Gibberellin maize

An excellent example nf the performance of gibherellins is given by S.B. Ross, el al. in "Gibberellins A Pllytohormonal Basis for Heterosis in Maize." Science. 1216 (September 2. 1988). 

Figure 2. Relation between sprouting of Red Pontiac potato tubers (A) and level of endogenous gibberellins in potato peels and buds during and after rest (C) as measured by internode elongation of maize mutant d5( B)...

Figure 3. Gibberellin-like activity in peels of Red Pontiac potatoes during and after rest as revealed by intemoae elongation of maize mutants 1,3, and 5...

Figure 1. Elongation of second leaf sheath of d-1 maize following application of various gibberellins (0.1 pg.) to base of first leaf sheath...

When 10 /J. of hydrangenol and 10 /J. of gibberellin, in appropriate concentrations, were placed separately at the base of the first sheath of d-1 maize, elongation of the second leaf sheath increased with increased concentrations of... 

Figure 4. Mean length of fully expanded second leaf sheath of d-1 mutant maize treated with gibberellin tmd hydrangenol...

Abscisic acid is a negative regulator in that it primarily antagonizes the action of cytokinins, auxins, and in particular, gibberellins. Abscisic acid decreased the activity of polymerase in radishes (52), peas (53), maize coleoptiles (54), and pear embryos (55). More detailed studies are needed before the question of ABA-induced "modification" of RNA polymerase (54) or "alterations" in the number of sites for template activity (56) can be answered. In barley aleurone cells, ABA-induced suppression of GA-induced <-amylase formation was presumed to involve the continuous synthesis of a short-lived RNA (57). 

Jankowski, J. Wielgat, B. Kleczkowski, K. Gibberellin-affected methylation and synthesis of ribosomal RNA in isolated maize seed scutellum. Plant Sci. Lett., 1975, 5, 347-350. 

Winkler, R.G. and Helentjaris, T. (1995) The maize dwarfS gene encodes a cytochrome P450-mediated early step in gibberellin biosynthesis. Plant Cell, 7,1307-17. 

Milborrow [102] first isolated 8 -OH-ABA, but since then this compound has remained elusive due to its spontaneous rearrangement to PA. However, 8 -OH-ABA has been identified by GC-MS in methylated and trimethylsilylated extracts from immature fruits of Vigna [103], maize seedlings [104], and tree ferns [105] that were analyzed for gibberellins. Also, the 3-hydroxy-3-methylglutaryl conjugate of 8 -OH-ABA, which upon alkaline hydrolysis yielded PA, has been isolated from the fruits of Robinia pseudoacacia [106,107] (Fig.4). Recently, it has been found that 8 -OH-ABA forms a complex with boric acid that dissociates in water. The liberated 8 -OH-ABA is relatively stable in acidic solutions, but cyclizes to PA under neutral or basic conditions [108]. These findings may explain why isolation of 8 -OH-ABA has been so difficult to reproduce. 

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. 

Fig. 3. Impaired arrangements of CMT arrays in cells of gibberellin (GA)-deficient mutant (d5) maize roots (a,b) and in cells of cv. LG-11 maize roots treated with inhibitor of GA biosynthesis 2S, 3S paclobutrazol (e,f). For more details on these treatments see [119]. Note that CMT arrays show abundant holes in the GA-deficient root cells (arrows). Addition of exogenous gibberellic acid rescues these lesions and well ordered transverse CMT arrays appear in cells of both d5 mutants (c,d) as well as of paclobutrazol-treated LG-11 root cells (g, h). Bar represents 10 pm.

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