Polyamine Levels in Petunia Genotypes with Normal and Abnormal Floral Morphologies

Abstract

We characterized the polyamine pathway in Petunia hybrida genotypes that were either wild type or that had been identified as having altered floral morphology. Analysis of four normal morphology lines revealed two patterns of endogenous levels of putrescine and arginine decarboxylase: two with higher levels of putrescine, two with lower levels of putrescine. Analysis of Fl and backcross progeny between high putrescine and low putrescine strains is consistent with their differences being due to a dominant allele for low putrescine content and arginine decarboxylase activity. Four Petunia mutants with floral morphology changes were also screened. One of these mutants, alf, showed high levels of putrescine and high levels of arginine decarboxylase late in development; these high levels were found whether the alfline was present in either of the two types of normal morphology genetic backgrounds that had been characterized. ment would be simply to perform crosses and test for linkage of the two traits, but the developmental anamolies were generally so severe that the flowers were completely sterile. In two cases, Mgr3 and Mgrl2 (15) we were able to obtain small numbers of Fl and backcross progeny. The phenotypes seen suggested both Mgr3 and MgrJ2 were nuclear dominant traits, and the floral phenotypes were linked to the MGBG resistant phenotypes, although the total number of progeny screened was quite small in each case.These results strongly suggested a correlation between altered polyamine synthesis and altered floral morphology, but only in the limited system ofcell culture derived tobacco plants. In order to test further the hypothesis of the involvement of polyamine biosynthesis in the differentiation of floral meristems, we undertook to characterize the polyamine content of several Petunia hybrida lines, including some with abnormal floral development.These Petunia genotypes were derived from whole plant studies as part of a search for genetic mutations in floral pigmentation and floral morphology (see Gerats et al. [8] for a brief description). These plants thus had no prior relationship with either cell culture or polyamine selections. Changes in polyamine concentration and in the activity levels of the various polyamine biosynthetic enzymes have been correlated with a wide variety of plant growth and environmental response phenomena, including cell division (9), responses to stress such as acid (21), and heavy metal (20), hormone response (3), and floral development (11,14). Polyamine-conjugates, covalently bound to phenolic acids, have also been found in high levels in plants, and may be the effectors of some of these phenomena (16).In previous reports (12, 13) we have described the isolation of tobacco cell cultures resistant to MGBG3 a potent inhibitor of SAMdc. All MGBG resistant cell lines that were successfully regenerated into whole plants revealed abnormnal differentiation of the floral meristems (14). The

Differential expression of two MADS box genes in wild-type and mutant petunia flowers.

“…For petunia, two homeotic flower morphology mutants, green petals (recessive for the gene gp) and blind (recessive for the gene bl), have been partially characterized (Gerats et al, 1988;van Tunen et al, 1990;Gerats, 1991). Flowers of the blind mutant have limbs replaced by antheroid structures on top of the tube (Wiering et al, 1979;Vallade et ai., 1987).…”

Involvement of Polyamine in Floral and Fruit Development

“…When the gap between exact amount and the threshold is quite large the action will be discordant. It has been documented that an abnormal level of polyamines has effects on floral morphology 28,41 . The underlying function of polyamine for regulating fertility remains unknown and work to decipher this is scarce.…”

“…A mutant line, Mgr 21, which had incomplete and abnormal floral organs, exhibited significantly lower polyamines compared with the wild type 23 . Petunia mutants with abnormal polyamine titers demonstrated irregular development of the floral organs 28 . Apart from the implication in floral development, polyamines are related to flower genders or fertility.…”

“…Thirdly, acquisition of some lines of mutants plays an active role in identifying the implication of polyamine in floral development. So far, mutants have been obtained in several crops, such as Arabidopsis 2 , tobacco 23,41 and Petunia 28 . For example, some of the tobacco mutants deficient in polyamine metabolism demonstrated aberrant morphology in anthers and ovules 41 .…”

Genetic control of branching pattern and floral identity during Petunia inflorescence development

“…2A, right; Doodeman et al, 1984;Gerats et al, 1988;Gerats, 1991). Because of the proliferation of green leaf-like structures the mutant was called aberrant leaf and flower (alf).…”