Galactose metabolism in cell walls of opening and senescing petunia petals

Abstract

Galactose was the major non-cellulosic neutral sugar present in the cell walls of 'Mitchell' petunia (Petunia axillaris x P. axillaris x P. hybrida) flower petals. Over the 24 h period associated with flower opening, there was a doubling of the galactose content of polymers strongly associated with cellulose and insoluble in strong alkali ('residual' fraction). By two days after flower opening, the galactose content of both the residual fraction and a Na(2)CO(3)-soluble pectin-rich cell wall fraction had sharply decreased, and continued to decline as flowers began to wilt. In contrast, amounts of other neutral sugars showed little change over this time, and depolymerisation of pectins and hemicelluloses was barely detectable throughout petal development. Size exclusion chromatography of Na(2)CO(3)-soluble pectins showed that there was a loss of neutral sugar relative to uronic acid content, consistent with a substantial loss of galactose from rhamnogalacturonan-I-type pectin. beta-Galactosidase activity (EC 3.2.1.23) increased at bud opening, and remained high through to petal senescence. Two cDNAs encoding beta-galactosidase were isolated from a mixed stage petal library. Both deduced proteins are beta-galactosidases of Glycosyl Hydrolase Family 35, possessing lectin-like sugar-binding domains at their carboxyl terminus. PhBGAL1 was expressed at relatively high levels only during flower opening, while PhBGAL2 mRNA accumulation occurred at lower levels in mature and senescent petals. The data suggest that metabolism of cell wall-associated polymeric galactose is the major feature of both the opening and senescence of 'Mitchell' petunia flower petals.

Spatial and temporal transcriptome changes occurring during flower opening and senescence of the ephemeral hibiscus flower,Hibiscus rosa-sinensis

“…3; Supplementary Table S3). This fits well with the documented profound structural and morphological changes that occur in petal cell walls of flowers as they open and senesce (O’Donoghue et al , 2009; O’Donoghue and Sutherland, 2012). …”

Three β-galactosidase cDNA clones related to fruit ripening in papaya (Carica papaya)

“…A similar case has been reported in strawberry fruit where Fabgal1 and Fabgal2 seem to be having longer sequences than Fabgal3 due to the presence of SUEL-type lectin domain at their C-termini (Trainotti et al 2001). The presence of lectin-like domain at the C-terminus has also been characterized in Cicer arietinum (Esteban et al 2005) and petunia petals (O'Donoghue et al 2009). The existence of this lectin-like domain in radish recombinant enzyme rRsBGAL1 seemed to have effects on its specific activity since it was ten times more than that of the native b-galactosidase, RsBGAL1, which lacked the domain (Kotake et al 2005).…”

Overexpression of OsSWEET5 in Rice Causes Growth Retardation and Precocious Senescence

“…It has been reported that galactose is an important component of the xyloglucans in the primary cell wall [62]. Nevertheless, free galactose has severe inhibitory effects on certain aspects of plant growth and development even at very low concentrations [21], [57], [63], and its inhibitory effect on auxin-induced growth could be explained by the inhibition of IAA transport [57].…”