Transfer cell induction in cotyledons ofVicia faba L.

Abstract

Summary.Immediately prior to seed fill, a dermal transfer cell complex, comprised of epidermal and subepidermal celis, differentiates on the abaxial surface of the cotyledons in seed of Viciafaba. Over the period of differentiation of this complex in vivo, the principal sugars of the seed apoplasmic sap change from hexoses, glucose and fructose, to sucrose. Cotyledons were removed from seeds before differentiation of the transfer cell complex and cultured for 6 days on an agar-based medium in the dark with their abaxial surface in contact with a medium containing either 100 mM hexoses (glucose and fructose in equimolar concentrations) or 100 mM sucrose. On both media, cotyledon growth rate was maintained throughout the culture period at, or above, that of in vivo grown cotyledons of equivalent developmental age. When cotyledons were cultured on a medium containing glucose and fructose, epidermal cells of both the ab-and adaxial surfaces developed wall ingrowths on their outer periclinal walls and their cytoplasm became dense, vesicular, and rich in mitochondria. Extensive ingrowth deposition also occurred on walls of the subepidermal cells and several rows of underlying storage cells where they abutted intercellular spaces. This latter ingrowth development was apparent on both cotyledon surfaces, but extended into more of the underlying cell layers on the abaxial surface at the funicular end of the cotyledon. In in vivo grown cotyledons, such ingrowth development is restricted to the subepidermal cells of the abaxial surface. Ingrowth morphology was commensurate with that of transfer cells of in vivo grown cotyledons. In contrast to the observed induction on a medium containing glucose and fructose, cotyledons cultured with sucrose as the sole sugar source exhibited no ingrowth deposition or small wall ingrowths in some abaxial epidermal cells. While the potential sugar signalling mechanism is unknown, this culture system offers an exciting opportunity to explore the molecular biology of transfer cell development. Abbreviations: DAA days after anthesis; GC-MS gas chromatography and mass spectrometry; PAR photosynthetically active radiation; RGR relative growth rate; SCM standard culture medium. Keywords:

New Insights into Roles of Cell Wall Invertase in Early Seed Development Revealed by Comprehensive Spatial and Temporal Expression Patterns of GhCWIN1 in Cotton

“…On the other hand, the sharp decrease of GhCWIN1 transcript level at 10 DAA probably terminates the inhibition, allowing TC differentiation to proceed. In agreement with this proposition, a progressive reduction of CWIN activity was also detected in faba bean cotyledon development, which temporally and spatially coincided with the onset of TC differentiation in abaxial epidermal cells (Weber et al, 1996(Weber et al, , 1997Offler et al, 1997). Significantly, in contrast to the absence of GhCWIN1 expression in the TCs during WI formation, Sus was highly expressed in TCs at 10 DAA onward and its abundance was strongly correlated with the degree of TC WIs in cotton seed (Pugh et al, 2010).…”

The Maize Transcription Factor Myb-Related Protein-1 Is a Key Regulator of the Differentiation of Transfer Cells

“…Consequently, the strong AL-9 promoter only achieved a limited expression of MRP-1: the transgene was neither expressed in all of the aleurone cells nor was it expressed at the expected intensity in those cells in which expression did occur (Figure 1). Although not a primary aim of this work, we have tested this hypothesis (see Supplemental Figure 6 online) using transient expression experiments in immature maize aleurones and V. faba abgerminal cotyledon epidermis, which is completely covered in TCs (Offler et al, 1997;Weber et al, 1997). These experiments suggest that limited ProAL-9:MRP-1 expression in the aleurone cells is not caused by a technical problem in the construct design, but by a regulatory mechanism specifically downregulating the MRP-1 transcript in the aleurone layer.…”

“…Little is known about the molecular signals that induce TC differentiation, but it is likely that transported solutes are involved (Offler et al, 2002). Certainly, it has been shown that a transient increase in monosaccharide concentration early in development induces the differentiation of TC in the adaxial surface of fava bean (Vicia faba) cotyledons (Offler et al, 1997;Farley et al, 2000). However, the molecular mechanisms underlying this induction are unknown.…”

Evolution and development of cell walls in cereal grains

“…Reticulate types are exemplified by TCs found in Vicia faba cotyledons whereas flange-like types are typically found in cereals (McCurdy et al, 2008; Figure 4 ). Reticulate TCs arise from re-differentiation of epidermal cells (Offler et al, 1997), which is a very different pathway from the direct differentiation of flange-like TCs from endosperm cells in developing cereal grains. The latter occurs opposite the nucellar projection as early as 5 DAP in barley, when the first wall ingrowths appear in the syncytium (Thiel et al, 2012b).…”