A series of experiments were carried out to investigate the appropriate plant density to get average yield of more than 300 kg/10 a continuously and to find the yield components that contribute to higher yield, i.e. the components that tend to prevent yield reduction due to dense planting. The experiments were conducted for three years at the experimental field of Faculty of Agriculture, Tohoku University, where five determinate cultivars (Fig. 1) were grown by single planting per hill with plant density ranged from 3 to 100 hills per m². The results are summarized as follows : 1. In general, the yield tended to increase with increase of plant density. More than 25 plants per m² and average maximum 6.0 LAI (Leaf Area Index) were necessary to harvest more than 300 kg/10 a continuously. To obtain high and stable yield under more than 25 plants per m², special attentions such as progresses of new cultural techniques to lodging or new cultivars with lodging resistance should be paid. 2. Relative values of most growth parameters per m² at the density of 100 plants/m², ranged from 2.1 to 3, 4 times larger, comparing with those at the density of 6 plants/m². Branch and node number per m², on the other hand, were 5.5 and 6.1 times larger respectively. Therefore the yield increase by denser planting was chiefly suggested to due to the increase of the two yield components.

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A new method determining base temperature (BT) was investigated, and temperature reaction of rice plant (O. sativa L.) in the vegetative phase was analized on the concept of the effective heat unit summation (EHUS). Periods or leaf emergence were observed on some rice varieties grown under three controlled temperatures. Relation between periods of a particular leaf emergence and temperature summations for the periods was expressed by a linear equation. In a temperature range in which the above relation is effective, constancy both of EHUS and BT was ascertained. In a linear regression equation which expresses a relationship between periods of development and temperature summations for the periods, BT and EHUS could be shown as the regression coefficient and the constant term, respectively. Theoretical BT and EHUS, therefore, can be determined quite easily in this manner if at least two temperature regimes are adopted in an experiment. This method was applied to the development of entire leaves on the stem. Theoretical BT for the lower leaves was 6-7°C, but it increased toward the upper leaves reaching its maximum of 12°C for the uppermost leaf. Rice plants in later stage of vegetative growth therefore seemed to require higher temperatures to develop themselves. BT's of japonica upland rice were obviously lower than those of japonica lowland rice, suggesting their advantageous growth in cool conditions. Some experimental formulas were presented for the estimation of specific periods such as from the infant stage of seedling to heading and from the stage of reduction division in pollen mother cell to heading, using EHUS and BT as fixed values, and assumed mean air temperature and number of leaves on the main stem as variables.

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Rice Plants were grown under different controlled temperatures in order to analize the effective heat unit summation (EHUS) and base temperature (BT) for the specific stages of reproductive phase in accordance with the method described in the previous report. BT for the emergence of panicle and flowering of cultivar Sasanishiki was 12.l°C and 11.5°C, respectively. In the ripening period, BT showed its highest value of 9.4 to 10.1°C at the ealiest stage, declining to 4 to 5°C toward the latest stage of ripening. BT of an indica rice (Ko-Sen) was 0.6-2.7°C higher than a japonica rice (Sasanishiki) throughout the ripening period, although EHUS was on the contrary obviously less than that of japonica one. It was thought therefore that indica rice requries a higher range of temperature and a lesser amount of effective heat for its kernel development as compared with japonica one. BT and EHUS for the entire period of kernel development of a japonica rice was 7.5°C and 690°C·days, respectively. Reasonability of these values was supported by a result calculated from the experimental report on rice crop situation in Japan 1973-1977. BT relating to the development of rice plant changed with the developmental stage showing its peak of 12 to 13°C at the stage from flag leaf emergence to heading.

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Methane fermentation of napiergrass (Pennisetum purpurum Schumach, cv. Merkeron) in the first year of growth at several places varying in the climate (Tokyo, Nagoya, Fukuoka, Miyazaki, Naha and Iriomote Island) was investigated. The gas evolution rate examined using fresh material of the plant at 37°C for 7 days, was 542 L per kg based on dry matter for leaf blade, 352 L for stem with leaf sheath and 342 L for dead parts, on an average for those harvested in above six areas. The gas volume evolved from the stem decreased as the growing days and the dry matter yield increased. The relation between dry matter yield and gas volume evolved from the whole shoot was similar to that observed for stem. The methane content of gas produced from any materials examined was estimated to be about 60% in volume. Thus the average annual yield of methane, if the whole shoot is fermented, will be be about 7, 000 m³ ha^-1 in any place of the areas tested. This is greater than the values obtained for several other C₄-and C₃-forage crops and grasses, indicating that napiergrass is a useful plant for production of not only forage but also methane as a fuel.

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Relationship between tiller top growth at the initial stage of internode elongation and the heading ratio was investigated using two wheat cultivars of West Japan, Shinchunaga and Omasekomugi, and one spring cultivar of Hokkaido, Norin 29. The heading ratio of tillers was lower in Shinchunaga than in Omasekomugi. The top dry weight increment (ΔD) for one week and total nitrogen content (N content) one week after transfer to greenhouse-longday, condition were larger in vigorous tillers of Shinchunaga than in those of Omasekomugi, and larger in weak tillers of Omasekomugi than in those of Shinchunaga. The thresholds of ΔD and N content of the tillers where the heading ratio dropped below 100% were higher in Shinchunaga than in Omasekomugi. Two weeks after transfer to greenhouse-longday condition, when tillers clearly belonged to one of the two types, namely, heading and non-heading, the tillers of heading type had larger dry weight, higher N content and higher nitrogen absorption ability than the other. In Norin 29, the ΔD of the vigorous tillers for one week after the daylength treatment started was larger in the longday plot and that of the weak tillers was larger in the shortday plof N content was higher in the heading tillers than in the non-heading tillers. There was no difference in N content in the heading tillers between those of the longday plot and the shortday plot. Until the tillers started to grow independently with their elongated roots, their growth and nitrogen absorption ability proportionately declined to their heading ratio.

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Rooting patterns of wheat were investigated using one old and one new cultivars of West Japan, Shinchunaga and Omasekomugi. The wheat plants were grown in small containers and distribution of roots was compared. The numbers of primary roots of main shoot and tillers did not differ between the two cultivars. However, the number of roots at each depth in the soil differed between the two cultivars; the number was larger in Omasekomugi than in Shinchunaga except at shallow depth. This difference became larger with increasing depth. Almost the same result as in the number of roots was obtained also in the fresh weight of roots. The average root lengths of main shoot and tillers were longer in Omasekomugi than in Shinchunaga. This difference may cause the difference in the distribution with depth of roots in the soil.

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Experiments were made in 1981, 1982 and 1984 to study the influence of planting date and planting density on vegetative growth and yield of a high yielding soybean cultivar 'Tamahomare' in Sanyo District, the westernmost part of the main inland. Maximum and ripened pod number per unit area and yield correlated with maximum LAI, stem dry weight per unit area and total node number per unit area, respectively. Yield increased linearly with maximum LAI increases until yield got to 596 gm^-2 at 9.1 of maximum LAI. Increased vegetative growth brought about greater pod number resulting in higher yield. Grain/stem ratio was negatively correlative with vegetative growth size. Favorable weather condition of this district with high temperature and much sunshine, and well drained, fertile and less water stressing paddy field conditions, seem to have supported the growth of soybean to get high yield. Both early planting and high planting density increased vegetative growth, but yield was increased only by the former treatment. Elongated seed fillig period by early planting seems also to have contributed to the yield increase.

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The effect of coated urea topdressing at the neck node initiation stage on rice growth and yield was evaluated in the field experiments in l985, l986 and l987. The following results were obtained: 1) Nitrogen from topdressed fertilizer (LP70) was progressively absorbed by the plants up to maturity. The percentage recoveries by plants were 65∼70% (equivalent to around 80% of released N from fertilizer). On the other hand, the duration of nitrogen absorption from ammonium sulfate (AS) topdressed at the panicle initiation stage was less than 14 days and percentage recoveries by plants werc 40-60%. As a result of N absorption pattern, the yield and sink size obtained in LP70 plots were higher. 2) There was no difference in the length of uppermost 4 leaf blades and clum between LP70 plots and AS plots in spite of the big difference in N absorption pattern.

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In order to make a mathematical model for soybean root system, the length, weight and diameter of the primary and lateral roots in soybean plants grown in pots were investigated and their mutual relationships were examined. (1) The elongation and branching of roots were vigorous from early to flowering stage, and the total length of roots per plant reached a maximum of about 3, 500 m at the flowering stage. The diameter of the primary root base also with growth time and reached approximately 20 mm at the flowering stage. (2) The relationship between the diameter of primary root base and the total root weight in a plant was represented by a cubic equation with a statistically high regression coefficient. Close mutual-relationships were also found among the other root characters. (3) When the roots in a plant were classified by 1 mm range of root diameter, the relationship between the total root length within each class and the diameter of primary root base was represented by the equation: F=4.78·D^3.45·X^4.8. Where F is the total length within a certain root diameter class, X is the class value of root diametcr and D is the diameter of the primary root base. The equation is applicable to the soybean root system at any growth stage. The relationship between the root length and the root diameter in a plant at various growth stages may be obtained by substituting the diameter of the primary root base into the equation.

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Using an unbonded strain gauge transducer (UT:1 kg type) and a null balancing recorder, the vertical elongation force (Ef) or lifting force of 3-cm tall seedlings in eight epigeal leguminous species grown under darkness at 25°C was measured. Using the same seedlings, hypocotyl diameter (stem thickness) and endogenous ethylene evolution were measured simultaneously. After setting the tip of a seedling against the force receptor, the Ef exerted by the seedling increased with time and reached a maximum after 15-50 hours. The pattern of Ef development differed significantly among the species. The maximum Ef was the largest (about 500 g) in peanut (Arachis hypogaea L.) and the smallest (about 30 g) in moth bean (Vigna aconitifolius Marechal). The mean value for the maximum Ef of a species was positively correlated with seed size (r=0.9636^**) and stem thickness at the center portion of the seedlings (r=0.9636^**), while each of the maximum Ef per unit mass of seed and per unit stem thickness differed among the species. In all species examined, hypocotyl elongation was inhibited and stem thickness found to be large in the seedlings used for the Ef test. Moreover, in a seedling whose hypocotyl elongation was inhibited, ethylene was increased largely compared with those not inhibited. The ethylene production from a seedling was higher in soybean (Glycine max Merr. cv. Akisengoku), kidney bean (Phaseolus vulgaris L.), cowpea (Vigna unguiculata Walp.) and hyacinth bean (Lablab purpureus Sweet) than in peanut, moth bean, mung bean (Vigna radiata R. Wilczek), black gram (Vigna mungo Hepper) and soybean (cv. Asoaogari). It was the lowest in peanut among the species. Thus, it is suggested that, in the seedlings of plant species which produce high ethylene, their hypocotyls become thicker and the Ef exerted by seedlings after bending of hypocotyl become larger. Further, the Ef of a seedling appears to be related intimately with anatomic structure and resistance of bending of hypocotyl.

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Old (resistered before 1945) and new (resistered after 1950) rice varieties were compared about single-leaf photosynthesis (CER) and stomatal conductance (g_s). (1) At the heading stage, no or little difference in CER was observed between the old and new variety groups. However, at the ripening stage, CER was clearly higher in new verieties. The new/old ratio in CER was 124.4% in the average for three years. (2) g_s was higher in the new variety groups than that in the old one at the ripening stage. (3) In most cases when CER and g_s were measured, correlation coefficients more than +0.8 were obtained between the two, suggesting the varietal difference in CER was mainly caused by that in g_s. However, the ΔCER/Δg_s ratio in the ambient air humidifying treatment (ΔCER and Δg_s are incremcnts in CER and g_s respectively caused by the treatment) was smaller than the regression coefficient for CER vs g_s in the varietal difference and the former was equivalent to ca. 70% of the latter in the average for 12 days. The findings suggested ca. 30% of the apparent effect of g_s on CER was attributable to the effect of the mesophyll photosynthetic activity which changed in parallel with g_s.

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Using many rice varieties differing in the year of registration, the physiological basis for higher stomatal conductance in new varieties at the ripening stage was examined. (1) At the heading stage, no varietal difference was observed in the rate of bleeding from the section of stem after sunset; whereas at the milk ripe stage, a marked varietal difference was found in the rate. Namely, the newer the variety was, the higher was the rate. (2) At the milk ripe stage, a positive and fairly close correlation existed between the bleeding rate and stomatal conductance (g_s) in most cases. This fact suggests that, in new varieties, the higher ability to supply water actively to leaves, based on the higher physiological activity of roots, resulted in the larger g_s. (3) No difference was found in aerenchyma resistance (the resistance to air flow through aerenchyma extending from leaves to roots in the plant body) before heading. After heading, however, the trend that the newer varieties had the lower aerenchyma resistance appeared and became more and more marked with time. From this, it was suggested that, in new varieties, the better development of the aerenchyma enabled the plant to supply root tissues with oxygen from the aerial part better, which maintained higher physiological activity of roots at the ripening stage.

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Using many rice varieties differing in the year of registration, the bases of the higher single-leaf photosynthesis (CER) in new varieties than that in old ones at the ripening stage were investigated in terms of nitrogen content and the nitrogen-CER relationship in leaves. In new varieties, the total nitrogen content of leaves was higher than that in old varieties at the ripening stage. Further, it was found that there was a fairly close positive correlation between total nitrogen content of leaves and CER. From this, it was concluded that one of the bases of the higher CER in new varieties was the higher leaf nitrogen. However, CER of new varieties was higher than that of old varieties even if they were compared under the same level of leaf nitrogen content and this was thought to be another basis for higher CER in new varieties. This kind of superiority of new varieties was found to be attributable to their g_s which was larger than that of old varieties even under the same level of leaf nitrogen.

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In order to clarify eco-physiological characteristics of high yielding rice varieties, two early varieties; Akihikari (Japanese cultivar) and Nanjing 11 (Chinese cultivar, Indica), and three medium varieties; Nippon-bare, Musasikogane (Japanese cultivars) and Milyang 23 (Korean cultivar, Japonica/Indica hybrid) were cultivated in 1985 and 1986. Both yield and dry matter production were higher in Nanjing 11 than those in Akihikari, and in Milyang 23 and Musasikogane than those in Nipponbare. These high dry matter production were due to high crop growth rates before heading time in the early varieties, and after heading time in the medium varieties. At the panicle development stage, every variety had erect foliage with small light extinction coefficients. At the early ripening stage, however, the coefficients increased remarkably in Akihikari and Nipponbare as compared with those in the other varieties owing to the increase of horizontal leaves and mutural shading effect of ears on the canopy. Increase in net assimilation rate by the thinning treatment (the planting density was reduced to half of control) at the early ripening stage was remarkably higher in Akihikari than that in Nanjing 11, and that in Nipponbare was higher than that in Milyang 23 and Musasikogane. These results indicate that Akihikari and Nipponbare canopies were changed into an unfavorable light intercepting structure after heading time. It became clear from these results that higher dry matter production of Nanjing 11 than that of Akihikari was mainly due to larger leaf area index before heading time, and that higher dry matter production of Milyang 23 and Musasikogane than that of Nipponbare was due to the differences in light intercepting characteristics of the canopy after heading time.

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This study was conducted to clarify the effects of leaf blade or top (containing leaf blade and leaf sheath) pruning in 6 leaf aged rice seedlings on transplanting injury, rooting and early growth after transplanting in comparison with the effects of root pruning. Pruning of whole leaf blade or top less than 50% in dry weight in seedling hardly affected transplanting injury as expressed by leaf emergence rate just after transplanting. However, in leaf-pruned seedlings, rooting or early growth after transplanting was inversely proportional to the extent of leaf pruning, because of the delayed development and growth of new roots and tillers caused by the lesser amount of carbohydrate in the top part of seedlings and the increase of its distribution to leaf blade. These results was striking contrast to those of root-pruned seedlings. Consequently, there was no parallel relationship between transplanting injury and rooting or early growth after transplanting among the seedlings damaged at different parts. Seedlings with completely pruned leaf blade and root exhibited lesser transplanting injury as compared with the seedlings with pruned roots, and took roots faster than leaf blade-pruned seedlings just after transplanting.

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This study was conducted to clarify photosynthesis and transpiration characteristics of the panicle in comparison with the flag leaf in the rice plant, cultivar Nipponbare. Transpiraion rate in the panicle was the maximum at heading time, decreasing with aging in the panicle. There was a slight difference in diffusive conductance between the light and dark. Transpiraion rate in the panicle increased linearly as vapor pressure difference increased, and there was no difference in the slopes of the straight lines between the light and dark. Diffusive conductance of the flag leaf in the dark was one tenth of that in the light. In the dark it was half of that in the panicle. Apparent photosynthesis and dark respiration rates of the panicle attained the maximum in five and ten to fifteen days after the heading time, respectively. The maximum rate of gross photosynthesis of N the panicle was about 6 mg CO₂ dm^-2hr^-1, which was one sixth of gross photosynthetic rate in the flag leaf. Furthermore, dark respiration rate was equal to the apparent photosynthetic rate in the panicle and it was higher than dark respiration rate in the flag leaf. Diffusive conductance and photosynthetic rate of the flag leaf decreased with increasing in vapor pressure difference. Since diffusive conductance and photosynthetic rate in the panicle did not change with increasing vapor pressure difference, it was thought that they were not affected by vapor pressure difference. It was considered from our experimental results and the other previous results in the panicle morphology that gas exchange of transpiration and photosynthesis in the panicle hardly took place through the stomata. The panicle was divided into the spikelets and the rachis-branches (including rachis), and their transpiration and photosynthetic rates in the light and dark were measured. The results showed that the characteristics of transpiration and photosynthesis in the panicle were mainly contributed by those of the spikelets.

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Changes in culm contents, cell wall constituents, net cellular matter and water soluble sugar content (WSC) were determined from anthesis to maturity in three parts of the main culm, peduncle, second and lower internodes, for three spring wheat varieties, tall Haruhikari, semi-dwarf Haruyutaka and tall late Selpek. After anthesis cell wall constituent and net cellular matter increased in peduncle and the second internode, associated with the elongation, but a little in the lower internodes, of which elongation has almost ceased at anthesis (Fig. 2). Contrary to this, WSC as a storage material increased in each part until milk ripening, decreasing to almost zero at maturity, presumably due to translocation to the ear. WSC has been rapidly accumulated before anthesis in the lower internode, but started to store at about anthesis in peduncle and the second internode, and attained the maximum at about a week before milk ripening in the lower internodes, just at the milk ripe stage in the second internode and several days after milk ripening in peduncle. For all varieties the percent WSC was higher in the second internode and the amount of WSC in the lower internodes was more than in peduncle and the second internode at milk ripe stage, suggesting that the second and lower internodes were main storage organs. In addition the percent and amount of WSC were larger for semi-dwarf Haruyutaka than for tall Haruhikari and Selpek.

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The authors examined the difference in the characteristics of rice seedlings (Oryza sativa L.) grown under different growth conditions, especially the relation between rooting activity and amylase activity. The characteristics ot rice seedlings on 14 days after seeding were judged by the rooting activity test. In the low density and high temperature plot the qualities of seedlings were good: in the upland, 1/2N, 3/2N and low temperature plots qualities were the same as in the control plot, but in the high density, lowland and shaded plots they were poorer than those in the control plot. While on 28 days after seeding, in the low density, upland and low temperature plots the qualities were better than those in the control plot: in the high density, lowland and high temperature plots the qualities were not so good, and in the shaded plot they were even poorer. On 14 days after seeding, rooting activity showed a significant correlation with leaf age, plant length, leaf sheath diameter, leaf dry weight root dry weight and amylase activity. While on 28 days after seeding, rooting activity showed a highly significant correlation with nitrogen content, starch content and amylase activity. Seedlings with higher starch accumulation, that is higher amylase activity, showed better rooting activity, and good quality.

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Japonica rice plants (cultivar, Koshihikari) were treated at high and low temperatures in the early and late ripening stages. Starches prepared from the outer layer and inner portions of these rice grains were tested for their physicochemical properties. Generally, starch in the inner portion of rice grains was affected by temperature in the early ripening stage; whereas in the outer layer it was more affected in the late ripening stage. Amylose content was determined by iodine colorimetry and iodine binding capacity method. The amylose content of the outer layer and inner portion starches increased at low temperatures during grain development. Miniviscographic parameters of both starches were affected mainly by temperature in the early ripening stage and modified by that in the late ripening stage. The differential scanning calorimetric (DSC) transition temperature and gelatinization heat increased under high temperatures for the inner portion starch in the early ripening stage and for the outer layer starch in the late ripening stage. While the lipid content of inner portion starch increased at high temperatures in the early ripening stage, the lipid content of the outer layer starch decreased under high temperature in the late ripening stage. The fatty acid composition of lipids of the outer layer starch responded to temperature in a manner different from that of the inner portion starch.

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The dedifferentiation of chloroplasts in synthetic Brassica napus mesophyll protoplasts in culture was examined. Protoplasts cultured in MS medium containing 0.5 mg/l kinetin and 3 mg/l 2, 4-D were divided frequently and maintained cell viability. This medium was used as a medium of the dedifferentiated system. In the above medium without kinetin, protoplasts were seldom divided and became senile. This medium was used as a medium of the senescent system. Physiological changes of protoplasts were compared between the both systems during culture. Chlorophyll content decreased in both systems. Soluble proteins in whole cells and the chloroplast fraction decreased in the senescent system. In the dedifferentiated system, soluble proteins of whole cells, however, increased and were accompanied by cell division and on the contrary, those of chloroplasts decreased. RNase activity increased in the dedifferentiated system. It increased at first, decreasing in the senescent system afterward. RNase activity in whole cells changed in parallel with that of chloroplasts. However, chloroplast fraction/whole cells in RNase activity gradually became low. SDS-PAGE showed that each chloroplast protein was degraded in both systerns. After 7 days of culture, most of the chloroplast proteins decreased in the senescent system, whereas RuBPCase and CF₁ were clearly identified in the dedifferentiated system. Protease activity tended to increase in both systems, and it was stronger in the chloroplast-free fraction than in the chloroplast fraction.

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A field experiment was conducted to investigate the effect of N application on cell membrane stability measured by the polyethylene glycol test and leaf water relations in maize. With increasing N levels leaf water potential was decreased while total plant weight and cell membrane stability were increased. Osmotic potential decreased with increasing N levels in order to maintain turgor at lower water potential conditions. Sugar and K were identified as the major osmotic contributors in maize. Osmotic adjustment was evident while concentrations of sugar, K and amino acids in cell sap increased with increasing N application.

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Several changes were shown in rice callus cultures with abscisic acid (ABA) treatment. First, callus growth was inhibited, especially at a high concentration (2×10^-4 M) of ABA. Secondly, white, dry and compact regions were formed in the callus at higher frequency. Thirdly, two kinds of callus structures were observed at ABA-treated culture stage with a scanning electron microscope (SEM). White regions and yellow regions at macroscopical level corresponded to relatively smooth, undulated structures and rough-surfaced structures, respectively at SEM level. Moreover, the dark condition in which ABA was treated enhanced the frequency of appearance of white regions in the callus and advanced the developmental stage leading to plant regeneration. When the calli having white regions were predominantly transferred on the regeneration medium, they showed the highest potential to regenerate plantlets. Nevertheless, the ability of such regions to regenerate plantlets was not affected by illumination in the ABA-treated culture at all. Several morphological types in plant regeneration processes could be observed after 7 days of the regeneration culture. Some of them showed ordinary organogenesis and others malformed processes.

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In order to determine the tiller-to-tiller translocation of nitrogen in rice plants, changes in the percentage content and percentage distribution of absorbed ¹⁵ in each tiller and the main stem were investigated by the ¹⁵ treatment of the roots of fourth tiller (the fourth tiller in primary tiller was expressed as T4) that emerged from the fourth node of the main stem. The quantity of translocated ¹⁵ in tillers after absorption by the roots of T4 was arranged in genealogical order by the site of its distribution as follows: daughter tillers of T4 (T41, T44; secondary tillers) > T4 itself > > mother stem (main stem) > younger sister tillers (T5, T7; primary tillers) that emerged from the upper nodes of the T4 emerging node > elder daughter tillers that emerged from elder sister tiller (niece tiller; T31, T34) > elder sister tiller (T3) that emerged from the lower node of the T4 emerging node. It was made clear that the nitrogen-distribution from T4 to T3 that emerged from lower node of the T4 emerging node and to secondary tillers on T3 was extremely low. It was therefore, presumed that a remarkably small quantity of nitrogen was translocated from tillers that emerged from the upper nodes to tillers that emerged from the lower nodes of the stem in rice plant.

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The surface feature on the initiation and development of callus, derived from coffee (Coffea arabica L. var. typica) leaf explants, was examined by scanning electron microscope (SENI). After about two weeks of culture, callus emerged mainly from cut leaf edges. After about 45 days, these callus masses turned into soft and translucent tissues which were like an assembly of numerous threads at a stereomicroscopical view. Ultrastructural observations by SENI revealed that callus proliferation mainly occurred from mesophyll cells near vascular bundles of cut leaf explants. A membranous layer covering the callus surface was broken by some ruptures at several places, and superficial cells appeared underneath the fragmented membrane. Furthermore, interesting morphology of the callus surface was revealed: spherical cells, elongated cells, and cylindrically elongated or curled cells were present.

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The mechanism of different water relations in each part of a wheat plant was examined to elucidate the physiological basis for the difference among plant parts in photosynthetic drought resistance. As the soil water deficit developed, the upper leaf blades maintained the higher turgor potential (TP) and relative water content (RWC) compared with the lower ones. The stem and the leaf sheath also maintained the similar level of Tp and RWC to the flag leaf. The ear, however, showed the highest RWC with a low TP. The mechanism for osmotic/adjustment was analyzed by separating the osmotic potential (OP) decrease into two components, the concentration effect and the solute accumulation effect. It was found that the solute accumulation effect was the highest in the ear, followed by the stem, the leaf sheath, the upper leaf blades and the lower ones in the last, and that the concentration effect showed the reverse order of the plant parts as above mentioned. In order to know the reason for this peculiar watch relations in the ear, the water relations were investigated in the glumes and the grain separately. It was found that the glumes showed a similar water relations to the flag leaf, whereas the grain maintained a extremely higher water content with much lower TP than any other plant part, even under severe soil water deficit condition. The strong maintaining ability of RWC seemed to be the main cause of the higher drought resistance in the ear.

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