Alginate-derived oligosaccharides promote water stress tolerance in cucumber (Cucumis sativus L.)

Marine alginate-derived oligosaccharides (ADOs) are prepared from degraded alginate. Our experiments were carried out to determine the mechanism of ADOs to improve resistance to water stress in cucumber (Cucumis sativus L.). We evaluated the effects of ADOs on physiological indices, photosynthesis, reactive oxygen species (ROS) levels, antioxidant enzyme activities, and relative expression levels of drought resistance genes. The growth of drought stressed cucumber decreased markedly. However, treatment with ADOs significantly improved the diameter, fresh weight, photosynthetic rate, transpiration rate, stomatal conductance, maximum quantum yield of photosystem II (Fv/Fm) and chlorophyll degradation; thus, reversing the effects of drought stress. Moreover, the antioxidant levels and ROS scavenging enzyme activities also increased in response to the ADOs. Additionally, the genes involved in abscisic aid (ABA) signaling and the drought stress response, such as superoxide dismutase [Cu-Zn] (CsSOD(Cu-Zn)), the peroxidase superfamily protein (CsPOD3), ABA deficient 2 (CsABA2), responsive to ABA 18 (CsRAB18), abscisic acid insensitive 5 (CsABI5), responsive to dehydration 22 (CsRD22), and responsive to dehydration 29A (CsRD29A) were upregulated by ADOs. The ABA content was also improved by ADOs. Our results suggest that ADOs induced the expression of some antioxidant enzyme synthetic genes involved in the ABA signaling pathway by stimulating ABA synthesis to improve the drought resistance capacity in cucumber.