Tree Age and Vegetative Rest: Impact on Budburst and Climate Change

Extract

[...] The first consisted of mutating a vp1 gene present in wheat and corn. This gene allows the synthesis of ABA. It was observed that when the mutated gene prevents the synthesis of ABA, wheat grains do not germinate, whereas when the gene is not mutated, the seeds can germinate. Therefore, ABA inhibits germination and its growth; it is an inhibitory hormone that regulates growth. ABA thus allows dormancy. It can be shown that ABA is synthesized before entering dormancy. Next, in a second experiment, it was about mutating the NCED gene in a tomato A stem to make the synthesis of ABA ineffective. [...]

[...] Therefore, the tree has accumulated enough heat for budburst. To come out of this dormancy, it must accumulate a certain number of hours of cold: this is the need for cold. We then looked for what allowed budburst, since the tree must well wake up For this, we went to see in BCPST prep courses as well as a study on the dormancy of the cherry tree. The tree waits for a final signal: a sufficient heat threshold. It adds up the daily temperatures exceeding approximately 7 °C. [...]

[...] Vegetative rest differs depending on the age of the tree, with hormonal, genetic, enzymatic and environmental reactions. Trees and plants in general adapt to the environment in order to survive. However, we have observed that in the mother tree, the branches are 'divided into 2'. In the area closest to the trunk, the foliar part develops very little compared to the end of the branch. We can assume that this is due to the fact that the end of the branches is more lignified and the presence of hormones is more important, with the presence of the meristematic zone. [...]

[...] The mechanisms of vegetative rest Forest phenology corresponds to the major stages of the annual cycle of trees, which is what intrigued us. In the autumn, the tree gradually reduces its metabolic activity. It limits the circulation of raw sap and begins to store organic matter in its tissues. The drop in temperatures then triggers what is called hardening, the tree drains a part of the water contained in its cells and increases the concentration of sugars and proteins. This allows it to better resist freezing. [...]

[...] We must also consider epigenetic memory: over the years, trees accumulate biochemical modifications that occur on histones such as methylation or acetylation. These processes allow inserting a methyl or acetyl group into certain nucleotide bases. This does not alter their genes, but modifies their expression. Young trees, on the other hand, do not yet have this memory, making them more vulnerable to "false springs". Then, young trees use a large part of the photosynthesis products for their growth. They therefore have fewer resources available to resist freezing. [...]