Bioindicators for the Dormancy Status of Fruit Trees | Bioindikatoren für den Dormanzstatus bei Obstgehölzen
2016
Hillmann, Laura | Kaufmann, Heiko | Blanke, Michael
This contribution is part of a bachelor thesis, which reviews the literature about suitable bio-indicators for the current dormancy status of a (fruit) tree in the winter. This is part of an on-going chilling research project and evaluation of the three chilling models as to their suitability for fruit growing in temperate zone regions with cool winters. The aim is to provide information on the dormancy status of a tree for the application of cultivation techniques to overcome dormancy.Potential bio-indicators could be grouped into one of 10 categories: Changes in 1) morphology, 2) bud respiration, 3) relative water content (RWC); 4) membrane permeability; 5) source : sink relationship viz cell communication; 6) carbohydrate content and metabolism; 7) polyamines, 8) phytohormones (plant growth regulators) and 9) flowering genes TFL1- and FT, 10) DAM (dormancy associated MADS box) genes and their expression. The literature review showed the following changes between paradormancy (facultative dormancy), endodormancy and ecodormancy:1) macroscopic and microscopic changes (until bud swell from February onwards);2) respiration of the buds hardly changed during endodormancy, but later indicative to predict the flowering date and number of buds e. g. in kiwi vines;3) Changes in relative water content (RWC) of the dormant buds with a) reduction in free water during paradormancy and b) appearance of bound water during endodormancy and c) induction and synthesis of dehydrins (hydrophilic proteins); 4) Changes in membrane permeability and cell to cell signaling with a decrease in both plasmodesmata density and activity from para to endodormancy in short days, which induce plasmodesmata clogging by glucans; chilling induces the synthesis of glucanase, an enzyme, which breaks down the clogging and re-opens plasmodesmata to enable Ca ²⁺ signaling; 5) changes in the carbohydrate metabolism, where a) sucrose contents in the buds peaks during endodormancy before release towards ecodormancy, b) sucrose (and sorbitol) can be transported in the xylem on frost free days from the roots, c) starch content decreases due to hydrolysis into glucose, i. e. monosaccharides increase in the bud;6) changes in the nitrogen metabolism; the protein content in the tree trunk increased during paradormancy and amino acids like the osmoticum proline in the buds during endodormancy;7) increase in polyamines during chilling in endodormancy and ecodormancy;8) the phytohormone ABA decreased during dormancy, while gibberellins (GA) and cytokinins played various roles in dormancy breaking;9) ca. 20 genes are up-regulated and ca. 30 genes are down-regulated; the expression of the flower-inhibiting gene TFL-1 (Terminal F flower Locus-1) peaked at the start of endodormancy, maybe associated with the chilling requirement, whereas expression of the flowering-promoting gene FT (Flowering Locus T) peaks during forcing;10) the expression of genes in the DAM (dormancy associated MADS box) 1 and DAM 4 as well as those of DAM 5 and DAM 6 both increased with the onset of cold temperatures and short days in the autumn. By contrast, DAM 2 is expressed under long day (summer) conditions and DAM 3 is continuously expressed irrespective of photoperiod and temperature. MicroRNA enabled the expression and translation of DAM genes; their activity is temperature dependent and increases under cold temperatures. All DAM genes, except for DAM 3, were dependent on photoperiod.Overall, relative water content (RWC), starch and glucose (or its ratio), amino acid (proline), ABA and DAM 1,4,5,6, seemed suitable bio-indicators for the dormancy status of a tree.The role and mode of action of traditional and alternative, new bud breaking enhancers (BBE), which often contain some of the above first eight compounds, are described in the second part.
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