Hs-ipt

Fig. 4. Release of axillary buds in uninduced transgenic petunia plants. Uppermost nodes of a hs-ipt transgenic petunia plant showing growth of axillary buds...

In order to verify the functionality of the chimeric hs-// f gene, plants were analyzed for induction of ipt mRNA. Leaves from four independent transgenic petunias were excised and incubated in a water bath in vitro at 42 ° C for 1 h. Figure 2 shows that the heat shock induced ipt mRNA in all four plants. No detectable ipt mRNA was found at the control temperature (25 °C) in the four independent plants. 

Fig. 2. Analysis of vs-ipt gene expression in response to temperature elevation. Leaves were excised from four independent transgenic petunias A-D) and incubated at 25 C or at 42 C for 2 h. Total RNA was extracted immediately thereafter and induction of the hs-// / gene analyzed by m m .r. i V...

The unexpected result of this work is that heat induced increases in the ipt mRNA (Figs. 2 and 3), but did not produce effective alterations in plant development. Preliminary analysis of cytokinin levels indicates that even without heat induction, the transgenic plants contain cytokinin levels 8-fold over that of control plants, while cytokinin levels in heat-induced plants is 60-170-fold over that found in control plants (Morgan, unpubl.). One explanation for these results is that the cytokinin levels after heat shock may be beyond the ability of the plant to respond. The supraoptimal cytokinin levels after hs may negate the developmental effects of cytokinins that were found at control temperatures. Our current work is focusing more closely on defining the optimal response times and processes. 

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