Polowick's (M.S. thesis, U.W.O., 1981) in vitro inflorescence techniques provide an opportunity to explore the regulation of sexuality more closely than heretofore. It allows for (1) more precise application of exogenous factors, (2) control of environmental factors like photoperiod, temperature, etc., (3) testing of only one growth regulator at a time, (4) more uniformity in supplying the nutrients with a defined media, and (5) considerable ease of observation.
In order to provide a basis for future studies of cultured immature ear shoots, we have explored the importance of sucrose and kinetin. Our basal medium consisted of Murashige and Skoog (1962) major and minor minerals, White's vitamins and glycine, and inositol (100 mg/l). Ears were explanted into 125 ml Erlenmeyer flasks containing 40 ml of media. They were first exposed to 3 days on an orbital shaker and another 20 + days unshaken, on a white reflective shelf in an illuminated incubator. A day/night cycle of 18/6 hours of light with 400-500 f.c. and 28 ± 2 C temperature was maintained throughout the growth period.
Table 1 summarizes the effect of the sucrose concentration on explanted ear shoots. In terms of fresh weight of the whole inflorescences, an optimum concentration is found at 0.6 M. This concentration is also apparently optimal for flower development. Representative experiments with kinetin are summarized in Table 2. Depending upon the concentration of sucrose, the level of kinetin for optimum growth (fresh weight) of the ear is 10-7 or 10-6 M. The proportion of male to female flowers developing on explanted ears under optimal kinetin and sucrose concentrations varies depending upon the size of the initial explants (Table 3). Short (young) ears produce more male flowers whereas longer (older) ears produce more female flowers. While the significance of this observation has yet to be explored, it should be noted that this differential result is achieved without the application of either IAA or GA3.
Table 1. Mean final fresh weight (gm) values of cultured Seneca-60 ear shoots (5.0-10.0 mm) after 25 days, under different sucrose conc. levels.
Table 2. Mean fresh wt. of cultured ear shoots after 20 days, under different kinetin and sucrose levels.
Table 3. Mean percentage of differentiated flowers of cultured Seneca-60 ear shoots after 20 days in the presence of kinetin (10-7 M); sucrose (0.6 M).
V. R. Bommineni and R. I. Greyson
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