The ratio of auxins and cytokinins is critical factor for plant response to differentiate, so, let us think, Is it possible to determine the type of response ( through the control of exogenous growth regulators) if the endogenous plant-hormones were determined for explant? Are there practical and applicable method to determine endogenous plant-hormones ? thanks in advance!
I'm not sure I follow.
You want to determine, whether callus will form roots or shoots based on endogenous phytohormones?
I do not think it is worth the time and effort to determine the level of endogenous hormones of the ex-plants. the relation between auxins and cytokinins in plant morphogenesis is well known and work for almost most plant species when propagated in vitro. so manipulating the ratio of auxins to cytokinins will give the response you are interested in.
Even you can easily quantify the amounts of auxin and cytokinin in certain cells in the explant, you cannot predict what these cells will become. The endogenous concentration of a hormone in a particular cell is the function of local synthesis and long-distance transport that are under positive and negative feedback regulations. In other words, the concentration determined at one time point may not be the same at another time point. And the location of the cells in the explant should also matter. In tissue culture, the external hormone concentrations should over-ride the endogenous hormone concentrations, rendering the endogenous hormone concentrations irrelevant.
The response of a system in the cell or the tissue is determined not only by the hormone level but by the sensitivity (or responsiveness) of the system to the hormone. The sensitivity is response-specific. On top of that, sensitivity changes with time and space (that is, location of the tissue in the plant or location of the cell in the tissue), and it is modified by external conditions (such as temperature, light, medium ingredients). Measurement of endogenous hormones in an explant used in tissue culture will not reveal a better understanding or will not yield you a hint about possible response of the tissue in vitro .
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