In spite of a large number of reports on the effects of cytokinin application on growth of wheat, barley and other crops, the impact of it on rice growth has rarely been investigated.The objective of this study was to examine the effects of benzylaminopurine(BA)on shoot and root development and growth of rice plants.Rice(Oryza sativa L.cv.North Rose)was grown in hydroponics under all NH₄+, all NO₃-and an equal mixture of both forms.From the 6th leaf stage on, 100μM BA was sprayed to the shoot once every two days for a total of 5 times.BA spray inhibited the development and growth of plant age, plant length, leaf blade lengh and the root as a whole with the exception that the length of advantituous roots was increased by BA in NH₄+-N-grown plants.BA spray also decreased the dry-matter production of both the shoot and root.Single NH₄+-N inhibited the shoot and root development and growth compared with NO₃--containing N sources.BA counteracted to some extent the inhibitory effect of NH₄+-N on plant length, average adventitious root length and the longest adventitious root length.We concluded that 100μM BA spray basically inhibited the shoot and root growth and development of rice(cv.North Rose)grow in hydroponics, but the effects on shoot development are temporary and the treated plants attain or exceed the development of the control plants while the inhibited development of the root did not recover within the experiment period.

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A large proportion of flowers abscise during development in soybean(Glycine max L.Merr.).A reduction in this abscission might increase pod and seed number, and thereby can lead to an increased yield.Previous studies showed that pod-set probability was greater at proximal positions of individual recemes, and that the probability was enhanced by the exogenously applied cytokinins.However, whether intra-raceme variation in the pod-set probability relates to endogenous cytokinin levels remains unknown.To address this question, intra-raceme variation in cytokinin content and pod-set probability was investigated.A soybean genotype IX93-100, which has long racemes, was grown in an environmentally controlled chamber(30/20°C day/night temperature, 15 h day length, 600 μmol m-2s-1 photosynthetic photon flux density).Flowers, which were divided into three floral positions(proximal, middle, distal)on individual racemes, were sampled at intervals after anthesis.The cytokinins in the samples were identified by gas chromatography-mass spectrometry(GC-MS)and further quantified by enzyme immunoassay(EIA).The GC-MS analysis revealed that cis-zeatin riboside(c-ZR)and isopentenyl-adenosine(iPA)were predominant forms of cytokinin in soybean racemes.The total amount of these cytokinins in racemes, which was monitored by EIA, peaked one to two weeks after the first flowering on a raceme, when pod development was initiated.Within individual racemes, the total cytokinin concentrations were greater at more proximal floral positions, as was the probability of pod set.Removal of proximal flowers at anthesis enhanced both cytokinin concentrations and pod set at middle positions on the receme.Thus, pod-set probability was significantly associated with the cytokinin concentration at different floral positions within individual soybean racemes.

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The effect of brassinolide at 10-9M to 10-5M on the growth of rice seedlings was examined in darkness and under the light.After treament in darkness for one week, 10-7M and 10-5M brassinolide strongly stimulated mesocotyl and coleoptile elongation in all rice cultivars.The treatment with 10-5M brassinolide also induced the formation of the MC-type seedling, which consisted of only mesocotyl and coleoptile, the leaves being enclosed by the coleoptile.Under the light(120μmol m-2s-1, 14 h/day), brassinolide stimulated the leaf sheath elongation and increased the number of leaves.Brassinolide at 10-5M stimulated the elongation of the second leaf sheath, but inhibited that of the third leaf sheath.

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To estimate the general and specific combining ability for direct seeding in flooded paddy field, we completed a 4×3 factorial crossing(design II)in 1998, and evaluated the 12 F₁ hybrids and their 7 parents, including selected lines for yield, yield components and culm traits in 1999.Generally, parents with good combining ability produce good lines in later generations.Therefore, the basic information about the general combining ability(GCA)and specific combining ability(SCA)is valuable for breeding cultivars.The effect of GCA was significant for culm length, culm thickness, panicle length, 1000-grain weight and grain yield, which indicate the importance of the additive effects of the genes for these traits.The effects of dominant genes were significant for culm length, culm thickness and grain yield, indicating that these traits were also controlled by nonadditive gene actions.Mid-parent heterosis ranged from -16.3% to 37% with an average value of 17.3% for grain yield, and from -1.7% to 30.0% with an average value of 13% for culm length, and from -6.1% to 23.9% with an average value of 4.2% for culm thickness.Some parents with positive GCA for yield, culm thickness and panicle length were identified.They would be useful for developing cultivars adapted to direct-seeding in flooded paddy fields.

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Much information is obtainable from hyper-spectral data, which measure solar radiation consecutively at less than about 10-nm intervals.In constructing statistical prediction models, however, problems pf overfitting may arise due to the excessive number of variables, and multicollinearity may occur between variables ; thus a few specific wavelengths must be chosen.Various multivariate regression models were examined with ten-fold cross-validation to develop effecient, accurate models to predict dry weight and nitrogen accumulation of rice crops from the maximum tiller number stage to the meiosis stage, using plant-canopy reflectance of hyper-spectra within the 400-1100 nm domain without any variable selection.The results showed that the principal component regression using hyper-spectra gave better fits and predictability than that using specific wavelengths.On the other hand, partial least squares regression was the most useful among the models tested ; this method avoided overfitting and multicollinearity by using all wavelength information without variable selection and by inclusion of both x and y variations in its latent variables.

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Rice(Oryza sativa L.)cv.Asahi has been proved to be a useful genetic resource with a unique regeneration ability in anther culture.Diallel analysis was employed using four varieties showing different responses to four different constituent media.The mode of inheritance in regeneration ability of Asahi changed between dominant and recessive expression depending on medium composition although its regeneration rate was constantly high.On the contrary, the low regeneration ability of Koshihikari behaved consistently in a dominant manner and the high regeneration ability of Tsukinohikari behaved in a recessive manner independent of medium composition.The basic medium used was N₆ medium containing 0.1μM, 2, 4-D, 5μM NAA and 70gL-1 sucrose and the others were supplemented with 0.1μM BAP, 0.1μM BAP+18mgL-1 glycine or 0.1μM BAP+18mgL-1 glycine+and 0.5gL-1 alanine.The difference of medium composition which affects dominance and recessiveness in regeneration ability of Asahi was affected by the presence or absence of 18 mgL-1 glycine supplemented in the medium.

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The effects of various carbon sources, sucrose, glucose and fructose alone or in combination on the in vitro growth of banana plantlets were studied.Banana plants were cultured on the media supplemented with these carbon sources at 0.08 M for 13 weeks.The water potential of the medium was highest in the medium supplemented with sucrose+glucose(-0.3 MPa), and was significantly lower in the medium supplemented with fructose alone or in combination with other carbon sources(-0.7 to -1.0 MPa)than in the other media.The leaf water potential was also the highest in the plants cultured on the medium supplemented with sucrose+glucose, and lowest in the plants cultured on that with fructose.The leaf water potential of plants cultured on suclose+glucose, sucrose and glucose correlated well with their growth and photosynthetic activity, but the correlation was not observed in the plants cultured on fructose alone or in combination with other carbon sources.Plants cultured on fructose had a lower chlorophyll content(400 μg dm-2)and lower photosynthetic rate(3 μmolO₂m-2s-1)than those cultured on sucrose+glucose(15, 950 μg dm-2 for chlorophyll and 8.5 μmolO₂m-2s-1 for photosynthesis), and these differences were statistically significant.Both chlorophyll content and photosynthetic oxygen evolution were the highest in the plants cultured on sucrose+glucose, and the superior growth of plants on this medium was attributed to their high photosynthetic effeciency.

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We examined the relationship between ethylene evolution and carbohydrate content in leaf blades excised from rice(Oryza sativa L.cv.Nipponbare)seedlings at the four-leaf stage.The rate ethylene evolution from the excised leaf blades sampled at various times exhibited diurnal fluctuation ; it was the lowest at 5:00, increased to the maxmum at 13:00, then decreased.The sucrose content in leaf blades showed the same fluctuation as the rate of ethylene evolution.Application of sucrose stimulated the evolution of ethylene and increased the contents of glucose, fructose and sucrose in the leaf blades.After the application of glucose or fructose, both the rate of ethylene evolution and sugar content increased, but glucose and fructose increased much less than sucrose.In these experiments, sucrose content was closely correlated with the rate of ethylene evolution in rice leaf blades.From these data we concluded that sucrose content regulated the rate of ethylene evolution from leaf blades in young rice seedlings.

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Prediction of mulberry(Morus alba L.cv.Shinn-ichinose)growth is necessary to cope with recent trends in mulberry cultivation.To develop a mulberry growth model, I investigated the response of mulberry growth to temperature.Mulberry saplings were growth in 1995 and 1996 at four constant(20, 24, 28, 32°C)and one diurnally fluctuating(32/24°C-mean 28°C)temperature conditions for 50-60 days in phytotrons under natural sunlight.Shoot length and leaf number were measured every 10 days during the temperature treatment and the dry matter of each plant part was measured at the end of the treatment period.Shoot length and leaf number increased expontially with time at all temperatures examined, and these values increased with the increase in temperature.Shoot dry weight, over the period of the treatment, increased with temperature but the dry weights of stump and root were not affected by temperature.The optimum temperature for mulberry growth and dry matter accumulation was approximately 32°C.

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To predict mulberry growth, modeling of shoot elongation and leaf appearance of potted mulberries was attempted.Potted mulberries were grow in temperature-controlled phytotrons.Changes in the rates of mulberry shoot elongation and leaf appearance, and the relationship between the rates and temperature were investigated.The rate of shoot elongation increased until the shoot length reached about 100cm, and became stable thereafter.The rates of both shoot elongation and leaf appearance increased with the increase in temperature from 15°C to 27°C, but not at higher temperatures.However, the rate of leaf appearance increased with the rise in temperature up to 31°C.On the basis of these results, the shoot elongation and leaf appearance of mulberry in phytotron were simulated in nonlinear regression models.The relationship between the rate of shoot elongation and temperature, and the rate of leaf appearance and temperature in the model fitted to measured values very well, and that between the rate of shoot elongation and shoot length in the models tended to be in accordance with the measured values.Shoot length and leaf number predicted by the model were in concurrence with the measured values.

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Glasshouse nutrient omission trials are useful in identifying nurient limitations for plant growth in soils under the same environmental conditions.Soils of low fertility are commonly used for production of rainfed lowland rice(Oryza sative L.), and the crop often encounters water stress.Nutrient requirements may be modified when standing water disappears from the field.Two experiments with rice seedlings were conducted in a glasshouse at Ubon Rice Research Center, Thailand to identify the untrients which limit rice growth in soils of Northeast Thailand, and to determine whether nutrient limitations are affected by water availability.In Experiment l, rice was grown on two soils(Roi et and Ubon series)under well-watered and water-limiting conditions, and 15 nutrient treatments were imposed.In Experiment 2, six soils from Northeast Thailand were examined using the same 15 nutrient treatments.The nutrients which clearly limited the growth of rice plants in soils of Northeast Thailand were nitrogen(N)and phosphorus(P).In some cases, potassium(K)and sulfur(S)also limited growth, and in one soil zinc(Zn)and boron(B)also limited growth.A shortage of N was the most important limitation for plant growth in all soils except one in which P was more important.The low supply of P decreased plant height and leaf area development during early growth ; low N supply had a greater effect later during growth.The omission of P has a larger detrimental effect on growth when water supply was limited.In the Roi et soil, the omission of S had a large effect on leaf area and total dry matter production only under water stress conditions, but this was not found in the other soils examined.These results from glasshouse studies show that the nutrients limiting rice growth depend on soil type and water availability in soils of Northeast Thailand.

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High concentrations of NaCl significantly reduced the fresh and dry weights and lengths of roots and shoots.NaCl exhibited a more rapid effect in water culture than in soil culture.In both water and solid cultures, root growth was suppressed more severely than shoot growth.Electron microscopic studies revealed that NaCl caused swelling of thylakoids, accumulation of starch grains and lipid droplets, distortion of grana stacking, increase in the size and number of plastoglobuli and vesiculation of cellular membrane.Mitochondria became deficient in cristae, swelled and the matrix appeared pale in salt-treated plants as compared with control plants.Disappearance of nucleolus and nuclear chromatin and destruction of vascular tissues were occasionally observed in salt-treated plants.

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To clarify the mechanism of high temperature-induced floret sterility in rice(Oryza sativa L.), we studied the effects of high temperature at flowering on the ability of thecae to dehisce and on pollen-grain swelling which causes thecae dehiscence.Two japonica rice cultivars, grown in four L pots under submerged soil conditions were subjected to high(39°C)and moderate (34°C)temperatures from 10:00 to 16:00 for three consecutive days at the flowering stage.The percentage of the thecae dehisced in response to artificial opening of the florets by removing lemma and the mean diameter of the pollen grains measured during four minutes after the artificial opening were examined to determine the ability of the thecae to dehisce and that of the pollen grains to swell, respectively.The high temperature given on the day of flowering decreased both the percentage of the dehisced thecae and the diameter of the pollen grains but did not affect the relationship between them.The thecae of the plants which had been subjected to the high temperature for one or two days before flowering however, showed a lower dehiscence percentage than those of the plant treated on the day of flowering against the same pollen-grain diameter.We concluded that high temperature given on the day of flowering decreased the ability of the pollen grains to swell resulting in poor thecae dehiscence, and that, besides this decrease, high temperature given just before the days of flowering lowered the function of thecae themselves to dehisce, causing poorer thecae dehiscence.

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Nodal root anatomy was compared among twelve upland and lowland rice(Oryza sative L.)varieties with tropical origin which were grown in hydroponic culture and under field conditions.The traditional upland japonica varieties showed the largest diameter of root, stele, and xylem vessel followed by modern upland varieties.There was a clear varietal difference in the ratio of stele to root diameter, which was associated with the genetic group rather than with the ecosystems.The japonica varieties had a significantly larger stele diameter relative to the root diameter than indica and aus varieties.The indica and aus varieties displayed more xylem vessels per unit area of stele than the japonica varieties, but the diameter of xylem vessel was smaller.Equivalent xylem vessel diameter(De)was more dependent on the number of xylem in the indica varieties than in the japonica varieties.Distinctly different types of sclerenchyma anatomy were identified among the varieties.The development of sclerenchyma was classified into four different types based on thickening of cell wall in the outer cortical parenchyma and the number of sclerenchymatous cell layers.Like the xylem anatomy, the varietal differences in sclerenchyma development were more associated with genetic group rather than the ecotype.The japonica varieties had higher frequency of the types which have a doubled cell layer in sclerenchyma with thick cell wall than indica and aus.The difference among the genetic groups was nearly consistent across growing conditions, aerobic and submerged soils.These results indicated that sclerenchyma development is controlled by a genetic factor.

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Events during the early development of rice endosperm were studied cyto-histologically.Attempts were made to clarify the sequential changes during the early developmental stages of endosperm to reveal the ultrastructural details of the first-anticlinal wall formation and the subsequent cellularization.Early development of nuclear endosperm rapidly proceeded after anthesis and a large number of free nuclei proliferated until 48 HAA.In a large central cell, phragmoplasts arose as a result of alignment of vesicles appeared between the free nuclei located in the peripheral cytoplasm layer along nucellus.The phragmoplasts initially fused with wall of the nucellus and formed the initials of anticlinal wall.The initial wall grew toward a large central vacuole and reached tonoplast of central vacuole.Thereby, alveolar typed cell compartments ensued.Furthermore, the anticlinal wall continuously arose to form a large number of alveolar typed compartments.The cellularization of compartments including a free nucleus was achieved during 48 to 72 HAA.Microtubules and Golgi apparatus seemed to contribute to cellularization.Lastly, the process forming first-anticlinal wall is followed on a representative diagram and compared with the cellularization in other cereal endosperms.

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