ent -Kaurene synthase is located in proplastids of meristematic shoot tissues

Abstract

Previous studies have indicated that entkaurene synthase (KS) is located in the proplastid stroma of rapidly dividing plant tissues. Here we present further and more direct evidence for this hypothesis and follow the activity of KS throughout the entire vegetative growth period of wheat plants. During germination of wheat caryopses, KS activity was maximal for a short period culminating on the third day in the scutellum and on the forth day in the meristematic shoot base. Throughout further development of the wheat plant, KS was found in the nodes but not in internodes or leaves. The activity of KS in each node increased when the internode above it was elongating and decreased again when this internode had almost reached its final size. The correlation of KS activity with growth was particularly striking in the case of tiller development from the forth node: here KS activity had already declined, but was restored when the tiller began elongating. Electron micrographs of wheat seedling tissue with high KS activity (shoot base) showed the presence of proplastids, whereas electron micrographs of tissue without such activity (primary leaves) showed only developing or mature chloroplasts. On densitygradient centrifugation, the plastids that yielded stroma preparations with KS activity became distributed over a greater density range and also had a lower NADP + -glyceraldehyde 3-phosphate dehydrogenase:shikimate oxidoreductase ratio than plastids yielding KS-inactive stroma preparations. Pea shoot apices contain both proplastids and mature chloroplasts. Here also, KS activity was associated with the stroma of plastids with characteristics similar to those of the wheat proplastids, indicating that KS is associated with proplastids in pea shoot apices as well. We conclude that the stromal location of KS may be a general feature of proplastids in rapidly dividing tissue.

Plastidial NAD-Dependent Malate Dehydrogenase Is Critical for Embryo Development and Heterotrophic Metabolism in Arabidopsis

“…significant metabolic activity and play a vital role in development of meristematic tissues (Aach et al, 1997).…”

The Five "Classical" Plant Hormones.

“…The genes encoding these enzymes have been cloned from Arabidopsis (GA7; Sun and Kamiya, 1994) and pumpkin endosperm (Yamaguchi et al, 1996), respectively. Biochemical evidence indicates that both enzymes are located in proplastids of meristematic shoot tissues but not in mature chloroplasts (Aach et al, 1997). Because conversions in stage 3 of the pathway can take place in mature leaves, it is likely that pathway intermediates move between different tissues and organs.…”

Mutation of RiceBC12/GDD1, Which Encodes a Kinesin-Like Protein That Binds to a GA Biosynthesis Gene Promoter, Leads to Dwarfism with Impaired Cell Elongation

“…A tentative GA metabolism pathway has been found in plants (Hedden and Phillips, 2000;Yamaguchi and Kamiya, 2000). GAs are biosynthesized from geranylgranyl diphosphate, which is converted to ent-kaurene by 2 terpene syntheses, ent-copalyl diphosphate synthase, and ent-kaurene synthase, in plants (Aach et al, 1997;Helliwell et al, 2001). Then ent-kaurene is converted to GA 12 by two cytochrome P450 enzymes, ent-kaurene oxidase (KO) and ent-kaurenoic acid oxidase (KAO).…”