Seedlings of Hong Mang Mai wheat (Triticum aestivum L.) emerge from much deeper in the soil than do other cultivars by elongating their first internode. We examined the roles of ethylene, gibberellins (GA) and potassium in the elongation of the first internode in wheat cultivars. Although ethylene stimulated the elongation of the first internode of Hong Mang Mai in the dark, the ethylene evolution and the expression level of ethylene-receptor-like gene of this cultivar were not greater than those of other cultivars. In Hong Mang Mai, gibberellin A3 (GA3) substantially stimulated the elongation of the first internode in the dark. Maximum elongation of the first internode was obtained by GA3 at the concentrations of 2.89 × 10-6 to 2.89 × l0-7 M. This cultivar responded markedly to gibberellins A1 and A3 by elongating the first internode in the dark. A mixture of gibberellins A4 and A7 (GA4+7) was not effective in inducing the elongation. Haruhikari, a cultivar having no GA -insensitive-reducing-height (Rht) genes, substantially responded to GA3, but other cultivars did not. The differences in the sensitivity to GA could account, at least in part, for the varietal differences in the elongation of the first internode in wheat. Takune-komugi, a cultivar whose first internode elongates in response to ethylene, did not respond to GA3. Thus, there are different mechanisms for the GA- and ethylene-stimulated elongation of the first internode in wheat. Also, it was suggested that potassium uptake from the soil might function together with endogenous GA in inducing the elongation of the first internode in Hong Mang Mai wheat.
High atmospheric humidity promotes vegetative growth and dry-matter production in japonica rice. In this study, the varietal differences in the response to atmospheric humidity were examined using three japonica varieties (Nipponbare, Kinmaze, Yamadanishiki), one indica variety IR24 and japonica × indica variety (Milyang 23). The indica and japonica × indica varieties are referred to as indica varieties hereafter. The growth of the japonica varieties was greatly promoted by high humidity (90%) and greatly reduced by low humidity (60%), but that of the indica varieties was less sensitive to humidity and the growth was hardly affected by low humidity. We compared the responses of the above varieties to low humidity (water stress) using the plants under high humidity as a control. Under low humidity, as compared to the indica varieties, the japonica varieties had a higher stomatal density, longer stomata and larger stomatal aperture, resulting in a lower water potential in leaf blades and lower water-use efficiency. Under high humidity, the japonica and indica varieties showed a similar transpiration rate (per unit area), stomatal aperture and water-use efficiency, but the japonica varieties had a higher water content than the indica varieties. This may be why the japonica varieties show greatly suppressed growth and dry matter production under low humidity. These differences between the japonica and indica varieties in morphophysiological characters under low humidity might cause the varietal differences in the plant growth and dry matter production in rice.
Germination percentages of wheat grains sampled at 3 grain-filling stages: yellow-ripe stage (water content 45-50%), dough-ripe stage (35-40%), and full-ripe stage (25-30%), and imbibed in water at 12°C and 20°C were examined in relation to the activities of α-amylase and endoprotease. Wheat varieties studied were Chihoku-komugi, which is susceptible to pre-harvest sprouting, and Satanta, which is resistant. Germination percentage was higher at l2°C than at 20°C in all grains sampled at all stages in both varieties, and was higher in Chihoku-komugi than in Satanta at 20°C. The activity of α-amylase in the grains at the yellow-ripe stage was higher at 12°C than at 20°C in both varieties, but that at the other 2 stages was higher only in Satanta. Endoprotease increased rapidly from 7 to 10 days after the start of imbibition, and exceeded 12 units only at 12°C in Chihoku-komugi grains at the dough and full-ripe stages. The results showed that α-amylase activity was lower than the value equivalent to 300 brabender unit (BU) in amylography when the germination percentage was 0%. Endoprotease activity exceeded 6 units when the germination percentage exceeded 90%.
The effects of short-term waterlogging on mungbean and recovery from the damage were studied in a plastic greenhouse. Pot-grown plants of two mungbean cultivars, KPS l and CNXP-49 were waterlogged for eight days, at the vegetative and reproductive growth stages. Photosynthetic rate (P), transpiration rate (Tr), diffusive resistance (rs) and leaf water potential (Ψl) were measured at the 1st, 4th and 8th day of the 8-day waterlogging treatment and at the 4th and 8th day after the end of waterlogging. P was reduced significantly by waterlogging. It was reduced by 58 and 64% at the 8th day of waterlogging at the vegetative and reproductive stages, respectively, in KPSl and, by 76 and 82%, respectively, in CNXP49. Tr was reduced by 48 and 66% in KPSl and CNXP-49 respectively, at the 8th day of waterlogging at both stages. The diffusive resistance at the 8th day of waterlogging was increased by 79 and 83%, in KPSl and CNXP-49, respectively, at the vegetative stage, and by 76 and 79% at the reproductive stage. AU these physiological parameters of both cultivars recovered to almost normal values within 4 days after the end of waterlogging at the reproductive stage and within 8 days at the vegetative stage. Waterlogging did not affect Ψι, indicating that the decrease in P and Tr was not associated with leaf dehydration. Waterlogging at the vegetative and reproductive stages significantly reduced the dry matter accumulation during and after the waterlogging in both KPSl and CNXP-49. Final seed yield in KPSI and CNXP-49 was reduced by 16 and 19%, respectively, by the waterlogging at the vegetative stage and by 23 and 30%, respectively, by that at the reproductive stage. Although even short-term waterlogging markedly affected P, Tr and rs of mungbean, the damage particularly in P and leaf growth was quickly recovered after the end of waterlogging and the reduction of seed yield was less than that expected from the damage in the physiological characteristics. These results, suggest that mungbean has an ability to recover from the short-term waterlogging damage and that the response to^- waterlogging varies with the cultivar.
In tropical and subtropical regions, soybean (Glycine max L.) often encounters a temporary water deficit in summer. Application of auxin during the reproductive period, when a water deficit and high temperature cause pod abscission, is expected to decrease pod abscission and thus increase seed yield. The present study was conducted in a greenhouse to assess the effects of Figaron (synthetic auxin) under various conditions of water deficiency in two soybean cultivars, Fukushirome and Miyagishirome. The plants were supplied with 500-, 300-, 200-, or 100-mL water per pot (5L) three times a day. Figaron (100mg L-1) was sprayed 10 days after opening of the first flower. The rate of photosynthesis and transpiration were greatly decreased by water deficit in both cultivars. Application of Figaron slightly increased the rates of photosynthesis and transpiration irrespective of the water condition, though it temporarily decreased the rates during the initial few days after Figaron application. Figaron decreased the abscission of reproductive organs and increased the percentage of pod set, irrespective of the water condition, resulting in increase of seed yield. However, seed yield was severely decreased by water deficit, and application of Figaron could not fully overcome the decrease of yield caused by a severe water deficit.
This study was carried out to determine heterosis in different photosynthetic and morphological characters, and to observe photosynthetic ability and dry matter production potentiality of two F1 hybrids of rice grown in pots supplied with N fertilizer in the normal or double dose. Photosynthetic rate in terms of CO2 exchange rate (CER), leaf N concentration, SPAD value, soluble protein content and ribulose-1, 5-bisphosphate carboxylase (Rubisco) activity was increased significantly by doubling the dose of fertilizer in most parental cultivars and F1 hybrids, but the rate of increase was higher in F1 hybrids than in their parents. Several morphological parameters were also increased significantly by doubling the dose of fertilizer, but not the percentage of dead leaf blades. The rates of increase of plant height, leaf area and dry matter production were higher in F1 hybrids. In particular, the rates of increase of total dry matter and root weight were very high in one of the F1 hybrids. The percentage of dead leaf blades decreased significantly in plants grown with a high dose of fertilizer as a result of higher leaf N concentration. At a normal fertilizer dose, both F1 hybrids failed to show positive heterosis in most photosynthetic characters. However, positive heterosis was found at a high fertilizer dose. Both F1 hybrids showed positive heterosis over mid-parent in dry matter production per plant at both fertilizer doses. One of the F1 hybrids also showed positive heterosis over the better parent. Heterosis in most photosynthetic and morphological characters was increased by increasing the dose of fertilizer. The sufficient supply by doubling the dose of fertilizer increased the leaf N concentration, chlorophyll content, soluble protein content and Rubisco activity in F1 hybrids, which led to higher positive heterosis in CER. A larger leaf area plus higher CER, especially at a high fertilizer dose, contributed to higher dry matter production in F1 hybrids of rice.
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.
The root system development and its localized distribution were examined using cassava plants grown in narrow root boxes of appropriate sizes which were adjusted to the root growth. Analyses based on fractal geometry were applied in addition to measurements of the weight and length of the root systems to evaluate the root distribution quantitatively. The root system distribution was converted to a digitized image, and the fractal dimension was calculated by the box-counting method (Dbox) for the whole root system and different positions in the soil. Furthermore, 1000 random measurements for local fractal dimension by the mass-radius method (Dlocal) were conducted per root system, and the multifractal spectrum was analyzed. The total root weight increased until 90 days after planting (DAP), whereas the total length ceased to increase at 60 DAP. Neither apparent bulking of storage root nor decrease in root length was observed during the experimental period. The potential rooting habit of cassava was two-dimensionally exhibited under a uniform soil environment in the boxes. The complexity in root distribution as a whole root system shown by the global D (Dbox) was almost constant. However, both the trends in positional Dbox difference and multifractal analysis showed that the root distribution was localized and heterogeneity in the localization changed with root system development. The root system of cassava grown in the boxes can be characterized as an abundant but uneven root distribution with a highly advanced branching pattern by large global D and kurtosis of the multifractal spectra.
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.
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.
In the dry regions, crops are often sown deeper than in the wet regions, because of the relatively high stability of water content of the deep soil layers. However, deep sowing may impair crop emergence and tolerant varieties are, therefore, necessary for successful crop production. The objectives of the present study were to identify and analyze the morphological basis of the varietal difference in tolerance to deep sowing in wheat (Triticum aestivum L.). Several morphological parameters of plumule were measured in five varieties. The varieties used were Hongwangmai, Ninchun No.10, Mianyang No.11, Sv 85131 and Haruhikari. Varieties tolerant to deep sowing, Hongwangmai, showed the highest emergence rate under deep sowing in tamped soil. The soil penetration force of plumule represented by ratio of emergence rate in tamped to that in untamped soil correlated with the cross-section area of coleoptile tip (r= -0.929, p<0.05) and with the final coleoptile length (r=0.974, p<0.01). It is confirmed in this study that the varietal difference in the tolerance of wheat to deep sowing is correlated with the final coleoptile length and the cross-section area of coleoptile tip. The final coleoptile length might be determined by the number of longitudinally arranged cells in the coleoptile. The tolerant variety, Hongwangmai, had the longest coleoptile and the smallest cross-section area of coleoptile tip.
The objective of this study was to obtain information about spatial heterogeneity as a basis for site-specific soil and crop management in small fields. The spatial variability patterns of wheat growth parameters and soil properties, e.g. nitrate, available phosphate, pH, and soil surface hardness, were investigated on a 0.25 ha field of Humic Andosol in 1998 - 1999. Two plots in the field had been tilled with different intensities since autumn 1997. A plot was minimum-tilled with a rotary tiller (MT) and the other plot was conventionally tilled with a moldboard plow and disc-harrowed (CT). Raw data, collected from 100 locations with 2.5 m×5 m spacing in each plot, were divided into trends (large-scale deterministic structure) and residuals (small-scale stochastic structure) by median polishing. Trends were more dominant in CT than in MT. The trend of wheat above-ground biomass at harvest was similar to those of soil nitrate and available phosphate. These trends were partly due to high variability across rows, possibly caused by the same traffic direction of farming operations for several years. The residual data, on the other hand, showed no correlation among the parameters. The spatial dependency of the residual data for soil properties, except for pH, was not apparent for distances larger than the minimum sampling distance (2.5 m). It is concluded that modification of fertilizer application based on the trend data may improve the efficiency of fertilizer use while small-scale site-specific management based on the residual data may be practically difficult.