Evidence for Phytochrome Regulation of Gibberellin A₂₀ 3β-Hydroxylation in Shoots of Dwarf (lele) Pisum sativum L.

Abstract

The effect of light on the dwarfing allele, le, in Pisum sativum L. was tested as the growth response to gibberellins prior to or beyond the presumed block in the gibberellin biosynthetic pathway. The response to the substrate (GA20), the product (GA1), and a nonendogenous early precursor (steviol) was compared in plants bearing the normal Le and the deficient lele genotypes in plants made low in gibberellin content genetically (nana lines) or by paclobutrazol treatment to tall (cv Alaska) and dwarf (cv Progress) peas. Both genotypes responded to GA1 under red irradiation and in darkness. The lele plants grew in response to GA20 and steviol in darkness but showed a much smaller response when red irradiated. The Le plants responded to GA20 and steviol in both light and darkness. The red effects on lele plants were largely reversible by far-red irradiation. It is concluded that the deficiency in 3j@-hydroxylation of GA20 to GA1 in genotype lele is due to a Pfr-induced blockage in the expression of that activity.Light grown dwarf peas lack the ability to convert GA202 to GA1 (6, 7), yet GA1 and GA8 were recently identified in extracts ofetiolated dwarf pea shoots (3). We will present evidence which suggests that etiolated dwarf pea plants lose the ability to convert GA20 to GA, upon formation of Pfr as a consequence ofexposure to R. Attempts by earlier workers to measure light-induced changes in GA metabolism or GA levels in tall and dwarf peas led to inconsistent results (reviewed in Smith [20]). Some experiments indicated phytochrome-mediated changes in GA metabolism, while other reports suggested an effect of light on "sensitivity" to endogenous GAs.Some genes which help determine plant stature in Pisum have recently been characterized (6,7,13,14,17). At least five loci have been shown to influence stem elongation, including the Na and Le loci, which affect GA metabolism. The recessive na allele apparently blocks an early step in GA biosynthesis, since nana plants do not contain detectable levels of GAs (13). The early C-13 hydroxylation pathway of GA biosynthesis predominates in peas (3,8

Use of an Acylcyclohexanedione Growth Retardant, LAB 198 999, to Determine Whether Gibberellin A20 Has Biological Activity per se in Dark-Grown Dwarf (le5839) Seedlings of Pisum sativum

“…9 responded to GA20 in the dark, even though this GA elicited no growth response in red light when applied in the same manner and at the same dosages (1,19). It was postulated that the conversion of GA20 to GA, is increased in the dwarf in the dark, although an alternative suggestion, namely that GA20 may have biological activity per se in the dark, was also made in both papers.…”

Changes in the Endosperm Cell Walls of Two Datura Species before Radicle Protrusion

“…The D. ferox seeds were decoated after 24 h of incubation to achieve a good response to light (25) and immediately irradiated with either FR or FR followed by R. Dark conditions were obtained by enclosing the Petri dishes in black plastic canisters and handling the imbibed seeds only under a dim green safe light. The green, R and FR sources were described previously (8). Irradiations with R and FR were of 20 min and carried out at 25°C.…”

“…Micropylar portions were dissected from induced and noninduced seeds at 64 h of incubation, suspended in 100 mm acetate buffer (pH 6.0) and incubated for an additional 8 h, either at 33 or 0°C. The sugar composition of the walls prepared from endosperms dissected from control seeds showed no change after the 8 h incubation at 33C.…”

Phytochrome, Gibberellins, and Hypocotyl Growth (A Study Using the Cucumber (Cucumis sativus L.) long hypocotyl Mutant)

“…Reports concerning pea (Campell and Bonner, 1986) and cowpea (García-Martínez et al, 1987) have suggested a basic action of phy through regulation of GA 3p-hydroxylation, namely in the conversion of inactive GA,, into active GA,. In cucumber, the most abundant (and most active when applied) 3P-hydroxylated GA is GA, (Nakayama et al, 1989), which is biosynthesized from GA, by 3P-hydroxylation.…”

“…Furthermore, the metabolism of GA has been shown to be affected by light exposure in dark-grown pea (Sponsel, 1986) or lettuce seedlings (Toyomasu et al, 1992). GA, biosynthesis has been indicated to be under phy control during de-etiolation in pea (Campell and Bonner, 1986) or after R or FR pulses increase in active GA, was found, but the mutant was observed to be "GA hypersensitive" (Reid and Ross, 1988;Weller et al, 1994). In rice mesocotyls, phy activation decreases GA "sensitivity" (Nick and Furuya, 1993).…”