The aurea mutant of tomato is deficient in spectrophotometrically and immunochemically detectable phytochrome

Abstract

The aurea locus mutant (au (w)) of tomato contains less than 5% of the level of phytochrome in wild-type tissue as measured by in vivo difference spectroscopy. Immunoblot analysis using antibodies directed against etiolated-oat phytochrome demonstrates that crude extracts of etiolated mutant tissue are deficient in a major immunodetectable protein (116 kDa) normally present in the parent wild type. Analyses of wild-type tissue extracts strongly indicate that the 116-kDa protein is phytochrome by showing that this protein: a) is degraded more rapidly in vitro after a brief far-red irradiation than after a brief red irradiation (Vierstra RD, Quail PH, Planta 156: 158-165, 1982); b) contains a covalently bound chromophore as detected by Zn-chromophore fluorescence on nitrocellulose blots; and c) has an apparent molecular mass comparable to phytochrome from other species on size exclusion chromatography under non-denaturing conditions. The demonstration that the aurea mutant is deficient in this 116-kDa phytochrome indicates that the lack of spectrally detectable phytochrome in this mutant is the result of a lesion which affects the abundance of the phytochrome molecule as opposed to its spectral integrity.

Altered Phytochrome Regulation of Greening in an aurea Mutant of Tomato

“…2). The aurea mutant contains at most a few percent of the normal phytochrome concentration (17). The threshold for the VLF approaches the theoretical limit of a few molecules of Pfr per cell, so the lack of VLF in the mutant is consistent with its low phytochrome levels.…”

“…Despite the lower levels of Chl, the enhancement by the red pulse was almost as large (twofold at 6 h) in the aurea seedlings as in the wild type (twofold at 3 h). This result was surprising in view of the low levels of spectrophotometrically and immunochemically detectable phytochrome in dark-grown aurea seedlings (17). We therefore carried out fluence-response and far-red reversal experiments to see whether the behavior of the mutant could be explained by phytochrome.…”

“…Chl content, seed germination, anthocyanin accumulation and hypocotyl elongation were altered (11). The au mutant line W616 has been used in several recent studies to ask questions about phytochrome action ( 17,21). The au mutant does show phytochrome responses attributable to the low level of stable phytochrome present in light-grown plants, such as promotion of hypocotyl elongation by end-of-day far-red light (1).…”

“…Fbark-grown au seedlings contain less than 5% of the wildtype level of phytochrome, as shown by spectrophotometric and immunochemical methods (16,17). The phytochrome deficiency in au probably results from instability of the apoprotein.…”

Illuminating Phytochrome Functions (There Is Light at the End of the Tunnel)

“…A vwildtype phenotype can be restored to h y l and 2 by feeding plants the tetrapyrrole precursor biliverdin IXa, indiceiting that these mutations affect steps in chromophore biosynthesis. The aurea mutant of tomato may have a similar defect, because levels of spectrophotometrically detectable phytochrome in both the light-and dark-grown plants are reduced (Parks et al, 1987).…”