Photosynthetic and transpiration rates of rice leaf were measured under light with an intensity fluctuating in a wide range of frequencies(2.8×10-4∼4Hz).The time course of photosynthetic rate differed with the frequency.Under the light with an intensity fluctuating at a frequency of lower than 0.05 Hz, the photosynthetic rate oscillated regularly, and the photosynthetic light-use efficiency(LUE:mean photosynthetic rate under fluctuating light)was constat, independent of the frequency.On the other hand, under the light with an intensity fluctuating at a high frequency(> 0.05 Hz), the time course of photosynthetic rate was constant without oscillation, and LUE increased with increasing frequency.The effect of the fluctuating light intensity was affected by ambient humidity.LUE was higher at the high ambient humidity, although the difference between the photosynthetic rates at high and low ambient humidities was reduced under the light with an intensity fluctuating at a high frequency(> 2 Hz).The present findings suggests that brief leaf movements by natural factors such as wind(leaf flutter)may provide effective intermittent light penetration to lower leaves, and increase the total photosynthetic rate in the canopy.Rapidly fluctuating light intensity may also alleviate the photosynthetic depression caused by stomatal closure frequency observed in the afternoon(known as midday depression).
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 applicatoin of much nitrogen in creased 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.
A pH indicator agar gel is widely used in rhizosphere pH studies, but its use was mostly confined to visualizatoin of pH changes.A few complex methods are available to meawure pH in agar gels.We improved such methods to enable non-destructive quantification of pH dynamics along a root axis by using an image scanner and image analysis software.A thin agar gel containing Bromocresol Purple was used for 2-dimensional image analysis.A taproot of cowpea was embedded in the agar gel containing 1 mM nitrate, and incubated in the dark at 30°C.Every 2 hours, the agar gel was scanned to capture a full color image that reflected rhizosphere pH.In image analysis, optical properties of the pH indicator showed a linear(R2=0.99)relationship between pH and optical density in the pH range of 4.4 to 7.2.This analysis allowed us to map the pH gradient in the rhizosphere at a reaolution of 0.2 pH.An apparent proton flux was calculated to integrate rhizosphere pH gradients, which quantifies alkalizing / acidifying abilities of the root at various portions.Using this protocol, we examined the effect of pre-cultural N-levels on alkalizing(proton influx)ability of root at various portions under subsequent uniformly nitrate-fed conditions.Results showed that the estimated cumulative proton production was about two times higher in high-N-than in low-N pre-cultured roots.The ratio of proton flux in high-N-to low-N pre-cultured roots was the greatest at the middle(2.94), followed by the basal(2.08)and the apical(1.23)portions of the root, suggesting that nitrate uptake is partitioned along the root axis.
Rhizosphere pH is known to be strongly influenced by nitrogen sources and plant species.We have evaluated whether the exposure of the shoot to light affect the pH changes in the rhizosphere of legumes and cereals in the presence of different forms of nitrogen(ammonium, nitrate or both).The pH changes in the rhizosphere were quantified as apparent proton fluxes by image analysis of agar gel containing a pH indicator, in which the root was embedded.In the presence of ammonium or ammonium nitrate, the rhizosphere was alkalized under dark conditions and acidified under light conditions in both cowpea and sorghum.This implied that, in the presence of ammonium, acidification of the rhizosphere is induced by exposure of shoot to light.In the presence of nitrate, both plants alkalized their rhizosphere in the dark, whereas in the light cowpea acidified its rhizosphere although sorghum alkalized it.Light-induced acidification, in the presence of nitrate, was also found in chickpea and adzuki bean, but not in maize.We found, that a particular part of the root axis strongly acidifies the rhizosphere in response to the exposure of shoot to ligh, especially in legumes.We conclude that rhizosphere pH is strongly affected by the light conditions encountered by the shoot, and the pH changes in response to the light locally along the root axis.
A field experiment was conducted to compare the below-ground competition between the intercropped maize(Zea mays L.)and two groundnut(Arachis hypogea L.)cultivars regarding the rooting soil layer.Three rows of each cultivar of groundnut(cvs.X-14 and Red Spanish)were planted in between two rows of maize(cv.Badra)with inter-row spacing of 30 cm and intra-row spacing of 15 cm.Aluminium sheets, 10 cm in height, were placed as a root barrier between the maize and groundnut rows at three depths, i.e., 0-10 cm, 10-20 cm and 20-30 cm from the soil surface.In the control plot, the soil was trenched and refilled without the aluminium partitions.The ear and total biomass yield of the maize intercropped with X-14 with the root barrier at 0-10 cm depth, were significantly larger than those with the root barriers at the depths of 10-20 cm, 20-30 cm and the control.The yield(crop or total biomass)of the maize intercropped with Red Spanish was not significantly affected by the root barrier.In conclusion, groundnut cultivar X-14 was more suitable for intercropping with maize than Red Spanish, probably due to the differences in the rooting properties in the top soil layer.
By selecting the optimal developmental stage of zygotic embryos used as explants and applying desiccation treatment, we improved direct somatic embryogenesis in rice scutellum from two cultivars, Nipponbare and Sasanishiki.Zygotic embryos isolated 14-17, 21, 28-30 and 35-40 d after anthesis(DAA)from Nipponbare and 14-17, 18-21, 28-30 and 40-42 DAA from Sasanishiki were cultured on the embryo induction medium(EIM).Then they were transferred to embryo maturation medium(EMM)and germinated on the embryo germination medium(EGM).Only immature zygotic embryo isolated 14-17 DAA from Nipponbare and Sasanishiki could develop somatic embryos that germinated.Explants from embryos at other developmental stages could develop somatic embryos only until the elongating or scutellar stage.They enlarged and formed callus without further development.The EIM and EMM consisted of N6 macronutrients, B5 micronutrients, and B5 vitamins, supplemented with 0.1 g L-1 casein hydrolysate, 1.5 g L-1 proline and 1 g L-1 MES buffer.EGM consisted of MS macro-and micronutrients and MS vitamins without organic supplement.In addition, 2 mg L-1 2, 4-D was added to EIM, 1 mg L-1 2, 4-D to EMM and 0.01 mg L-1 zeatin to EGM.Developmental processes of somatic embryos derived from the explants were observed by scanning electron microscopy.Desiccation treatment of maturing somatic embryo was proved to produce fully mature somatic embryos capable of germinating vigorously.
The field performance of in vitro-propagated banana(Musa spp.)plants was compared with that of the sucker-derived plants.In vitro-propagated plants established and grew faster, taller and bigger than the conventional sucker-derived plants.The former produced more leaves resulting in a larger total leaf area(8001.5 cm2 per plant)than the latter(6613.1 cm2 per plant)and could be harvested earlier.The former also produced heavier bunches and fruit(15.2 kg for bunch and 200 g per finger of fruit)than the latter(9.0 kg for bunch and 136.4 g per finger of fruit).In this experiment, the in vitro-propagated plants had many intact roots and a bulk of vermiculite around their roots but the sucker-derived plants had many damaged roots at the time of planting.In addition, in vitro-propagated plants started growth earlier and grew faster enabling them to intercept more light for photosynthesis than the sucker-derived plants.This may explain the higher yield in the in vitro-propagated plants.We conclude that in vitro-propagated Shima banana performs better in terms of growth and yield than the sucker-derived plants under field conditions.
The seedlings of rice(Oryza sativa cv.Nipponbare)at a plant age of 3 leaves, were cultured for 10 days in a 12-h light / 12-h dark cycle, and exposed to 60%(low)or 90%(high)relative humidity during the light and dark period in all combinations.Low humidity in light and high humidity in darkness, significantly increased tha rate of leaf emergence, plant height, leaf area, leaf blade length, the number of roots, total root length and dry matter production as compared with low humidity in both light and dark periods.These results suggested that the effects of high humidity during the dark period on the growth and dry matter production is not nullified by low humidity during the light period.High humidity during the light period was significantly more effective than that during the dark period for the growth expressed by these parameters.The effects of high humidity during the light and dark periods on the plant height, leaf sheath length and width of leaf blade were additive, but those on the leaf-emergence rate, number of roots, total length, leaf area, leaf blade length and dry matter production were not additive.
The effect of fluctuation in soil moisture on the root development of sweetpotato was studied during its establishment period, i.e., from planting to about one month after planting. The number of leaves, shoot dry weight and vine length were suppressed significantly by deficient moisture but the same were markedly increased by excessive moisture regardless of the time of occurrence relative to the initial development of the plant.In terms of its roots, the number and total length of the root system components were either increased or decreased depending upon the soil moisture regime in which they were subjected immediately prior to the time of sampling.Deficient soil moisture reduced the number and total length of the root system components while excessive moisture caused notable stimulation.Continuous exposure to noraml soil moisture caused substantial reduction in the number of adventitious roots and consequent depression in total length but this could be attributed to sink competition among adventitious roots.Under fluctuating soil moisture, normal moisture content appeared to restore the aberant development of the roots caused by deficient or excessive levels.The suppressed formation and elongation of the root system components under deficient soil moisture was alleviated when the soil moisture condition was changed to normal.On the other hand, the stimulated root formation and elongation in the excessive moisture was abated when the normal soil moisture condition prevailed afterwards.The result was the opposite when the soil moisture condition was reversed, i.e., normal then followed by either deficient or excessive soil moisture.
Biopores are tubular soil macropores left by plant roots after their decay or burrowed by soil animals, which provide channels for deep rooting and improve crop access to water and nutrients.The density of biopores, number of biopores per unit area, and proportion of biopores occupied by roots were measured on horizontal soil profiles at 30, 50, and 70 cm in depth in a fine-texture subsoil of Andosol(Light clay, a volcanic ash of the Kanto loam type)at the mature stage of wheat and maize.Images of 0.1 mm resolution from the pictures of cleaned profile surfaces were examined on a computer display.Dark spots with a circular and smooth boundary were regarded as biopores.The density of biopores larger than 1 mm in diameter ranged from 500 to 2, 000m-2.The percentage of biopores occupied by roots was more than 30% of biopores larger than 1 mm and increased with depth.Roots were accumulated in biopores.The proportion of biopores(>1 mm)with roots increased with depth.It was 28-35% in the wheat plot and 14-20% in the maize plot.This suggested that thinner wheat roots easily entered a biopore and remained in it.The possible influence of biopores on the spatial distribution of roots was discussed.
The physicochemical properties of the grains of 16 old- and 21 new-type rice cultivars in Japan were investigated in 1995 and 1996.Among the old- and new-type cultivars, we found a similar pattern of varietal differences in physicochemical properties in both years, and in both the fields with and without nitrogen fertilizer applied.Between the two types, no significant differences in the mean protein and amylose contents in the rice grain were observed.The old-type rice cultivars tended to be lower in mean maximum viscosity and breakdown values than the new-type cultivars, although the difference was not significant.Cooked rice of the old-type cultivars tended to be higher in mean hardness / adhesion ratio(H / -H)and hardness / adhesiveness ratio(H / A3)than that of the new-type cultivars.The physicochemical properties which showed superior values in the standard partial regression coefficients against the taste of cooked rice were the protein content, breakdown value and H / -H.These, physicochemical properties can be efficient indicators for evaluating the taste of cooked rice.The coefficient of parentage of each cultivar to cultivar Koshihikari showed tight negative correlations with amylose content, H / -H and H / A3, and tight positive correlations with maximum viscosity and breakdown values.The coefficients showed a loose positive correlation with protein content.However, Sasanishiki, Domannaka, Chiyonishiki, Nakate shinsenbon and Rikuu 132 were superior in their physicochemical indicators, in spite of their small coefficients of parentage to Koshihikari.This suggests that a highly palatable cultivar that is widely different from Koshihikari can be developed by utilizing genetic resources with superior physicochemical indicators.
The first step in the mobilization of the reserves in germinating rice seed was the decomposition of amylopllast 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.
Dry seeding advances establishment and harvest of rainfed rice and may help the crop escape late-season droughts.Early establishment, however, may expose the crop to early and mid-season droughts and periods of low radiation during the grain formation phase.We conducted experiments in the 1992 and 1993 rainy seasons at Tarlac, Philippines, to investigate factors that may hinder the performance and yield of dry-seeded rice cv.IR72.The treatments included three seeding dates and three water regimes(totally rainfed, irrigated from seeding to complete emergence followed by rainfed, and fully irrigated).Drough stresses between panicle initiation and flowering, with a matric potential of -25 kPa to -60 kPa in the 0-10 cm soil layer, reduced final biomass by 20%-30%.The same stresses occurring during the vegetative stage delayed flowering 3-5 d, but did not reduce total biomass at harvest.High plant density of the dry-seeding culture(325-450 seedlings m-2)resulted in excessive vegetative growth(1600-2200 tillers m-2 at maximum tillering stage).Inter- and intra-plant competition and low radiation(especially in typhoons)during anthesis and grain filling resulted in a high rate(40-70%)of tiller abortion, delay in flowering of later tillers, low percentage of filled spikelets(30-60%), and low yield(2.5-4.3 t ha-1), despite high blomass production(13-15 t ha-1).Selecting new varieties and devising cultural practies that ensure adepuate plant population and weed competitiveness in drought years and avoid excessive vegetative growth in years with low radiation are research challenges to make full use of the potential of dry seeding to increase the productivity of rainfed lowland rice.
The lack of information on the dynamics of crop growth and water use has limited the capacity for indirect selection through physiological traits that confer drought tolerance in rainfed lowland rice(Oryza sativa L.).Shoot growth and transpiration in response to drought and rewatering were studied among eight diverse rice genotypes in three sets of pot experiments:one under severe stress development after panicle initiation(average transpiration of 15.0 mm d-1;experiment 1), and two under slow and progressive stress development during tillering(average transpiration of 2.1 and 7.6 mm d-1 in experiments 2 and 3, respectively).Higher transpiration generally caused a higher plant growth rate in two periods, though there was some contribution of water use efficiency.The first period was soon after ponded water was drained and watering withheld(early drought phase), when soil became aerobic, soil water was still readily available, and transpiration continued at a rate comparable to the well-watered treatment.The second period was after rewatering when transpiration was again not limited by soil water supply.In experiment 1, the effect of plant size before stress imposition was large and genotypic variation for response to drought and rewatering was small, except for KDML105, which tended to show smaller growth during drought and had a more rapid recovery after rewatering.During early drought phase in experiments 2 and 3, genotypes differed in relative amounts of tiller and leaf area production compared with the well-watered treatment.Genotypes with high seedling vigor before stress imposition and during the early drought phase, such as NSG19, KDML105, Mahsuri and IR58821, produced greater root length during the following more severe drought period and had a larger greer leaf biomass at the end of the drought period in experiment 3.In these genotypes, transpiration increased sharply and leaf area expanded rapidly after rewatering, which caused superior drought recovery.
Genotypic variation in the root system is a potential source for improving drought tolerance of rainfed lowland rice(Oryza sativa L.).Our work aimed at characterizing both constitutive root traits(those present under well-watered conditions)and adaptive root traits(those developed in response to drought and rewatering)among eight diverse rice genotypes in three sets of greenhouse experiments(experiments 1, 2, and 3).Under well-watered conditions, genotypic variation was observed in root to shoot ratio, root growth rate, specific root length, deep root ratio, root mass per tiller, and root thickness.CT9993 and IR58821 had a high root to shoot ratio, deep and thick root system, and high root mass per tiller.However, CT9993 had a slow root growth rate and short specific root length.In response to drought in experiments 2 and 3, the total amount of assimilate distributed to roots was reduced and roots became thinner, but the proportion of total assimilate supply assigned to deeper layers increased, thereby maintaining deep root mass and increasing specific root length.On rewatering, root to shoot ratio increased, surface roots increased, and roots became thicker.During drought, NSG19, KDML105, Mahsuri, and IR58821 partitioned a larger proportion of assimilate to deep roots and had more deep root branching.
Soil water extraction was exmanied in relation to root system development and leaf osmotic adjustment in a pot experiment with eight rice genotypes(Oryza sativa L.).The time course of cumulative soil water extraction from layers between 5 and 45 cm estimated by time domain reflectometry(TDR)was similar to that of cumulative transpiration estimated from pot weighing for each genotype.The level of the TDR-estimated water extraction was 75% of the cumulative transpiration, and their coefficient of determination between the two was 96%.There was a 5-day difference(18 to 23 d)in transpiring 4 kg of water from the pots among genotypes, and the variation in daily transpiration rate was related to the extraction rate in the top-20 cm soil layers during the early half of the drought period, and to the extraction rate in the below-30 cm soil layers during the latter half of the drought period.The extraction rate in the subsoil was positively correlated with the average root length density at the corresponding depth during the latter half of the drought period, explaining 66% and 58% of the variation around the 30 cm and 40 cm depth, respectively.Mahsuri and IR58821 had higher water extraction rate from these subsoil layers than IR20 and IR62266 during the late drought period.Osmotic adjustment was higher in the genotypes that had a slower rate of transpiration and a lower pre-dawn leaf water potential at the end of the drought period.Among genotypes that extracted water rapidly, KDML105 had the highest osmotic adjustment.IR58821 and CT9993, known to have a deep and thick root system under well-watered condition, had the lowest levels of osmotic adjustment.This study demonstrated under the simulated rainfed lowland conditions genotypic variation in water extraction rate from the deep soil layers during the late drought period, which was primarily related to proliferation of roots in these layers.
Rice plants in the rainfed areas are mostly grown under fluctuating soil moisture.We examined responses in dry matter production, root development and water use to changing soil moisture in diverse rice cultivars.Rice plants were grown in polyvinyl chloride tubes under glasshouse conditions.Progressive drought right after planting greatly inhibited the shoot dry matter production, tiller development, nodal root development and water uptake in all cultivars tested.When the plants experienced soil submergence before being exposed to drought, all the cultivars exhibited higher dry matter production than well-watered counterparts.Cultivar differences were clearly noted in the growth responses to rewatering after these plants were droughted.With well-watered control as basis, IRAT 109 and KDML 105 plants increased efficiency in converting available dry matter to increase their total root length by means of enhanced lateral root development.In the latter, however, the dry weight of roots also increased and so did root water uptake.In Dular, droughted plants did not show a clear response in terms of root development and water uptake to rewatering while its shoot growth was much more severely inhibited than the other cultivars.These findings suggest that phenotypic plasticity in the root system structure exhibited by promoted lateral root development and new nodal root production play a key role in the growth of rice under changing moisture level in the soil.