The role of protein synthesis in auxin-induced cell elongation in lupin hypocotyl segments was studied using cycloheximide. Cycloheximide inhibited protein synthesis by 9 minutes. Experiments adding cycloheximide at various times before and after indolyl-3-acetic acid are reported. Estimates of the relative amounts of growth-limiting protein(s), and a first order rate constant for the apparent turnover of the growthlimiting protein(s) were made. It was shown that there is a sizeable growth promotion by auxin after protein synthesis has essentially ceased. It is concluded that the initial phases of auxin action do not require protein synthesis but that its action depends on the existing pool of growth-limiting proteins which is rapidly depleted, and protein synthesis is then required for continued elongation.It has been shown that inhibitors of protein synthesis have a rapid effect on IAA-induced growth (1,5,9,13,16,19). This has led to the suggestion that an unstable protein, which has been called growth-limiting protein (5), is necessary for auxin-induced cell expansion. It is not possible, however, to determine from these studies with inhibitors whether auxin acts on the synthesis of GLP' or whether the requirement for protein synthesis is a secondary (albeit rapid) effect of auxin action.Other evidence indicates that auxin acts on pre-existing macromolecules and that protein synthesis is not necessary for the initial action of auxin. This is the rapid change of growth rate by: (a) the methyl ester of indolyl-3-acetic acid (21, 22); (b) high temperature at high auxin concentration (14); and (c) the initial decline in growth rate before the auxin-induced stimulation (22). Although we have tried, without success, to obtain these results with lupin hypocotyl segments, they do illustrate the point for coleoptiles at least.In this paper the quantitative study of the effect of cycloheximide leads to a similar conclusion that protein synthesis is not required for the initial action of auxin on cell elongation in lupin hypocotyl. The measurements of elongation were made every minuLte in the apparatus described by Penny (17). Briefly, a segment was held in a chamber which was held on the stage of a microscope. The desired solution flowed through the chamber, and the flow rate of solution was maintained by a Watson Marlow model MHRE flow inducer. Tris-maleate buffer, pH 6.1, 20 mm, was used throughout; the concentration of IAA (when used) was 30 pM and the concentration of CH, when used, was 10 jug/ml. The solutions were aerated and the light energy at the surface of the segments was 3 wm-2 supplied by an incandescent lamp. Temperatures, except where otherwise stated, were maintained at 28 C. There was a tendency for the temperature to increase over the course of a long experiment. but the total difference in temperature during the experiment was never more than 0.5 C. MATERIALS AND METHODS SeedlingsFor measurement of protein synthesis, groups of 120 segments were pretreated in buffer for 2 hr and then blotted a...

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The kinetics of the effects of inductive photomorphogenically active light on etiolated peas have been studied by means of time‐lapse photography. The effects noted include: (1) A light‐induced decrease in the rate of stem elongation, beginning about 6 hr after the light treatment, and ending about 18 hr later. (2) A light‐induced opening of the apical hook, beginning ca. 2–5 hr after light treatment, and reaching its peak rate ca. 6 hr later. (3) A light‐stimulated circumnutation, starting usually about 15–22 hr after the light, and resulting in a decreased period of oscillation (from ca. 86 to ca. 76 min) and an increased amplitude (from 15° total angular displacement to about 40°). (4) A promotion of terminal bud growth, known from previous work to start at about 4 hr after irradiation and to reach a peak about 12 hr later. (5) A “bobbing” movement of the apex, apparently involving reversible hook and stem oscillations, which appears to be of endogenous origin and insensitive to light. These data furnish a kinetic background against which proposed biochemical mechanisms of de‐etiolation can be assessed.

Samples of six common plant species collected in the old mining areas near Prince George, British Columbia (Canada) and Mount Amiata, Tuscany (Italy) show remarkable similarities in the variation of plant/soil Hg concentration ratio with soil Hg content irrespective of species or other biological differences. In contrast, plants sampled in the geothermally active areas of New Zealand, Hawaii and around Mount St. Helens exhibit more individuality in the concentration ratio to soil Hg relationship, but the relationships are distinctly different from the mine site specimens. This distinction is particularly evident when the same species of Equisetum and Plantago taken from these two different areas are compared. These and other data support the hypothesis that specific local environmental factors strongly influence the accumulation of Hg in plants even when the immediate soil concentrations are the same. Our findings show that some plants contain concentrations of total Hg as high as 5500 to 14000 Ixg kg-~ (dw). Experimental STUDY SITES AND PLANTSThe Cominco Hg mine at Fort St. James and the nearby city of Prince George have been described (Johnston et aL, 1975;