Gibberellins during development

Fig. 3.26. Distribution of radioactive gibberellin during development and germination/ growth of Pisum sativum seeds. Developing seeds were fed with H-GAi in vitro and allowed to develop to maturity. The distribution of radioactivity during development and subsequent germination was traced. — developing seeds, germinating seeds/growing...

Fig. 3.25. Changes in gibberellin content during development of Phaseolus multiflorus seeds. After Durley etal., 1971 [48]...

Table III. Effect of Photoperlod and Gibberellin A3 Treatments during Seedling Development on Flowering of Cu umis sativus L., var. Wisconsin SMR-12...

Peas are a low-fat plant, and it is likely, therefore, that our results should not be freely extended to all other auxin- and gibberellin-induced systems. In fact, the equally classic oat coleoptile section hormone assay does not seem to respond to the fatty substances. Even the pea section fails to respond, unless the seedling has received some red light during the early part of its development. 

There are situations where, during the course of normal cellular development, holes appear in the CMT array. One such example is during the formation of bordered pits in secondary xylem vessel elements [61]. Pit fields also develop in the maturing cell walls of the maize root cortex and may be pre-figured by the occasional MT holes that are normally seen in these cells. However, it is too early to say whether intracellular changes in gibberellin levels are related to these particular intracellular morphogenetic events which, in the case of secondary xylem vessels, would be rather localized to only a fraction of the cells within the secondary xylem tissue as a whole. 

Seeds are a rich source not only of gibberellins and cytokinins but also of auxins. Relatively few generalizations can be made about auxin content, stage of endosperm development, and growth rate of embryos. During growth of apple seeds one finds two peaks of auxin accumulation (Luckwill et al. 

Loehwing WF (1938) Physiological aspects of sex in angiosperms. Bot Rev 4 581-625 Lorenzi R, Bennici A, Cionini P, Alpi A, D Amato F (1978) Embryo-suspensor relations in Phaseolus coccineus Cytokinins during seed development. Planta (Berl) 143 59-62 Luckwill LC, Weaver P, MacMillan J (1969) Gibberellins and other growth hormones in apple seeds. J Hortic Sci 44 413 24... 

Fig. 3.24 A and B. Changes in gibberellin content during seed development. (A) Echinocystis macrocarpa. After Corcoran and Phinney, 1962 [42]. (B) Hordeum vulgare cv. Brevia. After Mounla and Michael, 1973 [130]. — free gibberellin, bound gibberellin...

The auxins, like the gibberellins, show fluctuations in level during the course of seed development. Many examples of this have been reported but only a few will be mentioned here. In apple seeds there are two peaks in auxin content, the first coinciding with the change from a free nuclear (i.e. coenocytic) endosperm to a cellular one (Sect. 3.1). Digestion of the endosperm then begins, ac-... 

The next phase of fruit development starts with the double fertilization. During this phase the endosperm is formed. The embryo also grows by dividing. Evidently this is associated with active cell division, which takes place in the fruit tissue. Perhaps initially the regulating hormones come from the endosperm but in later stages they are derived from the embryo. In addition to lAA and gibberellins cytokinins in particular seem to be involved, as was shown by analyses of some fruits during this phase. 

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