Gibberellin's role in barley seed germination is significantly influenced by environmental factors such as light, temperature, and water availability. Light can affect the synthesis and activity of gibberellin, either promoting or inhibiting its production depending on the plant species and light conditions. Temperature plays a critical role, with optimal temperatures enhancing gibberellin activity, thereby promoting germination. Conversely, extreme temperatures may inhibit gibberellin synthesis or action, delaying or preventing germination. Water availability is also crucial; adequate moisture is necessary for gibberellin to exert its effects on seed germination. These environmental interactions highlight the adaptive mechanisms plants use to ensure germination occurs under favourable conditions.

Gibberellin can influence the development of secondary roots in barley, although its effect is somewhat indirect compared to its role in primary root and shoot development. Gibberellin indirectly promotes the growth and elongation of secondary roots by stimulating overall plant growth and the development of the primary root system. A well-developed primary root system and shoot increase the plant's overall ability to absorb water and nutrients, which in turn supports the growth of secondary roots. Additionally, gibberellin may interact with other hormones like auxins, which are more directly involved in lateral root formation, to regulate the growth and development of secondary roots.

While gibberellin is primarily known for its role in growth and development, there is emerging evidence suggesting it may also play a role in the defence mechanisms of barley seeds. Gibberellin can modulate the expression of certain genes involved in defence responses, such as those coding for pathogenesis-related proteins. These proteins are part of the plant's innate immune system and help defend against pathogens. Additionally, gibberellin may influence the production of secondary metabolites that have defensive functions against herbivores and pathogens. However, the exact mechanisms and extent of gibberellin's involvement in seed defence are still subjects of ongoing research, and its role may vary depending on the specific environmental stressors and pathogens encountered by the plant.

Gibberellin also plays a role in the mobilisation of stored fats in barley seeds, although this is less well-known compared to its effect on starch degradation. During germination, gibberellin helps in activating lipases, which are enzymes responsible for breaking down lipids (fats) stored in the seed. These lipids, when hydrolysed by lipases, release fatty acids and glycerol. These breakdown products are then metabolised by the seedling to generate energy and to form new cellular materials. This lipid mobilisation is particularly crucial during the early stages of germination when the seedling has not yet developed leaves for photosynthesis and hence relies heavily on the seed's stored reserves for energy.

Gibberellin has a significant impact on the aleurone layer of barley seeds during germination. When a barley seed begins to germinate, gibberellin is produced by the embryo and transported to the aleurone layer, a tissue layer surrounding the endosperm. In the aleurone layer, gibberellin triggers the synthesis of various digestive enzymes, most notably alpha-amylase. This enzyme plays a critical role in breaking down starch stored in the endosperm into simpler sugars, which are then transported to the growing embryo to provide the energy and building blocks needed for growth. This process is vital as it enables the seedling to utilise the energy reserves stored within the seed effectively, facilitating successful germination and early growth.