Enzyme synthesis gibberellins

Gibberellins Growth, complex 5-ring hydroxylated alicycle. Requires iron containing enzyme for synthesis... 

It is conceivable that several more than the five known gibberellins can and probably do exist. It might be, then, that rather than gibberellin stimulating one locus that synthesizes enzymes, a specific gibberellin stimulates the locus of synthesis of a specific enzyme or closely related systems of enzymes. 

MONNA, L., KITAZAWA, N., YOSHINO, R., SUZUKI, J., MASUDA, H., MAEHARA, Y., TANJl, M., SATO, M., NASU, S., MINOBE, Y., Positional cloning of rice semidwarfing gene, sd-1 rice "green revolution gene" encodes a mutant enzyme involved in gibberellin synthesis, DNA Res., 2002,9, 11-17. 

Morre et al. (1970) detected the synthesis of PC from CDP-choline in extracts from onion stem. The activity was associated with a particulate fraction. Devor and Mudd (1971b) found that the 100,000-g pellet from spinach leaves had the highest total amount and specific activity of this enzyme. The metal ion requirement could be satisfied by Mn + (saturating at 0.3 mM) or Mg + (saturating at 13 mM). The for CDP-choline was 10 pM, and the pH optimum was 7.5-8.0. Only modest stimulation could be achieved by the addition of DG. Johnson and Kende (1971) measured the enzyme in particulate fractions (44,000-g pellet) from barley (Hordeum vulgare L.) aleurone layers and found the activity greatly stimulated when the aleurone layers were exposed to gibberellin before extraction and assay of the enzyme. 

Attempts have been made to determine why a-amylase synthesis eventually declines in the intact grain (e.g. see the decline in rate of a-amylase synthesis in Figure 7.4A and B after three and two days respectively). One possible reason is that production of the stimulus (i.e. GA) for a-amylase synthesis decreases, perhaps because hormonal synthesis is itself inhibited by the products of starch degradation. Unequivocal evidence supporting this possibility is lacking. In any case, sufficient gibberellin is released into the endosperm during the first one or two days after the start of imbibition to support a-amylase synthesis for at least four to five days thereafter (Fig. 7.4 C). Thus any limitation in GA synthesis after one or two days is unlikely to affect enzyme production. 

Gibberellins are mainly responsible for triggering the synthesis of key enzymes that will degrade nntrients stored in the first and second reserve tissues of the germ and endosperm, respectively. Two gibberellic acids (GA, and GA3) are the major hormones produced by the anbryo. These hormones are later transported along with the absorbed water to the endosperm through the tube cells, and induce aleurone cells... 

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