Water stress and increased ploidy level enhance antioxidant enzymes, phytohormones, phytochemicals and polyphenol accumulation of tetraploid induced wallflower

Abstract

Wallflower (Erysimum cheiri (L.) Crantz) is a profitable plant in the food, cosmetic, and pharmaceutical industries, as it produces valuable phenolic compounds. It is also an important flower in the floriculture industry cultivated mainly in the gardens and pots. Nonetheless, water scarcity as a worldwide phenomenon has deteriorated its growth and productivity. A main mechanism for drought tolerance is genome duplication and increased ploidy level, where more metabolites are produced. In this regard, diploid and tetraploid-induced plants of E. cheiri were subjected to well-watered (100% field capacity) and water deficit (50% field capacity) conditions for 30 days. Under water deficit conditions, the tetraploid wallflowers conserved their relative water content (RWC) at 85%, while the RWC of diploid plants was reduced to 68%. The chromosome-doubled plants showed advantages under water stress due to their higher osmotic adjustment by increased total soluble sugar and proline content, stronger antioxidant enzymes’ activity of SOD, CAT, APX, and POD, and enhanced non-enzymatic defense systems (i.e., total phenolic and flavonoid contents), compared with their control diploids. Also, stress hormones such as abscisic acid, salicylic acid, jasmonic acid, and auxins were increased in tetraploid plants under low water conditions, though cytokinin and gibberellin phytohormones were decreased as an adaptive strategy in the stress condition. Furthermore, chlorogenic acid and gallic acid were identified as the main phenolic compounds in 4x Erysimum leaves. The superiority of tetraploids over the diploid plants under water stress might be attributed to the extensive reprogramming of genes involved in hormonal signaling, reactive oxygen species detoxification, osmotic adjustment, and enhanced antioxidant defense system. The polyploidization technique combined with water scarcity, have proved fruitful for the production of excess secondary metabolites for various industrial uses.