Sodium nitroprusside application enhances drought tolerance in marjoram herb by promoting chlorophyll biosynthesis and enhancing osmotic adjustment capacity

Abstract

Sodium nitroprusside (SNP) has a decisive function for mitigating water deficit; nevertheless, the specific roles of SNP on chlorophyll biosynthesis, water relation, and osmotic adjustment in marjoram (Origanum marjorana L., Lamiaceae) have not well been established. To assess the function of SNP in alleviating water stress (50% of field capacity), potted marjoram herbs were subjected to watering regimes (well-watered or water-deficit) with or without SNP concentrations (0, 30, 60 μM). Drought caused a significant reduction in water potential (Ψw), osmotic potential (Ψs), turgor potential (Ψp), relative water content (RWC), photosynthetic pigment, chlorophyllide (chlide)a, chlideb, chlorophyll (chl)a/chlidea, chlb/chlideb, and ions, however increased pheophytina (pheoa), protoporphyrin (Proto), Mg-protoporphyrin (Mg-proto), and protochlorophyllide (pchlide). Conversely, osmotic adjustment (OA) was improved, associated with the hyper-accumulation of osmotic adjustment solutes (OAS) leading to an increase in water saturation deficit (WSD), which induced a decrease in dry matter accumulation and shoot fresh weight. Application of SNP decreased Ψw, Ψs, and Ψp and WSD while maintained higher RWC, comparing the plants devoid of SNP supplementation. Supplementary SNP additionally motivated the energetic buildup of various OAO in drought-affected plants that improved OA aptitude, improved water retention capacity, and increased plant growth. Additionally, SNP application increased chlorophyll, carotenoid, pheoa, chlidea, chlideb, chla/chlidea, chlb/chlideb, and decreased Proto, Mg-proto, pchlide, and ions. The findings of the present study clarified that the SNP application improved drought tolerance of marjoram plants, through maintaining ion homeostasis, enhanced OA capacity, increased OAO accumulation, and stabilized chlorophyll biosynthesis.