Toshiaki Matsuda

Effect of High Temperature at Ripening Stage on the Reserve Accumulation in Seed in Some Rice Cultivars

Abstract The resistance to high-temperature stress and the structural appearance of the imperfect grains caused by a high temperature at the ripening stage were studied using 13 selected cultivars of rice. High temperature treatment (daily maximum temperature range, 32-40°C) given from the 4th day after heading caused the decrease in panicle weight in all of the cultivars examined. The number of empty grains in the upper and lower parts of a panicle was increased by the high temperature in 10 cultivars. Cultivars KRN, Citanduy, Belle patna and BPB were tolerant to the high-temperature treatment at the ripening stage, and cvs. Koshihikari, Sanlicun, Tainung 67, Yamada-nishiki and Lady Wright were sensitive. Light microscopic observation showed that, the whole endosperm was covered with a nucellar epidermis (NE) under both high and natural temperature (26-31°C) conditions at the first week after heading (WAH). Under high-temperature conditions the NE degenerated earlier than under natural temperature conditions. Scanning electron microscopic observation showed that, the endosperm cells of the seeds with a specific gravity (s.g.) of higher than 1.06 had large amyloplasts filled with starch granules. However, the endosperm cells of seeds with a s.g. of 1.00-1.06 had many small amyloplasts containing small single starch granules and had numerous spaces among the amyloplasts. In the endosperm cells at the dorsal side of imperfect grain, layered structures showing progressive decomposition of starch granules were observed.

Morphological development of rice caryopses located at the different positions in a panicle from early to middle stage of grain filling

Rice caryopses show different patterns of grain filling depending on position within a panicle. Caryopses located on the upper primary rachis branches generally accumulate larger amounts of starch at maturity than caryopses located on the secondary rachis branches of the lower primary rachis. In this study, the former and latter types of caryopses were defined as superior and inferior caryopses, respectively. Superior caryopses elongated soon after flowering, whereas inferior caryopses hardly elongated and were morphologically stagnant until the first 4 d after flowering (DAF). However, once inferior caryopses began elongation, their morphological development was the same as superior caryopses until the middle stage of grain filling. Cell division of the inner integument ceased before endosperm cellularization, pericarp functioned as a transient starch storage tissue until endosperm accumulated starch, and endosperm cell number was determined concomitantly with nucellus disintegration. These results implied the coordinated development of the endosperm with maternal tissues. In addition, differences of inner-integument cell number and endosperm cell number were related to a difference of endosperm size between superior and inferior caryopses.

Seven of eight species in Nicotiana section Suaveolentes have common factors leading to hybrid lethality in crosses with Nicotiana tabacum

BACKGROUND AND AIMS Reproductive isolation is a mechanism that separates species, and is classified into two types: prezygotic and postzygotic. Inviability of hybrids, or hybrid lethality, is a type of postzygotic isolation and is observed in some plant species, including Nicotiana species. Previous work has shown that the Q chromosome, which belongs to the S subgenome of N. tabacum, encodes one or more genes leading to hybrid lethality in some crosses. METHODS Interspecific crosses of eight wild species were conducted in section Suaveolentes (which consists of species restricted to Australasia and Africa) with the cultivated species Nicotiana tabacum. Hybrid seedlings were cultivated at 28, 34 or 36 degrees C, and PCR and chromosome analysis were performed. RESULTS AND CONCLUSIONS Seven of eight wild species produced inviable hybrids after crossing. Hybrid lethality, which was observed in all crosses at 28 degrees C, was Type II lethality, with the characteristic symptoms of browning of hypocotyl and roots; lethality was suppressed at elevated temperatures (34 or 36 degrees C). Furthermore, one or more genes on the Q chromosome of N. tabacum were absolutely responsible for hybrid lethality, suggesting that many species of section Suaveolentes share the same factor that triggers hybrid lethality by interaction with the genes on the Q chromosome. Exceptionally, only one wild species, N. fragrans, produced 100 % viable hybrids after crossing with N. tabacum, suggesting that N. fragrans has no factor triggering hybrid lethality.

Effects of nitrogen application on the development and accumulation of protein bodies in developing rice seed.

Abstract We examined the nature of protein bodies affected by nitrogen application in developing rice endosperm using scanning and transmission electron microscopes. Protein body type II, Pb-II, was observed at the first week after heading independent of nitrogen application, whereas protein body type I, Pb-I, was not observed in either the low nitrogen or non-fertilized group. However, in the high nitrogen group, Pb-I was also observed at 1 week after heading. Pb-I was formed by enlargement of endoplasmic reticulum cisternae, but Pb-II had a close relationship with the Golgi apparatus and was accumulated in the envelope-like vacuole. The smallest protein body, Pb-III, about 0.6-0.8 μm in diameter, appeared at 2 weeks after heading, and the amounts of this protein body increased substantially at 3 weeks after heading. This protein body also originated from endoplasmic reticulum cisternae. Pb-I was observed only in cytoplasm, but, Pb-II appeared in both the endoplasmic reticulum and envelope-like vacuole. The amount of protein bodies in the rice endosperm cell varied with the cultivar and amount of nitrogen applied. In cv. Koshihikari (Japonica), the application of much nitrogen increased the amount of protein bodies not only in the subaleurone, but even in the fifth layer from the aleurone layer. However, in cv. Belle patna (Indica), the application of much nitrogen increased the amount of protein bodies up to the sixth ayer of aleurone layer, and caused the accumulation of a few protein bodies even in the central part of endosperm. It was concluded that storage protein transported by Golgi vesicles and rough endoplasmic reticulum (RER) plays an important role in the accumulation of reserve substances in rice seed. Development of mitochondria and RER was enhanced by the application of nitrogen.

Morphological and Anatomical Observations of Adventitious and Lateral Roots of Sago Palms

Abstract Sago palm (Metroxylon sagu Rottb.), which produces starch in large quantities in its trunk, could become one of the most important nutritious food resources in the near future. Although its root functions are thought to be very important for the enormous shoot growth, the morphological and anatomical studies are limited. This study investigates external and internal structures of sago roots with reference to their functions to distinguish two types of roots in each plant; i.e., large (about 6-11 mm diameter) and small (about 4-6 mm diameter) roots. Large roots were adventitious roots whose primordia were formed just inside the epidermis in the stem, emerged from the trunk surface and grew downward into the soil. Small roots were lateral roots whose primordia were formed on large roots running horizontally or on other small roots, grew not only downward and obliquely in both deep peat and mineral soils, but also right above in deep peat soils. Anatomical observations revealed that both large and small roots had the same internal structures containing epidermis, exodermis, suberized sclerenchyma cells, cortex and stele, with only differences in their sizes or cell numbers. Both roots had characteristic development of schizogenous or lysigenous aerenchyma, but seem to have different functions. Root primordia were formed successively throughout the trunk. Root primordia in the lower trunk had a large diameter, while density of root primordia per unit trunk surface area was high in the upper trunk.

Morphological Studies on the Mobilization of Reserves in Germinating Rice Seed : Decomposition process of starch granules

Abstract The first step in the mobilization of the reserves in germinating rice seed was the decomposition of amyloplast envelopes in endosperm cells adjacent to scutellum. Destruction of amyloplast envelopes caused the separation of the starch granules. Small holes appeared on the surface of the released starch granule adjacent to scutellum at 3 days after imbibition (DAI). At later stages, the number and size of the holes increased on the surface of the starch granule. Ring-like structure in the interior of starch granule was recognized in endosperm cell adjacent to scutellum at 6 DAI. Like this structure appeared in the starch granule at the central part and at the top part of endosperm at 7 and 14 DAI respectively. At 18 DAI, the remaining starch granules became smaller in size and were covered with high-viscosity materials assumed to be soluble polysaccharides. Transmission electron microscopy showed that the intact starch granules were enveloped tightly within the amyloplast membrane. When the amyloplast was degraded, the exterior of the starch granules also started to decompose. The starch granules were decomposed from the exterior rather than the interior.

Morphological studies on the mobilization of reserves in Japanese yam (Dioscorea japonica Thunb.) seed tuber and eddo (Colocasia esculenta Schott var. antiquorum Hubbard & Rehder) seed corm on and after sprouting

Abstract We examined the mechanism of reserve mobilization in Japanese yam seed tubers and eddo seed corms on and after sprouting. The decomposition of starch in pith parenchyma cells of Japanese yam tubers and eddo corms progressed from the region distant from vascular bundles to that adjacent to vascular bundles. In eddo corms, the starch also decomposed from the proximal to the distal region adjacent to the sprout or regenerate plant body. In the yam tubers, the decomposition process was similar in the proximal, middle and distal regions. The first step in the reserve mobilization in pith parenchyma cells was the decomposition of the amyloplast envelope. Subsequently, starch granules decomposed. In Japanese yam tubers, the envelope and starch granules started to decompose from the peripheral regions of the amyloplasts. The observation of soluble polysaccharides, which was the decomposition product of starch granules, was made possible by the quick freezing-vacuum freeze-drying method. By this method, we demonstrated that the soluble polysaccharides in the parenchyma cells decomposed and decreased in density. In addition, the mucilage in the mucilage duct started to decompose and decreased in density from the proximal to the distal part of the corm and also from the periphery to the center of the duct. It was shown that not only starch mobilization but also mucilage mobilization mainly supported sprouting and the growth of the regenerate plant body during about the first half of the vegetative stage.

Anatomical Characteristics of the Formation of Crown Root Primordia in Unelongated Stems of Wheat

Abstract Anatomical observations were conducted to clarify some characteristics of the crown root primordia (CRP) formation in wheat stems. Unelongated portions of main stems were sampled from the plant at 3.2 and 7.2 plant age in leaf number, which were adopted as indexes because of the similarity to rice plants. Then, serial cross sections were made to investigate the position of CRP in the unelongated stem taking into consideration the running of vascular bundles in the stem. CRP were formed just outside tissues of the peripheral cylinder of longitudinal vascular bundles. The positions of CRP were not successive along the stem axis. They showed no definite relation to the running of vascular bundles. Diameters of CRP at the upper portion of the stems were larger than those at the lower portion. The positions of CRP along the stem axis were not distinguishable into nodal and internodal position. CRP and emerged CRs were not classified by the well-known ‘nodal root’ or ‘shoot unit root’, or the ‘unit’, which have been applied recently to rice plants. Further studies are necessary to clarify the factors controlling CRP formation anatomically and quantitatively.

Relation between Crown Root Primordia Formation and Stem Size in Unelongated Stems of Wheat (Triticum aestivum L.)

Abstract The number and thickness of crown root primordia (CRP) were examined with special reference to the size of the peripheral cylinder of longitudinal vascular bundles (PV), in which CRP are formed. Unelongated parts of main stems were sampled from the plant at 3.2, 5.2 and 7.2 plant age in leaf number; this index was adopted because of the morphological similarity to rice plants. Serial cross sections were made to investigate the position and the basal diameter of CRP in the unelongated stem. No relationship was observed between the CRP number and the PV side area in each growth stage. In contrast, the basal diameter of CRP increased with the increment of the circumference length of PV at each stage. Taken together, the number of CRP is not related to the PV size, whereas the CRP thickness shown by the basal diameter depend largely upon the PV size. Investigation using physiological approaches is necessary for further understanding of factors that determine CRP frequencies.

Structural and Immunocytochemical Characterization of the Synthesis and Accumulation of Starch in Sweet Potato (Ipomoea batatas Lam.) Tuberous Root.

Abstract The structural changes in the plastid-amyloplast system in the parenchyma cells of sweet potato tuberous roots during thickening were examined by electron microscopy. In the tuberous roots, proplastids and plastids that contain starch granules propagated in young parenchyma cells adjacent to the meristem, but amyloplasts did not in parenchyma cells. It was suggested that the number of amyloplasts in a parenchyma cell is determined by the propagation of the proplastids and plastids. The form of amyloplasts and the number, size and form of starch granules in them were various. Tubular membranes containing the electron-dense substance were formed in plastids and extended from the envelope membranes of plastids to the starch granules. The electron-dense substance also existed around the starch granules. Tubular membranes are converted into membrane-bound inclusion bodies as a result of loading of the electron-dense substance into these tubes in the plastids. The inclusion bodies were also at the periphery of the amyloplasts. In this study, the functions of both tubular membrane and the inclusion were discussed. The localization of starch branching enzyme in tuberous roots was examined by immunogold electron microscopy. The label for branching enzyme was localized predominantly throughout the surface of each starch granule, suggesting that this is the branching for amylopectin synthesis, but not throughout the stroma in the plastid-amyloplast system. Small and round starch granules were often formed at parts of the periphery in the amyloplast. Dense labeling for the enzyme was detected around the granules. The increase of the number of starch granules in an amyloplast is certainly made by means of the formation of new starch granules at the periphery of the amyloplast. It is likely that the new granules are intensively formed there.