Photobiology of Phytochrome-Mediated Growth Responses in Sections of Stem Tissue from Etiolated Oats and Corn

Abstract

The far-red reversibility of the phytochrome-controlled stimulation of elongation of coleoptile sections by low fluence red light has been characterized in subapical coleoptile sections from dark-grown Avena sativa L., cv Lodi seedlings. The fluence dependence of the far-red reversal was the same whether or not the very low fluence response is also expressed. The capacity of far-red light to reverse the red lightinduced response began to decline if the far-red light was given more than 90 minutes after the red irradiation. Escape was complete if the far red irradiation was given more than 240 minutes after the red irradiation.Sections consisting of both mesocotyl and coleoptile tissue from darkgrown Avena seedlings were found to have physiological regulation of the very low fluence response by indole 3-acetic acid and low external pH similar to that seen for sections consisting entirely of coleoptile tissue. The fluence-dependence of the red light-induced inhibition of mesocotyl elongation was studied in mesocotyl sections from dark grown Zea mays L. hybrid T-929 seedlings. Ten micromolar indole 3-acetic acid stimulates the control elongation of the sections, while at the same time increasing the sensitivity of the tissue for the light-induced inhibition of growth by a factor of 100.In previous papers, the physiology of phytochrome-mediated stimulation of coleoptile elongation induced by red light, both in terms of the nature of the change in elongation rate (15), and the nature of the coupling of the phytochrome signal to the response (13, 14) were described. A major finding was that alterations in the physiological state of the coleoptile cells can alter phytochrome signal transduction processes considerably. Decreasing the extracellular pH in section tissue caused the sensitivity of the sections to R3 to increase by as much as a factor of 10,000 (13,14). Certain assumptions about the responses seen have been made in interpreting the results, and assessing their significance. In the main, these assumptions have been: (a) that the performance of isolated coleoptile sections is relevant to the behavior of intact seedlings, (b) that the physiological altrations brought about by the changes in the extracellular milieu affect all of the cells of the section relatively equally, and (c) that the alterations in apparent light sensitivity of the sections is in fact an alteration in the properties of phytochrome signal transduction.

Phytochrome Control of Specific mRNA levels in Developing Pea Buds

“…Seed ofPisum sativum L. var Alaska were imbibed and grown in absolute darkness for 6 d as described previously (7,9). The light sources used have been described previously (7,9,14). For time course experiments, the 6 d old seedlings were irradiated with a 100 s pulse of R light with a total fluence of I03 Oimol m-2 (or, for controls, manipulated in the same way but given no light treatment).…”

Phytochrome Regulation of Greening in Pisum

“…The time courses for accumulation in response to a saturating LF pulse were also different for the various transcripts (17). Of all the transcripts studied, the Cab mRNA was the only one whose fluence-response behavior resembled that of greening (15,16 (30). The FR fluence rate was measured with a thermopile (Eppley) and corrected for IR radiation passed by a Corning 7-56 800 nm cutoff filter).…”

Maize mesocotyl: Role in response to stress and deep‐sowing tolerance

“…Previous studies demonstrated that red light (R) inhibited the elongation of the etiolated mesocotyl by reducing the auxin supply from the coleoptile unit; elongation was fluence‐dependent, and phytochrome was responsible for the elongation (Vanderhoef et al , Shinkle ; Barker‐Bridgers, Ribnicky, Cohen, & Kutschera, ). Compared to the rapid progress in dissecting the role of light signalling in the hypocotyl elongation of Arabidopsis, the mechanism of light signals affecting maize mesocotyl elongation remains largely elusive, especially the components of light signalling and the roles of individual phytochromes.…”