To clarify the factors causing the differences in the leaf-senescence pattern between the soybean cultivars, Tachinagaha (T, late senescing cv) and Enrei (E, early senescing cv), we grafted the T scion onto a T or E rootstock (T/T, T/E) and E scion onto an E or T rootstock (E/E, E/T) and investigated the effects of the roots on the senescene of scion leaves. At the early stage of ripening, the T and E scions on the T rootstock had a higher chlorophyll content than either the E or T scion on the E rootstock. Thus, the properties of the rootstock influenced the senescence of the scion. By contrast, at the late stage of ripening, the chlorophyll content of the T scion was higher than that of the E scion irrespective of the cultivar of the rootstock. Root length per plant was longer in the T rootstock than in the E rootstock irrespective of the cultivar of the scion. Moreover, root length did not change during the ripening phase. The exudation rate per plant and per unit leaf area at the early stage of ripening was higher in the plants with a T rootstock than an E rootstock and the exudation rate per plant and per unit leaf area were low and the differences between graft combinations were small at the late stage of ripening. From these results, it was clear that the physiological activity of the root (exudation rate) was more closely related to the delay of leaf senescence than the root length at the beginning of the ripening phase.
Spikelet number per unit area is a strong determinant of rice yield, and spikelet differentiation must be promoted to increase spikelet number. Nitrogen has been considered to be the most critical factor in promoting spikelet differentiation and the role of non-structural carbohydrates (NSCs) in spikelet differentiation is unclear. To reveal the relation between NSCs and the number of differentiated spikelets, we conducted a field experiment in Matsue, Shimane, Japan, using two japonica cultivars Koshihikari and Nipponbare. The NSC content was changed by shading and thinning during the early reproductive stage. These treatments did not change the amount of nitrogen per hill in the leaves and stems. The number of differentiated spikelets, which was defined as the sum of the numbers of surviving spikelets and vestiges of degenerated spikelets, was not influenced by NSC content in rice plants; neither was the number of primary rachis-branches, which is considered to determine spikelet number per panicle. The ratio of dry matter allocation to leaves and the rest of the plants was changed, but the morphological characteristics such as tiller number and plant length were not influenced by the treatments. It is concluded that the differentiation of spikelets was not influenced by the NSC content within the range examined in the present experiment. The role of NSC in the mechanism of spikelet differentiation is discussed.
An improved method for extraction and measurement of inorganic pyrophosphate (PPi) in the leaves of crassulacean acid metabolism (CAM) plants, Ananas comosus (pineapple), Kalanchoe pinnata and K. dagremontiana is described. Leaf samples were extracted with 5% (w/v) trichloroacetic acid (TCA) dissolved in water. The extracts without neutralizing with KOH or K2CO3 and those without washing with diethyl ether to remove TCA were directly used to measure PPi with PPi-dependent phosphofructokinase (PPi-PFK, EC 2. 7. 1. 90) coupled with the oxidation of NADH. The method is sensitive and simple, the lower limit of the measurement was less than 1 nmol PPi mL-1 reaction mixture and the recoveries of the PPi added were more than 96%. Moreover, the initial PPi levels in TCA extracts could be maintained for at least one day. This method was advantageous for extracting and measuring a large number of samples at the same time. In addition, we found that neutralizing the extract before determination was disadvantageous to PPi recovery.
Morphological changes in starch granules in endosperm cells of rice, cv. Cisadane (javanica) and cv. Koshihikari (japonica), during germination and early growth of seedlings at 17°C, ambient temperature (field condition, 16-24°C) and 38°C, respectively, were examined with scanning and transmission electron microscopes. With the treatment at 17°C, a groove-like structure appeared on the surface of amyloplasts at five days after seeding (DAS). After the amyloplast envelope disappeared and starch granules were separated from each other, small holes, which were observed at higher temperatures, did not appear, and a "rough structure" appeared on the granule surface. At 15 DAS, starch granules adjacent to scutellum were partly decomposed but those at the distal end of the seed did not decompose until 15 DAS. In the seed germinated at 38°C, starch granules in endosperm cells adjacent to scutellum began to decompose within one day after seeding, and small holes appeared on the surface of starch granules. At further stages of decomposition, a layer-like structures was observed inside of the starch granule that followed by the appearance of highly viscous materials on the resolving granules and decomposed almost completely at 15 DAS. At this time, many mitochondria that seemed to be related with decomposition of starch granules were observed by transmission electron microscopy. At an ambient temperature, the decomposition has progressed at 15 DAS with the vanishing of amyloplast envelopes in the whole of endosperm. In cv. Koshihikari most of the starch granules had decomposed at 20 DAS.
The fate of applied nitrogen (N) fertilizer in a barley-maize-barley crop sequence on an alluvial soil with four different histories of soil fertilization (main plots) was examined at Kyoto, Japan. The four main plots were not fertilized (NF), or fertilized with only chemical fertilizer (CF), only barnyard manure (MF) and chemical fertilizer + barnyard manure (CM) for nine years, and then two open-bottom boxes (mini-plot) were embedded in the middle of each main plot. 15N-labeled ammonium sulfate was applied to the mini-plots only before planting the first crop barley in group 1, and before planting the first and the second crops in group 2. The highest biomass yield and N uptake were observed in the CM main plot throughout the barley-maize-barley crop sequence, and in the MF main plot in the last two crops. In the mini-plots, recovery of 15N by the first barley ranged from 4% in MF to 11% in NF. After the third crop harvest, 11 to 23% of the labeled N remained in the soil in group 1. The rate of remaining 15N was notably higher in MF and CM than in CF and NF. Labeled N applied before planting the second crop maize in group 2 also remained in the soil at a higher rate and recovered less by the plants in MF than in the other mini-plots. Recovery of applied N by the second crop maize in group 1, was less than 2% in all mini-plots. The contribution of the applied N to the total N uptake in the first crops was higher in NF and CF (24-48%) than in MF and CM (7-15%), and that to the subsequent crop was negligible in all mini-plots. In the soils previously fertilized with manure for nine years, the applied N was held in the soil more abundantly, but was less utilized by the plants grown in the above crop sequence than in the soil not fertilized with manure previously.
Anthers of rice cultivar, cv. Nipponbare, which showed floret fertility even when the temperature at flowering was high (tolerant) and cv. Hinohikari, which showed floret sterility at high temperatures (susceptible) were compared. The anther of Nipponbare had better developed cavities for dehiscence and thicker locule walls than Hinohikari. The well-developed cavities enable easy rupture of the septa in response to swelling of the pollen grains. The thick locule walls promote the swelling of pollen grains by retaining water in the locules. Since the swelling of pollen grains is the driving force to open the theca and the septum rupture is an indispensable process for the theca dehiscence, the well-developed cavities and the thick locule walls may be responsible for the tolerance to high temperatures in Nipponbare.
Immunogold labeling was applied to scanning electron microscopy to examine the inner structure of leaves of C4 plants, maize and finger millet. Ultrastructural features of the C4 plant leaves were observed on cross sections in the secondary electron imaging mode of the scanning electron microscope. Immunogold localization was well recognized in the backscattered imaging mode at the low accelerating voltage of 5 kV on the specimens treated with tannic acid and OsO4 instead of metal coating. Gold labeling of ribulose 1, 5-bisphosphate carboxylase/oxygenase was specifically distributed on the cut surface of bundle sheath chloroplasts of the C4 plants. Gold particles were scarcely observed in mesophyll chloroplasts or other organelles. Freeze-cracking of the leaves was found to be effective to expose the inner structur of the organelles. The secondary and backscattered electron images were also compared under various accelerating voltages.
Seed hardening, wetting and redrying of the seed before sowing, promotes germination under low soil-moisture conditions in wheat varieties bred and grown in semi-arid areas. It is unknown, however, whether this is also the case in wheat varieties cultivated in a temperate humid zone. We examined the effect of the seed hardening on germination and seedling emergence under low soil-moisture conditions in a wheat variety, Norin 61, which is cultivated over a wide area of the temperate humid zone in Japan. We first determined the optimum temperature for germination (23°C) and the critical range of soil-moisture (CR) for germination (water-holding capacity of 24%; -0.30 MPa). Then, we imbibed the seeds of Norin 61 for various periods followed by air-drying, and compared the germination of these seeds and their seeding emergence with those in non-treated seeds at 23°C under CR condition. Imbibition of the seeds for 24 h, which increased the water content to 64%, followed by redrying significantly accelerated the germination and seedling emergence under such conditions. Even in the firld, the seed hardening treatment significantly accelerated germination and seedling emergence under both irrigated and non-irrigated conditions. We concluded that seed hardening treatment is available to accelerate the germination of a wheat variety of the temperate humid zone in Japan, Norin 61.
The objective of this study was to determine the concentration of nonstructural carbohydrate (NSC) reserves in the root at the early growth stage during the cool fall season in four temperate perennial grasses : orchardgrass (Dactylis glomerata L.), timothy (Phleum pratense L.), perennial ryegrass (Lolium perenne L.), and reed canarygrass (Phalaris arundinacea L.) and to examine the relationship between the overwintering ability and the concentration of NSCs. The concentration of NSCs in the root was the highest in reed canarygrass, and it was about three times higher than that in the tops. Timothy stored NSCs in the root at a higher level than orchardgrass and perennial ryegrass. The NSC concentrations in the top were similar in the four grasses. Fructose and especially sucrose concentrations in the root were the highest in reed canarygrass, intermediate in timothy and the lowest in orchardgrass. Also, the reserves in timothy and reed canarygrass were predominantly fructosans with high degrees of polymerization (DP). On the other hand, perennial ryegrass reserves were predominantly fructosans with a low DP. The DP of fructosans in orchardgrass was in between the two. Growth in the dark in spring was the highest in reed canarygrass, the second highest in timothy and the lowest in orchardgrass. From these results we conclude that at the early growth stage reed canarygrass has the highest level of NSCs in the root, followed by timothy, orchardgrass and perennial ryegrass. The wintering ability is regulated mainly by NSC in the roots rather than that in the tops. This is true even at the early growth stage.
The relationship between coleoptile elongation and ethanolic fermentation was investigated in five cultivars of germinating rice (Oryza sativa L.) seeds submerged for 48 h under anoxia. The coleoptile elongation of all cultivars was suppressed by the submergence stress, but their elongation relative to that of respective non-stressed control was the greatest in cv. Yukihikari followed in order by Nipponbare, Kinuhikari, Koshihikari and Sasanishiki. During the stress, alcohol dehydrogenase activity and ethanol concentration in the coleoptiles of all cultivars were increased. The increased activity and concentration were the greatest in Yukihikari followed by the other cultivars in the same order as above. The ethanol concentration in the stressed coleoptiles of five cultivars closely correlated with their coleoptile elongation. These results confirm that the ability to increase ethanolic fermentation may play an important role in the coleoptile elongation under the submergence stress condition.
Late-maturing cultivars of potato form tubers much later than early-maturing cultivars in a field. Jasmonic acid (JA) induced in vitro tuberization in various cultivars that differed greatly in maturing time. Airborne JA-Me was also able to induce tuberization in all the cultivars tested. However, the early- or late-maturing habit (maturity) affected largely their tuberizing response to JA; the later the maturing time of the cultivar, the lower the response. The etiolated shoots developed from the tubers of late-maturing cultivars had longer internodes than the early-maturing cultivars, suggesting that the levels of endogenous gibberellins (GA) in them are higher in the former than in the latter. Since gibberellic acid strongly inhibited JA-induced tuberization, the lower tuberizing response of late-maturing cultivars to JA may be attributable to high levels of endogenous GA. An exceptional result was obtained in an extremely late-maturing cultivar, which had a medium length of internodes but showed high tuberization in response to JA. These results suggest that not only GA but also jasmonates are the key factors determining maturity; either a higher level of GA or a lower level of jasmonates may predispose the cultivars to have a late-maturing habit.
We examined the palatability and physicochemical properties of milled rice for each grain-thickness group, and examined the influence of physicochemical properties on the grain-thickness-dependent differences of the evaluation of palatability. The thicker the grain, the higher the palatability. However, the palatability of the grains thicker than 2.0 mm did not vary with the grain thickness. For the grains thinner than 2.0 mm, the thinner the grain, the lower the evaluated value of palatability, and the palatability values were very low in the grains thinner than 1.9 mm. The thinner the grain, the higher the protein content. On the contrary, the thinner the grain, the lower the amylose content. The maximum viscosity and breakdown values in amylographic characteristics decreased with decreasing grain thickness. Hardness/adhesion (H/-H) ratio in textural characteristics tended to increase with decreasing grain thickness. The palatability of the cooked rice grains in each grain-thickness group showed a negative correlation with the protein content and H/-H ratio, and strong positive correlation with the amylose content and maximum viscosity. These results indicate that the lowering of palatability with decreasing grain thickness is due to the increase in protein content, the decrease in amylose content, and the decrease in amylographic and textural characteristics. The standard partial regression coefficients against palatability were the highest for the maximum viscosity in Koshihikari, for H/-H ratio in Nipponbare and for protein content in Hinohikari. Thus, in rice cultivated under a certain cultivation condition, physicochemical factors involved in the grain-thickness-dependent difference of palatability are suggested to vary with the cultivar.