Grandpa's biology - 10


Initially, fusariosis slows the natural evolution of the plant...
The reverse occurs with diseased plant suddenly
ageing later on.

Evolution of sugars and nitrogen concentrations
in healthy and diseased leaves assayed at the
start and end of the experiment in a "fusariosis"
series, expressed in mg per gram of dry material

Sugar concentrations in healthy
and diseased leaves

Corresponding nitrogen concentrations

- Remark n° 1: In control leaves, the sugars concentration increases with the age of the plant, whereas the N concentration falls, these two phenomena being all the more sensitive the higher the dose of GA, and less sensitive the higher the dose of IAA. This appears to be normal, in view of the results already obtained.

- Remark n° 2: In diseased plants treated with GA (the least affected), these same sugars and nitrogen concentrations evolve in the same way as in corresponding healthy plants, but more slowly. This leads to the idea that the diseased leaves are younger and richer in auxins than the corresponding healthy leaves (see remark 1). This also matches the data given in the literature (leaves of plants suffering from fusariosis are characterised by hyperauxinia).

- Remark n° 3: In untreated plants and plants treated with IAA (the most affected), the reverse is observed. Sugars concentrations assayed at the end of the experiments in diseased leaves, which were expected to be lower than sugars concentrations in control leaves, were found to be distinctly higher. As for nitrogen concentrations, which were expected to be slightly higher, they were found to be virtually the same.

In the end, these results indicate:
- that initially the fusariosis slows the natural evolution of diseased leaves, since these leaves are physiologically younger than the control leaves (plants treated with GA);
- that the reverse then occurs, with diseased leaves suddenly ageing (untreated plants and plants treated with IAA).

Why does the diseased plant first show signs of rejuvenation? Why does it then suddenly age? If you want to know the answer to these existential questions, read the next chapter.

N.B. Nitrogen was assayed here using Kjeldahl's method, which takes into account any organic nitrogen in the tissues: ammonium ions, amino acids, nucleic acids, proteins of all kinds etc. which necessarily involves slow evolution of this element in the plant. The same does not apply to sugars, the method used only taking free sugars into account (sugars found in large molecules: starch, cellulose, lignin, nucleic acids, etc. are not assayed), which gives a much faster evolution of this element.

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 - 10