Under conditions of a combination of an external (light/dark) factor and a hormonal factor (gibberellic acid) during germination, changes in the functioning of the source-sink system in heterotrophic phase of horse beans development were studied. The increase in the epicotyl, root and seedling length, both in light and dark, as well as in the dry matter of the mass of the seedling organs, was found under drug action. Reserve substances were used more intensively under gibberellin and skotomorphogenesis influence. It is evidenced by the minimum dry matter of cotyledons and higher reserve utilization rates for root and epicotyl formation. Gibberellin stimulated starch breakdown in both, but during germination in dark, the rate of starch use was higher. Other content of sugars in skotomorphic seeds was associated with more intensive outflow for organogenesis needs: formation of root and epicotyl structures. The changes in the content of starch were higher than the changes in nitrogen content in skotomorphic and photomorphic seedlings. This indicates that gibberellin stimulates hydrolysis of reserve protein only after starch hydrolysis in dark. No specific gibberellin regulation of phosphorus and potassium outflow from seeds for organogenesis needs was found, suggesting sufficient mineral nutrients supply to ensure their re-utilization during germination, photo- and skotomorphogenesis processes.

Functional changes in the source-sink system of maize sprouts under combination of external (light/dark) and hormonal (gibberellic acid/retardant) factors during germination were studied. It was found that the phytohormone action significantly increased the coleoptile, root and seedling length, dry matter mass of organs, both in light and in dark. Tebuconazole caused the opposite effect due to its retardant action. The inactivation of endogenous phytohormone was confirmed by less intensive use of seed substances, the minimum dry matter of root and coleoptile and lower reserve utilization rates under tebuconazole influence, in particular under photomorphogenesis condition. The non-maximum mass of cotyledons may indicate a kind of optimization of use of reserves under tebuconazole treatment. Gibberellin stimulated starch breakdown in both light and dark, but starch usage was higher in dark. The lower content of sugar in the seeds of skotomorphic plants in control and under gibberellin action was explained by intense outflow for the organogenesis needs. Gibberellin stimulated the hydrolysis of reserve protein after intensive starch hydrolysis in dark. Specific gibberellin regulation of phosphorus outflow for the organogenesis processes under the photo- and skotomorphogenesis conditions and no regulation for potassium under photomorphogenesis conditions were found.

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The combination of light/dark external factor, GA 3 and GA 3 synthesis inhibitor tebuconazole significantly changed the pattern of the source-sink relationship in sprouts of horse bean during seed germination. The usage of gibberellin at light leads to increase of reserve starch hydrolysis in germinating horse bean seeds. The absence of light was a more significant factor for the starch hydrolysis than the exogenous use of gibberellin and the antigibberellin substance tebuconazole. The nitrogen-containing compounds content and reserve fats at early stages of germination in cotyledons did not change significantly, indicating less intensive use of these compounds for morphogenesis during this period. Seed germination was accompanied by a decrease under the action of gibberellin at light, and under the action of tebuconazole -an increase, in root and epicotyl diameter due to the peculiarities of histogenesis. Under the influence of gibberellic acid, total epiblem and the primary root cortex thickened at light, and the epidermis and the primary cortex of hypocotyl -at light and dark. The opposite change was caused by tebuconazole -the increase of tissue complex thickness occurred under both photoand scotomorphogenesis conditions. The number of xylem vessels in the vascularfibrous bunches in roots increased under the influence of tebuconazole in dark. In epicotyls, the increase occurred in the number of vessels in bunches under the action of tebuconazole both at light and in dark. Insofar as histogenesis is controlled by phytohormones, established histological changes indicated a significant re-structuring of the entire hormonal complex of seedlings.

Peculiarities of leaf mesostructure formation, synthesis of photosynthetic pigments under the impact of gibberellic acid and its antagonist tebuconazole in scoto- and photomorphic seedlings of horse beans were analyzed. It was established that gibberellins take an active part in the regulation of scoto- and photomorphogenesis. Gibberellic acid and tebuconazole (retardant) significantly affected the histogenesis in leaves of scoto- and photomorphic seedlings. Under the conditions of photomorphogenesis, leaves were formed thicker in comparison to seedlings that developed in the dark. At the same time, under the influence of tebuconazole the highest thickening of leaves was noted both in the dark and light. There was a decrease in leaf thickness in scotomorphic seedlings under gibberellin action. In the dark, the gibberellin effect caused the formation of thinner tissues complexes — chlorenchyma, abaxial and adaxial epidermis. The ratio between chlorophyll a and b in the control was 4.3, under the impact of tebuconazole— 4.5, and gibberellin — 3.7. Insofar as the content and ratio of chlorophylls a and b decreased under the action of gibberellin, and increased under the action of antigibberellic drug tebuconazole, this indicates the gibberellin influence on the formation of photosynthetic apparatus light-harvesting complexes. In scotomorphic seedlings, the process of conversion of unsaturated to saturated fatty acids (FA) was most inhibited by tebuconazole, and under the action of gibberellin the ratio was less. In photomorphic seedlings, this process was not inhibited either by exogenous gibberellin or by retardant, compared to control. Thus, light affects the processes of FA metabolism during the heterotrophic phase of development. Blocking the native gibberellin synthesis by tebuconazole in seedlings leads to a decrease in linolenic acid outflow from the cotyledons due to growth retardation and, consequently, the use of this fatty acid in chloroplastogenesis.