It is assumed that plant growth regulators (PGR's) are important, possibly causal, factors in the determination of sex expression in higher plants. There are, basically, three ways to test this hypothesis: measurement of endogenous levels of these substances, their exogenous application to the intact plant and their more direct addition in vitro. In some cases the consistency of data from these sources is striking and compelling. For corn, however, present information is incomplete and the relationship remains problematic.
We now report that Zea tassels (var. "Seneca-60") have been successfully cultured in sterile liquid medium. Immature tassels (approximately 1 cm long from 4-week-old plants) possessing spikelets with stamen and ovary primordia grow and differentiate over a 2-3 week period up to 20 cm and resemble normal tassels in many ways.
Maximum growth in the basal medium (BM) is expressed in plump florets with green, highly veined, papery and hairy glumes. Stamens differentiate into anthers and filaments and, occasionally, microspores, complete with wall, are obtained. Normal lodicule development is also observed. The conditions used for this surprisingly rapid response are simple. Tassels are dissected from surface sterilized stem-tips and explanted into 125 ml Erlenmeyer flasks containing 40 ml of liquid medium. The BM which supports this growth contains Murashige and Skoog minerals, White's vitamins and glycine, i-inositol and 3% sucrose. Flasks are shaken in a lighted growth chamber.
Addition of plant growth regulators to the basal medium induces interesting, and perhaps instructive, modifications. Better stamen development is achieved with IAA added to the basal medium. GA3 at 10-7 and 10-6 M enhances elongation of the main axis, branches and glumes but detracts from stamen and ovary differentiation, making these organs watery and filmy. A general proliferation of organs and also callus is obtained with cytokinins. In the presence of cytokinins, especially zeatin, ovary and silk differentiation is elicited.
These primary results indicate that despite difficulties with in vitro culture of other corn organs and tissues, the tassel possesses considerable potential for study via this technique. In addition to the tests on the sensitivity of the tassel to added PGR's these could include: (1) comparison of the sensitivities and requirements of tassel and ear, (2) analysis of the response and capacities of flower mutants such as an1, Tu, ts, Vg, etc., (3) the exploration of meiosis via various biochemical probes. The evaluation of some of these possibilities is under way.
Patricia L. Polowick, K. Raman and R. I. Greyson
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