Shoot Growth Of Rice Research Articles

'Preferential' ammonium uptake by rice does not always turn into higher N recovery of fertilizer sources under water-saving irrigation

Ammonium (NH4+) has been reported as the preferred mineral N source (a preference for NH4+ uptake over NO3-) for rice (Oryza sativa L.), the predominant supply of NH4+ has been hypothesized as a means of increasing the N recovery efficiency (NRE). However, the contribution of NH4+ preference to NRE is unclear under different irrigation regimes. To evaluate the NRE of rice as affected by varied N supply forms, rice (cv. 'Suijing 18') was grown in a pot experiment with 15N-NH4+ or 15N-NO3- applied to flooded and water-saving irrigation regimes. At harvest, plant biomass, N accumulation, and the fate of 15N-labeled N in the plant-soil system were assessed. Ammonium-N application enhanced rice shoot growth compared with nitrate-N under both irrigation regimes. This enhancement by NH4+ was further promoted under water-saving irrigation. In contrast, nitrate-N enhanced rice root growth, more fertilizer-derived N residues in the soil compared with those of NH4+ treated, regardless of the irrigation regimes. Ammonium enhanced the NRE of rice compared with NO3- treated under flooded irrigation. However, the so-called 'preference' for NH4+ by rice did not always turn into high N recovery efficiency, and there was no difference in NRE of rice between varied N supply forms under water-saving irrigation. Even if NH4+ is 'preferred' by the rice, the N cycle in the paddy soil is complex and dynamic, especially under water-saving irrigation which resulted in a rapid conversion of the applied 15NH4+ to NO3-, and hence less opportunities for rice to take up the applied 15NH4+. Therefore, the nitrogen preference of plants is not the only critical factor in selecting a proper nitrogen fertilizer source for rice, it is better to take the match of plant N preference, N fertilizer type, and irrigation regime into consideration to optimize irrigation and fertilization management and increase the NRE of plants.

Effects of Aluminium Toxicity on Root and Shoot Growth Of Rice and Chickpea Seedlings

Increasing concentrations of aluminium progressively declined primary root length and number of lateral roots in rice and chickpea seedlings grown in rhizobox. It also inhibited the root and shoot length, dry weight of root and shoot of rice and chickpea seedlings grown in solution culture. On the other hand, it enhanced shoot/root length ratio and dry weight ratio for both the genera. Bangladesh J. Bot. 50(4): 1195-1201, 2021 (December)

Glycinebetaine: a versatile protectant to improve rice performance against aluminium stress by regulating aluminium uptake and translocation.

Glycinebetaine alleviates the detrimental effects of aluminium stress by regulating aluminium uptake and translocation, maintaining PSII activity, and activating the oxidative defence, thereby maintaining the growth and development of rice. Aluminium (Al) toxicity is one of the primary growth-limiting factors that limits plant growth and crop productivity in acidic soils. Rice (Oryza sativa L.) plants are susceptible to Al stress and do not naturally accumulate glycinebetaine (GB), one of the most effective protectants. Therefore, the objective of this study was to investigate whether exogenous GB can ameliorate the detrimental effects of Al stress on rice plants. Our results showed that the growth, development and biomass of rice were clearly inhibited under Al stress. However, exogenous GB application increased rice shoot growth and photosynthetic pigments contents, maintained photosystem II (PSII) activity, and activated the antioxidant defence system under Al stress. More importantly, GB may mediate the expression of Al uptake- and translocation-related genes, including OsALS1, OsNrat1, OsSTAR1 and OsSTAR2, and the galacturonic acid contents in rice roots under Al stress. Therefore, our findings highlight exogenous GB application is a valid approach to effectively combat Al toxicity by regulating physiological and biochemical processes in crops.

Varietal variation and formation of iron plaques on cadmium accumulation in rice seedling

This study examined the impact of iron (Fe) plaque deposition and varietal variation on cadmium (Cd) accumulation in the rice plants (Oryza sativa L.) in a hydroponic experiment under controlled conditions. Fe was applied at the rate of 0, 50 and 100 mg L−1 to the nutrient solution to generate varying amounts of Fe plaque deposition around the root of the rice seedlings. The seedlings were then treated with Cd at the rate of 0, 0.5 and 1.0 mg L−1 in the nutrient solution. Reddish-brown colored Fe plaque is induced gradually on the roots of rice seedlings after Fe supplementation in the nutrient solution. Results showed that the biomass production differed markedly among the rice varieties due to the application of Fe with or without Cd stress. The Quest variety demonstrated the highest capacity of Fe plaque formation compared to the other varieties. The application of Fe and Cd significantly affected the Cd concentration in the citrate-bicarbonate-dithionite (CBD) extracts of roots and in the rice seedlings. The exogenous application of Cd significantly increased the root Cd content, which was greater than the shoot Cd content. The Fe plaque deposition capacity markedly varied among the examined varieties. The Cd concentrations in shoots declined by adding Fe. This study results demonstrated that boosted Fe plaque formation can minimize detrimental effects of Cd on rice shoot growth to some extent, but the root tissues are the main barrier to Cd accumulation and movements in the interior of the rice plants.

Co-planted barnyardgrass reduces rice yield by inhibiting plant above- and belowground-growth during post-heading stages

Barnyardgrass (Echinochloa spp.) is the most common noxious weed in rice paddies as it inhibits rice growth and reduces grain yield. To date, little information is available on above- and belowground-growth changes in rice due to neighboring barnyardgrass. This study aimed to investigate the changes in root traits and shoot growth of rice when it is grown with different kinds of barnyardgrass. Japonica rice plants (var. Nanjing 9108) were co-cultured with two varieties of Echinochloa crusgalli (L.) Beauv. (EP, var. mitis (pursh) Petern; EH, var. zelayensis (H.B.K.) Hitchc), and E. colonum (L.) Link (EL) in the field in 2017 and 2018. Four treatments included control (i.e., weed free rice plants) and co-cultures with each of three barnyardgrasses (EP, EH, and EL). The results revealed that EP, EH, and EL treatments significantly reduced rice grain yields by 30.6%–36.2%, 42.5%–46.5%, and 10.6%–14.3%, respectively. Shoot growth including shoot dry weight, leaf photosynthetic rate, zeatin (Z) and zeatin riboside (ZR) in grains, and activities of key enzymes involved in sucrose-to-starch conversion in grains and root traits, such as length density, root dry weight, total absorbing surface area, active absorption surface area, oxidation activity, and Z + ZR contents in roots were dramatically reduced during post-heading stages of rice when grown with the three kinds of barnyardgrass. Moreover, above-mentioned rice shoot growth indices were strongly and positively correlated with root traits. These results suggested the decrease in rice shoot growth and root traits during post-heading stages contributes to the reduction in the rice yield when it grows with barnyardgrass neighbors.

OsCYCP4s coordinate phosphate starvation signaling with cell cycle progression in rice.

Phosphate starvation leads to a strong reduction in shoot growth and yield in crops. The reduced shoot growth is caused by extensive gene expression reprogramming triggered by phosphate deficiency, which is not itself a direct consequence of low levels of shoot phosphorus. However, how phosphate starvation inhibits shoot growth in rice is still unclear. In this study, we determined the role of OsCYCP4s in the regulation of shoot growth in response to phosphate starvation in rice. We demonstrate that the expression levels of OsCYCP4s, except OsCYCP4;3, were induced by phosphate starvation. Overexpression of the phosphate starvation induced OsCYCP4s could compete with the other cyclins for the binding with cyclin-dependent kinases, therefore suppressing growth by reducing cell proliferation. The phosphate starvation induced growth inhibition in the loss-of-function mutants cycp4;1, cycp4;2, and cycp4;4 is partially compromised. Furthermore, the expression of some phosphate starvation inducible genes is negatively modulated by these cyclins, which indicates that these OsCYCP4s may also be involved in phosphate starvation signaling. We conclude that phosphate starvation induced OsCYCP4s might coordinate phosphate starvation signaling and cell cycle progression under phosphate starvation stress.

The Rice Actin-Binding Protein RMD Regulates Light-Dependent Shoot Gravitropism.

Light and gravity are two key determinants in orientating plant stems for proper growth and development. The organization and dynamics of the actin cytoskeleton are essential for cell biology and critically regulated by actin-binding proteins. However, the role of actin cytoskeleton in shoot negative gravitropism remains controversial. In this work, we report that the actin-binding protein Rice Morphology Determinant (RMD) promotes reorganization of the actin cytoskeleton in rice (Oryza sativa) shoots. The changes in actin organization are associated with the ability of the rice shoots to respond to negative gravitropism. Here, light-grown rmd mutant shoots exhibited agravitropic phenotypes. By contrast, etiolated rmd shoots displayed normal negative shoot gravitropism. Furthermore, we show that RMD maintains an actin configuration that promotes statolith mobility in gravisensing endodermal cells, and for proper auxin distribution in light-grown, but not dark-grown, shoots. RMD gene expression is diurnally controlled and directly repressed by the phytochrome-interacting factor-like protein OsPIL16. Consequently, overexpression of OsPIL16 led to gravisensing and actin patterning defects that phenocopied the rmd mutant. Our findings outline a mechanism that links light signaling and gravity perception for straight shoot growth in rice.

Leveraging Breeding Values Obtained from Random Regression Models for Genetic Inference of Longitudinal Traits.

Understanding the genetic basis of dynamic plant phenotypes has largely been limited because of a lack of space and labor resources needed to record dynamic traits, often destructively, for a large number of genotypes. However, the recent advent of image-based phenotyping platforms has provided the plant science community with an effective means to nondestructively evaluate morphological, developmental, and physiological processes at regular, frequent intervals for a large number of plants throughout development. The statistical frameworks typically used for genetic analyses (e.g., genome-wide association mapping, linkage mapping, and genomic prediction) in plant breeding and genetics are not particularly amenable for repeated measurements. Random regression (RR) models are routinely used in animal breeding for the genetic analysis of longitudinal traits and provide a robust framework for modeling trait trajectories and performing genetic analysis simultaneously. We recently used a RR approach for genomic prediction of shoot growth trajectories in rice ( L.) from 33,674 single nucleotide polymorphisms. In this study, we have extended this approach for genetic inference by leveraging genomic breeding values derived from RR models for rice shoot growth during early vegetative development. This approach provides improvements over conventional single time point analyses for discovering loci associated with shoot growth trajectories. The RR approach uncovers persistent as well as time-specific transient quantitative trait loci. This methodology can be widely applied to understand the genetic architecture of other complex polygenic traits with repeated measurements.

OsNRT2.4 encodes a dual-affinity nitrate transporter and functions in nitrate-regulated root growth and nitrate distribution in rice

Plant NRT2 nitrate transporters commonly require a partner protein, NAR2, for transporting nitrate at low concentrations, but their role in plants is not well understood. In this study, we characterized the gene for one of these transporters in the rice genome, OsNRT2.4, in terms of its activity and roles in rice grown in environments with different N supply. In Xenopus oocytes, OsNRT2.4 alone without OsNAR2 co-expression facilitated nitrate uptake showing biphasic kinetics at a wide concentration range, with high- and low-affinity KM values of 0.15 and 4 mM, respectively. OsNRT2.4 did not have nitrate efflux or IAA influx activity. In rice roots, OsNRT2.4 was expressed mainly in the base of lateral root primordia. Knockout of OsNRT2.4 decreased lateral root number and length, and the total N uptake per plant at both 0.25 and 2.5 mM NO3- levels. In the shoots, OsNRT2.4 was expressed mainly in vascular tissues, and its knockout decreased the growth and NO3--N distribution. Knockout of OsNRT2.4, however, did not affect rice growth and N uptake under conditions without N or with only NH4+ supply. We conclude that OsNRT2.4 functions as a dual-affinity nitrate transporter and is required for nitrate-regulated root and shoot growth of rice.

Phosphorus and Iron Deficiencies Influences Rice Shoot Growth in an Oxygen Dependent Manner: Insight from Upland and Lowland Rice.

Rice is the main staple crop for one-third of the world population. To maximize yields, large quantities and constant input of fertilizers containing essential nutrients such as phosphorus (P) and iron (Fe) are added. Rice can germinate in both aerobic and anaerobic conditions, but the crosstalk between oxygen (O2) and nutrients such as P and Fe on plant growth remains obscure. The aim of this work was to test whether such interactions exist, and, if so, if they are conserved between up- and lowland rice varieties. To do so, we assessed shoot and root biomass as well as inorganic phosphate (Pi) accumulation in four rice varieties, including two lowland rice varieties Nipponbare and Suphanburi 1 (SPR1) (adapted to non-aerated condition) and two upland rice varieties CMU122 and Sew Mae Jun (SMJ) (adapted to aerated condition) under various conditions of Pi and/or Fe deficiencies, in aerated and non-areated solution. Under these different experimental conditions, our results revealed that the altered shoot biomass in Nipponbare and SPR1 was O2-dependent but to a lesser extent in CMU122 and SMJ cultivars. In this perspective, discovering the biological significance and molecular basis of these mineral elements and O2 signal interaction is needed to fully appreciate the performance of plants to multiple environmental changes.

UvHOG1 is important for hyphal growth and stress responses in the rice false smut fungus Ustilaginoidea virens.

Rice false smut caused by Ustilaginoidea virens is one of the most important diseases of rice worldwide. Although its genome has been sequenced, to date there is no report on targeted gene deletion in U. virens and no molecular studies on genetic mechanisms regulating the infection processes of this destructive pathogen. In this study, we attempted to generate knockout mutants of the ortholog of yeast HOG1 MAP kinase gene in U. virens. One Uvhog1 deletion mutant was identified after screening over 600 hygromycin-resistant transformants generated by Agrobacterium tumefaciens mediated transformation. The Uvhog1 mutant was reduced in growth rate and conidiation but had increased sensitivities to SDS, Congo red, and hyperosmotic stress. Deletion of UvHOG1 resulted in reduced expression of the stress response-related genes UvATF1 and UvSKN7. In the Uvhog1 mutant, NaCl treatment failed to stimulate the accumulation of sorbitol and glycerol. In addition, the Uvhog1 mutant had reduced toxicity on shoot growth in rice seed germination assays. Overall, as the first report of targeted gene deletion mutant in U. virens, our results showed that UvHOG1 likely has conserved roles in regulating stress responses, hyphal growth, and possibly secondary metabolism.

Effects of benzoxazinoids in wheat residues may inhibit the germination, growth and gibberellin-induced α-amylase activity in rice

There is a rotational cropping system of wheat and rice in many areas. Wheat plants contain significant amounts of glucopyranosides of 6-methoxy-benzoxazolin-2(3H)-one (MBOA) and benzoxazolin-2(3H)-one (BOA). After crop harvesting, MBOA and BOA are produced during the degradation process of wheat residues left in the field. The purpose of this study was evaluation for the effect of MBOA and BOA on rice growth and germination. MBOA and BOA significantly inhibited the rice germination and the rice shoot growth at concentrations of 0.1 and 0.3 mM and higher, respectively. MBOA and BOA also inhibited the induction of α-amylase in rice seeds significantly at concentrations of 0.03 and 0.1 mM and higher, respectively, and inhibited gibberellin-induced α-amylase activity in de-embryonated rice. Significant inhibitions in germination, growth, and α-amylase activity were observed as MBOA and BOA concentrations increased. The inhibitions on the germination, growth, and α-amylase by MBOA were greater than those by BOA, which is the demethoxylated analogue of MBOA. These results suggest that MBOA and BOA may inhibit the germination and subsequent seedling growth of rice by inhibiting the gibberellin-induced α-amylase production. Therefore, wheat straw and roots left in the field after crop harvesting may suppress rice germination and growth, because of MBOA and BOA in the soil originated from wheat residues. Further studies are necessary for the determination of MBOA and BOA levels in field condition after the crop harvesting.

An Alternate Wetting and Moderate Soil Drying Regime Improves Root and Shoot Growth in Rice

ABSTRACTA major challenge in rice (Oryza sativa L.) production is to achieve the dual goal of increasing food production and saving water. This study aimed to investigate if alternate wetting and drying regimes could improve root and shoot growth and consequently increase grain yield and water use efficiency (WUE). Two rice varieties were field‐grown at Yangzhou, China in 2005 and 2006. Three irrigation regimes, alternate wetting and moderate soil drying (WMD, re‐watered when soil water potential reached −15 kPa at 15–20 cm depth), alternate wetting and severe soil drying (WSD, re‐watered when soil water potential reached −30 kPa), and a conventional irrigation (CI, continuously flooded), were imposed during the whole growing season. Compared with the CI, the WMD regime significantly increased, whereas the WSD regime reduced, root oxidation activity, cytokinin concentrations in roots and shoots, leaf photosynthetic rate, and activities of key enzymes involved in sucrose‐to‐starch conversion in grains. Grain yield of the two varieties, on the average, was increased by 11% under the WMD regime, and was reduced by 32% under the WSD regime when compared with that under the CI regime. Averaged WUE of the two varieties was increased by 55% under the WMD regime and 36% under the WSD regime. We conclude that a moderate wetting and drying regime can enhance root growth which benefits other physiological processes and result in higher grain yield and WUE.

Seasonal changes in the effects of free‐air CO2 enrichment (FACE) on growth, morphology and physiology of rice root at three levels of nitrogen fertilization

AbstractOver time, the relative effects of elevated [CO2] on the aboveground photosynthesis, growth and development of rice (Oryza sativa L.) are likely to be changed with increasing duration of CO2 exposure, but the resultant effects on rice belowground responses remain to be evaluated. To investigate the impacts of elevated [CO2] on seasonal changes in root growth, morphology and physiology of rice, a free‐air CO2 enrichment (FACE) experiment was performed at Wuxi, Jiangsu, China, in 2002–2003. A japonica cultivar with large panicle was exposed to two [CO2] (ambient [CO2], 370 μmol mol−1; elevated [CO2], 570 μmol mol−1) at three levels of nitrogen (N): low (LN, 15 g N m−2), medium (MN, 25 g N m−2) and high N (HN, 35 g N m−2). Elevated [CO2] increased cumulative root volume, root dry weight, adventitious root length and adventitious root number at all developmental stages by 25–71%, which was mainly associated with increased root growth rate during early growth period (EGP) and lower rate of root senescence during late growth period (LGP), while a slight inhibition of root growth rate occurred during middle growth period (MGP). For individual adventitious roots, elevated [CO2] increased average length, volume, diameter and dry weight early in the season, but the effects gradually disappeared in subsequent stages. Total surface area and active adsorption area per unit root dry weight reached their maxima 10 days earlier in FACE vs. ambient plants, but both of them together with root oxidation ability per unit root dry weight declined with elevated [CO2] during MGP and LGP, the decline being larger during MGP than LGP. The CO2‐induced decreases in specific root activities during MGP and LGP were associated with a larger amount of root accumulation during EGP and lower N concentration and higher C/N ratio in roots during MGP and LGP in FACE vs. ambient plants. The results suggest that most of the CO2‐induced increases in shoot growth of rice are similarly associated with increased root growth.

Experimental complexities in evaluating the allelopathic activities in laboratory bioassays: A case study

Soil is the major player in deciding allelopathic activities. A study was designed to examine experimental complexities in determining the allelopathic behavior of soil amended with water-soluble leachates from Chenopodium murale. Chenopodium murale interferes with the growth and establishment of crop seedlings. The present study examined the role of water-soluble organic substances, if any, in the shoot growth suppression of rice ( Oryza sativa L.). Rice seeds were grown on C. murale leaf leachate-amended soil to investigate the phytotoxic effects of C. murale leachates. Any modification of C. murale phytotoxic activities was studied through using abiotic soil, activated charcoal and nitrogen (N) fertilization. Chemical and microbiological analysis of C. murale-amended soil was made to evaluate the role of soil components in C. murale phytotoxicity. Significant inhibition in the shoot growth of rice was observed when abiotic or biotic soil was amended with full-strength leaf leachate (T1) of C. murale compared to unamended soils. The inhibitory effect of T1 is maintained when rice seeds were placed on T1-amended soil after 0, 24 or 48 h; however, the inhibitory effects were eliminated when seeds were placed on amended soil after 72, 96 h or 1 wk of incubating soil with T1. Activated charcoal (1, 2 or 4 g) could not eliminate the inhibitory effects of T1-amended soil to the shoot length of rice. The phytotoxic effects of T1-amended soil to the shoot length of rice, however, were largely eliminated after the addition of N fertilization. Interference of C. murale leaf leachate to rice shoot growth could be due to number of effects that could be misconstrued as allelopathy effects.

Effects of Chitosan Application on the Shoot Growth of Rice and Soybean.

キトサンを土壌中に0.1%あるいは0.5%混和処理した後にイネ及びダイズを植え付け,それらの茎葉部の生育経過を調査した.イネは,無施肥区ではキトサン処理により草丈や葉齢などの生育促進やSPAD値の上昇が見られたが,施肥区では生育に差異は見られなかった.ダイズは,キトサン処理により本葉の葉位などの初期生育は促進されたが,その後は差異が見られなくなった.またイネとは異なり,キトサン処理の影響は施肥により変化は見られず,作物によって処理による地上部生育への影響は異なると考えられた.

Activity of insect juvenile hormone III: seed germination and seedling growth studies

Juvenile hormones are sesquiterpenoids that regulate developmental processses such as metamorphosis and reproduction in insects. Insect juvenile hormone III (JH III), methyl-10R,11-epoxy-3,7,11-trimethyl-2E,6E-dodecadienoate, has also been identified in two sedge species, Cyperus iria and C. aromaticus (Toong et al. 1988). Potential allelopathic activity of this compound and the structurally related sesquiterpenoid farnesol was investigated using seed germination and seedling growth assays with radish, lettuce and rice. Treatment of seeds with JH III delayed lettuce seed germination and potently inhibited rice shoot growth. Both farnesol and JH III inhibited the growth of C. iria seedlings. The antimicrobial activity of JH III was also tested on a taxonomic and ecologically diverse range of fungi. Using the classic cytotoxic disk assay, JH III did not effect growth of the fungal species tested. We believe that JH III may contribute to the aggressive nature of this invasive weed species.

Allelopathic Substance Exuded from a Serious Weed, Germinating Barnyard Grass (Echinochloa crus-galli L.), Roots.

The allelopathy of a serious weed, barnyard grass (Echinochloa crus-galli L.), was investigated. Root exudates of young barnyard grass showed allelopathic effects and plant-selective activity and inhibited root elongation of all plants tested. With respect to shoot growth, the exudates did not show inhibition of barnyard grass only. The allelopathic substance was isolated and identified as p-hydroxymandelic acid by NMR. p-Hydroxymandelic acid strongly inhibited shoot growth and root elongation of all plants tested. The effects of three congeners of p-hydroxymandelic acid were tested on rice shoot growth. In the biological activity exhibited in rice, shoot growth was related to the hydroxyl groups.

Tolerance of wheat (Triticum aestivum cvs Gamenya and Kite) and triticale (Triticosecale cv. Muir) to waterlogging

summaryResponses of two genotypes of wheat (Triticum aestivum cvs. Gamenya and Kite) and one genotype of triticale (Triticosecale cv. Muir) were evaluated in stagnant solution culture and in waterlogged soil, using 23‐ to 36‐d‐old plants. Stagnant nutrient solutions decreased shoot fresh weight of Gamenya by 21% compared with aerated plants, while shoot fresh weight of Muir was unaffected. Reductions in nodal root fresh weight under stagnant conditions were also less for Muir than Gamenya.Aerenchyma in nodal roots of stagnantly grown plants accounted for 6.7 and 12.7% of the root cross sectional area for Gamenya and Muir, respectively. Oxygen supplied via this aerenchyma was substantially greater for Muir than Gamenya, and greatest for nodal roots of Kite. Elongation rates of stagnantly grown nodal roots in an Oa‐free medium reflected the amount of O2 supplied via the aerenchyma, and were 0.11, 0.17 and 0.27 mm h−1 for Gamenya, Muir and Kite, respectively.Waterlogging in soil decreased the redox potential from +600 to − 200 mV after 35 d. Waterlogging decreased shoot fresh weight of Gamenya, Kite and Muir by 63–82% compared with drained plants, with similar reductions in growth of seminal roots. Nodal root growth was little affected by waterlogging in soil, although Muir had a 1.6‐2.4‐fold greater nodal root mass than Gamenya and Kite. Furthermore, after two cycles of 7 d waterlogging and 7 d drainage the seminal roots of Muir were at least double the length of Gamenya and Kite.Under the same waterlogged conditions, the shoot growth of rice (Oryza sativa cv, Calrose) was much greater than for wheat and triticale, and this reflected differences in morphology and anatomy of the root systems. Nodal root/shoot ratios indicated the major factor limiting shoot growth of wheat was the small mass of nodal roots per plant. However, a possible additional factor is the poor function of nodal roots of wheat and triticale in waterlogged soil.

Synergistic interaction of gibberellic acid and triazinone derivatives in the promotion of rice shoot growth

Forty-five 1,3,5-triazine-2,6-dione derivatives were synthesized and their plant growth-promoting activities examined by the rice ( Oryza sativa) seedling test in the presence or absence of gibberellic acid (GA). For high activity in promoting the growth of rice seedlings and acting as active GA-synergists, a para-substituted or a 2,4-disubstituted phenyl group, a hydrogen atom and an alkoxy group were required in the 1-, 3- and 4-positions of the 1,3,5-triazine-2,6-dione molecule. 4-Ethoxy-1-( p-tolyl)- s-triazine-2,6(1H, 3H)-dione [TA], one of the most potent triazinones, synergized the effect of GA on the shoot elongation of different varieties of rice including normal type, dwarf mutants and chlorophyll-mutants. TA synergistically increased the growth-promoting activity of GA by both a simultaneous treatment at the same sites and separate treatments at separate sites of rice seedlings.