Studies on Extension Growth in Coleoptile Sections

Abstract

One of the problems involved in carrying out large-scale coleoptile cylinder straight growth assays is the effect of coleoptile age upon the behaviour of the sections. This effect, as measured both by the length of coleoptile and the time from sowing the seeds, has been investigated by an examination of the growth of sections cut from coleoptiles of several length grades on five occasions 6–10 hours apart. The response of these sections to a range of concentrations of β-indolylacetic acid (IAA) was followed during the period of growth to ascertain the most suitable time for measurement of sections in a routine test. A number of general trends associated with coleoptile age (whether measured by length, or time from planting) were observed in amount of growth, growth-rate, period of growth, and sensitivity. It is suggested that these characteristics are associated with the amount of the total growth already made by the parent coleoptile at the time of taking the section, and also that the section exhibits an ‘intrinsic growth-rate’ related to the growth-rate of the coleoptile at the time the section is cut. A period of growth of 17–20 hours seems satisfactory for routine tests except where very young coleoptiles are used; in this case growth less than that in water is sometimes observed in very low concentrations of IAA.