Title: Germination and early root growth of sugar beet (Beta vulgaris L.), the functioning of ethylene.
Other Titles: Kieming en wortelgroei van suikerbiet (Beta vulgaris L.), de functie van ethyleen
Authors: Abts, Willem; S0171218
Issue Date: 11-Feb-2015
Abstract: Sugar beet production contributes to 25 % of total world sugar production. Sugar beet growers face regularly problems during field emergence, especially during unfavourable growth conditions. To overcome these problems, it is important to gain more insight in the processes involvedin germination and seedling growth. Ethylene is known to be involved inthe germination of several species (e.g. Arabidopsis, Nicotiana, lettuce), but its function during germination and subsequent early root growthof sugar beet is lacking. In addition, possible interactions between ethylene and other plant hormones during these processes in sugar beet areunresolved. Consequently, the current knowledge about the role of planthormones during the germination and seedling growth of sugar beet should be elaborated to improve field establishment.Physiological, biochemical and molecular data obtained from detailed sampling series allowed to unravel the kinetics of the ethylene biosynthesis during germination and early root growth. These results showed that ethylene has no influence on the germination process of sugar beet. Also the effect of priming and different environmental conditions on the germination pattern and ethylene production was studied. Under each of the tested conditions/seed treatments, ethylene was only detected after the start of germination, proving that ethylene is not involved during the germination of sugar beet.However, ethylene influenced early root growth in a concentration-dependent manner, whereby low concentrations of 1-aminocyclopopane-1-carboxylic acid (ACC; precursor of ethylene) stimulate root elongation, while high concentrations inhibit root elongation. Thus, exogenous application of a certain plant growth regulator at a dose higher than the physiological levels can have a different effect on the plant morphology compared to the application of physiological relevant concentrations. A detailed study of the gene regulation of ACC synthase (ACS) and ACC oxidase (ACO) showed that ACS is the rate limiting step of ethylene production during seedling growth of sugar beet, while both ACS and ACO can have a rate limiting function during the start of ethylene production. Also the function of IAA (indole-3-acetic acid) and its interaction with ethylene during early root growth was studied. We proved that IAA inhibits the conversion of ACC to malonyl-ACC (MACC), resulting in a prolongedperiod of high rates of ethylene production. Consequently, this resulted in a stimulated root elongation. In contradiction to the generally assumed model where ethylene regulates the auxin production, we did not find such a control mechanism in sugar beet. Finally, we proved that abscisic acid inhibits sugar beet germination. In contradiction to previously published literature, no interaction between abscisic acid and ethylene was found. Interestingly, levels of several endogenous plant growth regulators, which were shown to influence the germination or early root growth, greatly differed between the pericarp and the true seed. Consequently, the pericarp is assumed to play an important role during thegermination and seedling growth of sugar beet.In conclusion, we showed that ethylene and auxins play an important role during the early root growth of sugar beet, whereby both plant hormones have a stimulating effect on root elongation. We also showed that abscisic acid inhibits thegermination of sugar beet.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Division of Crop Biotechnics

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