Ameliorative Effects of Paclobutrazol via Physio-Biochemical and Molecular Manifestation in Rice under Water Deficit Stress

doi:10.1016/j.rsci.2024.03.004

Abstract

Abstract:

To comprehensively explore the physio-biochemical and molecular changes of paclobutrazol (PBZ) at the ideal dose under water deficit stress (WDS) conditions, we investigated the effects of 100 mg/kg PBZ applied via drenching on various physio-biochemical and molecular parameters in three rice varieties (N22, IR64, and IR64 DTY1.1) under both mild [75%‒80% relative water content (RWC)] and severe (60%‒65% RWC) WDS conditions. The results showed that PBZ treatment positively influenced the physio-biochemical parameters, significantly increasing dry matter (16.27%‒61.91%), RWC (6.48%‒ 16.34%), membrane stability index (4.37%‒10.35%), and total chlorophyll content (8.97%‒29.09%) in the rice varieties under both mild and severe WDS. Moreover, PBZ treatment reduced drought susceptibility (0.83‒0.95) and enhanced drought tolerance efficiency (60.92%‒86.78%), indicating its potential as a stress-mitigating agent. Global methylation analysis revealed changes in DNA methylation patterns, indicating the regulatory influence of PBZ on gene expression. The expression analysis of genes involved in the diversification of geranylgeranyl pyrophosphate towards the biosynthesis of abscisic acid, gibberellin acid, and chlorophyll showed alterations in their expression levels, suggesting the involvement of PBZ in the isoprenoid pathway. Overall, this study provides valuable insights into the potential mechanisms by which PBZ modulates physiological and molecular responses in rice plants under WDS. The findings highlight the importance of PBZ as a promising agent for enhancing drought tolerance in rice and offer valuable information for future research in crop stress management.

Key words: rice, paclobutrazol, drought stress, abscisic acid, gibberellic acid

Chirag Maheshwari, Nitin Kumar Garg, Archana Singh, Aruna Tyagi. Ameliorative Effects of Paclobutrazol via Physio-Biochemical and Molecular Manifestation in Rice under Water Deficit Stress[J]. Rice Science, 2024, 31(5): 603-616.

Figures/Tables 4

Fig. 1. Effect of 100 mg/kg paclobutrazol (PBZ) on dry matter (A), relative water content (RWC, B), membrane stability index (MSI, C), total chlorophyll content (D), chlorophyll stability index (CSI, E), drought susceptibility index (DSI, F), drought tolerance efficiency (DTE, G), grain yield (H), and global methylation level (I) in contrasting rice genotypes at the reproductive stage. WP0, Well-watered without PBZ; WP100, Well-watered with 100 mg/kg of PBZ; MSP0, Mild drought stress without PBZ; MSP100, Mild drought stress with 100 mg/kg of PBZ; SSP0, Severe drought stress without PBZ; SSP100, Severe drought stress with 100 mg/kg of PBZ. Vertical bars represent Mean ± SE (n = 6). Different lowercase letters above the bars indicate significant differences among treatments for the same variety by the least significant difference (LSD) test (P < 0.05).

Fig. 2. Effect of 100 mg/kg paclobutrazol (PBZ) on abscisic acid (ABA) content (A), gibberellic acid (GA) content (B), and total antioxidant activity (TAA, C) in contrasting rice genotypes at the reproductive stage. WP0, Well-watered without PBZ; WP100, Well-watered with 100 mg/kg of PBZ; MSP0, Mild drought stress without PBZ; MSP100, Mild drought stress with 100 mg/kg of PBZ; SSP0, Severe drought stress without PBZ; SSP100, Severe drought stress with 100 mg/kg of PBZ. Vertical bars represent Mean ± SE (n = 3). Different lowercase letters above the bars indicate significant differences among treatments for the same variety by the least significant difference (LSD) test (P < 0.05).

Fig. 3. Effect of 100 mg/kg paclobutrazol (PBZ) on relative expression levels of geranylgeranyl pyrophosphate (GGPP) biosynthesis, abscisic acid (ABA) metabolism, gibberellic acid (GA) biosynthesis, and chlorophyll metabolism relative genes. A‒L, Relative expression levels of GGPPS1 (geranylgeranyl diphosphate synthase 1, A), GGPPS2 (B), PSY2 (phytoene synthase 2, C), PSY3 (D), ZEP (zeaxanthin epoxidase, E), NCED3 (9-cis-epoxycarotenoids dioxygenase, F), ABA8OX1 (aba-8ʹ-hydroxylase 1, G), ABA8OX2 (H), CPS1 (ent-copalyl diphosphate synthase 1, I), GGR1 (geranylgeranyl reductase 1, J), GGR2 (K), and CHS (chlorophyll synthase, L) genes. WP0, Well-watered without PBZ; WP100, Well-watered with 100 mg/kg of PBZ; MSP0, Mild drought stress without PBZ; MSP100, Mild drought stress with 100 mg/kg of PBZ; SSP0, Severe drought stress without PBZ; SSP100, Severe drought stress with 100 mg/kg of PBZ. Leaf tissue was collected from control and water-stressed plants while rice Actin served as an internal control. Vertical bars represent Mean ± SE (n = 3). Different lowercase letters above the bars indicate significant differences among treatments for the same variety by the least significant difference (LSD) test (P < 0.05).

Fig. 4. Diagrammatic explanation of PBZ effect on GA, chlorophyll, and ABA biosynthesis pathways. The effect of PBZ on genes involved in the biosynthesis of ABA, GA, and chlorophyll was studied. CPS, which is involved in the biosynthesis of GA, was down-regulated, leading to a decrease in GA levels. PBZ enhanced the expression of PSY, ZEP, and NCED, which are involved in the biosynthesis of ABA, and decreased the expression of ABA8OX, involved in the degradation of ABA, resulting in an increase in endogenous ABA levels. The expression of geranylgeranyl reductase (GGR) and CHS, involved in the biosynthesis of chlorophyll, was enhanced, resulting in increased chlorophyll content and stability. ABA, Abscisic acid; ABA8OX, ABA- 8ʹ-hydroxylase; CHS, Chlorophyll synthase; CPS, ent-Copalyldiphosphate synthase; GA, Gibberellic acid; GGRS, Geranyl geranyl reductase; GGPS, Geranyl geranyl diphosphate synthase; IPI, Sopentenyl pyrophosphate: dimethyllallylpyrophosphate isomerase; KAO, ent-Kaurenoic acid oxidase; PBZ, Paclobutrazol; KS, ent- Kaurene synthase; NCED, 9-cis- Epoxycarotenoid dioxygenase; PSY, Phytoene synthase; ZEP, Zeaxanthin epoxidase.

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