Stamen development and microsporogenesis in cultured ear shoots

We reported previously (MGCNL 59:74-75, 1985) on the differential flower development in cultured ear shoot primordia. We noted that the optimum expression of this phenomenon depended on the concentration of kinetin (K) in the medium and the developmental stage of the initial explant. With K = 10-7M, young (< 10 mm long) ear shoots produced primarily male flowers whereas older shoots produced only female flowers. Based upon these observations, we have studied stamen development of cultured ear primordia more closely. Our observations are from experiments with Seneca 60 (Se60) ears under conditions which favor male flower development. These included the same medium as reported (MGCNL 59:74-75, 1985) with the following specific conditions: K = 10-7M; sucrose = 6% w/v; flasks maintained without shaking on a white reflective surface in a lighted incubator.

After 24 hours of culture, 2-3 explants were sacrificed at 2-day intervals and fixed in Carnoy's fixative. Analyses of flower development and stamen growth were recorded and cytological observation made from anther squashes.

As documented in Figure 1, both upper and lower flowers at 16 days possess three stamens and lodicules and are morphologically similar to those that develop normally in the tassel. The dimensions of the stamens at different times during the experiment are summarized in Table 1.

After 7 days in culture, anther sporogenous tissue (squashed and stained according to the procedure of Kindiger and Beckett, (Stain Tech. 60:265, 1985) was, for the most part, in early prophase of meiosis. The uninucleate microspore stage was reached after 10-12 days and binucleate pollen was found in cultures 13-18 days old. While we have not yet demonstrated that pollen from these cultured ear shoots will germinate and produce seed, we see no reason at present to expect failure. (NOTE OF CORRECTION: All references to sucrose concentration in our earlier note, MGCNL 59:74-75 (1985), should be expressed as % w/v and not M. Thus the values in Table 1 are 0%, 3%, 6%, 9% and 12%. Table 2 values are 2% and 6% and Table 3 value is 6%.)

Table 1. Mean lengths (mm) of stamens (n = 100).

Figure 1. Differentiated anthers from the upper and lower flowers of an ear shoot spikelet after 16 days of culture. (An = anthers; Fi = filament; L = lower flower; Lo = lodicule; and u = upper flower). 12x

Figure 2. Pollen mother cell (pachytene) after 8 days of culture. 1600x

Figure 3. Mature pollen after 20 days of culture of ear shoot. (op = operculum; Sn = sperm nuclei; and v = vegetative nucleus). 880x

V. R. Bommineni and R. I. Greyson
 
 


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