Nitric oxide secures reproductive efficiency in heat-stressed lentil (Lens culinaris Medik.) plants by enhancing the photosynthetic ability to improve yield traits

Abstract

Rising temperatures, globally and locally, would be detrimental for cool- and summer-season food legumes, such as lentil (Lens culinaris Medik.). Lentil is highly sensitive to supra-optimal temperatures (> 30 °C), particularly during reproductive growth, resulting in flower and pod losses. Thus, suitable strategies are needed to introduce heat tolerance in this legume. Here, we evaluated the efficacy of nitric oxide (NO)-applied as foliar treatment of 1 mM sodium nitroprusside (SNP), twice (one day before final exposure to high temperature, and again five days later)-on heat-stressed (32/20 °C) lentil genotypes, differing in heat sensitivity. As a result of heat stress, endogenous NO increased significantly in heat-tolerant genotypes (46-62% in leaves and 66-68% in anthers, relative to the respective controls), while it decreased in heat-sensitive (HS) genotypes (27-30% in leaves and 28-33% in anthers, relative to the respective controls). Foliar supplementation with SNP markedly increased endogenous NO in leaves and anthers of both the control and heat-treated plants. Heat stress significantly accelerated phenology, damaged membranes, chlorophyll, chlorophyll fluorescence, cellular viability, and decreased leaf water status, carbon fixing and assimilating ability, less so in plants treated with SNP. Heat stress plus SNP significantly improved carbon fixation (as RuBisCo activity) and assimilation ability, (as sucrose concentration (in leaves and anthers), sucrose synthase and vacuolar acid invertase activity, reducing sugars), as well as osmolyte accumulation (proline and glycine betaine) in leaves and anthers. Moreover, SNP-treated plants had significantly less oxidative damage-measured as malondialdehyde and hydrogen peroxide concentrations-in leaves and anthers, relative to the respective control. Reproductive function-assessed as pollen grain germination and viability, stigma receptivity, and ovular viability-decreased markedly in plants exposed to heat stress alone, more so in HS genotypes, but increased significantly with SNP treatment as a consequence of improved leaf and anther function, to significantly increase the pod and seed numbers in heat-stressed lentil plants, relative to heat-stress alone.

Keywords: Crops; Growth hormones; High temperature; Legumes; Lentil; Osmolytes.

Fig. 1

Temperature profile (maximum/minimum) data from sowing (November 1st) to flower initiation (February 11–14th) in an outdoor environment

Fig. 2

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on a membrane damage, b cellular viability, c relative leaf water content, and d stomatal conductance in heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Vertical bars represent standard errors (n = 3). Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). LSD for genotype × stage × treatment interaction (P < 0.05): Membrane damage: 2.3; Cellular oxidizing ability: 0.024; Relative leaf water content: 2.1; Stomatal conductance: 21.1

Fig. 3

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on endogenous nitric oxide concentration in leaves and anthers of heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Vertical bars represent standard errors (n = 3). Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). LSD for genotype × stage × treatment interaction (P < 0.05): 0.087

Fig. 4

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on a pollen viability, b pollen germination, c stigma receptivity, and d ovule viability in heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Vertical bars represent standard errors (n = 3 Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). LSD for genotype × stage × treatment interaction (P < 0.05): Pollen germination: 6.7; Pollen viability: 6.1; Stigma receptivity: 0.21; Ovule viability: 0.23

Fig. 5

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on pollen germination in growth medium (details in methods) in control (25 °C), heat-stressed (32 °C), and SNP supplemented at high temperature (32 °C) in heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). Vertical bars represent standard errors (n = 3). Vertical bars represent standard errors (n = 3). LSD for genotype × treatment interaction (P < 0.05): 2.6

Fig. 6

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on a malondialdehyde and b hydrogen peroxide concentrations in heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Vertical bars represent standard errors (n = 3). Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). LSD for genotype × stage × treatment interaction (P < 0.05): Malondialdehyde: 2.2; Hydrogen peroxide: 1.6

Fig. 7

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on a proline and b glycine betaine concentrations in heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Vertical bars represent standard errors (n = 3). Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). LSD for genotype × stage × treatment interaction (P < 0.05): Proline: 2.2; Glycine betaine: 1.6

Fig. 8

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on a chlorophyll, b PSII activity, and c RuBisCo activity in heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Vertical bars represent standard errors (n = 3). Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). LSD for genotype × stage × treatment interaction (P < 0.05): Chlorophyll; 1.3, PSII activity: 0.034, RuBisCo activity: 0.10

Fig. 9

Effect of nitric oxide [(as sodium nitroprusside (SNP); 1 mM)] on a sucrose, b sucrose synthase, c acid invertase, and d reducing sugars in heat-stressed heat-tolerant (G1: IG2507; G2: IG3263) and heat-sensitive (G1: IG2821; G2: IG2849) lentil genotypes. Vertical bars represent standard errors (n = 3). Different lower case letters on vertical bars indicate significant differences in mean values from each other (P < 0.05). LSD for genotype × stage × treatment interaction (P < 0.05): Sucrose: 1.8, Sucrose phosphate synthase: 0.87, Acid invertase: 0.67, Reducing sugars: 9.3