Caryopsis Development Research Articles

Determining Physiological Maturation of Jointed Goatgrass (Aegilops cylindricaHost) Caryopses

Information on jointed goatgrass caryopsis development is currently lacking in published literature. It is hoped that through a better understanding of jointed goatgrass caryopsis ontogeny more effective weed-management strategies will be developed. Greenhouse experiments were initiated in fall 2002 and 2003 and completed the following spring seasons. Jointed goatgrass plants were started from spikelets, vernalized for 8 wk at 4 C, and grown in a greenhouse. Treatments were the number of days after anthesis (DAA) that a spike was allowed to remain on the plant before harvesting and ranged from 2 to 34 DAA, in increments of 1 (2002) or 2 (2003) d. Individual spikes were divided at harvest into three sections: top, middle, and bottom, disarticulated from the rachis, placed into a germinator, and germination recorded each day. Goatgrass spikelets germinated as early as 2 DAA, although spikelets harvested <7 DAA had <3% germination for all spike sections and were extremely variable, especially for the middle and bottom sections. Time to germination was similar for all sections of the spike. Maximum average germination of the top section was 72% compared with 86% for the bottom and middle sections. Our data suggest that factors other than developmental rate (i.e., dormancy) may affect germination in sections of the spike. A second year of the experiment was conducted for validation. Model validation suggested that although trends were similar in both years, variation in germination response might be too great for accurate, predictive model construction. The early germination shown in this research demonstrates that control measures must be implemented earlier than previously prescribed to prevent jointed goatgrass reproduction.

SAGE of the developing wheat caryopsis

Understanding the development of the cereal caryopsis holds the future for metabolic engineering in the interests of enhancing global food production. We have developed a Serial Analysis of Gene Expression (SAGE) data platform to investigate the developing wheat (Triticum aestivum) caryopsis. LongSAGE libraries have been constructed at five time-points post-anthesis to coincide with key processes in caryopsis development. More than 90,000 LongSAGE tags have been sequenced generating 29,261 unique tag sequences across all five libraries. Tag abundance, generated from cumulative tag counts, provides insight into the redundancy and diversity of each library. Annotation of the 500 most abundant tags spanning development highlights the array of functional groups being expressed. The relative frequency of these more abundant transcripts allows quantitative analysis of patterns of expression during grain development. We have identified activities of cellular proliferation/differentiation, the accumulation of storage proteins and starch biosynthesis. The abundance of calcium-dependent protein kinases indicate their importance in signalling across development. Acquisition of a broad array of defence coincides with storage accumulation and is dominated by inhibitors of amylase activity. Differential expression profiles of abundant tags from each library reveal the coordinated expression of genes responsible for the cellular events constituting caryopsis development. This SAGE platform has also provided a resource of novel sequence and expression information including the identification of potentially useful promoter activities. Further investigations into both the abundant and low expressing transcripts will provide greater insight into wheat caryopsis development and assist in wheat improvement programmes.

Developmental regulation of a VEIDase caspase-like proteolytic activity in barley caryopsis

Caspases are essential in animal programmed cell death both as initiator and executioner proteases. Plants do not have close caspase homologues, but several instances of caspase-like proteolytic activity have been demonstrated in connection with programmed cell death in plants. It was asked if caspase-like proteases are involved during development of the barley caryopsis. The presence of a caspase-6-like proteolytic activity that preferentially cleaved the sequence VEID was demonstrated. A range of protease inhibitors was tested and only caspase-specific inhibitors showed major inhibitory effects. The profile of VEIDase activity in developing starchy endosperm, embryo, and whole caryopsis was measured and showed a general trend of higher activity in young, rapidly developing tissues. The VEIDase activity was localized in vivo to vesicles, shown to be autophagosomes, in randomly distributed cells of the starchy endosperm. The VEIDase activity detected in barley caryopsis is similar to activities described previously in mammals, spruce, yeast, and thale cress. In mammals, spruce, and yeast, VEIDase activity has been shown to be positively correlated with the occurrence of programmed cell death. Several manifestations of programmed cell death exist in developing barley caryopsis, indicating a connection between VEIDase activity and developmental programmed cell death in barley.

Responses of Caryopsis Germination, Seedling Emergence, and Development to Sand Water Content of Agropyron cristatum (L.) Gaertn. and Bromus inermis Leyss

Abstract: Responses of caryopsis germination, seedling emergence, and development of Agropyron cristatum (L.) Gaertn. (Gramineae) and Bromus inermisLeyss. (Gramineae), two dominant perennial grasses in the Otindag Sandland of China, to different sand water content (SWC; 1%, 2%, 3%, 4%, 6%, 8%, 12%, 16%, and 20%) were studied comparatively. The results showed that the germination responses of the two grasses to SWC were similar (i.e. caryopses could not germinate when the SWC was below 3%; at SWC ranging from 3% to 12%, the higher the SWC, the higher the germination percentage; and at a SWC of 12%‐20%, germination reached similarly high percentages). At a sand burial depth of 0.5 cm, the threshold of SWC for seedling emergence was 6% for A. cristatum and 8% for B. inermis; at 12%‐20% SWC, the seedling emergence of both species reached similarly high percentages. The seedling growth responses of these two species to SWC gradients were different. For A. cristatum, the biomass of seedlings increased with SWC from 6% to 12%, and decreased with SWC from 12% to 20%. For B. inermis, the biomass of seedlings always increased with SWC from 8% to 20%. The results also showed that the seedlings of both species allocated more biomass to the roots with decreases in SWC. The SWC changes from April to October in natural microhabitats of both species suggested that the SWC may play an important role in caryopsis germination, seedling emergence, and the growth characteristics of the two grasses. The responses of caryopsis germination, seedling emergence, and the growth characteristics of these two species to SWC may determine their distribution patterns in the Otindag Sandland.(Managing editor: Ya‐Qin HAN)

Systematic Spatial Analysis of Gene Expression during Wheat Caryopsis Development

The cereal caryopsis is a complex tissue in which maternal and endosperm tissues follow distinct but coordinated developmental programs. Because of the hexaploid genome in wheat (Triticum aestivum), the identification of genes involved in key developmental processes by genetic approaches has been difficult. To bypass this limitation, we surveyed 888 genes that are expressed during caryopsis development using a novel high-throughput mRNA in situ hybridization method. This survey revealed novel distinct spatial expression patterns that either reflected the ontogeny of the developing caryopsis or indicated specialized cellular functions. We have identified both known and novel genes whose expression is cell cycle-dependent. We have identified the crease region as important in setting up the developmental patterning, because the transition from proliferation to differentiation spreads from this region to the rest of the endosperm. A comparison of this set of genes with the rice (Oryza sativa) genome shows that approximately two-thirds have rice counterparts but also suggests considerable divergence with regard to proteins involved in grain filling. We found that the wheat genes had significant homology with 350 Arabidopsis thaliana genes. At least 25 of these are already known to be essential for seed development in Arabidopsis, but many others remain to be characterized.

Expressions of rice sucrose non-fermenting-1 related protein kinase 1 genes are differently regulated during the caryopsis development

The rice sucrose non-fermenting-1 related protein kinase 1 ( SnRK1) family consists of three genes, which were named OSK1, OSK24 and OSK35. In order to elucidate the distinct functions of OSK genes, we identified precise regions for their expression by the promoter: GUS expression analyses as well as in situ mRNA localization experiments. At first, we isolated genomic clones corresponding to each member of OSKs in order to obtain the promoter sequences. All OSK genes house 11 exons and 10 introns and the positions of introns within the coding regions are fully conserved in all these genes. Histochemical analyses using OSK promoter: β-glucronidase ( OSKP:GUS) reporter genes showed that expression patterns of OSK1P:GUS and OSK24P:GUS were quite different in the developing caryopsis. The expression of OSK1P:GUS was nearly restricted in the vascular tissues during the caryopsis development. In contrast, the OSK24P:GUS expression was detected in the pericarp at the early stage with a shift to the endosperm as the endosperm cells were formed, and GUS staining was confined to both aleurone layer and endosperm cells around 15 days after flowering, when cell division of cellular endosperm were almost finished. The shifting pattern of the OSK24 expression was correlated with the appearance of starch granules in each tissue. Similar correlation between OSK24 expression and emergence of starch granules was also observed at another temporal sink organ, the basal part of leaf sheath. These results suggest that OSK24 (rice SnRK1b) most probably have a special role in carbohydrate metabolism of the sink organs.

Proteomic analysis of the expression of proteins related to rice quality during caryopsis development and the effect of high temperature on expression

Proteins are essential to rice caryopsis development and quality formation. High temperature is an important environmental factor, which may decrease grain quality. In the present study rice caryopsis proteins were profiled by two-dimensional polyacrylamide gel electrophoresis, and differentially expressed proteins were analyzed by liquid chromatography/tandem mass spectrometry. Expressions of more than 400 polypeptide spots during caryopsis development, in response to temperature treatments or between varieties were monitored. Among them, more than 70 differentially expressed polypeptides were analyzed by liquid chromatography/tandem mass spectrometry. We identified 54 proteins with known functions. Of these, 21 were involved with carbohydrate metabolism, 14 with protein synthesis and sorting, and 9 with stress responses. Waxy (Wx) proteins and glutelins were the most significant spots, which increased significantly during development. Allergen-like proteins, PPDK and NADH-SDH, also were expressed during development, implying their physiological roles in caryopsis. Expression of large isoforms of Wx proteins was correlated with the amylose content of rice caryopses. One protein with high GC content in its DNA sequence was correlated with the chalky trait of kernels. High temperature (35/30 degrees C) decreased the expression of Wx proteins, allergen-like proteins, and elongation factor 1beta, but increased the expression of small heat shock proteins (sHSP), glyceraldehyde-3-phosphate dehydrogenase, and prolamin. sHSP was positively correlated with the appearance of chalky kernels. During development, glutelins were phosphorylated and glycosylated, indicating that these molecules were post-translationally modified. Possible functions of the expression of candidate proteins on the grain quality are discussed.

Characterisation and functional analysis of two barley caleosins expressed during barley caryopsis development

Two full-length cDNA sequences homologous to caleosin, a seed-storage oil-body protein from sesame, were identified from a series of barley grain development cDNA libraries and further characterised. The cDNAs, subsequently termed HvClo1 and HvClo2, encode proteins of 34 kDa and 28 kDa, respectively. Real-time RT-PCR indicated that HvClo1 is expressed abundantly during the later stages of embryogenesis and is seed-specific, accumulating in the scutellum of mature embryos. HvClo2 is expressed mainly in the endosperm tissues of the developing grain. We show that HvClo1 and HvClo2 are paralogs that co-segregate on barley chromosome 2HL. Transient expression of HvClo1 in lipid storage and non-storage cells of barley using biolistic particle bombardment indicates that caleosins have different subcellular locations from the structural oil-body protein oleosin, and by inference participate in different sorting pathways. We observe that caleosin sorts via small vesicles, suggesting a likely association with lipid trafficking, membrane expansion and oil-body biogenesis.

Tocopherol and tocotrienol accumulation during development of caryopses from barley (Hordeum vulgare L.)

Tocotrienols are lipophilic antioxidants belonging to the tocochromanols, better known as vitamin E. Although present in cereal grains in high quantities not much is known about their function in plants. In a detailed study the temporal and spatial accumulation of tocotrienols and tocopherols during grain development in two barley cultivars was analyzed. Tocochromanols and lipids accumulated in parallel until 80% of the final dry weight of the kernels was reached. Later on the tocochromanol content did not change while the lipid content decreased. Generally, only about 13% of the tocochromanols were found in the germ fraction, whereas the pericarp fraction contained about 50% and the endosperm fraction about 37% of the tocochromanols. Altogether, about 85% of the tocochromanols were tocotrienols in both cultivars. In case of the tocopherols about 80% were found in the germ fraction and the remaining 20% in the pericarp fraction. Tocotrienols were almost equally present in the pericarp and the endosperm fraction. Individual forms of tocopherols and tocotrienols accumulated with different kinetics during barley grain development. The differences in distribution and accumulation indicate different functions of the individual tocochromanols during grain development.

Characterization of the expression of a wheat cystatin gene during caryopsis development.

A cDNA coding for phytocystatin, a protease inhibitor, was isolated from wheat embryos by differential display RT-PCR and the corresponding full-length cDNA (named WC5 for wheat cystatin gene 5) subsequently obtained by RACE. The deduced primary sequence of the protein suggests the presence of a 28 amino acid N-terminal signal sequence and a 100 amino acid mature protein containing the three consensus motifs known to interact with the active site of cysteine peptidases. Northern and western analysis revealed a spatio-temporal pattern of the cystatin gene expression during caryopse development. In the embryo, WC5 was only expressed during early embryogenesis whereas, in seed covering layers, WC5 expression was restricted to the maturation stage of grain development. In addition, immunolocalization experiments showed that cystatin accumulated in the aleurone layer of the maturating seed and in the parenchymal tissues of the embryo scutellum. A recombinant form of the wheat cystatin was shown to be able to inhibit peptidase activities present in whole seed protein extracts. In addition, immunological techniques allowed us to identify two putative target peptidases. The possible roles of the cystatin protein are discussed in relation with tissular localization and putative peptidase targets during seed maturation.

Identification of genes specifically expressed in maternal and filial tissues of barley caryopses: a cDNA array analysis.

Developing seeds consist of genetically distinct maternal and filial tissues, whose interactions during development are largely unknown. To better understand the molecular physiology of developing seed tissues in barley, we created a high-density cDNA macroarray bearing 711 cDNA fragments from 691 clones representing at least 620 unique genes mainly derived from a cDNA library constructed with mRNA from the early stages of caryopsis development. This array has been used to compare gene expression patterns in maternal pericarp and filial embryo sac tissues of caryopses sampled 1-7 days after flowering (DAF). The profiles obtained for both tissues revealed that at least 26 genes in pericarp and 12 genes in embryo sac tissues were up-regulated by more than a factor of two during this period. RNAs expressed at high levels in the pericarp mainly encode enzymes involved in carbohydrate and lipid metabolism, but also include mRNA for a transcription factor related to FILAMENTOUS FLOWER (FIL). Genes preferentially expressed in the embryo sac are mainly related to degradation and/or processing of proteins or are involved in the process of starch accumulation, which begins in the seed at this time. Some of the most conspicuously regulated genes were studied in more detail by Northern analysis and in situ hybridization. The mRNA with the highest apparent signal intensity encodes a methionine synthase (MSY). MSY is highly expressed throughout the pericarp and to a lower extent in the transfer cell layer of the endosperm. Of special interest is a gene of unknown function because its high-level expression is restricted to the nucellar projection, the maternal transfer tissue of the caryopsis. This gene, represented by clone HY09L21, may play a central role in transport processes and thus in embryo growth.

Analysis of chromatin and DNA during chromosome endoreduplication in the endosperm ofTriticum durum Desf.

Chromatin structure was studied in nuclei of the endosperm of durum wheat (Triticum durum Desf., cv. Creso), where a large number of cells undergo chromosome endoreduplication during caryopsis development. Optical density profiles of interphase nuclei at different ploidy levels after Feulgen staining were determined cytophotometrically. It was observed that, within each development stage, polyploid nuclei (6–12C and 12–24C) show more condensed chromatin than euploid nuclei (3–6C): this should indicate that endoreduplication is accompanied by some reduction of nuclear activity. Within the same ploidy level, 3–6C and 6–12C nuclei become increasingly condensed with development (except for the last stage), while 12-24C nuclei are identical at all stages. DNA methylation at different stages of caryopsis development was then analyzed in genomic DNA, highly repeated sequences and ribosomal DNA, by digestion with cytosine-methylation-sensitive restriction enzymes. We observed that (i), depending on the enzyme, DNA from caryopses may show higher mean length than DNA from shoot apices and variations occur during endosperm development; (ii) highly repeated DNA sequences also show some variation in base methylation between apices and endosperms and among endosperm development stages, even though to a lesser extent than genomic DNA; (iii) rDNA shows variations only between endosperm and apices while no variation was observed among endosperm development stages in relation to chromosome endoreduplication. Our data may be explained by assuming the occurrence, during endosperm development, of processes of chromatin condensation possibly involved in silencing the activity of extra copies of DNA resulting from chromosome endoreduplication. At least in part, DNA methylation is involved in the process of chromatin condensation. rDNA shows no variation during endosperm development: this suggests that rDNA copies are actively transcribed in both triploid and endoreduplicated nuclei.

Physiological Changes in Sorghum Antifungal Proteins

Changes in sorghum caryopsis antifungal proteins (AFP) in different tissues and during development, imbibition, and germination, were determined. Sormatin, chitinase, and glucanase levels increased during caryopsis development and peaked at physiological maturity (30 days after anthesis (DAA)). Ribosome-inactivating protein levels were higher at 15 DAA and decreased subsequently. Sormatin and chitinase levels were significantly different between sorghum cultivars. Sormatin content at physiological maturity correlated with mold rating (R2 = 0.65). Seed AFPs were present in the endosperm and migrated toward the exterior of caryopsis upon imbibition. AFPs leached out of immature seeds but were retained in the pericarp of mature seeds. Levels of these proteins also changed significantly during seed germination and were present in the shoots of germinating caryopsis. Keywords: Sorghum; chitinase; sormatin; glucanase; RIP; seed development; germination; grain molding

Differential expression of two β‐amylase genes of rye during seed development

The expression of two β‐amylase loci was analysed in the developing seeds of two inbred lines of rye (Secale cereale L.), one of which was a β‐amylase deficient mutant. Enzymatic activity and the contents of enzymatic protein and mRNA specific for each of an endosperm‐characteristic and ubiquitous β‐amylase were determined throughout the course of caryopsis development. Both loci were expressed in the developing normal line caryopses according to different temporal and quantitative patterns. The ubiquitous enzyme‐specific locus β‐Amy 2 was expressed earlier; both mRNA and enzymatic protein accumulated to a maximum extent at 10 to 15 days after pollination. In contrast, the highest content of mRNA for endosperm β‐amylase (encoded by the β‐Amy I locus) was found 20 days after pollination, and the corresponding enzymatic protein accumulated throughout seed development. The expression of the β‐Amy I locus was 30‐ to 40‐fold higher than that of the β‐Amy 2 locus in terms of maximum specific mRNA accumulation. The expression product of only the β‐Amy 2 locus was found in the developing mutant line caryopses. The expression pattern of this locus was similar in the developing normal and mutant line seeds in terms of the temporal accumulation of mRNA and enzymatic protein. However, an approximately 4‐fold higher level of ubiquitous β‐amylase‐specific mRNA was found in the mutant than in the normal line caryopses, and the content of ubiquitous β‐amylase protein decreased to near zero at seed maturity in the mutant line, but not in the normal line, caryopses. The enzymatic activities of both β‐amylases appeared to be regulated at the level of accumulated enzymatic protein.

Hormonal and environmental responsiveness of a developmentally regulated protein repair L-isoaspartyl methyltransferase in wheat.

The L-isoaspartyl protein methyltransferase (EC 2.1.1.77) has been proposed to be involved in the repair of spontaneously damaged proteins by facilitating the conversion of abnormal L-isoaspartyl residues to normal L-aspartyl residues. Based on the abundance of this enzyme in the seeds of a variety of plants and its unique substrate specificity, it has been hypothesized that it functions to prevent the accumulation of abnormal aspartyl residues in the proteins of aging seeds that can limit the viability of the embryo or its chances for germination. In this work, we show that the expression of the L-isoaspartyl methyltransferase is under developmental regulation in the winter wheat, Triticum aestivum. Methyltransferase mRNA and active enzyme are first detected in seeds during the late stages (III-IV) of caryopsis development. As mature seeds germinate, methyltransferase mRNA levels decline and are nearly undetectable by 72 h post-imbibition. Enzyme activity remains constant for 24 h post-imbibition and then decreases rapidly following the reduction of its corresponding mRNA. Methyltransferase activity is very low or undetectable in wheat seedlings, including leaf and root tissues. We show, however, that the L-isoaspartyl methyltransferase can be induced in vegetative tissues in response to hormone treatment and environmental stress. Abscisic acid, a phytohormone involved in seed development and desiccation tolerance, induces both methyltransferase mRNA and enzyme activity in 4-day-old wheat seedlings. Dehydration and salt stress also induce its transcription and enzymatic activity in seedlings. The ability of a plant to regulate methyltransferase activity in its seeds and vegetative tissues in response to desiccation, aging, and environmental stress may allow the plant to efficiently repair protein damage associated with these physiological changes.

Spatial and temporal patterns of B hordein synthesis in developing barley (Hordeum vulgare L.) caryopses

AbstractmRNA species encoding B hordeins and B hordein protein have been localised in developing barley caryopses using in situ hybridisation and immunocytochemistry. B hordeins are first detected immunocytochemically in sections from 5 dpa (days post anthesis) barley caryopses. At this stage the endosperm is well differentiated and hordein levels are relatively constant across the starchy endosperm though notably absent from the aleurone layer. Analysis of serial transverse sections through later stages of caryopsis development (7‐10 dpa) show a distinct differential accumulation of B hordeins. Hordeins accumulate at the periphery of the starchy endosperm, towards the apex and along the endosperm/scutellum boundary. Using in situ hybridisation B hordein mRNA was detected in equivalent patterns to the protein indicating that there is regulation of gene product accumulation at a transcriptional level. 3‐D reconstruction of hordein in developing barley caryopses have been made using data from multiple serial sections in conjunction with a commercial computer‐aided design package.

β-Amylases in Cereals

beta-Amylase of maize (Zea mays L.) caryopses was studied during development and germination by means of enzymic, electrophoretic, and immunochemical techniques. beta-Amylase activity increased during caryopsis development to a maximum value at the beginning of the water content plateau (at this stage the enzyme was located primarily within the pericarp) and then decreased. Almost no beta-amylase (activity or antigen) was found in either free or bound forms in the mature maize caryopsis. The activity increased again during seedling growth and reached much higher values. Both the aleurone layer (to a major extent) and the scutellum produced and secreted beta-amylase during germination, the secretion being stimulated by Ca(2+). No posttranslational modification of the enzyme was detected during germination. The molecular specific activity of the enzyme remained unchanged during the observed periods, indicating that the regulation of the activity is based essentially on protein turnover. The enzyme from developing and germinating caryopses was found to be identical in terms of antigenicity, isoelectric point, and molecular mass to the beta-amylases extracted from the roots and the leaves of the maize seedling. The maize beta-amylase resembles in all respects the ubiquitous beta-amylase described for rye and wheat, whereas the major beta-amylase of those cereals appears to be lacking in the maize caryopsis.

Import of sucrose and its transformation to starch in the developing sorghum caryopsis

Levels of soluble and bound invertases and amylases were studied in relation to the changes in the free sugars and the accumulation of starch in the developing sorghum [Sorghum bicolor (L.) Moench, cv. spv. 351] caryopsis and its associated bractspedicel. Besides sucrose, glucose and fructose as the principal sugars, small amounts of sugars of the raffinose series were detected in the developing caryopsis. Through out the period of caryopsis development, the amount of reducing sugars was higher than that of sucrose. With the advancement in the development of the caryopsis, the contents and levels of sucrose rose with a concomitant fall in the activity of soluble acid (pH 4.8) invertase (EC 3.2.1.26) in the endosperm. In the pericarp‐aleurone layer, the activity of soluble acid invertase predominated over soluble neutral (pH 7.5) invertase (EC 3.2.1.27). The activity of bound acid invertase declined with the ageing of the caryopsis. In bracts‐pedicel, the activity of bound invertase and the levels of reducing sugars peaked around 18 days post anthesis. In these organs, the level of starch gradually decreased concomitantly with an increase in its level in the developing caryopsis. Amylases (EC 3.2.1.1 and 3.2.1.2) are distributed in the endosperm as well as in the pericarp‐aleurone layer. On culturing detached ears in [U‐14C]‐sucrose solution for 6 h in the dark at 25°C, 80–90% of the 14C of extracted major sugars (i.e. sucrose + glucose + fructose) of the caryopsis appeared in sucrose alone. In comparison with the effects of glucose or fructose, transport into the caryopsis of 14C from [U‐14C]‐sucrose supplied to detached ears was promoted by the addition to the radiolabelled sucrose solution of 1% unlabelled sucrose. Addition to the [U‐14C]‐sucrose solution fed to the detached ears of 20 mM NaN3 or HgCl2 or galactose, lowered the amount of 14C in the free sugars and starch of the earyopsis.

Temperature response of caryopsis elongation in relation to grain notching of rice.

Many researchers have reported that unsuitable ripening conditions such as low temperature, drought, shading, or fertilizer deficiency lead to grain notching of rice. In this study the mechanism of grain notching has been re-investigated from a view point of temperature effect on the caryopsis elongation. As the caryopsis of rice plant develops encased in floral glumes, the size and shape of the caryopsis are restricted by the floral glumes. However, it has been clarified that the caryopsis is capable of elongating longer than the floral glumes in general, and that the varieties in which the potential volume of the caryopsis far exceeds the capacity of floral glumes tend to produce such mulformed grains as notched or hull-cracked ones. In this study, for allowing full growth of the potential length of caryopsis (T1), upper parts of the floral glumes on two or three panicles of each plant were clipped off three days after anthesis, and these panicles were protected by parchment bags. The rest of panicles were kept untreated to determine the natural length of caryopsis (C1) which developed within the floral glumes. Seven rice cultivars (Table 1) were grown in pots and kept outdoors until heading time. Thereafter, they were divided into three lots and moved to phytotrons in which the temperature was maintained high (33/23°C), medium (28/18°C) or low (23/13°C), and grown under 30, 000 lux artificial light for 14 hours a day. Humidity was regulated to 70-80% and 85-95% during the light and dark period, respectively. As shown in Table 2, actual temperature inside the floral glumes and parchment bag was a little higher than ambient air temperature under illumination. Twenty-30 caryopses were sampled every, other day and measured to give growth curves for T1 and C1. Several growth parameters were estimated according to Robertson's equation. At maturity, rest of materials were harvested to examine seed fertility, notched grain percentage, and the size and shape of the caryopses. The result of present investigation has indicated followings : Although the growth late of C1 is lowered under low temperature, the maximum value of C1 is not different with temperature conditions, because C1 is restricted by the scope of floral glumes. As shown in Fig. 2, C1 reaches to its ceiling at 7 days (at high temp.), 9 days (at medium temp.) and 11 days (at low temp.) after anthesis. Under low temperature condition the growth rate of T1 is reduced, but because the growth duration is extended, the final length of T1 is the longest. Thus, the unbalance between the potential length of caryopsis and the capacity of floral glumes, or T1/C1 is higher under low temperature condition. Notched grain percentage increases under low temperature condition, and as shown in Fig. 3, it correlates with T1/C1 ratio. From these observations it may be concluded that under low temperature condition T1 shows excessive elongation, which leads to stronger unbalance between T1 and C1. When T1 is much longer than C1, the longitudinal development of caryopsis is restricted by floral glumes resulting in grain notching.

Development of the Vascular Tissue of the Wheat and Barley Caryopsis as Related to the Rate and Duration of Grain Filling1

An anatomical study of developing wheat (Triticum aestivumL.) and barley (Hordeum vulgare L.) caryopses was conducted in order to relate the development of the vascular and associated tissues to the rate and duration of grain filling. Caryopsis development of the two species was similar, differing mainly in the timing of events, including the date of flowering and the duration of the grain‐filling period. The main vascular bundle began to differentiate after anthesis and differentiation was completed at about the same time elongation of the kernel ended. The sieve tubes of the main bundle remained open and visually functional until the end of grain filling. The cell walls of the chalaza began to lignify midway through the grain‐filling period, but lignification was not a barrier to grain filling. Yellow or brown‐colored compounds (possibly phenolics) accumulated within the vacuoles of the chalazal cells of barley, but these did not adversely affect the rate of grain filling. In both wheat and barley, the marked decline in the rate of dry matter accumulation occurred prior to the collapse of the phloem and chalaza. Thus, the collapse of these tissues did not trigger events leading to the termination of grain filling. Barley had more sieve tubes than wheat, yet the rate of grain filling was similar for the two species. Thus the number of sieve tubes was not related to the rate of grain filling.