeatable stimulation of elongation when treated with 10⁻⁵ M IAA. Two separate mechanisms that initiate elongation appear to control coleoptile growth; one produces the initial growth seen in all coleoptiles and the second initiates rapid growth and operates at different times in different coleoptiles.

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