Gibberellins bioassay for

In the germination of cereal seeds, it was long known by brewers that if the embryo was excised (or dead) the endosperm would not be hydrolyzed and sugars would not be released. In 1960, Paleg showed that amylolytic activity in the embryo-less half could be fully restored in the presence of gibberellin. In other words, the substance that passed from the embryo to the endosperm (or rather, to the living cells of the aleurone layer that encloses the dead endosperm) induces there the synthesis of a-amylase which is responsible for hydrolysis of the stored starch reserves held in the endosperm. The extent to which the a-amylase was induced became another bioassay for gibberellin. 

Figure 1. Effects of CaCl2 on bioassays for auxin, gibberellin, and cytokinin. A effects of CaCl2 on elongation of oat coleoptile sections in the presence and absence of indoleactic acid B effects on elongation of lettuce hypocotyls in the presence and absence of gibberellic add and C effects on enlargement of Xanthium cotyledon pieces in the presence and absence of benzyladenine (13).

Brassinolide was tested on 17 bioassays for growth substance. The results led to claims that brassinolide possesses a broad spectrum of biological activity, including gibberellin-, auxin- and cytokinin-like activity (32,34). These claims must be treated with some caution however, since the claimed "specificity of some of the bioassays selected is questionable. At present three bioassay techniques (35,36,37) are used routinely for the detection of brassinolide activity. All three assays are sensitive to auxin, which is a prerequisite for the detection of brassinolide-like compounds. This is not to say that brassinolide has auxin-like activity, but rather there seems to be an interaction of cooperative action between auxin and BR. 

In Plant growth substances 1973. Hirokawa, Tokyo, pp 917-924 Bentley-Mowat JA, Reid SM (1967) Effect of gibberellins, kinetin and other factors on the growth of unicellular marine algae in culture. Bot Mar 12 185-199 Bentley-Mowat JA, Reid SM (1968) Investigation of the radish leaf bioassay for kinetins, and demonstration of kinetin-like substances in algae. Ann Bot 32 23-32 Bergmann L (1965) The effect of kinetin on the metabolism of plant tissue cultures. 

Bioassay procedures for the determination of gibberellic acid have been developed (2, 5), but more recent chemical fluorometric assay methods are equally specific. However, both assay methods show a low response with samples containing less than 10 /x/xg. of the gibberellins. Consequently, in determining residual amounts within the part per billion (p.p.b.) range, relatively large samples must be extracted and extracts partially purified to satisfy the assay conditions. These operations are usually accompanied by some material losses or degradation, which impair quantitative interpretation of the results. Natural inhibitors can influence the results in the bioassay method (2), and fluorescent contaminants can interfere with the spectrophotometric analysis. 

Plants were grown and treated with CCC as in bioassay procedure (15). Two days after CCC treatment, plants were sprayed until wet with gibberellin solutions. Two weeks after CCC treatment lengths between bases of nrst and second leaf blades were measured and expressed as per cent of length for untreated controls. Results are average of several experiments. 

Improved methodology for the rapid assay of hepatic HMG-CoA reductase has been described and new and simplified assays are available for cholesterol 7a-hydroxylase, 4-methylsterol oxidase, 3/3-hydroxy-steroid dehydrogen-ase, the biosynthesis of bile acids, and microsomal cholesterol levels.The rate of biosynthesis of gibberellins has been monitored by a bioassay based on /3-amyrin production of Amaranthus seeds. 

In subsequent years, John W. Mitchell developed two bioassays, popularly known as the bean first intemode and the bean second internode bioassays. The first intemode test was successfully used for screening several commercial chemicals, including such popular pesticidal chemicals as 2,4-D, 2,4,5-T, and Amo 1618. The bean second intemode bioassay did not find immediate application, although gibberellins, including gib-berellic acid (GA showed elongating properties in this test. 

Gibberellin A4 in most bioassays shows activity intermediate between that of gibberellins Ai and A2. However, it has been noted that many species of Cucurbitaceae show distinct growth responses to gibberellin A4 at levels where none of the other gibberellins induce any response. The basis for this differential response is not understood. 

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