Phytochrome Control of Two Low-Irradiance Responses in Etiolated Oat Seedlings

Abstract

Light-induced coleoptile stimulation and mesocotyl suppression in etiolated Avena sativa (cv. Lodi) has been quantitated. Etiolated seedlings showed the greatest response to light when they were illuminated 48 to 56 hours after imbibition. Two low-irradiance photoresponses for each tissue have been described. Red steps found in oats (1). They did not find in corn the very sensitive response detected in oats. Generally, the characteristics of the two responses ofthe corn mesocotyl were similar in magnitude, relative sensitivity, R/FR reversibility, and time dependence to those described for oats (29, cf. 1). Corn coleoptiles, however, under the conditions used to study mesocotyl suppression, showed no response at all to R for doses from 100 to 105 nE cm-2 for any wavelengths from 600 to 700 nm (Vanderhoef, unpublished).Other workers have also failed to obtain reproducible red light responses with coleoptiles (e.g. 17).The vast literature on photomorphogenesis in Avena was confusing for two major reasons: first, growth ofthe etiolated seedlings was highly variable, and second, the responses to light were often not reproducible. This report described the elongation growth of etiolated oat coleoptiles and mesocotyls in a growth system in which these problems have been solved and which has facilitated analysis of large groups of seedlings. METHODSGrowth of Uniform Etiolated Seedlings. A 9 x 6 cm piece of absorbent paper (Kimpak, Perf'd, Kimberly-Clarke) was placed in the middle of a 17 x 3.5 cm glass plate so that one long side of the paper and glass were even. Groups of 25 dry oat seeds (Avena sativa L. cf. Lodi, Lot No. 0170-B, Dakota Seed and Grain Co., Inc., Watertown, SD) with husks present were placed side by side onto strips of masking tape 12.7 mm in width (Scotch Brand, Part No. 6201, 3M Co.) with the embryos against the tape. About 5 cm of bare tape extended on either side of each group of seeds. A group of seeds was then laid against absorbent paper with the bare ends of the tape affixed to the glass plate beyond the paper. The ends of the seeds farthest away from the embryo and the padding were even with the aligned edges of the glass plate and paper, and any projecting glumes, etc., were excised. These drymounted seeds could be stored for several weeks at 4 C without loss of viability. They were imbibed by inserting this asembly with the seeds up into distilled H20 just to the level of the middle of the seeds for 0.5 h in absolute darkness. Uniformity ofgermination and growth was improved if the seeds themselves were not entirely submerged during imbibition. The plates were then transferred to racks which held them at an angle 450 from the vertical with the seeds up and the other edge of the absorbent paper immersed about 5 mm deep in distilled H20 in plastic boxes. These boxes were then tightly closed and kept in darkness until seedling treatment. The absorbent paper under the seeds acted as a wick to provide water to the seedlings for the duration of the experiments. This method yielded fro...

Blue Light and Phytochrome-Mediated Stomatal Opening in the npq1 and phot1 phot2 Mutants of Arabidopsis

“…3). Green light stimulated a far-red lightreversible opening in a response similar to the reported green light-stimulated phototropism in oat and Arabidopsis (Mandoli and Briggs, 1981;Steinitz et al, 1985). Finally, a dose response curve for white light-stimulated opening was inhibited by far-red light in the low fluence rate portion of the curve (Fig.…”

“…No aperture changes were elicited by the same green light treatment in WT stomata. A positive effect of green light on phytochromemediated phototropism in oat (Avena sativa) and Arabidopsis has been reported (Mandoli and Briggs, 1981;Steinitz et al, 1985).…”

The function of phytochrome A

“…The VLFR Different aspects of the de-etiolation process show biphasic responses to light treatments that provide a range of Pfr/P (Mandoli & Briggs 1981). As in the case of seed germination, the first phase, i.e.…”

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

“…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. It is known, in many cases, that the responsivity toward photomodulation is increased by a prior light treatment (1,13,15,16).…”

“…Whether this inhibition is mediated by pytochrome is unclear as FR reversibility often is partially (19) or totally absent (2,10). The mesocotyl growth region which is located just below the coleoptile node (8,14), is not an homogeneous tissue.…”