Irrigation regimes modulate non-structural carbohydrate remobilization and improve grain filling in rice(Oryza sativa L.)by regulating starch metabolism

Recently developed ‘super’ rice cultivars with greater yield potentials often suffer from the problem of poor grain filling, especially in inferior spikelets. Here, we studied the activities of enzymes related to starch metabolism in rice stems and grains, and the microstructures related to carbohydrate accumulation and transportation to investigate the effects of different water regimes on grain filling. Two ‘super’ rice cultivars were grown under two irrigation regimes of well-watered(WW) and alternate wetting and moderate soil drying(AWMD). Compared with the WW treatment,the activities of ADP glucose pyrophosphorylase(AGPase), starch synthase(StSase) and starch branching enzyme(SBE), and the accumulation of non-structural carbohydrates(NSCs) in the stems before heading were significantly improved, and more starch granules were stored in the stems in the AWMD treatment. After heading, the activities of α-amylase, β-amylase, sucrose phosphate synthase(SPS) and sucrose synthase in the synthetic direction(SSs)were increased in the stems to promote the remobilization of NSCs for grain filling under AWMD. During grain filling, the enzymatic activities of sucrose synthase in the cleavage direction(SSc), AGPase, StSase and SBE in the inferior spikelets were increased, which promoted grain filling, especially for the inferior spikelets under AWMD.However, there were no significant differences in vascular microstructures. The grain yield and grain weight could be improved by 13.1 and 7.5%, respectively, by optimizing of the irrigation regime. We concluded that the low activities of key enzymes in carbon metabolism is the key limitation for the poor grain filling, as opposed to the vascular microstructures, and AWMD can increase the amount of NSC accumulation in the stems before heading, improve the utilization rate of NSCs after heading, and increase the grain filling, especially in the inferior spikelets, by altering the activities of key enzymes in carbon metabolism.

The auxin transporter OsAUX1 regulates tillering in rice(Oryza sativa)

Tillering is an important agronomic trait of rice(Oryza sativa)that affects the number of effective panicles,thereby affecting yields.The phytohormone auxin plays a key role in tillering.Here we identified the high tillering and semi-dwarf 1(htsd1)mutant with auxin-deficiency root characteristics,such as shortened lateral roots,reduced lateral root density,and enlarged root angles.htsd1 showed reduced sensitivity to auxin,but the external application of indole-3-acetic acid(IAA)inhibited its tillering.We identified the mutated gene in htsd1 as AUXIN1(OsAUX1,LOC_Os01g63770),which encodes an auxin influx transporter.The promoter sequence of OsAUX1 contains many SQUAMOSA PROMOTER BINDING PROTEIN-LIKE(SPL)binding sites,and we demonstrated that SPL7 binds to the OsAUX1 promoter.TEOSINTE BRANCHED1(OsTB1),a key gene that negatively regulates tillering,was significantly downregulated in htsd1.Tillering was enhanced in the OsTB1 knockout mutant,and the external application of IAA inhibited tiller elongation in this mutant.Overexpressing OsTB1 restored the multi-tiller phenotype of htsd1.These results suggest that SPL7 directly binds to the OsAUX1 promoter and regulates tillering in rice by altering OsTB1 expression to modulate auxin signaling.

The Magnaporthe oryzae effector Avr-PikD suppresses rice immunity by inhibiting an LSD1-like transcriptional activator

Avirulence effectors(Avrs),encoded by plant pathogens,can be recognized by plants harboring the corresponding resistance proteins,thereby initiating effector-triggered immunity(ETI).In susceptible plants,however,Avrs can function as effectors,facilitating infection via effector-triggered susceptibility(ETS).Mechanisms of Avr-mediated ETS remain largely unexplored.Here we report that the Magnaporthe oryzae effector Avr-PikD enters rice cells via the canonical cytoplasmic secretion pathway and suppresses rice basal defense.Avr-PikD interacts with an LSD1-like transcriptional activator AKIP30 of rice,and AKIP30 is also a positive regulator of rice immunity,whereas Avr-PikD impedes its nuclear localization and suppresses its transcriptional activity.In summary,M.oryzae delivers Avr-PikD into rice cells to facilitate ETS by inhibiting AKIP30-mediated transcriptional regulation of immune response against M.oryzae.

DDG1 and G Protein α Subunit RGA1 Interaction Regulates Plant Height and Senescence in Rice(Oryza sativa)

Many studies have already shown that dwarfism and moderate delayed leaf senescence positively impact rice yield,but the underlying molecular mechanism of dwarfism and leaf senescence remains largely unknown.Here,using map-based cloning,we identified an allele of DEP2,DDG1,which controls plant height and leaf senescence in rice.The ddg1 mutant displayed dwarfism,short panicles,and delayed leaf senescence.Compared with the wild-type,ddg1 was insensitive to exogenous gibberellins(GA)and brassinolide(BR).DDG1 is expressed in various organs,especially in stems and panicles.Yeast two-hybrid assay,bimolecular fluorescent complementation and luciferase complementation image assay showed that DDG1 interacts with theα-subunit of the heterotrimeric G protein.Disruption of RGA1 resulted in dwarfism,short panicles,and darker-green leaves.Furthermore,we found that ddg1 and the RGA1 mutant was more sensitive to salt treatment,suggesting that DDG1 and RGA1 are involved in regulating salt stress response in rice.Our results show that DDG1/DEP2 regulates plant height and leaf senescence through interacting with RGA1.

Transcription factor OsSPL10 interacts with OsJAmyb to regulate blast resistance in rice

Transcription factors(TFs)play essential roles in transcriptional reprogramming during activation of plant immune responses to pathogens.OsSPL10(SQUAMOSA promoter binding protein-like10)is an important TF regulating trichome development and salt tolerance in rice.Here we report that knockout of OsSPL10 reduces whereas its overexpression enhances rice resistance to blast disease.OsSPL10 positively regulates chitin-induced immune responses including reactive oxygen species(ROS)burst and callose deposition.We show that OsSPL10 physically associates with OsJAmyb,an important TF involved in jasmonic acid(JA)signaling,and positively regulates its protein stability.We then prove that OsJAmyb positively regulates resistance to blast.Our results reveal a molecular module consisting of OsSPL10 and OsJAmyb that positively regulates blast resistance.

Conventional Breeding and Molecular Markers for Blast Disease Resistance in Rice (Oryza sativa L.)

Monogenic lines,which carried 23 genes for blast resistance were tested and used donors to transfer resistance genes by crossing method.The results under blast nursery revealed that 9 genes from 23 genes were susceptible to highly susceptible under the three locations(Sakha,Gemmeza,and Zarzoura in Egypt);Pia,Pik,Pik-p,Piz-t,Pita,Pi b,Pi,Pi 19 and Pi 20.While,the genes Pii,Pik-s,Pik-h,Pi z,Piz-5,Pi sh,Pi 3,Pi 1,Pi 5,Pi 7,Pi 9,Pi 12,Pikm and Pita-2 were highly resistant at the same locations.Clustering analysis confirmed the results,which divided into two groups;the first one included all the susceptible genes,while the second one included the resistance genes.In the greenhouse test,the reaction pattern of five races produced 100%resistance under artificial inoculation with eight genes showing complete resistance to all isolates.The completely resistant genes:Pii,Pik-s,Piz,Piz-5(=bi2)(t),Pita(=Pi4)(t),Pita,Pi b and Pi1 as well as clustering analysis confirmed the results.In the F1 crosses,the results showed all the 25 crosses were resistant for leaf blast disease under field conditions.While,the results in F2 population showed seven crosses with segregation ratio of 15(R):1(S),two cross gave segregated ratio of 3 R:1 S and one gave 13:3.For the identification of blast resistance genes in the parental lines,the marker K3959,linked to Pik-s gene and the variety IRBLKS-F5 carry this gene,which was from the monogenic line.The results showed that four genotypes;Sakha 105,Sakha 103,Sakha 106 and IRBLKS-F5 were carrying Pik-s gene,while was absent in the Sakha 101,Sakha 104,IRBL5-M,IRBL9-W,IRBLTACP1 and IRBL9-W(R)genotypes.As for Pi 5 gene,the results showed that it was present in Sakha 103 and Sakha 104 varieties and absent in the rest of the genotypes.In addition,Pita-Pita-2 gene was found in the three Egyptian genotypes(Sakha 105,Sakha 101 and Sakha 104)plus IRBLTACP1 monogenetic.In F2 generation,six populations were used to study the inheritance of blast resistance and specific primers to confirm the ratio and identify the resistance genes.However,the ratios in molecular markers were the same of the ratio under field evaluation in the most population studies.These findings would facilitate in breeding programs for gene pyramiding and gene accumulation to produce durable resistance for blast using those genotypes.

Synthetical Evaluation on the Qualitative and Quantitative Resistance of Rice Germplasms to Magnaporthe oryzae

[Objectives]This study was conducted to screen out rice resources resistant to rice blast(Magnaporthe oryzae).[Methods]The qualitative and quantitative resistance of 1659 rice resources from 45 countries and regions to rice blast were evaluated by disease nursery in upland condition and the test of the spectrum to rice blast isolates.[Results]There were 292 entries which accounted for 17.6%showed high blast resistance(0 and 1 disease scale),68 entries(counted for 4.1%)showed resistance to blast(3 disease scale);and the number of the entries showed intermediate resistance,intermediate susceptible and susceptible were 208(with the corresponding percentage of 12.5%),471(28.4%),620(37.4%)respectively.Among the tested entries,27 entries including BG1222,BL122,BTX,IR37704-131-2-3-2,and LEBONNET had showed broad-spectrum blast resistance with the resistance frequency of higher than 90%,Quantitative resistance evaluation was conducted on some key resources,and 14 entries,of which are BR27,DRAGO,IR100,QINLIUAI、SERIBU GANTANG,YUEXIANGZHAN and so on,showed good quantitative resistances,and 8 entries had higher quantitative resistances than IR36.[Conclusions]This study provides important blast resistance resources for the local rice breeding program and has a significant value for the discovery of new blast resistance genes and its application in the blast resistance breeding.

The OsBSK1-2-MAPK module regulates blast resistance in rice

Receptor-like cytoplasmic kinase OsBSK1-2 was reported to play an important role in regulation of response to rice blast,but the signaling pathway remained unknown.In this study,we identified OsMAPKKK18 and previously uncharacterized MAPKKKs OsMAPKKK16 and OsMAPKKK19 that interact with OsBSK1-2.Expression of all three MAPKKKs was induced by Magnaporthe oryzae infection,and all three induced cell death when transiently expressed in Nicotiana benthamiana leaves.Knockout of OsMAPKKK16 and OsMAPKKK18 compromised blast resistance and overexpression of OsMAPKKK19 increased blast resistance,indicating that all three MAPKKKs are involved in regulation of rice blast response.Furthermore,both OsMAPKKK16 and OsMAPKKK19 interacted with and phosphorylated OsMKK4 and OsMKK5,and chitin-induced MAPK activation was suppressed in osmapkkk16 and osbsk1-2 mutants.OsMAPKKK18 was earlier reported to interact with and phosphorylate OsMKK4 and affect chitin-induced MAPK activation,suggesting that OsBSK1-2 is involved in regulation of immunity through multiple MAPK signaling pathways.Unlike BSK1 in Arabidopsis,OsBSK1-2 was not involved in response to avirulent M.oryzae strains.Taken together,our results revealed important roles of OsMAPKKK16/18/19 and a OsBSK1-2-OsMAPKKK16/18/19-OsMKK4/5 module in regulating response to rice blast.

A Farmer’s Approach to Detecting Photoperiod Sensitivity in Rice (Oryza sativa ssp. indica) Landraces

Most indigenous rice landraces are sensitive to photoperiod during short day seasons,and this sensitivity is more pronounced in indica than in japonica landraces.Attempts to identify photoperiod sensitive(PPS)cultivars based on the life history stages of the rice plant,and several models and indices based on phenology and day length have not been precise,and in some cases yield counterfactual inferences.Following the empirical method of traditional Asian rice farmers,the author has developed a robust index,based on the sowing and flowering dates of a large number of landraces grown in different seasons from 2020 to 2023,to contradistinguish PPS from photoperiod insensitive cultivars.Unlike other indices and models of photoperiod sensitivity,the index does not require the presumed duration of different life history stages of the rice plant but relies only on the flowering dates and the number of days till flowering of a rice cultivar sown on different dates to consistently identify photoperiod sensitive cultivars.

The response of roots and the rhizosphere environment to integrative cultivation practices in paddy rice

Integrative cultivation practices(ICPs)are essential for enhancing cereal yield and resource use efficiency.However,the effects of ICP on the rhizosphere environment and roots of paddy rice are still poorly understood.In this study,four rice varieties were produced in the field.Each variety was treated with six different cultivation techniques,including zero nitrogen application(0 N),local farmers’practice(LFP),nitrogen reduction(NR),and three progressive ICP techniques comprised of enhanced fertilizer N practice and increased plant density(ICP1),a treatment similar to ICP1 but with alternate wetting and moderate drying instead of continuous flooding(ICP2),and the same practices as ICP2 with the application of organic fertilizer(ICP3).The ICPs had greater grain production and nitrogen use efficiency than the other three methods.Root length,dry weight,root diameter,activity of root oxidation,root bleeding rate,zeatin and zeatin riboside compositions,and total organic acids in root exudates were elevated with the introduction of the successive cultivation practices.ICPs enhanced nitrate nitrogen,the activities of urease and invertase,and the diversity of microbes(bacteria)in rhizosphere and non-rhizosphere soil,while reducing the ammonium nitrogen content.The nutrient contents(ammonium nitrogen,total nitrogen,total potassium,total phosphorus,nitrate,and available phosphorus)and urease activity in rhizosphere soil were reduced in all treatments in comparison with the non-rhizosphere soil,but the invertase activity and bacterial diversity were greater.The main root morphology and physiology,and the ammonium nitrogen contents in rhizosphere soil at the primary stages were closely correlated with grain yield and internal nitrogen use efficiency.These findings suggest that the coordinated enhancement of the root system and the environment of the rhizosphere under integrative cultivation approaches may lead to higher rice production.

Quantifying source-sink relationships in leaf-color modified rice genotypes during grain filling

Leaf-color modification can affect canopy photosynthesis,with potential effects on rice yield and yield components.Modulating source-sink relationships through crop management is often used to improve crop productivity.This study investigated whether and how modifying leaf color alters source-sink relationships and whether current crop cultivation practices remain applicable for leaf-color modified genotypes.Periodically collected data of total biomass and nitrogen(N)accumulation in rice genotypes of four genetic backgrounds and their leaf-color modified variants(greener or yellower)were analyzed,using a recently established modelling method to quantify the source-sink(im)balance during grain filling.Among all leaf-color variants,only one yellower-leaf variant showed a higher source capacity than its normal genotype.This was associated with greater post-flowering N-uptake that prolonged the functional leaf-N duration,and this greater post-flowering N-uptake was possible because of reduced pre-flowering N-uptake.A density experiment showed that current management practices(insufficient planting density accompanied by abundant N application)are unsuitable for the yellower-leaf genotype,ultimately limiting its yield potential.Leaf-color modification affects source-sink relationships by regulating the N trade-off between pre-and post-flowering uptake,as well as N translocation between source and sink organs.To best exploit leaf-color modification for improving crop productivity,adjustments of crop management practices are required.

Appropriate Supply of Ammonium Nitrogen and Ammonium Nitrate Reduces Cadmium Content in Rice Seedlings by Inhibiting Cadmium Uptake and Transport

Reasonable nitrogen(N) application is a promising strategy for reducing crop cadmium(Cd) toxicity. However, the specific form of N and the required amount that affect Cd tolerance and accumulation in rice remain unclear. This study explored the influence of different N-fertilizer forms(NH_4NO_3, NH_4Cl, and KNO_3) and dosages on Cd tolerance and uptake in Cd-stressed N-sensitive and N-insensitive indica rice accessions. The results indicated that the Cd tolerance of N-sensitive indica accessions is more robust than that of N-insensitive ones. Furthermore, the shoot Cd content and Cd translocation rate in both N-sensitive and N-insensitive indica accessions decreased with an appropriate supply of NH_4NO_3 and NH_4Cl, whereas they were comparable or slightly increased with increased KNO_3. Unfortunately, we did not find significant and regular differences in Cd accumulation or translocation between N-sensitive and N-insensitive rice accessions. Consistent with the reduction of shoot Cd content, the addition of NH_4NO_3 and NH_4Cl also inhibited the instantaneous root Cd^(2+) uptake. The expression changes of Cd transport-related genes under different N forms and dosages suggested that the decreased shoot Cd content, caused by the increased supply of NH_4NO_3 and NH_4Cl, is likely achieved by reducing the transcription of OsNRAMP1 and OsIRT1. In summary, our findings reveal that an appropriate supply of NH_4NO_3 and NH_4Cl could reduce Cd uptake and transport in rice seedlings, suggesting that rational N management could reduce the Cd risk in rice production.

A 9.5-kb deletion in the 1st intron of OsMADS51 enhances temperature sensitivity in rice

Temperature is an important environmental factor affecting heading date of rice.Despite its importance,genes responsible for temperature-sensitive heading in rice have remained elusive.Our previous study identified a quantitative trait locus qHd1 which advances heading date under high temperatures.A 9.5-kb insertion was found in the first intron of OsMADS51 in indica variety Zhenshan 97(ZS97).However,the function of this natural variant in controlling temperature sensitivity has not been verified.In this study,we used CRISPR/Cas9 to knock out the 9.5-kb insertion in ZS97.Experiments conducted under cotrolled conditions in phytotrons confirmed that deletion increased temperature sensitivity and advanced heading by downregulating the expression level of OsMADS51.One-hybrid assays in yeast,ChIP-quantitative polymerase chain reaction,electrophoretic mobility shift,and luciferase-based transient transactivation assays collectively confirmed that OsMADS51 affects heading date by regulation of heading date gene Ehd1.We further determined that the long non-coding RNA HEATINR is generated from the first intron of OsMADS51,offering an explanation for how the 9.5-kb insertion affects temperature sensitivity.We also found that OsMADS51 was strongly selected in early/late-season rice varieties in South China,possibly accounting for their strong temperature sensitivity.These insights not only advance our understanding of the molecular mechanisms underlying the temperature-responsive regulation of heading date in rice but also provide a valuable genetic target for molecular breeding.

Genome-wide association study reveals that JASMONATE ZIM-DOMAIN 5 regulates seed germination in rice

Seed germination is a complex trait regulated by multiple genes in rice.However,the regulators of rice seed germination have yet to be sufficiently determined.Here,a quantitative trait locus(QTL)for rice seed germination was identified in a genome-wide association study.The candidate gene JASMONATE ZIM-DOMAIN 5(OsJAZ5)of the QTL was verified that positively regulates seed germination.OsJAZ5 regulation of seed germination involves an OsABI3-mediated abscisic acid pathway.Overexpression of OsJAZ5 facilitated seed germination.The application of OsJAZ5 might be useful for increasing seed germination for rice direct seeding.

OsWRKY65 enhances immunity against fungal and bacterial pathogens in rice

Diverse bacterial and fungal pathogens attack plants,causing biotic stress and severe yield losses globally.These losses are expected to become more serious as climate change improves conditions for many pathogens.Therefore,identifying genes conferring broad-spectrum disease resistance and elucidating their underlying mechanisms provides important resources for plant breeding.WRKY transcription factors affect plant growth and stress responses.However,the functions of many WRKY proteins remain to be elucidated.Here,we demonstrated the role of rice(Oryza sativa)WRKY groupⅢtranscription factor OsWRKY65 in immunity.OsWRKY65 localized to the nucleus and acted as transcriptional repressor.Genetic and molecular functional analyses showed that OsWRKY65 increases resistance to the fungal pathogen Fusarium fujikuroi through downregulation of GA signaling and upregulation of JA signaling.Moreover,OsWRKY65 modulated the expression of the key genes that confer susceptibility or resistance to Xanthomonas oryzae pv.oryzae to enhance immunity against the pathogen.In particular,OsWRKY65directly bound to the promoter region of OsSWEET13 and repressed its expression.Taken together,our findings demonstrate that the OsWRKY65 enhances resistance to fungal and bacterial pathogens in rice.

Rice AGL1 determines grain size and sterile lemma identity

The grass spikelet is a unique inflorescence structure that determines grain size.Although many genetic factors have been well characterized for grain size and glume development,the underlying molecular mechanisms in rice are far from established.Here,we isolated rice gene,AGL1 that controlled grain size and determines the fate of the sterile lemma.Loss of function of AGL1 produced larger grains and reduced the size of the sterile lemma.Larger grains in the agl1 mutant were caused by a larger number of cells that were longer and wider than in the wild type.The sterile lemma in the mutant spikelet was converted to a rudimentary glume-like organ.Our findings showed that the AGL1(also named LAX1)protein positively regulated G1 expression,and negatively regulated NSG1 expression,thereby affecting the fate of the sterile lemma.Taken together,our results revealed that AGL1 played a key role in negative regulation of grain size by controlling cell proliferation and expansion,and supported the opinion that rudimentary glume and sterile lemma in rice are homologous organs.

Mitigating Iron Toxicity by Using Rock Phosphate to Improve Rice Productivity

Iron toxicity is a major constraint to rice production, particularly in highly weathered soils of inland valleys in Sub-Saharan Africa where the rice growing area is rapidly expanding. This study aimed to improve the productiveness of iron toxicity sensitive’s rice fields as well as in the unsensitive fields by using local phosphate fertilizers. Eighteen (18) rice genotypes were been assessed in a split plot design in two areas: without iron toxicity and with iron toxicity. NPK, NK, Rock Phosphate, Triple super phosphate, Calcined phosphate and Acidulated phosphate were used as fertilizers. Data collection was focused on agronomic traits and yield (g/m2). The best fertilizers in the area without iron toxicity were NPK (820.2 g/m2) and triple super phosphate (751.7 g/m2). In the iron toxicity area, the best yields were performed by NPK (785.5 g/m2) and raw calcined phosphate (698.3 g/m2). Yet, the Accessions 15, Accessions 225, Accessions 226 and Accessions 270 were rainfed rice genotypes while CC109 A, HB 46 and HB 62 were low-land/irrigated rice genotypes. NPK, NK and acidulated phosphate fertilizers alleviate the best, iron toxicity in both sensitive and unsensitive rice fields.

Influence of Epistasis and QTL×Environment Interaction on Heading Date of Rice(Oryza sativa L.)

QTLs for heading date of rice （Oryza sativa L.） with additive, epistatic, and QTL × environment （QE） interaction effects were studied using a mixed-model-based composite interval mapping （MCIM） method and a double haploid （DH） population derived from IR64/Azucena in two crop seasons. Fourteen QTLs conferring heading date in rice, which were distributed on ten chromosomes except for chromosomes 5 and 9, were detected. Among these QTLs, eight had single-locus effects, five pairs had double-locus interaction effects, and two single-loci and one pair of double-loci showed QTL × environment interaction effects. All predicted values of QTL effects varied from 1.179 days to 2.549 days, with corresponding contribution ratios of 1.04%-4.84%. On the basis of the effects of the QTLs, the total genetic effects on rice heading date for the two parents and the two superior lines were predicted, and the putative reasons for discrepancies between predicted values and observed values, and the genetic potentiality in the DH population for improvement of heading date were discussed. These results are in agreement with previous results for heading date in rice, and the results provide further information, which indicate that both epistasis and QE interaction are important genetic basis for determining heading date in rice.

Advances in Physiological-biochemical and Genetic Mechanisms of Seed Aging in Rice(Oryza sativa L.)

Reasons causing or accelerating seed aging are mainly damage of mem- branes, DNA and proteins, decline of protein synthesis capacity and excessive ac- cumulation of reactive oxygen species. With the application of natural aging or artifi- cial aging methods, it was reported that quantitative trait loci （QTLs） of seed stora- bility in rice were widely distributed on the chromosomes except the 10th chromo- some. In this paper, we reviewed the progresses in the research on physiological- biochemical and genetic mechanisms of seed aging, and analyzed the existing problems and developing prospect in molecular breeding of rice with improved seed storability, in order to provide reference for the basic research and genetic improve- ment of rice seed storabUity.

Comparative Studies on the Changes of Microtubule Distribution and Reorganization During the Meiotic Stages of Development in Normal (IR36) and a Temperature/photoperiod Sensitive Male Sterile Line (Peiai 64S) of Rice ( Oryza sativa )

Changes in the pattern of organization of microtubules in the meiotic stages of development of pollen (i.e. from pre-meiotic interphase to more or less metaphase I) of a normal (IR36) and a temperature/photoperiod sensitive male sterile line (Peiai 64S) of rice were studied using immunofluorescence confocal microscopy. In IR36, from pre-meiotic interphase to metaphase I, the pattern of microtubule distribution in the meiocytes underwent a series of changes. Some new organizational patterns of microtubules (that have not been described before) were observed during microsporogenesis, including the existence of a broad band of perinuclear microtubules at the diakinesis stage of development. The pattern of microtubule distribution in the meiocytes of the male sterile line, Peiai 64S, was quite different front that seen in IR36. In Peiai 64S, the microtubules showed abnormal patterns of distribution from pre-meiotic interphase to metaphase I. For example the broad band of perinuclear microtubules seen at diakinesis in IR36 was much disorganized and loosened in Peiai 64S. The spindles formed were also very abnormal and different from the normal spindle. The appearance of abnormal microtubule distribution in the early stages of microsporogenesis may contribute to the malformation and ultimate abortion of pollen in Peiai 64S.