Gibberellin production

If gibberellins produced in seeds are the main cause of flower inhibition and hence of biennial bearing in fruit trees, we might expect to find differences in gibberellin production between strongly biennial and more regular cropping varieties. 

Figure 2. Gibberellin production in seeds of apple compared with rate of increase in fruit volume (cv. Coxs Orange Pippin)...

Distribution of gibberellin biosynthetic genes and gibberellin production in the Gibberella fujikuroi species complex, S. Malonek, C. Bomke, E. Bomberg-Bauer, M.C. Rojas, P. Hedden, P. Hopkins and B. Tudzynski, Phytochemistry, 2005, 66, 1296. 

Most work on GA biosynthesis has utilised cell-free systems from immature seed tissues (endosperm and cotyledons), which contain much higher GA concentrations than those present in other parts of the plant [2]. Such systems have been particularly useful for characterizing the enzymes involved in GA biosynthesis, but, since the function of GAs in these tissues is unknown, it has not been possible to relate the biosynthesis to any physiological processes. Moreover, the endogenous GAs and their metabolism in immature seeds are often atypical of other plant tissues. Gibberellin production is also... 

B. O. Phinney and C. Spector, Genetics and gibberellin production in the fungus, Gibberella fujikuroi, Ann. New York Acad. Sci. 144, 204-210 (1967). 

Malonek S, Bomke C, Bomberg-Bauer E, Rojas MC, Hedden P, Hopkins P, Tudzynski B (2005) Distribution of gibberellin biosynthetie genes and gibberellin production in the Gibberella fujikuroi species eomplex. Phytochemistry 66 1296-1311... 

Effects on Gibberellins. Exposure to cold enhances subsequent GA biosynthesis in certain seeds (Ross and Bradbeer 1971). The increase appears to arise from de novo GA biosynthesis and cannot be inhibited by concentrations of ABA which inhibit germination (Arias et al. 1976) and suppress apparent GA biosynthesis in maize shoots (Wareing et al. 1968). Cold increases GA in potato tubers (Thomas and Wurr 1976), while low temperature during tuber germination increases both GA and auxin activity in leaves of potato (Romanova et al. 1975). In corn roots, on the other hand gibberellin production or export is severely inhibited by prolonged exposure to cold (Atkin et al. 1973). 

Pioneering work on the desulphonylation of jS-ketosulphones was carried out by Corey and Chaykovsky - . This reaction was part of a sequence which could be used in the synthesis of ketones, as shown in equation (53). The main thrust of this work was in the use of sulphoxides, but Corey did stress the merits of both sulphones and sulphonamides for different applications of this type of reaction. The method soon found application by Stetter and Hesse for the synthesis of 3-methyl-2,4-dioxa-adamantane , and by House and Larson in an ingenious synthesis of intermediates directed towards the gibberellin skeleton, and also for more standard applications . Other applications of the method have also been madealthough it does suffer from certain limitations in that further alkylation of an a-alkyl- -ketosulphone is a very sluggish, inefficient process. Kurth and O Brien have proposed an alternative, one-pot sequence of reactions (equation 54), carried out at — 78 to — 50°, with yields better than 50%. The major difference between the two routes is that the one-pot process uses the desulphonylation step to generate the enolate anion, whereas in the Corey-House procedure, the desulphonylation with aluminium amalgam is a separate, non-productive step. 

For the gibberellin 71 discussed above, it would have been impossible to predict a priori the structure of the photoproduct. However, for simpler and more symmetrical monomers one might hope to be able to predict the crystal structure and thence the stereochemistry of the product. But even here the nature of the intermolecular forces involved in determining the crystal structure is not... 

In continuation of previous work, the reactions of gibberellin A, and Aj with neutral manganese dioxide have been examined. The products include those of decarboxylation and of lactonization on to C-15. The full paper describing the interesting bridgehead C-13 fluorination of gibberellins with fluoramine has appeared. ... 

Takano et al. 69) exploited the asymmetric aldolization for the synthesis of more functionalized chiral products which possess units suitable for the construction of certain tetracyclic triterpenes, such as gibberellins and kaurenes. They described the enantioselective synthesis of the tricyclic enone (33) from the symmetric triketone (32) and its conversion into the gibbane framework. Again, (S)-proline was used as the catalyst. 

Figure 2. Effect of weekly sprays of gibberellin solutions on nitrogen ( J and total sugar ( ) concentration in apple leaves and consequent effect on mite progeny production (M) (13).

The most commercially successful PGRs are those that operate either through the inhibition of gibberellin biosynthesis, from mevalonic acid (Knee, 1982) or through the production of ethylene. These represent the two most valuable pathways for growth modification since they have key roles in extension growth, ripening, fruit set and dominance. 

Some bourbon distillers use gibberellin-treated malt along with glucoamylase to reduce by 50% the amount of malt in their grain bills and thereby lower production costs. 

Other experiments with Gibberellafujikuro] the fungus that produces gibberellin, indicate that GA3 production is blocked by BAS 111. Very detailed and careful experiments conducted with enzymes in cell-free systems strongly support this mode of action, ie, using ent-kaurene oxidase and cinnamate 4-mono-oxygenase isolated from pea apices and soybean suspension cells, and flavanone-2-hydroxylase and dihydroxypterocarpane 6-hydroxylase from soybean suspension cells (31). 

---