Adaptation to Dim-Red Light Leads to a Nongradient Pattern of Stem Elongation in Cucumis Seedlings

Abstract

Relative growth rate determinations on 5-millimeter regions of cucumber (Cucumis sativus L.) hypocotyls show that dim-red lightgrown seedlings have an even distribution of growth along the stem axis. This contrasts with the apical to basal graded decline in growth rate seen in dark-grown seedlings, including dark-grown cucumber seedlings used as controls in this study. Dark-grown seedlings convert to the nongradient pattern when transferred to dim-red light. The small amount of light required suggests that the change in developmental pattern may happen in the natural light environment.A consensus characteristic of stem elongation is a gradient of elongation rates along the stem axis, with high rates of elongation near the apex and a graded decline toward the base. Etiolation is characterized by rapid stem elongation exhibiting a graded pattern (8,9,23,25,28), whereas stem elongation following deetiolation is relatively slow but still exhibits the apical to basal gradient of extension rates (9,10,25). The hypothesis that changes in cell structure and function follow the gradient in growth rate has been tested for several developmental processes (23,25,28).Germinating cucumber (Cucumis sativus L.) seedlings in continuous DRL3 (21) MATERIALS AND METHODSCucumber seedlings (Cucumis sativus L. cv Burpee's pickler) were germinated in moist vermiculite and grown under DRL as described previously (21) or in a similar dark room at 24 ± 10C. Experiments were carried out in growth rooms at two locations (Berkeley, CA, and San Antonio, TX). For both locations, the DRL field in the growth room had fluence rates ranging from 0.3 to 0.5 ,Imol m-2 s-'. The light source for DRL emitted 90% of its total output between 600 and 700 nm, with peaks at 638 and 648 nm (13; data not shown).For determination of RGRs (18, 22), marks (carborundum chips, 100 ,um diameter) were placed at 5-mm intervals along hypocotyls of 3.5-to 4-d-old seedlings for total length of 40 to 60 mm. Seedlings were allowed to recover from handling for 2 h before data were taken. Video images were obtained from a Panasonic WV-1850 video camera (Matsushita Electronics, Seacaucus, NJ) that has a high sensitivity to red and IR light. Images of DRL-grown seedlings were obtained using light available in the DRL growth room. DG seedlings were imaged under photomorphogenetically inactive IR illumination (12). For marking and placement for imaging, DG seedlings were exposed to 1 to 2 min of green work light, which was previously shown not to affect growth in this cultivar (8). The images were processed by a personal computer running video digitizer board (Video-Van-Gough, Tekmatic Systems, Ben Lomond, CA) and programs used previously (18). The digitizer located the marks and recorded their position in x and y coordinates on an arbitrary scale. Region lengths were determined by calculating distances between marks and converting numbers from computer units to millimeters using a conversion factor established by measuring known distances. Marks were tracked for 2 h, ...

Cotyledon-Generated Auxin Is Required for Shade-Induced Hypocotyl Growth in Brassica rapa

“…Generally, plant elongation occurs in a gradient along the stem, with most growth occurring at the apex (Gotô and Suzuki, 1980;Martinez-Garcia and Garcia-Martinez, 1992;Shinkle et al, 1992). These results are consistent with our observation that hypocotyl growth in B. rapa occurs in a basipetal gradient.…”

The rib1 Mutant of Arabidopsis Has Alterations in Indole-3-Butyric Acid Transport, Hypocotyl Elongation, and Root Architecture

“…Exactly where and how RIB could be integrated in this complex regulatory web is unclear at present, but it would affect IBA transport in response to light. Light has been shown previously to affect auxin transport in cucumbers (Shinkle et al, 1992), but also to specifically affect IBA transport in Arabidopsis (Rashotte et al, 2003).…”

“…Light quality, intensity, and direction can all affect auxin response and transport (Swarup et al, 2002). Dim red light was shown to cause an increase in polar auxin transport in cucumber (Cucumis sativus) hypocotyls (Shinkle et al, 1992). Steindler and coworkers (1999) have shown that shade-induced hypocotyl elongation was dependent on auxin transport, as it can be inhibited by NPA, and the auxin response mutant axr1-12 is defective in this response.…”

Dim-Red-Light-Induced Increase in Polar Auxin Transport in Cucumber Seedlings1

“…Boxes were placed in 42-ϫ 27-ϫ 16-cm clear, plastic storage boxes with a 2-to 4-mm layer of distilled water on the bottom and with lids that were not tightly sealed, but that did limit evaporation. Storage boxes were placed in a growth room maintained at 24 Ϯ 1°C in complete darkness or under DRL at 0.5 mol m Ϫ2 s Ϫ1 , as described by Shinkle et al (1992), or in similar growth rooms at the University of North Carolina-Chapel Hill. Plants were grown for varying periods and transferred between darkness and DRL as indicated below and in "Results.…”

“…To resolve this difficulty, we studied auxin transport using an intermediate state of photomorphogenesis induced by growth in continuous DRL (0.5 mol m Ϫ2 s Ϫ1 ). Under DRL plants exhibit an altered pattern of stem elongation, but an "etiolated" morphology is preserved (Shinkle et al, 1992). Seedlings grown under DRL have closed hooks, high hypocotyl elongation rates, and cotyledons that expand and green minimally.…”