Physiological Characteristics of Cotton Subtending Leaf Are Associated With Yield in Contrasting Nitrogen-Efficient Cotton Genotypes

Abstract

Nitrogen (N) plays an important role in various plant physiological processes, but studies on the photosynthetic efficiency and enzymatic activities in the cotton subtending leaves and their contribution to yield are still lacking. This study explored the influence of low, moderate, and high N levels on the growth, photosynthesis, carbon (C) and N metabolizing enzymes, and their contribution to yield in CCRI-69 (N-efficient) and XLZ-30 (N-inefficient). The results showed that moderate to high N levels had significantly improved growth, photosynthesis, and sucrose content of CCRI-69 as compared to XLZ-30. The seed cotton yield and lint yield of CCRI-69 were similar under moderate and high N levels but higher than XLZ-30. Similarly, moderate to high N levels improved the C/N metabolizing enzymatic activities in the subtending leaf of CCRI-69 than XLZ-30. A strong correlation was found between subtending leaf N concentration with C/N metabolizing enzymes, photosynthesis, sucrose contents, boll weight, and seed cotton yield of N-efficient cotton genotype. These findings suggest that subtending leaf N concentration regulates the enzymatic activities and has a key role in improving the yield. These parameters may be considered for breeding N-efficient cotton genotypes, which might help to reduce fertilizer loss and improve crop productivity.

Keywords: cotton; cotton subtending leaf; enzymatic activities; nitrogen; photosynthesis; yield.

FIGURE 1

(A–F) Root dry matter (g plant^–1), shoot dry matter (g plant^–1), leaf dry matter (g plant^–1), total plant dry matter (g plant^–1), shoot length (cm), and leaf area per plant (cm²), and plant phenotypes of CCRI-69 and XLZ-30 in response to low (LN; 0.25 mM), moderate (MN; 2.5 mM), and high (HN; 5 mM) N levels. Error bars with different small letters show significant differences between genotypes under different N levels (p < 0.05).

FIGURE 2

(A–D) Net photosynthetic rate (μmol m^–2 s^–1), transpiration rate (mmol m^–2 s^–1), intercellular CO₂ concentration (μmol CO₂ mol^–1 air), and stomatal conductance (mmol H₂O m^–2 s^–1) of cotton subtending leaves of CCRI-69 and XLZ-30 in response to low (LN; 0.25 mM), moderate (MN; 2.5 mM), and high (HN; 5 mM) N levels at 10, 25, and 40 days post-anthesis (DPA). Error bars with different small letters show significant differences between genotypes under different N levels, and capital letters in the brackets show significant differences among growth stages (10, 25, and 40 DPA) at p < 0.05.

FIGURE 3

(A–D) Nitrate reductase activity (μg g^–1 FW h^–1), glutamine synthetase activity (μmol g^–1 FW h^–1), glutamate synthase (U mg^–1 protein), and glutamate dehydrogenase activity (U mg^–1 protein) in cotton subtending leaves of CCRI-69 and XLZ-30 in response to low (LN; 0.25 mM), moderate (MN; 2.5 mM), and high (HN; 5 mM) N levels at 10, 25, and 40 days post-anthesis (DPA). Error bars with different small letters show a significant difference between genotypes under different N levels and capital letters in the brackets show significant differences among growth stages (10, 25, and 40 DPA) at p < 0.05.

FIGURE 4

(A–C) Glutamate oxaloacetic transaminase activity (nmol min^–1 mL^–1), glutamate–pyruvic transaminase activity (nmol min^–1 mL^–1), and protease activity (nmol min^–1 g^–1) in cotton subtending leaves of CCRI-69 and XLZ-30 in response to low (LN; 0.25 mM), moderate (MN; 2.5 mM), and high (HN; 5 mM) N levels on 10, 25, and 40 days post-anthesis (DPA). Error bars with different small letters show a significant difference between genotypes under different N levels, and capital letters in the brackets show significant differences among growth stages (10, 25, and 40 DPA) at p < 0.05.

FIGURE 5

(A–F) Root N concentration (%), shoot N concentration (%), leaf N concentration (%), total plant N concentration (%), NUpE (mg N g^–1 RDW), and NUtE (g TDW mg^–1) of CCRI-69 and XLZ-30 in response to low (LN; 0.25 mM), moderate (MN; 2.5 mM), and high (HN; 5 mM) N levels. Error bars with different small letters show significant differences between genotypes under different N levels (p < 0.05).

FIGURE 6

(A–F) Number of fruiting branches plant^–1, number of bolls plant^–1, boll weight (g), seed cotton yield (g plant^–1), lint yield (g plant^–1), and lint percentage (%) of CCRI-69 and XLZ-30 in response to low (LN; 0.25 mM), moderate (MN; 2.5 mM), and high (HN; 5 mM) N levels. Error bars with different small letters show significant differences between genotypes under different N levels (p < 0.05).

FIGURE 7

Relationships of subtending leaf N concentration (%) with nitrate reductase (μg g^–1 FW h^–1), glutamine synthetase activity (μmol g^–1 FW h^–1), glutamate synthase (U mg^–1 protein) and dehydrogenase activity (U mg^–1 protein), glutamate–pyruvic transaminase activity (nmol min^–1 mL^–1), glutamate oxaloacetic transaminase activity (nmol min^–1 mL^–1), sucrose phosphate synthase (μg min^–1 g^–1 FW), sucrose synthase (μg min^–1 g^–1 FW), sucrose content (mg g^–1 FW), net photosynthetic rate (μmol m^–2 s^–1), boll weight (g), and seed cotton yield (g plant^–1) of N-efficient (CCRI-69) and N-inefficient (XLZ-30) cotton genotypes under hydroponic condition.

FIGURE 8

(A) Relationships of subtending leaf N concentration (%) with nitrate reductase (μg g^–1 FW h^–1), glutamine synthetase activity (μmol g^–1 FW h^–1), glutamate synthase (U mg^–1 protein), and glutamate dehydrogenase activity (U mg^–1 protein), glutamate–pyruvic transaminase activity (nmol min^–1 mL^–1), glutamate oxaloacetic transaminase activity (nmol min^–1 mL^–1) of N-efficient (CCRI-69) and N-inefficient (XLZ-30) cotton genotypes under pot condition in 2018 and 2019. (B) Relationships of subtending leaf N concentration (%) with boll weight (g), sucrose synthase (μg min^–1 g^–1 FW), sucrose phosphate synthase (μg min^–1 g^–1 FW), sucrose content (mg g^–1 FW), net photosynthetic rate (μmol m^–2 s^–1), and seed cotton yield (g plant^–1) of N-efficient (CCRI-69) and N-inefficient (XLZ-30) cotton genotypes under pot condition in 2018 and 2019.

FIGURE 9

(A) Relationships of subtending leaf N concentration (%) with nitrate reductase (μg g^–1 FW h^–1), glutamine synthetase activity (μmol g^–1 FW h^–1), glutamate synthase (U mg^–1 protein), and glutamate dehydrogenase activity (U mg^–1 protein), glutamate-pyruvic transaminase activity (nmol min^–1 mL^–1), glutamate oxaloacetic transaminase activity (nmol min^–1 mL^–1) of N-efficient (CCRI-69), and N-inefficient (XLZ-30) cotton genotypes under field condition in 2018 and 2019. (B) Relationships of subtending leaf N concentration (%) with boll weight (g), sucrose synthase (μg min^–1 g^–1 FW), sucrose phosphate synthase (μg min^–1 g^–1 FW), sucrose content (mg g^–1 FW), net photosynthetic rate (μmol m^–2 s^–1), and seed cotton yield (kg ha^–1) of N-efficient (CCRI-69) and N-inefficient (XLZ-30) cotton genotypes under field condition in 2018 and 2019.