Biomacromolecules of algae and plants and their fossil analogues

Abstract

A review of our current understanding of resistant biomacromolecules derived from present and past algae and higher plants is presented. Insight in the nature of recent and fossil macromolecules is strongly hampered by the difficulties in obtaining the material in pure and unaltered form. For the extant material, avoiding artificial condensation and structural alteration as a result of chemical isolation and purification of biomacromolecules requires constant attention. To date, several types of sporopollenin seem to occur. One type is characterised by oxygenated aromatic building blocks, in particular p-coumaric acid and ferrulic acid. The other type is thought to consist predominantly of an aliphatic biopolymer. In this review it is concluded that extant sporopollenin consists of the aromatic type, whereas the aliphatic component of fossil sporopollenin is due to early-diagenetic oxidative polymerization of unsaturated lipids. The cuticles of most higher plants contain the aliphatic biopolyester cutin. Additionally, cuticles of drought-adapted, mostly CAM plants, seem to contain the non-hydrolysable aliphatic biopolymer cutan. Only a very few algae are able to biosynthesize resistant, (fossilisable) cell walls: some Chlorophyta, Eustigmatophyta and Prasinophyta produce the aliphatic biopolymer algaenan. Some Dinophyta are also capable of producing algaenan cell walls. Additionally, some taxa produce highly resistant cyst-walls with a high proportion of aromatic moieties. For the morphologically well-preserved fossil material, contamination by organic particles other than the target taxon is hard to eliminate and can contribute to either the aliphatic or aromatic signal. Furthermore, post-mortem migration of aliphatic moieties into, and their condensation onto the macromolecule might occur, e.g. by oxidative polymerization. These phenomena hamper the evaluation of the aliphatic signature of fossil plant material and may for example explain the preservation of initially cutin-based cuticles or non-algaenan containing algae. The extent to which migration and in situ formation of aromatic moieties plays a role in modifying resistant algal macromolecules, notably under elevated temperature and/or pressure conditions, still remains an open question.

Radiocarbon Dating of Late Pleistocene Marine Shells from the Southern North Sea

“…Such series of n-alkenes/n-alkanes are generally attributed to biochemically resistant aliphatic biopolymers and geopolymers. Given their absence from the modern shell, these aliphatic polymers are likely derived from other sources (microorganisms, algae) or formed from (unsaturated) fatty acids through oxidative polymerization (de Leeuw et al 2006). …”

A Large-Scale Genetic Screen in Arabidopsis to Identify Genes Involved in Pollen Exine Production

“…Previously, the in vitro studies of 4CL3 enzymatic activities demonstrated that although the enzyme had the strongest substrate specificity toward 4-coumarate, it also possessed a noticeable activity toward ferulate (Ehlting et al, 1999;Costa et al, 2005). Results of chemical analyses of sporopollenin suggested that both ferulic and 4-coumaric acids are possible constituents of sporopollenin (Schulze Osthoff and Wiermann, 1987;Wehling et al, 1989;Rozema et al, 2001;de Leeuw et al, 2006). Based on our results, we hypothesize that among the roles of 4CL3 in anthers may be the synthesis of phenolic components of sporopollenin and that ferulate-CoA and 4-coumarate-CoA may either be directly incorporated in sporopollenin or act as precursors for sporopollenin's phenolic components.…”

Defective Pollen Wall 2 (DPW2) Encodes an Acyl Transferase Required for Rice Pollen Development

“…Sporopollenin is thought to be composed entirely of polyalkyl and aromatic macromolecules as well as aliphatic and aromatic monomers, particularly ferulic and p-coumaric acids that are hinged together (Guilford et al, 1988;Wehling et al, 1989;Mösle et al, 1997;Blokker et al, 2005;De Leeuw et al, 2006;Watson et al, 2007). Intine, the innermost layer of the pollen wall, mainly consists of pectin, cellulose, hemicellulose (Kress and Stone, 1983;Edlund et al, 2004;Fang et al, 2008), and also of hydroxycinnamic acids (Meychik et al, 2006).…”