International Journal of Molecular Evolution and Biodiversity, 2025, Vol.15, No.2, 84-98 http://ecoevopublisher.com/index.php/ijmeb 85 2 Impact of Drought Stress on Rapeseed 2.1 Physiological and biochemical effects of drought on rapeseed Drought is one of the important abiotic stress factors affecting the growth and development of rapeseed (Brassica napus L.). Under drought conditions, the chlorophyll content in plant leaves is often significantly reduced, and the reduction of chlorophyll directly inhibits the efficiency of photosynthesis. Due to the damage to the photosynthetic system, reactive oxygen species (ROS) are easily accumulated in cells, causing oxidative stress, thereby damaging the cell membrane system (Teymoori et al., 2020). To alleviate this oxidative damage, plants accumulate osmotic regulating substances such as proline, betaine and trehalose. These small molecules not only help maintain the osmotic balance of cells, but also play an important role in enhancing the activity of antioxidant enzymes, which can effectively reduce the content of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) and alleviate cellular oxidative stress (Bhuiyan et al., 2019). Drought stress profoundly affects the metabolic regulatory network of rapeseed, especially during the reproductive growth stage. When water is deficient, the oil synthesis pathway of rapeseed grains is reprogrammed, which is manifested by an abnormal increase in the proportion of long-chain fatty acids such as erucic acid, resulting in the deterioration of edible oil quality. At the same time, secondary metabolic pathways are activated, and defensive substances such as phenolic compounds and glucosinolates accumulate in large quantities. These changes may reduce the feeding value of rapeseed meal (Bouchereau et al., 1996). Physiological index monitoring shows that the proline content of rapeseed leaves increases in a dose-dependent manner under drought conditions, and its accumulation level is significantly positively correlated with biomass and yield indicators (Norouzi et al., 2008), indicating that this osmotic regulating substance has an important physiological function in drought adaptation. 2.2 Effects of water deficiency on yield and quality Drought stress directly affects the yield components of rapeseed, among which the decline in the number of siliques and the number of grains per silique is the most prominent (Norouzi et al., 2008). In severe drought conditions, yield losses can reach significant levels, especially when water is insufficient during the flowering or silique formation period, which will adversely affect grain yield and its oil content. The decline in oil quality caused by drought is often manifested as an increase in palmitic acid and erucic acid content, which is a disadvantage for edible oil use (Khodabin et al., 2021). Protein content will also decrease due to reduced water content, thus affecting the overall nutritional value of seeds (Germchi et al., 2010; Shekari et al., 2016). In order to alleviate the adverse effects of drought, some studies have tried to regulate by applying trace elements. For example, spraying zinc or manganese sulfate can improve the oil composition to a certain extent, reduce the accumulation of erucic acid and glucosinolates (Khodabin et al., 2021), and thus improve the quality of oil products. 2.3 Environmental regulatory factors of drought stress intensity There are many factors that affect the effects of drought stress, among which soil moisture, temperature and the time when water deficiency occurs are particularly critical. Especially after the plant enters the flowering period and silique development period, insufficient water supply often aggravates the negative impact on yield and quality. Climate type also has a regulatory effect on stress manifestations. For example, the Mediterranean climate is characterized by high temperatures and droughts in summer and wet winters, which makes rapeseed more susceptible to water stress in the late growth period (Teymoori et al., 2020). Rising temperatures will accelerate transpiration, thereby increasing soil water loss and worsening drought conditions. At the same time, the effects of water stress at different growth stages vary. Early drought may have long-term effects on grain quality, while water shortage during flowering will directly weaken seed formation and yield potential (Bouchereau et al., 1996).
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