Numerous studies have demonstrated the impact of exogenous gibberellin on fleshy fruit formation, but the effect on dry fruits is not yet well known. To test the role of gibberellin (GA3) in dry fruit formation, we analysed the impact of exogenous GA3 on the invasive plant Sosnowsky’s hogweed (H. sosnowskyi Manden.) seed development and germination. Treatment of GA3 concentrations of 0.07 mM, 0.14 mM, 0.28 mM, 0.43 mM was applied to flowers at the early stage of development. Seeds were collected from treated satellite umbels. It was observed that GA3treatment did not have a significant effect on the size of H. sosnowskyi seeds, but caused various changes in their shape. The data on semi-thin longitudinal sections of H. sosnowskyi mericarps and SEM micrographs of embryos showed that the embryos in GA3 (0.43 mM) treated variants were at torpedo stage, while in control variants—mature embryos. The germination of seeds of each variant was estimated by burying them in the soil. Our studies indicated that GA3 application reduced the germination of H. sosnowskyi seed from 98.0% (control) to 16.5% (GA3 concentration 0.43 mM). It was assumed that exogenous application of GA3 had influence on the development of dry Sosnowsky’s hogweed seeds and could be used to inhibit the spread of this invasive plant.

Sosnowsky’s hogweed (Heracleum sosnowskyi Manden.) mericarps were collected from satellite and stem branch umbels for comparative anatomical investigation. Located near Vilnius city, the habitat of Heracleum sosnowskyi, formerly a natural forest edge has recently been densely occupied by plants of this species. SEM micrographs of abaxial and adaxial surfaces of mericarps obtained from satellite and stem branch umbels of H. sosnowskyi were similar, but morphometrical analysis revealed statistically significant differences in mericarps collected from satellite umbels, which were longer and wider than mericarps from stem branch umbels. The data on longitudinal sections of H. sosnowskyi mericarps clearly showed that embryos of satellite umbels were at later torpedo stage compared to embryos of stem branch umbels, which were at earlier heart stage. These data represent unequal development of the embryos in mericarps from different types of umbels. Such different development can be treated as an adaptation of the invasive plant to occupy the current habitat and survive in the seed bank by allowing the embryo to complete development within a seed and germinate when new conditions permit.

Sosnowsky’s hogweed (Heracleum sosnowskyi Manden.), an important invasive species in Eastern Europe, is a monocarpic perennial plant that propagates exclusively by seeds. Hence, interfering with seed viability could help control its spread. In the present study, we investigated the effect of exogenous GA3 (25, 100 and 150 mg/L) sprayed twice onto flowering H. sosnowskyi plants on the development of fruits (mericarps) and their ability to germinate under field conditions over the growing seasons of 2018 and 2019. Mericarps from plants sprayed with GA3 failed to develop normally. The width/length ratio of mericarps decreased by 23% to 25% after 150 mg/L GA3 application and their average weight decreased between 7% and 39% under all GA3 treatments. X-ray radiographs revealed that the internal structure was malformed, with many of the mericarps lacking well-developed seeds. Proportionally fewer well-developed mericarps were produced by GA3-treated plants than water-sprayed control plants in 2018. Seed germination assessed outdoors in seeds buried in the ground was also severely reduced (from 58% to 99% after 150 mg/L GA3 application). This indicates that exogenous GA3 sprays result in incomplete seed development and a consequent decrease in viability and germination. As the highest GA3 dose used resulted in significantly reduced propagation of Sosnowsky’s hogweed through seeds in the field, GA3 provides a promising approach to the control of the spread of this invasive weed species.

This study was carried out to evaluate the effect of exogenous proline on the growth, biochemical responses, and plant recovery of drought-stressed oilseed rape plants after renewed irrigation. The experiment was conducted under controlled laboratory conditions. After 21 days of cultivation, 3–4 leaf stage seedlings were sprayed with proline (1 mM), then subjected to prolonged drought stress for 8 days to achieve a severe water deficit, next, irrigation was resumed and recovery was assessed after 4 days. The results show that exogenous application of proline reduced the drought-induced growth inhibition of seedlings while maintaining relative water content (RWC) and growth parameters closer to those of irrigated plants. Proline had a positive effect on chlorophyll accumulation and membrane permeability while decreasing ethylene, H2O2, and MDA levels. Moreover, after 4 days of recovery, the H2O2 content of the proline-treated plants was significantly lower (2-fold) and the MDA content was close to that of continuously irrigated plants. Thus, all these biochemical reactions influenced plant survival: after drought + proline treatment, the number of surviving plants was two times higher than that of drought-treated plants. The findings show that exogenous proline has antioxidant, osmotic, and growth-promoting properties that improve the drought tolerance of winter oilseed rape plants and is, therefore, beneficial for drought adaptation in oilseed rape.

This study was carried out to evaluate the effect of exogenous proline on growth, biochemical responses, and plant recovery of drought-stressed oilseed rape plants after renewed irrigation. The experiment was conducted under controlled laboratory conditions. After 21 days of cultivation, 3-4 leaf stage seedlings were sprayed with proline (1 mM), then subjected to prolonged drought stress for 8 days to achieve a severe water deficit, then irrigation was resumed and recovery was assessed after 4 days. The results show that exogenous application of proline reduced drought-induced growth inhibition of seedlings while maintaining relative water content (RWC) and growth parameters closer to those of irrigated plants. Proline had a positive effect on chlorophyll accumulation and membrane permeability while decreasing ethylene, H2O2, and MDA levels. Moreover, after 4 days of recovery, the H2O2 content of the proline-treated plants was significantly lower (2-fold) and the MDA content was close to that of continuously irrigated plants. Thus, all these biochemical reactions influenced plant survival: after drought + proline treatment, the number of surviving plants was 2 times higher than that of drought-treated plants. The findings show that exogenous proline has antioxidant, osmotic, and growth-promoting properties that improve the drought tolerance of winter oilseed rape plants and is, therefore, beneficial for drought adaptation in oilseed rape.