Biology of a process
The majority of higher plants derive energy for growth and development solely from photosynthesis (autotrophic nutrition). However, each plant undergoes in its ontogenesis a short but important stage of heterotrophic nutrition. The germinating embryo prior appearance of the first photosynthetic structures is fed exclusively by storages accumulated during the seed formation (i.e., proteins, fats, and carbohydrates) [West M.A.L. and Harada J.J. 1993, Shewry P.R., 1995]. As is well known, the main function of a plant seed is to provide a viable offspring. The storage substances play a key role, by providing nutrition of a seedling during the heterotrophic stages of its development. Seed formation passes several overlapping but rather independent stages. Before the beginning of flowering, an embryonic structures are formed out of apical meristem. The switch from the vegetative stage of development to the reproductive one is regulated by different mechanisms. Among these mechanisms are inner biological clock, hormonal background, and environmental conditions such as a day length, temperature fluctuations, humidity, etc.
1. At the first stage, a pollination followed by fertilization occur.
2. The second stage is characterized by establishment of a general composition of the future plant. Embryonic tissues (protoderm, procambium, ground meristem) are being differentiated. The axis of development of an embryo is being formed, with apical meristem of a root from one side and apical meristem of a stem - from the other.
3. At the following stage, storage substances are being intensively worked out, these substances will be necessary at subsequent stages, during seed germination.
4. Seed development is finished by preparation of a seed to the dormancy stage and final maturation at the dormancy stage.
5. Dormancy stage.
The gene networks conception allows considering a separate phenotypic feature, separate
process, stage of development, and ontogenesis in a whole as a result of functioning of
gene networks, which are organized hierarchically [Kolpakov F.A. et al., 1998]. Every
stage of ontogenesis can be figured out as a result of interaction between gene networks.
Elementary events occurring at the cellular level play a considerable role. One and the
same gene networks function synchronically in all cells of a certain tissue. The presence
of regulatory contours supports a definite functional state of a gene network, i.e.,
timely transport of nutrients into developing embryo) or its transformation into another
regime of functioning, which may occur under the action of environmental factors (e.g.,
change of dominant storage protein under nitrogen deficiency). The action of external
signals turns one gene network off and turns on the others. Hormones, Ca++ ions and other
low-molecular compounds are molecular carriers of the signals. A gene network with a
higher range provides the coordination of this process. A gene network on biosynthesis of
storage proteins in plant seeds is under the control of the gene network supporting
development of viable seeds. This gene network, in its turn, gets on after a flowers
fertilization and is governed by a gene network of a maternal plant having initiated a
generative phase of development.
The gene network on storage proteins biosynthesis provides a transition of a seed from the stage of main embryonic structures formation to almost mature state. After accumulating of a sufficient amount of resources, the gene network considered stops its functioning and the genes of storage proteins biosynthesis are repressed. The mechanism terminating an accumulation of storage substances is still unknown.