Pollen wall development in flowering plants

Abstract

Contents Summary 483 Introduction 483 Progress of research on pollen wall development 485 The developmental role of the special cell wall 487 Meiosis and the establishment of microspore symmetry 489 The origins of the exine during the tetrad stage 490 The free microspore stage to pollen maturation 495 Conclusions 495 Acknowledgements 496 References 496 Summary The outer pollen wall, or exine, is more structurally complex than any other plant cell wall, comprising several distinct layers, each with its own organizational pattern. Since elucidation of the basic events of pollen wall ontogeny using electron microscopy in the 1970s, knowledge of their developmental genetics has increased enormously. However, self‐assembly processes that are not under direct genetic control also play an important role in pollen wall patterning. This review integrates ultrastructural and developmental findings with recent models for self‐assembly in an attempt to understand the origins of the morphological complexity and diversity that underpin the science of palynology.

Experimental modelling of exine-like structures

“…The vicinity of a callose-like layer is important because earlier studies have shown that callose probably promotes structure-forming processes at the interface. The importance of callose for sporoderm development has been emphasised earlier (Barnes & Blackmore, 1986;Blackmore & Barnes, 1990;Hesse, 1995;Blackmore et al, 2007Blackmore et al, , 2010, shown sub-structurally (Gabarayeva et al, 2011a(Gabarayeva et al, , 2011b and is in accordance with the data on callosedeficiency mutants (Dong et al, 2005;Nishikawa et al, 2005;Ariizumi & Toriyama, 2011).…”

“…The idea of the universal importance of physicochemical interactions for pattern formation in nature was put forward about a century ago (d'Arcy Thompson, 1917Thompson, , 1959 and was then developed by many biologists (see Blackmore et al, 2007). A growing body of experimental evidence obtained through the observation and analysis of recent studies favours an emerging image of the cell as a dynamic integrated system of interconnected and interdependent metastable molecular organisations realised through stochasticity and self-organisation (Kurakin, 2005).…”

Analysis of TETRAKETIDE α-PYRONE REDUCTASE Function in Arabidopsis thaliana Reveals a Previously Unknown, but Conserved, Biochemical Pathway in Sporopollenin Monomer Biosynthesis

“…Resulting polyhydroxylated tetraketide compounds may then be exported by ABCG26 and lipid transfer proteins (LTPs) to the locule as sporopollenin building units or further processed before transport and polymerization in the pollen wall. conquest of land by plants (Rozema et al, 2001;Blackmore et al, 2007). Indeed, the widespread occurrence of sporopollenin in pollen grains and spores of land plant lineages indicates the conservation of an ancient biosynthetic pathway during plant evolution.…”

“…These studies unequivocally demonstrate that fatty acids are essential precursors of sporopollenin. At late stages of pollen grain development, lipophilic tryphine is deposited on the surface and within the chambers of exine and constitutes the pollen coat (Scott et al, 2004;Blackmore et al, 2007;Grienenberger et al, 2009), but this is a process distinct from exine formation and probably involves a distinct biosynthetic pathway or pathways.…”

“…The different stages of pollen development have been carefully documented (Owen and Makaroff, 1995;Sanders et al, 1999;Scott et al, 2004;Blackmore et al, 2007). Meiosis in anthers gives rise to haploid microsporocytes arranged in tetrads surrounded by a callose wall.…”