Root Growth Of Rice Seedlings Research Articles

Changes in Metabolites and Allelopathic Effects of Non-pigmented and Black-pigmented Lowland indica Rice Varieties in Phosphorus Deficiency

Phosphorus (P) levels alters the allelopathic activity of rice seedlings against lettuce seeds. Here, we investigated the effect of P deficiency on allelopathic potential in non-pigmented and pigmented rice varieties. Rice seedlings of the white variety Khao Dawk Mali (KDML105, non-pigmented) and the black varieties Jao Hom Nin (JHN, pigmented) and Riceberry (RB, pigmented) were grown in high P (HP) and low P (LP) conditions. Morphological and metabolic responses to P deficiency were investigated. P deficiency inhibited shoot growth but promoted root growth of rice seedlings in all three varieties. Moreover, P deficiency led to decreased cytosolic phosphate (Pi) and total P in shoot and root tissues. The subsequent reduction of internal P enhanced the accumulation of phenolic contents in both shoot and root tissues of the seedlings. Subsequently, allelopathy-based inter- and intraspecific interactions were validated by using water extracts from seedlings of the three varieties grown under HP and LP conditions. The extracts were tested on seeds of lettuce, the weed Dactyloctenium aegyptium, and the same rice variety. Shoot and root extracts of P-deficient seedlings reduced the germination of all the receiver plants. The shoot extract of P-deficient KDML105 seedlings reduced the germination index of lettuce seeds to 1%, while the shoot extracts of P-deficient RB and JHN seedlings produced GIs of 32% and 42%, respectively. However, when rice seeds were exposed to their own LP shoot and root extracts, their germination indices were enhanced up to 4-fold, compared with the HP extracts. Shoot extracts of P-deficient plants also promoted the germination of D. aegyptium by about 2–3-fold whereas root extracts of P-deficient plants did not. Therefore, P starvation led to the accumulation and exudation of phenolics in the shoots and roots of rice seedlings, which then changed their allelopathic activities. To thrive under P deficiency, rice seedlings potentially release signaling chemicals to suppress different species nearby and simultaneously promote their own germination and growth.

Gibberellin-Mediated Sensitivity of Rice Roots to Aluminum Stress.

Aluminum toxicity poses a significant constraint on crop production in acidic soils. While phytohormones are recognized for their pivotal role in mediating plant responses to aluminum stress, the specific involvement of gibberellin (GA) in regulating aluminum tolerance remains unexplored. In this study, we demonstrate that external GA exacerbates the inhibitory impact of aluminum stress on root growth of rice seedlings, concurrently promoting reactive oxygen species (ROS) accumulation. Furthermore, rice plants overexpressing the GA synthesis gene SD1 exhibit enhanced sensitivity to aluminum stress. In contrast, the slr1 gain-of-function mutant, characterized by impeded GA signaling, displays enhanced tolerance to aluminum stress, suggesting the negative regulatory role of GA in rice resistance to aluminum-induced toxicity. We also reveal that GA application suppresses the expression of crucial aluminum tolerance genes in rice, including Al resistance transcription factor 1 (ART1), Nramp aluminum transporter 1 (OsNramp4), and Sensitive to Aluminum 1 (SAL1). Conversely, the slr1 mutant exhibits up-regulated expression of these genes compared to the wild type. In summary, our results shed light on the inhibitory effect of GA in rice resistance to aluminum stress, contributing to a theoretical foundation for unraveling the intricate mechanisms of plant hormones in regulating aluminum tolerance.

Plant growth regulators improve root growth of rice seedlings after mechanical transplanting and increase grain yield – CORRIGENDUM

Plant growth regulators improve root growth of rice seedlings after mechanical transplanting and increase grain yield – CORRIGENDUM

Plant growth regulators improve root growth of rice seedlings after mechanical transplanting and increase grain yield

Summary Enhancing seedling quality and promoting root growth post-transplantation are crucial for improving mechanically transplanted rice productivity. Here we investigated the impact of various plant growth regulators on hybrid and conventional rice varieties. Treatments, including two-diethylaminoethyl hexanoate (DA-6, 10 mg L−1), a combination of potassium 3-indole-butyrate + potassium 1-naphthylacetate + 6-benzylaminopurine (C3, 50 + 50 + 10 mg L−1), potassium 3-indole-butyrate + potassium 1-naphthylacetate + 1-triacontanol (C4, 50 + 50 + 50 mg L−1), potassium 3-indole-butyrate + potassium 1-naphthylacetate + 1.8% sodium nitrophenolate (C5, 50 + 50 + 1 mg L−1), and a combination of potassium 3-indole-butyrate + potassium 1-naphthylacetate + 1.8% sodium nitrophenolate + DA-6 (C6, 50 + 50 + 1 + 10 mg L−1), were sprayed either 3 or 10 days before transplanting. Seedlings sprayed 10 days before transplanting exhibited a higher number of white roots and total roots at the returning green stage, along with increased grain yield, irrespective of the plant growth regulator used. The C6 combination emerged as the most effective treatment, enhancing the growth of both hybrid and conventional rice seedlings, accelerating the growth rate of white roots and total roots, and increasing the length of the longest white root during the greening period, ultimately resulting in higher grain yield. Our findings demonstrate that pre-transplantation application of a combination of plant growth regulators positively influences rice seedling growth.

Nitrogen Deficiency-Induced Decrease in Cytokinins Content Promotes Rice Seminal Root Growth by Promoting Root Meristem Cell Proliferation and Cell Elongation.

Rice (Oryza sativa L.) seedlings grown under nitrogen (N) deficiency conditions show a foraging response characterized by increased root length. However, the mechanism underlying this developmental plasticity is still poorly understood. In this study, the mechanism by which N deficiency influences rice seminal root growth was investigated. The results demonstrated that compared with the control (1 mM N) treatment, N deficiency treatments strongly promoted seminal root growth. However, the N deficiency-induced growth was negated by the application of zeatin, which is a type of cytokinin (CK). Moreover, the promotion of rice seminal root growth was correlated with a decrease in CK content, which was due to the N deficiency-mediated inhibition of CK biosynthesis through the down-regulation of CK biosynthesis genes and an enhancement of CK degradation through the up-regulation of CK degradation genes. In addition, the N deficiency-induced decrease in CK content not only enhanced the root meristem cell proliferation rate by increasing the meristem cell number via the down-regulation of OsIAA3 and up-regulation of root-expressed OsPLTs, but also promoted root cell elongation by up-regulating cell elongation-related genes, including root-specific OsXTHs and OsEXPs. Taken together, our data suggest that an N deficiency-induced decrease in CK content promotes the seminal root growth of rice seedlings by promoting root meristem cell proliferation and cell elongation.

Shoot and root growth of rice seedlings as affected by soil and foliar zinc applications

The present study investigated how foliar zinc (Zn) application affects seedling growth and Zn concentration of rice grown in a Zn-deficient calcareous soil with different soil Zn treatments. Seeds were sown in soil with five rates of Zn (0, 0.02, 0.1, 0.5 and 5.0 mg kg−1 soil) with and without foliar application of 0.5% ZnSO4. Seedlings were harvested at 35 days and separated into (i) the youngest leaves, (ii) the remaining shoot parts and (iii) roots. In soil with no Zn supply, shoot and root dry weight of the rice seedlings were significantly increased by foliar and soil Zn treatments. Plant growth was not clearly increased in low soil Zn treatments, while at each soil Zn treatment, foliar Zn application promoted growth of plants. Plants with adequate Zn supply had the highest Zn concentrations in the youngest leaf. Foliar Zn spray improved Zn concentration of the new growth formed after foliar spraying which shows that Zn is phloem mobile and moved from treated leaves into youngest new leaves. The results indicate clearly in rice seedlings that shoot growth shows more responsive to low Zn than the root growth. The results obtained in the present study are of great interest for proper rice growth in Zn-deficient calcareous soils but needs to be confirmed in other rice genotypes.

Rice yield corresponding to the seedling growth under supplemental green light in mixed light-emitting diodes

The objective of this study was to investigate the effect of different supplemental intensity of green light in mixed light-emitting diodes (LEDs) on rice (Oryza sativa L.) seedling growth, and their after-effect on grain yield. The rice seedlings were nursed in greenhouse with 30-days continuous supplemental lighting (6 h/day) from three light sources: 75% red + 25% blue (photon flux density) LED (RB), 62.5% red + 25% blue + 12.5% green LED (RBG12.5) and 50% red + 25% blue + 25% green LED (RBG25), and then transplanted into paddy field in two consecutive years (2014 and 2015). The results showed that both shoot and root growth of rice seedlings were enhanced by the addition of green light into red and blue LEDs, but the response of different organ systems depended on the intensity of green light. The low percentage of green light in the light source (RBG12.5) could not only promote the stem elongation, the shoot dry weight accumulation and the root respiration activity but also could change the root morphology (indicated by the total surface area and the average diameter of root), while the high percentage of green light (RBG25) only changed the root morphology and increased the root respiration activity. The influence of light on rice during the seedling stage extends to the end of the maturity stage, with the highest rice grain yield, spikelets per panicle and the grain filling percentage in RBG25.

Overexpression of OsKTN80a, a katanin P80 ortholog, caused the repressed cell elongation and stalled cell division mediated by microtubule apparatus defects in primary root in Oryza sativa

Katanin, a microtubule-severing enzyme, consists of two subunits: the catalytic subunit P60, and the regulatory subunit P80. In several species, P80 functions in meiotic spindle organization, the flagella biogenesis, the neuronal development, and the male gamete production. However, the P80 function in higher plants remains elusive. In this study, we found that there are three katanin P80 orthologs (OsKTN80a, OsKTN80b, and OsKTN80c) in Oryza sativa L. Overexpression of OsKTN80a caused the retarded root growth of rice seedlings. Further investigation indicates that the retained root growth was caused by the repressed cell elongation in the elongation zone and the stalled cytokinesis in the division zone in the root tip. The in vivo examination suggests that OsKTN80a acts as a microtubule stabilizer. We prove that OsKTN80a, possibly associated with OsKTN60, is involved in root growth via regulating the cell elongation and division.

Effects of 5-aminolevulinic acid (ALA)-containing supernatants from selected Rhodopseudomonas palustris strains on rice growth under NaCl stress, with mediating effects on chlorophyll, photosynthetic electron transport and antioxidative enzymes

Rice is globally one of the most important food crops, and NaCl stress is a key factor reducing rice yield. Amelioration of NaCl stress was assessed by determining the growth of rice seedlings treated with culture supernatants containing 5-aminolevulinic acid (ALA) secreted by strains of Rhodopseudomonas palustris (TN114 and PP803) and compared to the effects of synthetic ALA (positive control) and no ALA content (negative control). The relative root growth of rice seedlings was determined under NaCl stress (50 mM NaCl), after 21 d of pretreatment. Pretreatments with 1 μM commercial ALA and 10X diluted culture supernatant of strain TN114 (2.57 μM ALA) gave significantly better growth than 10X diluted PP803 supernatant (2.11 μM ALA). Rice growth measured by dry weight under NaCl stress ordered the pretreatments as: commercial ALA > TN114 > PP803 > negative control. NaCl stress strongly decreased total chlorophyll of the plants that correlated with non-photochemical quenching of fluorescence (NPQ). The salt stress also strongly increased hydrogen peroxide (H2O2) concentration in NaCl-stressed plants. The pretreatments were ordered by reduction in H2O2 content under NaCl stress as: commercial ALA > TN114 > PP803 > negative control. The ALA pretreatments incurred remarkable increases of total chlorophyll and antioxidative activities of catalase (CAT), ascorbate peroxide (APx), glutathione reductase (GR) and superoxide dismutase (SOD); under NaCl stress commercial ALA and TN114 had generally stronger effects than PP803. The strain TN114 has potential as a plant growth stimulating bacterium that might enhance rice growth in saline paddy fields at a lower cost than commercial ALA.

Effects of Soil Types on Phytotoxic Activity of Pretilachlor in Combination with Sunflower Leaf Extracts on Barnyardgrass (Echinochloa crus-galli)

The increasing use of synthetic chemicals for pest control in rice has become an overwhelming economical border, and more important, it could pose a serious threat of the environment. In addition, the extensive use of synthetic herbicides has been the cause for the evolution of herbicide-resistant barnyardgrass worldwide. This weed species is the most competitive weed in rice after the red rice. Thus, this study was conducted to examine the combination effects of aqueous sunflower leaf extracts with lower rate of pretilachlor on barnyardgrass emergence and growth in Marang (sandy loam) and Seberang (silt loamy) soil series under glasshouse conditions. Interestingly, the ED95values (rate that causes 95% inhibition) of pretilachlor for emergence and shoot fresh weight (SFW) of barnyardgrass were reduced by 79 and 82%, respectively, when being mixed with sunflower leaf extracts in Marang series. In contrast, the addition of sunflower leaf extracts increased ED95value of pretilachlor in Seberang series. Rice seedlings at 4 and 8 d after sowing (DAS) were found to be tolerant to this mixture treatment. However, root growth of rice seedlings were inhibited at 0 and 2 DAS. These results suggest that sunflower leaf extracts have potential to reduce rate of pretilachlor for inhibiting emergence and growth of barnyardgrass without injuring rice seedlings in rice fields depending on soil types and growth stage of rice.

The role of hydrogen peroxide in cadmium-inhibited root growth of rice seedlings

Cadmium (Cd) is readily taken up by the roots of rice seedlings, leading to growth reduction. H2O2 is a constituent of oxidative metabolism and is itself a reactive oxygen species. In this study, the participation of H2O2 in CdCl2-inhibited growth of rice roots was investigated. CdCl2 treatment increased H2O2 production in rice roots. CdCl2 treatment had no effect on the activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase, but inhibited the activity of catalase (CAT) in rice roots. CdCl2-inhibited root growth and -increased H2O2 content were lessened in the presence of diphenyleneiodonium chloride, an inhibitor of H2O2 generating NADPH oxidase. However, this stimulation of root growth in CdCl2-treated seedlings is small (about 5%). Calcium (Ca) is important in many physiological processes in plants. Attempts were also made to determine whether the action of Ca on CdCl2-inhibited growth of rice roots is associated with H2O2. CaCl2 application reduced the production of H2O2, the decrease in CAT activity, and the inhibition of root growth caused by CdCl2. The effects of CaCl2 application could be reversed by exogenous H2O2. Our results indicate that the Cd causes a decline in CAT and to a lower extent a stimulation of NADPH oxidase in rice roots, with the subsequent generation of H2O2, an agent responsible for growth inhibition.

A proteomic approach to investigating the promotive effects of brassinolide on root growth of rice seedlings

Brassinolide influenced rice (Oryza sativa L.) root growth in a concentration-dependent manner. Roots grown in 0.1 nmol/L BL were 28% longer than those in the control. On the other hand, the roots grown in 1000 nmol/L BL were 65% shorter in comparison with those in the control. To investigate how BL influences rice root growth, proteome analysis techniques were applied. After BL treatments, total proteins from rice root were extracted separately. Extracted proteins were separated by two-dimensional polyacrylamide gel electrophoresis and analyzed using an automated protein sequencer and mass spectrometer. There were 33 proteins that showed differences in the accumulation levels as a result of treatments with BL. Proteins related to stress tolerance, enzymes, and cell structure were mainly found in the root. There were many proteins regulated by other hormone or light also. Results suggest that the physiologic functions of these proteins detected using powerful proteome analysis are implicated in root elongation triggered by BL. High-level brassinosteriod (BR) indicated that IAA amidohydrolase, which can release active IAA from IAA pool was increased, and the IAA level was so high that the root length was inhibited.

Enantioselective Separation and Phytotoxicity on Rice Seedlings of Paclobutrazol

The environmental significance of enantioselectivity in chiral insecticides and herbicides has been widely studied. However, little information is currently available on the enantioselective behavior of chiral plant growth regulators. In this study, paclobutrazol enantiomers were resolved and prepared by chiral high-performance liquid chromatography with a Sino-chiral OJ column. The relationship among absolute configuration, optical activity and circular dichroism of paclobutrazol enantiomers was established. The enantioselective behavior of paclobutrazol, including enantioselective effect of paclobutrazol on the growth of rice seedlings and cyanobacteria and enantioselective loss of paclobutrazol in rice seedling growth media, in rice culture system was studied. The (2S,3S)-(-)-enantiomer was almost 3.1 times more active than the (2R,3R)-(+)-enantiomer toward shoot growth as measured by 7 day EC50 values. Enantioselectivity could not be determined with respect to root growth of rice seedlings because a typical dosage response was not observed in the range of the concentrations studied. The dissipation of paclobutrazol in rice growth medium is not enantioselective. Enantiomers and diastereoisomer of paclobutrazol all facilitated the growth of cyanobacteria, which increase the effectiveness of rice biofertilizers. The (2S,3S)-(-)-enantiomer showed stronger stimulatory activity on Microcystis aeruginosa cyanobacteria than the (2R,3R)-(+)-enantiomer, whereas the latter was a more potent stimulator of Anabaena sp. growth. These observations indicate that application of the (2S,3S)-(-)-enantiomer of paclobutrazol and Microcystis aeruginosa in rice cultivation is a good strategy for improving rice seedling performance.

Epigenetic interaction of OsHDAC1 with the OsNAC6 gene promoter regulates rice root growth

Histone deacetylases (HDACs) modulate chromatin structure and transcription. Previously, we have shown that transgenic overexpression of OsHDAC1gene alters the seedling root growth. In the current report, we have identified a group of genes that are transcriptionally repressed in the OsHDAC1overexpressors(OsHDAC1OE) by performing a global profiling of root expressed genes. The OsNAC6 gene, a member of NAC family, was identified as a key component of the OsHDAC1 regulon and found to be repressed in OsHDAC1OE. The root growth of OsNAC6 knock-out (OsNAC6KO) seedlings was observed to be similar to that of the OsHDAC1OE seedlings. Conversely, the root growth of the OsNAC6 overexpressors (OsNAC6OE) was similar to that of the OsHDAC1 knock-out (OsHDAC1KO) seedlings. We further demonstrated that OsHDAC1 interact with the OsNAC6 gene promoter at a epigenetic level by deacetylating K9, K14, and K18 on H3 and K5, K12, and K16 on H4. Overall, our results suggest that OsHDAC1 represses the OsNAC6 gene expression, which is primarily responsible for the alteration of root growth of rice seedlings.

Submergence Acclimation to Low-Temperature Stress in Rice Roots

A low temperature (10ºC, 48 h) inhibited primary root growth of rice seedlings (Oryza sativa L.). However, the inhibition was significantly mitigated by submergence for 24 h before the exposure to low temperatures, which induced alcohol dehydrogenase and increased the ethanol concentration in roots. Exogenous application of ethanol also had a similar mitigating effect. These results suggest that submergence pretreatment increases the tolerance to low temperature in rice roots due to ethanol accumulation in the roots.

Aluminum-inhibited root growth of rice seedlings is mediated through putrescine accumulation

The effects of AlCl3 on growth and polyamine levels of rice roots were investigated. When rice roots were treated with AlCl3, root growth was markedly inhibited. AlCl3 treatment resulted in a higher putrescine content and lower spermidine and spermine contents in rice roots. d-Argnine and α-methylornithine, inhibitors of putrescine biosynthesis, caused a reduced content of putrescine in rice roots under Al stress. AlCl3 treatment also resulted in a decrease in diamine oxidase activity in rice roots. The growth of rice roots in the presence of AlCl3 was recovered after the addition of d-arginine or α-methylornithine. The protective effect of d-arginine or α-methylornithine in counteracting AlCl3-inhibited growth of rice roots is unlikely caused by reduction of Al uptake. Furthermore, the effect of the growth recovery in AlCl3-treated rice roots by d-arginine or α-methylornithine was reversed by the addition of putrescine. Our results strongly suggest that putrescine accumulation is a factor causing growth inhibition of rice roots under Al tress. Evidence is also presented to show that lignification is responsible for putrescine- and AlCl3-inhibited growth of rice roots.

Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil‐applied pethoxamid [2‐chloro‐N‐(2‐ethoxyethyl)‐N‐(2‐methyl‐1‐phenyl‐1‐propanyl) acetamide], (TKC‐94), on the plant growth of rice (Oryza sativa cv. Kiyohatamochi) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide‐applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol‐6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.

Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil-applied pethoxamid [2-chloro-N-(2-ethoxyethyl)-N-(2-methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice (Oryza sativa cv. Kiyohatamochi) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.

Amelioration of the salt-stressed root growth of rice and normalization of the Na+ distribution between the shoot and root by (S)-alpha-methylbenzyl-2-fluoro-4-methylphenylurea.

Optically active alpha-methylbenzyl phenyl ureas (MBPUs) show diverse plant physiological properties. Experiments were conducted to evaluate the salt-stress response of just-germinated rice seedlings supplemented with the S-enantiomer of MBPUs by assessing the growth and Na+ content. This study indicates that S-MBPUs served as a unique stress reliever for just-germinated young seedlings of rice injured by salinity. NaCl severely affected the root growth of rice seedlings. Concomitant treatment with S-MBPUs effectively ameliorated the growth inhibition of rice by NaCl. Glycine betaine (GB) did not act as a reliever of the NaCl stress. The addition of S-alpha-methylbenzyl 2-fluoro-4-methylphenyl urea (7, denoted as S-FM) to the saline medium ameliorated not only the root growth but also the protein content and dry weight of roots depending upon its concentration. The protein content, Na+ content and growth rate were correlated to each other with a positive relationship. The Na+ distribution ratio (S/R(Na+)) between the shoot and root increased with increasing concentration of NaCl when added alone, viz. with increasing growth reduction. A concomitant treatment with S-FM (7), however, resulted in the S/R(Na+) value becoming smaller with growth amelioration. This indicates that S-FM (7) controlled the translation of Na+ from the roots to shoots. S-FM (7) would have influenced some inherent functions connected with the Na+ behavior in the rice plant, although details of the mechanism for normalization of the S/R(Na+) ratio are still not clear.

Relative importance of Na+, Cl−, and abscisic acid in NaCl induced inhibition of root growth of rice seedlings

The relative importance of endogenous abscisic acid (ABA), as well as Na+ and Cl− in NaCl-induced responses related to growth in roots of rice seedlings were investigated. The increase in ammonium, proline and H2O2 levels, and cell wall peroxidase (POD) activity has been shown to be related to NaCl-inhibited root growth of rice seedlings. Increasing concentrations of NaCl from 50 to 150 mM progressively decreased root growth and increased both Na+ and Cl−. Treatment with NaCl in the presence of 4,4′-diisothiocyano-2,2′-disulfonic acid (DIDS, a nonpermeating amino-reactive disulfonic acid known to inhibit the uptake of Cl−) had less Cl− level in roots than that in the absence of DIDS, but did not affect the levels of Na+, and responses related to growth in roots. Treatment with 50 mM Na-gluconate (the anion of which is not permeable to membrane) had similar Na+ level in roots as that with 100 mM NaCl. It was found that treatment with 50 mM Na-gluconate effected growth reduction and growth-related responses in roots in the same way as 100 mM NaCl. All these results suggest that Cl− is not required for NaCl-induced responses in root of rice seedlings. Endogenous ABA level showed no increase in roots of rice seedlings exposed to 150 mM NaCl. It is unlikely that ABA is associated with NaCl-inhibited root growth of rice seedlings.