The influence of chronic gibberellin treatment on the expression of the heterochronic mutation Cg2
--N. V. Krivov and V. N. Lysikov

In order to understand a specific nature of the hormonal disequilibrium in corn heterochronic mutations and its influence on developmental processes, plants of Cg1 and Tp1 were treated with a gibberellin solution (Nickerson, Am. J. Bot. 47:809, 1960). Recently, this experiment has been carried out once more (Ritchings and Tracy, Maydica 34:297, 1989).

One of the sublines of the heterochronic mutation Cg2 carriers (Cg2/Cg2) was also GA3 treated according to Nickerson's protocol at a dose of 82 ppm. Twenty-three corn plants were GA3 treated, and 25 plants were treated with H2O. Gibberellin changed the corngrass phenotype, i.e. the plant grew significantly higher and side shoots were not formed (Fig. 1). The node number and leaf length increased, leaf width remaining nearly unchanged. The male inflorescence in the form of a spikelet was observed only in single corn plants, and ears were small as before (Table 1).

Table 1. Response of the Cg2 220-569-205-315 subline to gibberellin treatment.
 
Treatment Plant height, cm Tassel length, cm Cobs no. Stems no. Stem diameter, mm Nodes no. Leaf length, cm Leaf width, cm
Control 75.1±7.8 7.3±3.6 9.9±1.4 10.3±2.6 8.9±1.6 12.6±1.2 41.9±3.0 2.1±0.4
GA 113.3±11.6 -- 1.8±0.5 1.0 9.1±0.5 17.3±1.2 46.7±2.2 2.3±0.2

According to its response to exogenic gibberellin application, the heterochronic mutation Cg2 is deficient in the growth hormone. Nevertheless, like the heterochronic Cg1 mutation, Cg2 is not a simple biochemical mutant resembling dwarf mutants and, despite the absence of a complete and clear pattern of hormonal balance changes occurring in heterochronic corn mutations, a hormonal explanation of the sex display in corn does exist. This explanation implies a seasonal alteration of the hormonal balance between cytokinins, which cause a female expression, and gibberellins, which are produced by leaves and cause a male expression (Iltis, Science 222:886, 1983). Apparently, something like that occurs in heterochronic corn mutations.

Figure 1. The corn plant (left) was chronically treated with a GA3 solution. The corn plant (right) was chronically treated with H2O.


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