Enhanced Chlorophyll Accumulation is Early Response of Rice to Phosphorus Deficiency

doi:10.1016/j.rsci.2025.08.004

Abstract

Abstract:

Phosphorus (P) deficiency is a major constraint in rice production, causing significant reductions in growth and yield. While P deficiency typically decreases chlorophyll content in many plant species, our previous studies revealed an unexpected increase in chlorophyll content in P-deficient rice seedlings. Here, we investigated this phenomenon in KDML105 rice under various P regimes and analyzed the physiological mechanisms involved. We found that P-deficient rice seedlings significantly increased chlorophyll a, chlorophyll b, and carotenoid contents in young leaves while reducing photosystem II quantum yield and enhancing non-photochemical quenching. This response was specific to P deficiency and was not observed under other stress conditions such as salinity or copper toxicity, which induced oxidative stress. Time-course experiments revealed that increased chlorophyll accumulation was an early adaptive response that occurred primarily in young leaves, while older leaves eventually developed chlorosis under prolonged P deficiency. The increased chlorophyll content may be attributed to reduced leaf width and altered leaf morphology under P-limited conditions. Furthermore, using custom hyperspectral imaging analysis coupled with machine learning classification, we successfully differentiated P status in rice leaves with 98.96% accuracy in older leaves. This study demonstrates that enhanced chlorophyll accumulation is a characteristic early response to P deficiency in rice, rather than a typical general stress response observed in other conditions. Our findings highlight the limitations of relying solely on chlorophyll-based indices as indicators of plant health in precision agriculture, especially regarding phosphorus (P) nutrition management. This underscores the need for a more comprehensive approach and lays the groundwork for developing advanced remote sensing technologies aimed at accurately assessing P status in rice cultivation.

Key words: chlorophyll accumulation, dark-green leaf, hyperspectral imaging analysis, phosphorus deficiency, quantum yield of photosystem II, non-photochemical quenching

Pattanapong Jaisue, Chalongrat Daengngam, Panuwat Pengphorm, Surapa Nutthapornnitchakul, Sompop Pinit, Lompong Klinnawee. Enhanced Chlorophyll Accumulation is Early Response of Rice to Phosphorus Deficiency[J]. Rice Science, 2025, 32(6): 831-844.

Figures/Tables 4

Fig. 1. Effect of environmental inorganic phosphate (Pi) concentrations on photosynthetic pigment content, photosynthesis, and oxidative stress indicators. A-I, Contents of Pi (A), photosynthetic pigments [chlorophyll a (B), chlorophyll b (C), and carotenoids (D)], photosynthetic parameters [the quantum yield of photosystem II (Phi2, E) and non-photochemical quenching (PhiNPQ, F)], and oxidative stress indicators [H2O2 (G), malondialdehyde (MDA, H), and phenolic (I) contents] were measured in the first (L1) and second (L2) fully expanded leaves in rice seedlings grown hydroponically for 2 weeks with Pi concentrations varying from 0 to 500 µmol/L. Data are mean ± SD (n = 3). Different lowercase letters above bars indicate significant differences among the treatments in each leaf age by one-way analysis of variance, with the Least Significant Difference test.

Fig. 2. Effect of phosphorus (P) deficiency on photosynthetic pigment content and photosynthesis of KDML 105 rice at the tillering stage. A-G, Contents of inorganic phosphate (Pi, A), photosynthetic pigments [chlorophyll a (B), chlorophyll b (C), and carotenoids (D)], and SPAD (Soil plant analysis development) value (E) were assessed in shoot (S), and the first (L1) and second (L2) fully expanded leaves, and photosynthetic parameters [the quantum yield of photosystem II (Phi2, F) and non-photochemical quenching (PhiNPQ, G)] were determined in L1 and L2 of 6-week-old KDML105 rice seedlings grown in pots under high (HP) and low P (LP) conditions. Data are mean ± SD (n = 3). * represents significant differences at the 0.05 level between the HP and LP treatments using the Student’s t-test.

Fig. 3. Effects of various phosphorus (P) conditions on photosynthetic pigment content, photosynthetic parameters, and oxidative stresses in KDML 105 rice seedlings. A and B, Shoot dry weights (A) and root dry weights (B) were recorded in 2-week-old and 4-week-old seedlings. C, Inorganic phosphate (Pi) contents in the first (L1) and second (L2) fully expanded leaves and roots of rice seedlings. D-K, Photosynthetic pigments [chlorophyll a (D), chlorophyll b (E), and carotenoids (F)], photosynthetic parameters [the quantum yield of photosystem II (Phi2, G) and non-photochemical quenching (PhiNPQ, H)], and oxidative stresses [H2O2 (I), malondialdehyde (MDA, J), and phenolic (K) contents] were measured in L1 and L2 leaves of rice seedlings grown under hydroponic conditions for 4 weeks. Rice seedlings were subjected to the high P (HP), withdrawn P (WP), resupplied P (RP), and low P (LP) conditions. Data are mean ± SD (n = 3). Different lowercase letters above bars indicate significant differences among the treatments in each leaf age or root by one-way analysis of variance, with the Least Significant Difference test.

Fig. 4. Hyperspectral analyses of rice seedling leaves treated with different phosphorus (P) regimes. A and B, Reflectance spectra of the first (L1, A) and second (L2, B) fully explanded leaves across different treatments. C and D, Principal component (PC) analysis score plots for the first three components are shown for L1 (C) and L2 (D) samples, where color labels represent the different treatments. E and F, Percentage-based confusion matrices represent classification accuracy across P treatments for L1 (E) and L2 (F) samples. Data are from three biological replicates. Rice seedlings were hydroponically grown for 4 weeks in four different P treatments: high P (HP), P withdrawal (WP), P resupply (RP), and low P (LP).

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