Grandpa's biology - 06









How to verify this hypothesis in a case
chosen at random: the host-parasite
relations between a tomato,
a fungus and a virus



To verify this hypothesis, Grandpa proposed the following experiment: a series of identical young plants would be split into batches of five or six individual plants. The first batch would then be treated with water, the others with solutions of auxin or gibberellin at equivalent and increasingly strong concentrations. He would then wait for long enough for the effects of treatment to be visible to the naked eye (it is better to avoid statistics), ensuring that all the plants received the same environmental conditions.

At the end of the experiment, leaves and roots would be taken from each batch for analysis… analysis of what? We shall see shortly. In any case, whether the hypothesis was right or wrong, the evolution of the control plants would show what would normally have happened in all these plants, in both basic metabolism (gene activity, RNA and enzyme synthesis) and intermediate metabolism (synthesis and breakdown of sugars, fats and proteins) or the plant phenotype (growth, differentiation, reproduction, etc.) There could be one of two results:


1. The hypothesis is right. The auxins and gibberellins really do act on DNA AT and GC groups, thereby controlling enzyme synthesis
- Everything that happened in the control plants during this experiment was therefore linked to the evolution of a complex endogenous auxin/gibberellin balance;
- The different treatments modified this natural auxin/gibberellin balance in favour of auxins or gibberellins, this modification being more intense the stronger the dose of treatment used;
- And the results obtained clearly demonstrated that, when treatment with auxin is "white", treatment with gibberellin is "black", the reaction being more marked with increasingly strong doses.

2. The hypothesis is wrong. Auxins and gibberellins do not act on DNA AT and GC groups. What happened in the control plants is not linked to the evolution of endogenous hormone balance. IAA and GA treatments do not alter this balance. A miracle would be needed to make the results obtained match the hoped for results.


The director, who did not believe in miracles, agreed. The equipment then had to be chosen. Grandpa had no preferences. If the hypothesis was right, it should be verified in every case and under all kinds of conditions. The director would therefore decide. His choice was to use a variety of tomato called Supermamande, sensitive to fusariosis, from which he could obtain selected, homogenous seeds, and one pathogenic fungus, Fusarium lycopersici. This was a plant physiopathology laboratory, so the hypothesis would not be verified by growth but by the evolution of host/parasite relations.



presentation/contentsa work of popularizationstory of modern biologythe point of view of French citizenssome basic concepts to recallgrandpa's hypothesishow to verify this hypothesisfirst testsevolution of plants according to auxin and gibberellin treatmentshost-parasite relationsaction of the fungus on the plantaction in return of the plant on the fungusaction of the virus on the plantaction in return of the plant on the virusa plant subjected to double attack by both fungus and virusthe scientific debatethe Peter principleconclusion - answer to some questionsimages




Grandpa's biology - 06