Carbohydrate and plant hormone regulate the alkali stress response of hexaploid wheat (Triticum aestivum L.)

Most types of stress influence crop plants at intervals. Unlike other stresses, salt and alkali stresses influence crop plants for their entire life cycle. However, little is known about physiological and molecular response of crop plants to long-term salinity or long-term alkali stress (LAS) condition. In the present study, we subjected hexaploid wheat seeds to LAS treatment (NaHCO3/Na2CO3, 9:1; 50 mM, pH 8.7) across the germination and seedling stages for 30 days. To elucidate gene expression and physiological adaptation strategies of wheat plants to LAS, we measured the anatomy, plant hormones, compatible solutes, inorganic ions, and transcriptomic profiling of control plants and stressed plants. The results showed that LAS strongly influenced the signaling transduction systems involved in plant hormone. Although LAS did not decrease concentrations of jasmonic acid (JA), salicylic acid (SA) and indole-3-acetic acid (IAA) in leaves of hexaploid wheat, LAS upregulated expression of AUX/IAA gene (suppressor of IAA pathway) and JAZ gene (suppressor of JA pathway), as well as downregulated expression of TGA and PR-1 genes (core genes of SA pathway). We propose that hexaploid wheat may suppress the IAA, JA, and SA signaling pathways in leaves via regulating expression of down-stream key genes not via altered concentrations of these plant hormones. The suppression of the IAA, JA, and SA signaling pathways may shift energy from general metabolism to stress response. The upregulation of protective protein genes (LEA and dehydrin) and the accumulation of carbohydrates may relieve Na +/- toxicity in cytosol under LAS. In addition, under LAS, in most salinity-tolerant triads, A, B, and D homeologs had similar expression levels and exerted a dosage effect. Such dosage effects may contribute to the development of strong alkali tolerance of hexaploid wheat because function of most critical stress tolerance proteins relies on their absolute abundance.