Calcium Nanoparticles and Abscisic Acid Improve Drought Tolerance, Mineral Nutrients Uptake and Inhibitor-Mediated Photosystem II Performance in Brassica napus

Plant yield is severely hampered by drought, affirming the urgent need to develop strategies to improve plant growth and drought tolerance. The synergistic application of ABA and calcium nanoparticles (Ca-NPs) has emerged as a promising approach for sustainable crop production and improved resistance to abiotic stress, although the underlying mechanism for foliar application of growth regulator ABA and Ca-NPs in regulating plant growth and drought tolerance in rapeseed ( Brassica napus L.) remains poorly understood. To address this knowledge gap, the current study was conducted to investigate the protective role of 100-µM ABA and 100 ppm Ca-NPs in alleviating the drought stress (15% PEG-6000) in B. napus following further application with 100 µM solution of photosynthesis inhibitor 3-(3,4-dichlorophyllorophenyl)-1,1-dimethylurea (DCMU). Foliar application of 100 ppm Ca-NPs and 100-µM ABA significantly reduced the drought stress by increasing chl a, chl b, total chlorophyll, carotenoids, xanthophyll by 86, 63, 78, 56, 68%; nutritional profile Ca, K, P, Mg, Mn, B by 131, 108, 98, 111, 82, 67% of B. napus plants, respectively. Moreover, under drought condition the combined treatment of Ca-NPs + ABA along with the DCMU increased the Pn, Gs, Ci, Tr by 30, 24, 37, 22% and transcript abundance of transcription factors and ROS homeostasis genes ( CDPK5, MYC2, TGA1, CAS , and POD ), and photosynthetic proteins expressions ( NCED3, PsbB, CP29, CP24, PCaA, CP26 and cytochrome f) . Overall, this study provides the evidence of effectiveness of combined application of Ca-NPs and ABA in alleviating drought stress in rapeseed.