Investigation of morpho-physiolgical traits and gene expression in barley under nitrogen deficiency

Abstract

Nitrogen (N) is an essential element for plant growth, and its deficiency influences plants at several physiological and gene expression levels. Barley (Hordeum vulgare) is one of the most important food grains from the Poaceae family and one of the most important staple food crops. However, the seed yield is limited by a number of stresses, the most important of which is the insufficient use of N. Thus, there is a need to develop N-use effective cultivars. In this study, comparative physiological and molecular analyses were performed using leaf and root tissues from 10 locally grown barley cultivars. The expression levels of nitrate transporters, HvNRT2 genes, were analyzed in the leaf and root tissues of N-deficient (ND) treatments of barley cultivars after 7 and 14 days following ND treatment as compared to the normal condition. Based on the correlation between the traits, root length (RL) had a positive and highly significant correlation with fresh leaf weight (FLW) and ascorbate peroxidase (APX) concentration in roots, indicating a direct root and leaf relationship with the plant development under ND. From the physiological aspects, ND enhanced carotenoids, chlorophylls a/b (Chla/b), total chlorophyll (TCH), leaf antioxidant enzymes such as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT), and root antioxidant enzymes (APX and POD) in the Sahra cultivar. The expression levels of HvNRT2.1, HvNRT2.2, and HvNRT2.4 genes were up-regulated under ND conditions. For the morphological traits, ND maintained root dry weight among the cultivars, except for Sahra. Among the studied cultivars, Sahra responded well to ND stress, making it a suitable candidate for barely improvement programs. These findings may help to better understand the mechanism of ND tolerance and thus lead to the development of cultivars with improved nitrogen use efficiency (NUE) in barley.

Keywords: Barley; Correlation; Gene expression; Nitrogen deficiency; Physiological traits.

Figure 1

The effects of ND on 10 barley cultivars for chlorophyll a (a), chlorophyll b (b), total chlorophyll (c), carotenoid (d), and protein content (e) at 7 and 14 days stress periods. Values represent means of three replications per treatment. Different letters demonstrate significant differences between treatments (P < 0.05, Duncan’s Multiple Range Test). NC7:7 days after ND application; NC14: 14 days after ND application.

Figure 2

The effects of ND on APX (a), CAT (b), and POD (c) antioxidative enzyme activities in shoot of barley cultivars under different concentrations. The error bars (mean ± SE) followed by various letters are statistically significant (P < 0.05, Duncan’s Multiple Range Test). Significant differences between the two concentrations are marked with different letters. NC7:7 days after ND application; NC14: 14 days after ND application.

Figure 3

The effects of ND on APX (a), CAT (b), and POD (c) antioxidative enzyme activities in root of barley cultivars under different concentrations. The error bars (mean ± SE) followed by various letters are statistically significant (P < 0.05, Duncan’s Multiple Range Test). Significant differences between the two concentrations are marked with different letter. NC7:7 days after ND application; NC14: 14 days after ND application.

Figure 4

Heatmaps representing the expression profiles of leaf HvNRT2 genes in response to ND, and their gene expression at 7 (a) and 14 (b) days after ND application for leaf. The heat map was generated using TBtools.

Figure 5

Heatmaps representing the expression profiles of leaf HvNRT2 genes in response to ND, and their gene expression at 7 (a) and 14 (b) days after ND application for root. The heat map was generated using TBtools.

Figure 6

The correlation coefficients of physiological and morphological traits and gene expression at 7 (a) and 14 (b) days after ND application. Protein content (PC); plant height (PH); leaf dry weight (LDW); leaf fresh weight (LFW); root fresh weight (RFW); root dry weight (RDW); HvNRT2r (root HvNRT2); HvNRT2l (leaf HvNRT2).

Figure 7

The clustering of cultivars (a) and principle component analysis of 10 barley cultivars (b).