Phytochrome Control of Longitudinal Growth and Phytochrome Synthesis in Maize Seedlings

Abstract

The active, far‐red light absorbing, form of phytochrome was found to inhibit growth and phytochrome levels in the mesocotyl and coleoptile of 4‐ to 5.5‐day‐old seedlings of Zea mays L. Short, low‐irradiance red or far‐red light treatments were used to produce different proportions of active phytochrome at the end of highdirradiance white‐light periods, which left different levels of total phytochrome in the plants. After light treatments which left relatively high levels of spectrophotometrically assayable phytochrome in the seedlings, apparent phytochrome synthesis in the subsequent dark period was low regardless of the proportions of each form of the pigment present at the beginning of the dark period. In light treatments producing relatively low levels of assayable phytochrome, levels of apparent phytochrome synthesis in both red and far‐red treatments and differences between apparent synthesis in red and far‐red treatments were maximal. No simple correlation was found between growth and apparent phytochrome synthesis. However, growth and total phytochrome levels were positively correlated in both organs. Using a subtractive method of correlation, in which only phytochrome effects were plotted, strong linear relationships between phytochrome levels or longitudinal growth and Pfr levels were found in those light treatments leaving greater than 8% of dark control levels of phytochrome in the tissues. Using this technique non‐linear, inverse relationships between Pfr and apparent phytochrome synthesis was found, indicating that modes of phytochrome control over phytochrome synthesis and growth differ. Our results are consistent with the view that in vivo assays of “bulk’ phytochrome reflect levels and states of the physiologically active phytochrome fraction under our experimental conditions in maize.

A Kinetic Analysis of Phytochrome Controlled Mesocotyl Growth in Zea mays Seedlings

“…Our results that the exposure of etiolated maize seedlings to W increases the responsiveness of mesocotyl extensive growth to phytochrome control, is in agreement with the results of Duke et al (4). Maximum responsiveness is after about 2.5 to 3 h of W. With completely etiolated seedlings, the inhibitory effects of R are not photoreversible by low intensities of FR (10,19), but requires FR fluences, about three orders of magnitude more than that reported here.…”

“…However, Duke et aL. (4) in studies made with maize seedlings given a prior W irradiation, and Vanderhoef et al (19) working with maize seedlings which had received only 5 min R, found no such recovery. In studies with etiolated oat seedlings given a brief R, no recovery was found (14,15).…”

Phytochrome Responses to End-of-Day Irradiations in Light-grown Corn Grown in the Presence and Absence of Sandoz 9789

“…One layer of 3-mm thick "black" Plexiglas (FRF 700, Westlake Plastics, Lenni Mills, Pa.) blocked radiation with wavelengths shorter than 700 nm. When R reversibility of the effects of end-of-day FR was tested, R was provided by 4 Sylvania warm-white fluorescent bulbs (F20T 12WW). The red filter was a single layer of red Plexiglas (Rohm and Haas No.…”

Light or Ethylene Treatments Induce Transverse Cell Enlargement in Etiolated Maize Mesocotyls

“…Both responses occur primarily as changes in growth pattern of the tissues in the meristematic and cell enlarging regions of the mesocotyl near the coleoptilar node (4,12,13,21), although some inhibition of elongation can occur in more mature tissues (4,12). Inhibition of mesocotyl elongation can be induced by short-time exposures (<5 min) to red light of low total fluence, and the induction exhibits some red/far red reversibility (13).…”

“…This swelling response was an allor-none response, and the fraction of the seedling population that showed the response depended on seedling age at irradiation. Mesocotyls of dark-grown maize seedlings exhibit two photomorphogenic responses following a light interruption of the dark growth: inhibition of mesocotyl elongation (4,13,19,26,27) and a transverse enlargement of the mesocotyl apical diameter (11,12). Both responses occur primarily as changes in growth pattern of the tissues in the meristematic and cell enlarging regions of the mesocotyl near the coleoptilar node (4, 12, 13, 21), although some inhibition of elongation can occur in more mature tissues (4, 12).…”