Modes of Action of Phytochromes in Establishing Different Phototropic Responsiveness of Maize Coleoptiles

Previous studies have examined the effects of red light (R) on phototropism of maize ( Zea mays L. cv. Royaldent Hit 85) coleoptiles. The R effect on time-dependent phototropism (TDP) was further studied by characterizing its fluence-response relationship. The results showed the R effect was a low-fluence-response, unlike those on pulse-induced phototropisms that show a very-low-fluence-response mode. A subsequent pulse of far-red light (FR) could reverse the R effect. TDP responsiveness, however, recovered as the following FR was extended, The FR-dependent increase in TDP responsiveness was obtained even coleoptiles were pretreated only with FR. It suggested that TDP responsiveness could also be established in response to a FR signal. The fluence-response relationship for the effect of FR was then investigated. The effect of FR depended on the time of irradiation and required high photon fluences. Because reciprocity was invalid at the higher fluence range, the effect of FR would be a high-irradiance-response mode. Relation between phytochrome action modes and possible multiple pathways for phototropic signal transduction was analyzed based on the experiment results.

Research on Callus Induction from Coleoptile Explants of Amorphophallus

[Objective] The aim was to explore the ways of callus induction and the effect that different culture condition exerted on the callus induction from coleoptile explants of Amorphophallus. [Method] The test used konjac coleoptile as materials and designed four hormones, including 6-BA, NAA, KT and 2, 4-D, grouping 8 treat- ments to conduct statistics on callus induction in different test conditions. [Result] The result showed that multi-location generation and polymorphism was the impor- tant feature of callus induction from coleoptile explants of Amorphophallus; culture condition had significant influence on callus induction from coleoptile explants （P〈 0.01）. [Conclusion] It reached the best effect of callus induction when the culture condition was MS ＋ 1.0 mg/L 6-BA ＋ 2.0 mg/L NAA or MS ＋ 1.0 mg/LKT ＋ 2.0 mg/L 2, 4-D.

The Effects of Dwarfing Genes (Rht-B1b, Rht-D1b, and Rht8) with Different Sensitivity to GA_3 on the Coleoptile Length and Plant Height of Wheat

Understanding the effects of wheat dwarfing genes on the coleoptile length and plant height is crucial for the proper utilization of dwarfing genes in the improvement of wheat yield. Molecular marker analysis combined with pedigree information were used to classify wheat cultivars widely planted in major wheat growing regions in China into different categories based on the dwarfing genes they carried. The effects of the dwarfing genes with different sensitivity to gibberellins （GA3） on the coleoptile length and plant height were analyzed. Screening of 129 cultivars by molecular marker analysis revealed that 58 genotypes of wheat contained the dwarfing gene Rht-B1b, 24 genotypes of wheat contained Rht-D1b gene and 73 genotypes of wheat possessed Rht8 gene. In addition, among these 129 cultivars, 35 genotypes of wheat cultivars contained both Rht-B1b and Rht8 genes and 16 genotypes of wheat cultivars contained both Rht-D1b and Rht8 genes. Wheat cultivars with the dwarfing genes Rht-B1b or Rht-D1b were insensitive to GA3, while the cultivars with the dwarfing gene Rht8 were sensitive to GA3. Most of the wheat genotypes containing combination of Rht8 gene with either Rht-B1b or Rht-D1b gene were insensitive to GA3. The plant height was reduced by 24.6, 30.4, 28.2, and 32.2%, respectively, for the wheat cultivars containing Rht-B1b, Rht-D1b, Rht-B1b ＋ Rht8, and Rht-D1b ＋ Rht8 genes. The plant height was reduced by 14.3% for the wheat cultivar containing GA3-sensitive gene Rht8. The coleoptile length was shortened by 25.4, 31.3, 28.4 and 31.3%, respectively, in the wheat cultivars containing Rht-B1b, Rht-D1b, Rht-B1b ＋Rht8 and Rht-D1b ＋ Rht8 genes, while the coleoptile length was shortened only by 6.2% for the wheat cultivar containing Rht8 gene. We conclude that GA3-insensitive dwarfing genes （Rht-B1b and Rht-D1b） are not suitable for the wheat improvement in dryland because these two genes have effect on reducing both plant height and coleoptile length. In contrast, GA3- sensitive dwarfing gene （Rht8） is a relatively ideal candidate for the wheat improvement since it significantly reduces the plant height of wheat, but has less effect on the coleoptile length.

Relationship Between Coleoptile Length and Drought Resistance and Their QTL Mapping in Rice

By using a set of recombinant inbred line （RIL） population involving in 195 lines derived from a cross of Zhenshan 97B （lowland variety） and IRAT109 （upland variety）, the correlation analysis between coleoptile length （CL） and drought resistance index （DRI） and their QTL identification were conducted. There existed a significantly positive relationship between CL and DRI with the correlation coefficient of 0.2206＊＊ under water stress conditions. Under normal and water stress conditions, a total of eleven and four QTLs for CL and DRI, respectively, were detected on chromosomes 1,2, 4, 5, 6, 7, 9, 11 and 12 by using a linkage map including 213 SSR markers, which explained 4.84% to 22.65% of phenotypic variance. Chromosomes 1 and 9 possessing the QTLs for DRI harbored simultaneously QTLs for CL, and qCL9 shared the same chromosome location with qDR19 （RM160-RM215）. Comparing the QTLs related to drought resistance in other studies, QTLs for CL and DRI were located in the same or adjacent marker interval as those related to root traits, such as number, dry weight, depth, and length of root. Moreover, sixteen and three pairs of epistatic loci for CL and DRI were found, which accounted for 56.17% and 11.93% of the total variation in CL and DRI, respectively.

Coleoptile Purple Line Regulated by A-P Gene System Is a Valuable Marker Trait for Seed Purity Identification in Hybrid Rice

In plants,a large number of anthocyanin biosynthetic genes encoding enzymes and regulatory genes encoding transcription factors are required for anthocyanin synthesis.Coleoptile purple lines are two purple lines on both sides of coleoptiles after seed germination.However,the molecular mechanism of coleoptile purple line is not clear in rice so far.In this study,two major dominant genes,coleoptile purple line 1(OsCPL1,also known as OsC1)and coleoptile purple line 2(OsCPL2),were isolated via map-based cloning,and both of them were required for anthocyanin biosynthesis of coleoptile purple line in rice.The knockout and complementation experiments confirmed that OsC1 was required for purple color in most organs,such as coleoptile line,sheath,auricle,stigma and apiculus,whereas OsCPL2 was just required for coleoptile purple line.OsC1 was predominantly expressed in coleoptiles,flag leaves,and green panicles,and highly expressed in young leaves,whereas OsCPL2 was predominantly expressed in coleoptiles,and extremely lowly expressed in the other tested organs.Loss-of-function of either OsC1 or OsCPL2 resulted in significant reduction of transcript levels of multiple anthocyanin biosynthesis genes in coleoptiles.Coleoptile purple line was further used as a marker trait in hybrid rice.Purity identification in hybrid rice seeds via coleoptile purple line just needed a little water,soil and a small plate and could be completed within 5 d.Molecular marker and field identification analyses indicated that coleoptile purple line was reliable for the hybrid seed purity identification.Our findings disclosed that coleoptile purple line in rice was regulated by two major dominant genes,OsC1 and OsCPL2,and can be used as a simple,rapid,accurate and economic marker trait for seed purity identification in hybrid rice.

Sprouted Sorghum Extract Elicits Coleoptile Emergence, Enhances Shoot and Root Acclimatization, and Maintains Genetic Fidelity in indica Rice

The high growth-stimulating effect of plant extract has urged the plant biotechnologists to use natural supplements in the culture media instead of synthetic phytohormones. We advocated the effect of sprouted sorghum extract(SSE) on emergence, in vitro acclimatization, and genetic fidelity in coleoptile derived callus of indica rice variety ADT36. The use of SSE with Murashige Skoog medium efficiently acclimatized the root and shoot apical systems. A higher mat and seminal roots(3.4 g biomass) with an efficient shoot primordium elongation were observed with an increase in the concentration of SSE. Seeds treated with SSE medium showed higher germination and earlier coleoptile maturation about 48 h compared to untreated seeds, and there was a higher expression of e EF-1α with an increase in coleoptile length. B5 medium was effective on inducing embryogenic and nodular callus from 3-day-old coleoptile with 3.0 mg/L 2,4-dichlorophenoxyacetic acid and further proliferated effectively with 0.8 mg/L kinetin with a fresh weight of 180 mg. Highly significant regeneration was observed with combination of 2.5 mg/L 6-benzylamino purine and 3.0 mg/L α-naphthaleneacetic acid. The metabolic and genetic profiles of in vitro and directly cultivated plants were the same, examined through Fourier-transform infrared spectroscopy, random amplified polymorphic DNA(RAPD), inter-simple sequence repeat(ISSR) and R-ISSR(combination of RAPD and ISSR) markers, respectively, and thus confirming the significant efficacy of the SSE incorporated medium. Disarmed T-DNA was transformed to coleoptile derived callus through Agrobacterium tumefaciens LBA4404 and confirmed by GUS assay. The T-DNA integration was confirmed by DNA blot analysis using DNA from transient GUS-expressed explants. Thus, SSE can be used as a natural and organic supplement for organogenesis and efficient acclimatizations of shoot and root apical meristems in regenerated plants.

OsEIL1 and OsEIL2,two master regulators of rice ethylene signaling,promote the expression of ROS scavenging genes to facilitate coleoptile elongation and seedling emergence from soil

Successful emergence from the soil is a prerequisite for survival of germinating seeds in their natural envi-ronment.In rice,coleoptile elongation facilitates seedling emergence and establishment,and ethylene plays an important role in this process.However,the underlying regulatory mechanism remains largely unclear.Here,we report that ethylene promotes cell elongation and inhibits cell expansion in rice coleoptiles,result-ing in longer and thinner coleoptiles that facilitate seedlings emergence from the soil.Transcriptome analysis showed that genes related to reactive oxygen species(ROS)generation are upregulated and genes involved in ROS scavenging are downregulated in the coleoptiles of ethylene-signaling mutants.Further investiga-tions showed that soil coverage promotes accumulation of ETHYLENE INSENSITIVE 3-LIKE 1(OsEIL1)and OsEIL2 in the upper region of the coleoptile,and both OsEIL1 and OsEIL2 can bind directly to the promoters of the GDP-mannose pyrophosphorylase(VTC1)gene OsVTC1-3 and the peroxidase(PRX)genes OsPRX37,OsPRX81,OsPRX82,and OsPRX88 to activate their expression.This leads to increased ascorbic acid content,greater peroxidase activity,and decreased ROS accumulation in the upper region of the coleoptile.Disruption of ROS accumulation promotes coleoptile growth and seedling emergence from soil.Thesendings deepen our understanding of the roles of ethylene and ROS in controlling coleoptile growth,and this information can be used by breeders to produce rice varieties suitable for direct seeding.

Vital contribution of brassinosteroids to hypoxia-stimulated coleoptile elongation in submerged rice

The rapid elongation of rice(Oryza sativa)coleoptile is pivotal for the plant plumule to evade hypoxia stress induced by submergence,a condition often arising from overirrigation,ponding,rainstorms,or flooding.While brassinosteroids(BRs)are recognized for their diverse roles in plant growth and development,their influence on coleoptile elongation under hypoxic conditions remains largely unexplored.In this study,we demonstrate the significant requirement of BRs for coleoptile elongation in deep water.During coleoptile development,Glycogen Synthase Kinase3-Like Kinase2(GSK2),the central inhibitor of BR signaling in rice,undergoes substantial suppression in deep water but induction in air.In contrast,the dephosphorylated form of BRASSINAZOLE RESISTANT1(OsBZR1),representing the active form of the key BR signaling transcription factor,is induced in water but suppressed in air.Remarkably,the knockout of GSK3-like kinase genes significantly enhances coleoptile elongation in deep water,strongly indicating a vital contribution of BR response to hypoxia-stimulated coleoptile elongation.Transcriptome analysis uncovers both BR-associated and BR-independent hypoxia responses,implicating substance metabolism,redox reactions,abiotic stress responses,and crosstalk with other hormones in the regulation of BR-induced hypoxia responses.In summary,our findings suggest that rice plumules rapidly elongate coleoptiles through the activation of BR response in deep water,enabling them to escape from submergence-induced hypoxia stress.

Overexpression of OsJAC1, a Lectin Gene, Suppresses the Coleoptile and Stem Elongation in Rice

Lectin plays an Important role In defense signaling In plants, but its function In plant growth and development is not well known. Previously, we cloneds rice （Oryza sativa L.） gene OsJAC1 encoding s msnnose-blndlng Jscslln-relsted lectln, and found that OsJAC1 was Jssmonlc acid （JA） Inducible. Here we cloned the promoter of OsJAC1, and GUS activity was detected In young roots, coleoptlles, sheaths, leaves, nodes of stems, stems, rschlses, pistils, stsmens and lemmss of OsJAC1：：GUS trsnsgenlc rice, suggesting that OsJAC1 Is s constitutive expression gene In rice. Moreover, OsJAC1-overexpressed （Ubi：：OsJAC1） rice showed dwarfism with shorter coleptlles resulting from the failure of cell elongation of coleoptlles. In addition, compared with coleoptlles of wild-type plants, those of OsJAC1 overexpresslon rice were more sensitive to JA treatment. These data revealed that, besides Its roles in defense response, lectin plays an Important role in rice growth and development.

Embryogenesis,Germination,Structure and Cotyledon Dimorphism of Zea mays Embryo

A series of new cognitions on the morphogenesis of maize ( Zea mays L.) embryo have been obtained with scanning electron microscopy and semi-thin section techniques. 1. The proembryo. The proembryo from zygotic cell divisions may be divided into three parts: proper, hypoblast and suspensor. The suspensor is short and small, and only exists transiently. As to the hypoblast there is a growth belt, which promotes elongation of the hypoblast. Eventually the upper portion of the hypoblast contributes to the formation of the coleorhiza and the remainder dries up, sticking to the end of the coleorhiza. 2. The maize embryo possesses dorsiventrality and cotyledon dimorphism. During early proembryo stage, the dorsiventrality appears in the proper of the embryo. On the ventral side, the cells are small with dense cytoplasm and few vacuoles. On the dorsal side, the cells are larger with lower cytoplasmic density and have more vacuoles. During later proembryo stage, the proper develops into two parts: the ventrum and the dorsurn. The ventrum rises up from the center of the ventral side. The dorsurn is composed of the marginal area of the ventral side and the whole dorsal side of the proper. During young embryo development, the ventrum differentiates into the coleoptile, apical meristem, hypocotyl, radicle and the main part of the coleorhiza. What is more important, the emergence of coleoptile primordium and radicular initials occur at the axis of the proper, then the coleoptile primordium expands from its two ends toward left and right to form a ring, and the endogenous radicular initials expand in all directions to form a conical radicular tip. All these morphogenetic activities of the ventrum follow a bilateral symmetrical pattern. The dorsurn forms the scutellum. primordium. Then the scutellum primordium, expands rapidly toward the left, right, front and back, while thickening itself, so as to make all components originating from the ventrum become hidden in the longitudinal groove of the scutellum. Lastly, the left and right lateral scales emerge from the edges of the longitudinal groove and expand toward the central line of the axis. As a consequence, morphologically, the bilateral symmetry of the ventral side of the embryo is revealed entirely. Morphogenetically, the coleoptile primordium and apical meristem in maize are similar to the coleoptile (apical cotyledon) and apex formation of the nice embryo, so the coleoptile of the maize embryo can also be considered as an apical cotyledon. The scutellum is a lateral cotyledon. These dimorphic cotyledons of the maize embryo originate from the dorsiventrality of the proper. 3. The true morphological structure of the maize embryo is recognized and its developmental stages are established. A maize embryo is a hypocotyl, in which the apical part is the shoot apex (or plumule) with the coleoptile, the central part consists mainly of the hypocotyl with a lateral cotyledon (scutellum), and the basal part is the radicle with coleorhiza. The left and right lateral scales derived from the scutellum overlap at the ventral side, leaving only two little pores at both ends of the seam from which the coleoptile and coleorhiza can be seen. The four sequential stages of maize embryonic development are as follows: (1) proembryo, stage. This stage covers a period from zygotic cell division to the appearance of the dorsum and ventrum. (2) ventrum rapid differentiation stage. (3) scutellum rapid expansion stage. (4) lateral scale development stage (or embryonic envelope formation stage). 4. To obtain a median longitudinal section perpendicular to the ventral surface is crucial for recognizing the genuine morphological structure of the maize embryo.

The Structure of Oryza Embryos and Their Dimorphic Cotyledons

It has been generally held in botany that Oryza sativa L. is a monocotyledon. Based on studies of rice embryo development we confirmed that rice embryo has two dimorphic cotyledons rather than just one cotyledon. In the present study we attempt to know if the morphology of embryos in other species of Oryza differs from O. sativa and if these embryos have dimorphic cotyledon. Two types of embryo structures were observed in 22 species and/or subspecies of genus Oryza under the scanning electron microscope. Type 1, the O.sativa type, which is characterized by ventral scale and lateral scales, was found in 16 species. Type 2, the O. meyeriana (Zoll. et Mor. ex Steud.) Baill. ssp. tuberculata W. C. Wu et Y. G. Lu, G. C. Wang type, with no ventral scale and lateral scales, was found in 6 species and subspecies. The embryogenic process of O.sativa and O.meyeriana sub. tuberculata showed that the scutellum primordium, coleorhiza primordium, coleoptile primordium and shoot apical meristem directly differentiate from proembryo. The former two later develop into the embryo envelope, which is the outside cotyledon; the coleoptile primordium develops into the coleoptile with the shape of inverted empty cone surrounding and covering the growth cone, which is the apical cotyledon. Both types of rice embryos have dimorphic cotyledons. The structural difference between them is that the scutellum primordium of the young embryo in type 2 does not differentiate ventral scale and lateral scales while the embryo of type 1 does. The dimorphic cotyledons of embryo of Oryza plants originate from the dorsiventrality of proembryo.

Mapping of dwarfing gene Rht14 in durum wheat and its effect on seedling vigor, internode length and plant height

Short coleoptiles associated with GA-insensitive Rht-1 alleles in wheat reduces yield due to poor seedling establishment under dry, or stubble-retained conditions. Hence there is a need for alternative dwarfing genes for wheat improvement programs. GA-sensitive dwarfing gene Rht14 confers semidwarf stature in wheat while retaining longer coleoptiles and early seedling vigor. Two RIL populations were used to identify the map position of Rht14 and to estimate its effect on plant height, coleoptile length, seedling shoot length,spike length and internode length. Rht14 on chromosome 6 A was mapped in the genomic region 383–422 Mbp flanked by GA2oxA9 and wmc753 in a Bijaga Yellow/Castelporziano RIL population. Recombination events between Rht14 and GA2oxA9 in the RIL population indicated that Rht14 might not be allelic to GA2oxA9. The conserved DNA sequence of GA2oxA9 and its flanking region in Castelporziano also suggested that the point of mutation responsible for the Rht14 allele must be a few Mbp away from GA2oxA9. The dwarfing effects of Rht14 on plant height, internode length and seedling vigor were compared with those of Rht-B1 b in an HI 8498/Castelporziano RIL population. Both genes significantly reduced plant height and internode length. Rht-B1 b conferred a significant reduction in coleoptile length and seedling shoot length, whereas Rht14 reduced plant height, but not coleoptile and seedling shoot length. Therefore, Rht14 can be a used as an alternative to Rht-B1 b for development of cultivars suitable for deeper sowing in dry environments and in conditions of conservation agriculture where crop residues are retained.

Analysis on Factors Affecting Seedling Establishment in Rice

Elongations of coleoptile and mesocotyl are related directly to rice seedling establishment in soil and height of plant is related to lodging in rice production. Twelve typical rice cultivars with different lengths of coleoptile and mesocotyl （long, medium and short） were selected by screening the lengths of coleoptile and mesocotyl in 1500 accessions. The seedling establishments of these typical cultivars were compared under the combinations of different sowing depths and flooding durations, and two semi-dwarf varieties （G140, Zhong 96-21） with good seedling establishments and optimum mesocotyl lengths were found. The length of mesocotyl was completely fitted negative binomial distribution and the length of coleoptile was nearly fitted Iognormal distribution. Analysis of the relationships among mesocotyl, coleoptile, seeding depth, flooding duration, and their interactions to seedling establishment percentage showed that there existed significant relations among mesocotyl, coleoptile, mesocotyl x coleoptile, seeding depth, flooding duration and mesocotyl x sowing depth in the experiment for seedling establishment.

Evaluation on Sixty-eight Rice Germplasms in Cold Tolerance at Germination Stage

Sixty-eight rice germplasms were used for cold tolerance evaluation at the germination stage in laboratory. Seeds of rice germplasms germinated at three different temperatures containing low temperature （constant 13°C for 28 days）, alternative temperature （a temperature cycle of 12 h at 20°C and 12 h at 23°C for 14 days） and control （constant 26°C for 7 days）. Analysis of variance revealed that temperature had a significant effect on germination rate, coleoptile length and radicle length. Germination rate was strongly affected by the low temperature and alternative treatments. Stress of low temperature at the germination stage on the tested rice germplasms caused a reduction in final germination rate and the lengths of coleoptile and radicle. The normal and healthy seeds began to germinate within 36 h after imbibition and germination were completed on the 7th day in the control, but delayed under the low and alternative temperature treatments. The low and alternative temperature treatments delayed the growth of coleoptile and radicle compared to the control, and the average lengths of coleoptile and radicule were strongly inhibited with the decreasing temperature in all of the tested germplasms. Taichung, a semi-dwarf, low amylose content and early maturing rice variety, showed a significantly higher germination rate at the three temperature treatments and its coleoptile length was significantly higher than other germplasms.

The auxin concentration in sixteen Chinese marine algae

The author determined the occurrence of indole-3-acetic acid in sixteen Chinese marine algae collected from the east coast of China with fluorescence spectrophotometry (FS) and wheat coleop- tile bioanalysis methods (WCB). The concentration of indole-3-acetic acid (IAA) presented was from 1.1–46.9 ng/g Fw (fresh weight) with FS and 5.3–110.2 ng/g Fw with WCB. The results by the two meth- ods were in the orders of 10-3–103 ng/g Fw reported previously from multiple references.

Effects of dwarfing genes on water use efficiency of bread wheat

Climate change has increased the risk of drought, which significantly limits plant productivity.Various ways of increasing water availability and sustaining growth of crop plants in drought-prone environments are available. Genetic advances in grain yields under rainfed conditions have been achieved with the introduction of dwarfing genes. A thorough understanding of the effects of different dwarfing genes on root growth, coleoptile length, grain yields and water using efficiency(WUE) will provide opportunities to select appropriate Rht genes for breeding high WUE and grain yield cultivars. This review focuses on the mechanism involved in Rht genes that reduce plant height and affect root and coleoptile length, their consequent effects on grain yields and WUE, and suggests that for rainfed and irrigation-limited environments, combining GAR and GAI dwarfing genes in breeding may help boost WUE and yields, and more materials from different parental sources should be collected to assess opportunities for potential comprehensive application of specific Rht genes.