Potato is known to produce stable tuber yield as compared with other field crops. For a better understanding this reason, we observed growth pattern and tuber yield in the two years (1982 and 1983) under different climatic conditions in the early half of the growing seasons. Five main cultivars, early to late, were grown and the observation was made at the same date in the both years. 1. Climatic conditions before early August were substantially contrast between the two years; they were dry with abundant radiation in 1982, while wet with short radiation and low temperature in 1983. After middle August, however, they became near to those of the average year in the both years (Fig. 1). 2. Growing period and tuber dry matter yield were not significantly different between the years, although tuber fresh yield was significantly larger in 1983 than in 1982 (Table 1.). Patterns of total and tuber dry matter accumulation were quite different between the years (Fig. 2). The rates of dry matter production in the early season were smaller in 1983. On July 15th, there were large differences in percentages of dry weight in each organ ; they were smaller in leaf and stem, and larger in tuber dry weight in 1982 than those in 1983 (Table 2). 3. Leaf area index (IJAI), crop growth rate (CGR), net assimilation rate (NAR) and tuber growth rate (TGR) showed quite different seasonal changes between the years (Fig. 3). LAI in 1982 and CGR, NAR and TGR in the early growing season of l983 were rather low values. Significant differences were also found in specific leaf area (SLA) between the years, the values in 1983 were higher than those in 1982 (Table 3). 4. During the experimental period, the solar radiation in 1983 amounted to only 75% of that in 1982. However, there was no signifierence between the years in intercepted photosynthetically active radiation by crops (ΔPAR), because of larger LAI in 1983. The efficiencies of dry matter accumulation per ΔPAR (E_PAR) in 1983 were slightly larger than those in 1982 (Table 4). Tuber dry yield was correlated positively with ΔPAR (r=0.760^*).

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It had been reported by the authors that leaf stomatal aperture in the rice plant under submerged condition decreased in fine midday with high evaporative demand and that close relation was found between diffusive conductance and photosynthetic rate in rice leaves. From these results it had been predicted that photosynthesis would reach the maximum early in the morning and then decrease gradually toward the afternoon with increase in light intensity and vapour pressure deficit. This study was conducted to ascertain this prediction by measuring the diurnal courses of photosynthetic rate (P), transpiration rate (T), P/T ratio (water use efficiency) and diffusive conductance in the single-leaf of the rice plant in paddy field under submerged condition on fine and cloudy days and to clarify the factors determining the diurnal courses of photosynthesis in a fine day using the simultaneous measurement system of photosynthesis and transpiration developed by K_OCH, S_CHULTZ and L_ANGE (Siemens Co. Ltd.). The photosynthetic rate on a fine day increased with increase in light intensity, reached the maximum early in the morning and then gradually decreased down to 75% of the maximum rate toward afternoon even under sufficient light intensity and this was accompanied by a decrease of diffusive conductance (Figs. 2A and 4). The photosynthetic rate in the morning was higher than that in the afternoon under the same light intensity more than 600 μE/m²/sec (Fig. 3A). Transpiration rate increased toward the midday with the increase of light intensity and vapor pressure deficit, and reached the maximum at about 13:00 PM. Water use efficiency was higher early in the morning and late in the evening and lower in the midday (Fig. 2A). The photosynthetic rate, transpiration rate and diffusive conductance on a cloudy day changed according to the change in light intensity (Figs. 2B and 3B). Therefore, light intensity was the dominant factor determining diurnal courses of photosynthetic rate and transpiration rate on a cloudy day. It was found that the time of the daily maximum of diffusive conductance was different from the time of that of photosynthetic rate in their diurnal changes, that is, diffusive conductance had already started to decrease even before the photosynthetic rate reached the maximum early in the morning. Under sufficient light intensity with artificially reflected sunlight by the mirror when diffusive conductance reached the maximum early in the morning, the time when both photosynthetic rate and diffusive conductance reached the maximum coincided. The maximum rater of the photosynthesis was higher than that of the day without the reflected light (Fig. 5). This result suggested that leaf photosynthetic capacity was not always fully realized in diurnal courses of photosynthesis on a fine day. To examine the factor reducing the photosynthetic rate on a fine day, diurnal courses of photosynthetic rate was measured under lower vapor pressure deficit by humidifying air in the chamber. The photosynthetic rate was much higher under lower vapor pressure deficit at least up to noon compared with that under the same vapor pressure deficit as outside (Fig. 6). This fact showed that water stress related to high vapor pressure deficit was the main factor for the decrease of photosynthesis in the midday even though the effects of photosynthate accumulation in the leaf blade and photoinhibition could not be neglected. From these results it was clarified that leaf photosynthetic rate in the rice plants under submerged condition decreased to some extent in the midday on fine days and they could not utilize high solar energy fully for dry matter production. [the rest omitted]

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Soybean plants grown in a green house were allowed to assimilate ¹³CO₂ for 10 hrs under steady-state conditions at 13 (Exp. 1), 26 (Exp. 2) and 40 (Exp. 3) days after anthesis. The partitioning of labelled carbon into individual plant parts and th significance of carbon assimilated at different growth stages for seed-filling were investigated by periodic sampling of labelled plants until harvesting time (50 days after anthesis). The plants were treated with (+N plants) or without (-N plants) supplement nitrogen 9 days after anthesis. Carbon assimilated 13 days after anthesis (Exp. 1) was most actively used for pod formation. Incorporation of labelled carbon into seeds was continued until harvesting time. Fifty per cent or more of labelled carbon found in the seeds at harvesing time was transported mainly from the leaves, pods and stems + petioles during the late reproductive stage from 26 to 50 days after anthesis (Fig. 2). Carbon assimilated 26 (Exp. 2) and 40 (Exp. 3) days after anthesis was utilized mainly as carbon sources for seed-filling. In these experiments, however, the most of labelled carbon found in the seeds at harvesting time was transported into the seeds directly from the leaves within 4 days after the ¹³CO₂ assimilation (Fig. 2). Contribution of assimilated carbon to seed production was highest in Exp. 2 accounting for 4.37% in -N plants and 4.21% in +N plants. They accounted respectively for 1.25 and 1.66% for Exp. 1, and 2.70 and 2.15% for Exp. 3 (Table. 1). Supplement application of nitrogen increased seed yield at about 7% (as carbon content). This increase was due mainly to the efficient contribution of carbon assimilated during the early stage of seed filling.

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Petioles of sugar beet plants, Beta vulgaris var. saccharifera Alef. serve not only as conductive tissues but also as intermediate storage pools^{11∼14, 18)}. Enzymatic conversion systems of sugars should be localized within the phloem and parenchyma cells of the petiole. In the previous papers, the histochemical detection of UDPG-pyrophosphorylase⁶⁾, phosphoglucomutase⁷⁾, phosphoglucose isomerase⁸⁾ and glucose-6-phosphatase⁹⁾ in the petiole tissues were reported. In this paper, The histochemical detection of phosphorylase in the petiole tissues is described. The histochemial method described by Y_IN and S_UN¹⁷⁾ was employed with slight modification. The reaction mixture was summarized in Table 1. Based on the formula (1), newly synthesized polysaccharides were detected with iodine reaction technique¹⁵⁾. (GlP)_n + (Starch)_m ⇆ (Starch)_m+n + nH₃PO₄ ···(1) Procedure : Non-fixed sections obtained from the fresh petioles of sugar beet cv. Mono-hikari were used. After infiltration in distilled water under reduced pressure¹⁰⁾, the sections were incubated in the test solution covered with toluene (Table 1)²⁾ and kept for 1-3 days at room temperature. Before observation under a light microscope, the sections stained with the diluted Gram's iodine solution were mounted on slides, covered with iodine glycerol (Gram's iodine solution : glycerol/1 : 10) and sealed with paraffin¹⁰⁾. Histochemical observations : The site of newly synthesized polysaccharides stained clear deep blue with iodine indicates the localization of phosphorylase. In the epidermal system of the abaxial side of young petioles, guard cells exclusively showed marked formation of polysaccharides in the section incubated in the test solution (Figs. la and lb). In the pith parenchyma cells, the newly synthesized polysaccharides were deposited as tiny granules independently of intracellular particles and nucleus (Fig. 2). In the xylem, phosphorylase activity was not detected in most of its parenchyma, but in the parenchyma cells surrounding the vessel, the vigorous activity was observed frequently (Fig. 3). In the phloem and cambium, phosphorylase activity was not almost observed, but is some cases, marked activity was detected in companion cells and phloem parenchyma (Fig. 4). In the bundle sheath, the newly synthesized polysaccharides appeared in two different states, one gathered around one pole of each cell forming a large ellipsoid, and the other scattered in the cytoplasm forming tiny granules (Fig. 5). From the observation mentioned above, phosphorylase activity occurred in the pith parenchyma cells of young petioles where polysaccharides were not present but large amounts of glucose were stored¹⁰⁾ physiologically. This discrepancy remains to be resolved.

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The present study was aimed to obtain basic knowledge to monitor remotely the physiological-ecological functions and status of crop community. In this paper the features of canopy temperature in corn crop field and its relations with climatic factors measured simultaneously by a multi-sensing system were investigated. The results obtained are summarized as follows: 1. The coefficients of variance of canopy temperature were as small as around 1% for uniform communities (Table 1). 2. The mean temperature of leaves measured by thermocouples differed between adaxial and abaxial surfaces by 0∼0.3°C under cloudy conditions and 0.1∼1.2°C under sunny conditions. The temperature of adaxial surface was always higher than abaxial one. The coefficients on variance of leaf temperature within upper layer of crop community were 1.3∼2.5% under cloudy conditions and 2.5∼6.5% under sunny conditions. 3. The canopy temperature measured by an infrared thermometer was relatively lower than the mean temperature of upper layer of the crop community measured by thermocouples. Because of high correlation between them, the latter could be successfully estimated by the former (Fig. 2, Eq. 1). 4. The canopy temperature varied in the same pattern as that of ambient air temperature keeping lower by 2∼5°C under steady conditions of the other factors. A very high correlation was observed (r = 0.989) between the simultaneous values of them. The time constant of the response of canopy temperature was estimated to be very short and the temperature seemed to respond almost instaneously (Fig. 3). 5. A linear relationship (r = 0.8) was obtained between the air-canopy temperature difference and the vapor pressure deficit of air, and the canopy temperature decreased in proportion to the increment of the vapor pressure deficit (Fig. 4). The depression of the canopy temperature is caused by the cooling effect of the transpiration. It is considered that this relationship was brought about under such conditions that crop water deficit was so small as to give no significant influence on stomatal resistance and the potential transpiration. The above result suggests that the air-canopy temperature difference may be a good index of crop water stress in arid zones where the deficits of air vapor pressure and soil water, both, are large. 6. According to a multiple regression analysis, variance of canopy temperature was estimated almost fully by the three climatic factors ; air temperature, vapor pressure deficit and PAR (r = 0.91∼0.96). Canopy temperature had close relation with these three variables as indicated by the partial correlation coefficients : 0.87 for air temperature, -0.74 for VPD and 0.82 for PAR. And the mean ratio of the contribution of them were estimated as 0.86 for air temperature, -0.62 for VPD and 0.60 for PAR. These relationships were obtained within a wide range of those three factors (Table 2, Fig. 5).

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It was clarified in the previous papers that leaf water potential, stomatal aperture and photosynthetic rate in rice plants decreased with increase in solar radiation and vapor pressure deficit even though rice plants grew under the condition where sufficient water was supplied to roots in submerged paddy field, and that the decrease in leaf water potential, stomatal aperture and photosynthetic rate were more remarkable in rice plants with low root activity or with poor root system. The present study was conducted to investigate the relationship between water uptake and transpiration rates and the effects of this relation on leaf water potential and stomatal aperture through their diurnal changes, and to discuss the characteristics for maintaining water balance in rice plants. Transpiration rate was higher than water uptake rate in the morning when transpiration was increasing rapidly with rapid increase in solar radiation and vapor pressure deficit. Both rates were practically the same in the midday and then transpiration rate was lower than water uptake rate in the evening when transpiration rate was decreasing rapidly with rapid decrease in solar radiation and vapor pressure deficit (Fig. 2 A). The difference between water uptake and transpiration rates was very small even when transpiration rate was changing rapidly (Fig. 2 B). In case of reduced water uptake due to low water potential of culture solution or NaN₃ treatment to roots, transpiration rate decreased remarkably due to increase of stomatal closure in the daytime (Figs. 3 and 4). Therefore, the difference between water uptake and transpiration rates did not increase so much and leaf water potential decreased a very little even in the midday with high transpiration demand compared with decrease of water uptake rate and stomatal aperture (Figs. 3 and 4). These results suggested that water balance in rice plants was maintained by the process as follows: There is too much transpiration in the daytime with high solar radiation and valor pressure deficit, so water uptake could not overtake the transpiration, and leaf water potential decreased to a certain extent. As stomata in rice plants were very sensitive to change of leaf water potential compared with those of other plants, stomata closed very rapidly with response to the decrease of water potential, so that transpiration rate decreased to almost the same as water uptake. Therefore, the difference between water uptake and transpiration rates was very small, and decrease of leaf water potential was prevented. Futhermore, in case of rice plants with reduced water uptake due to low water potential of culture solution or NaN₃ treatment to roots, all were the same as in the process of maintaining water balance. From these results and the high correlation between stomatal aperture and photosynthetic rate, it was considered that water uptake ability directly affected photosynthetic rate under sufficient solar radiation in rice plants with stomata responding very sensitively to change of leaf water potential. Futhermore, it was suggested that rapid wilting often observed in rice, soybean and cucumber under very large vapor pressure deficit or on water saturated soil in rainy season, baiu, could arise from both decrease of water uptake ablility and loss of sensitivity of stomata to decrease of leaf water potential.

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[in Japanese]

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The following system was devised to meet the requirement to measure carbon exchange rate (CER) and the related factors of single rice leaves in situ efficiently. 1. A small leaf chamber (100 × 23 × 8 mm) which is connected with two differential type IRGAs (one is for CO₂ and the other for H₂O), is attached to a central part of a leaf blade and CER and transpiration rate are measured (Fig. 2). 2. Leaf temperature is measured with two thermocouples simultaneously with CER and transpiration rate. Based on the transpiration rate, absolute humidity of the surrounding air of the leaf and leaf temperature, "stomatal conductance" (g_s, CO₂ diffusion conductance for the path from the surrounding air to the intercellular space of leaf) is evaluated. 3. The time required to measure CER and g_s of a single leaf is about 1.5 min. The g_s value evaluated in such a way is considered to be that corresponding to stomatal aperture just before attaching the leaf chamber. It was proved that repeated attachment of the chamber to leaves has little aftereffect on g_s and CER of the same leaves. 4. Light intensity, temperature and CO₂ concentration inside the leaf chamber are similar to those outside the chamber. 5. From the above mentioned, this system is considered to be suitable for measuring CER of many single leaves in situ to examine its dependence on related factors, especially on g_s under field conditions.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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