Gymnosperms differences from angiosperms

The PAL activity that is necessary for lignin formation occurs in the cytoplasm or bound to the cytoplasmic surface of the endoplasmic reticulum membranes. The cinnamic acid produced is probably carried on the lipid surface of the membranes, since it is lipophilic, and it is sequentially hydroxylated by the membrane-bound hydroxylases (47,50). In this way there is the possibility of at least a two-step channeling route from phenylalanine to p-coumaric acid. The transmethylases then direct the methyl groups to the meta positions. There is a difference between the transmethylases from angiosperms and those from gymnosperms, since with the latter... 

Lignins are natural polymers occurring in plant cell walls - wood and other plants (878940) [a.447]. It has been shown that the structnres of lignins are very different from various sources, such as gymnosperm, dicotyledonous angiosperm and wheat straw (Scheme 32) among many others [a.223]. 

The two types of wood differ, however, in their nature and structure. The main structural characteristic of the hardwoods (which are botanically known as angiosperms, plants that flower to pollinate for seed reproduction) is that in their trunks or branches, the volume of wood taken up by dead cells, varies greatly, although it makes up an average of about 50% of the total volume. In softwoods (from the botanical group gymnosperms, which do not have flowers but use cones for seed reproduction) the dead cells are much more elongated and fibrous than in hardwoods, and the volume taken up by dead cells may represent over 90% of the total volume of the wood. 

Fig. 5.3 Plots of some monosaccharides (expressed as wt % of total amount of combined lyxose, arabinose, ribose, xylose, rhamnose, fucose, mannose and galactose), showing (a) differentiation of angiospermous and gymnospermous vascular plant sources from total marine plankton, and (b) distinction between different types of higher plant sources (after Cowie Hedges 1984).

The problem is to find a reliable estimate of tbe age of divergence of the two lines of evolution. Angiosperm pollen has been found in the Jurassic era, 180-140 million years ago, and ginkgo ancestors can be traced back to the early Permian, around 270 million years ago. Both of these dates are irrelevant, unfortunately, for what is needed is the time in the past at which the gymnosperm ancestors of modem angiosperms and ginkgo separated. If both can be traced back to the pterido-sperms or seed ferns of the Carboniferous (139,140), then the age of the evolutionary branch point approaches 350 million years. Eighteen sequence differences per hundred residues in 350 million years lead to a unit evolutionary period essentially identical with that calculated from vertebrates, but the fossil record is so poor that the calculation can only be considered approximate. 

The immense diversity of terpene metabolites known today is especially due to the large terpene synthase (TPS) gene family evolution and the versatility of the enzymes encoded by it. Most gymnosperm terpene synthases form a different family from those in angiosperms. However, phylogenetic analyses support the fact that all plant TPS have evolved from an ancestral diterpene synthase implicated with primary metabolism [4]. 

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