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Modification of the polypeptides pattern during installation and elimination of the apple seeds dormancy

Author: Vitalie Samoil
Degree:doctor of biology
Speciality: 03.00.04 - Biochemistry
Scientific adviser: Alexandru Dascaliuc
doctor habilitat, professor, Institute of Genetics, Physiology and Plant Protection of the ASM
Scientific council:


The thesis was presented on the 31 March, 2005
Approved by NCAA on the 21 April, 2005


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The goal of our investigations was to determine the specificity of the processes of protein accumulation and degradation as well as their possible correlative relations with the installation and elimination of dormancy of Malus domestica Borkh. (cv. Slava pobediteleam) seeds. The germination capacity of immature seeds was determinate firstly. It was demonstrated that about 60% of seeds, collected at 39-45 days after flowering (DAF), are capable to germinate without stratification. After this and until completion of the maturation, the seeds have not demonstrated the germination capacity without stratification.

From 39 to 45 DAF, when developmental transition of the embryo from morphological to physiological maturity take place, the apparition of a 28 kDa polypeptide and decrease of the content of the 44, 46 kDa polypeptides are detected. The similar changes in polypeptide content are observed during increase of germination capacity of mature apple seeds under stratification. These changes correlate with increase of germination capacity in both cases. The deepness of modifications of the content of 28, 44 and 46 kDa polypeptides during seed development (when immature seeds are able to germinate without stratification) is less pronounced than during stratification of that in the mature seeds. Increase of 28 kDa polypeptide content marks both: the onset of dormancy of immature seeds during development, as well as the complete release of dormancy of mature seeds under stratification. This phenomenon proves interdependence between processes of embryo protein degradation and seed germination capacity.

Apple seeds reach the germination capacity during maturation and under stratification in parallel with modification of the isoelectric point of several polypeptides. This happens thanks to the degradation of some basic amino acids at C-side of corresponding polypeptides. Reaching of full germination capacity of the seeds is accompanied by dramatic changes in polypeptide spectra as a result of modification of molecular weights as well as of isoelectric points. These changes are induced by modification of protease content and activity.

It was established that the rate of proteolysis of proteins in extracts from embryonic axes of seeds at 39-42 DAF is higher than that from the embryonic axes at other periods of development. Exact during this short period, the immature seeds are able to germinate without stratification. Increase of germination capacity of mature seeds under stratification is accompanied by decrease of proteolytic activity of protein extracts as well as by decrease of the time required for reaching the maximal rate of proteolysis.

Experimental data, obtained as result of comparative stratification of seeds in fruit, in sand (classical stratification), and in consecutive combination fruit/sand are in accordance with hypothesis that support implication of several factors in elimination of seed dormancy under stratification.