Diurnal changes in carbon dioxide exchange rate (CER), stomatal conductance (gs), photosynthetic enzyme activities and metabolite levels relating to the C4 pathway and the Calvin cycle in sugarcane (Saccharum sp. cv. NiF4) leaves were characterized during a natural 24 h day-night cycle. The activities of phosphoenolpyruvate carboxylase (PEPcase), NADF-malic enzyme (NADP-ME), pyruvate, P1 dikinase (PPKD), ribulose-1, 5-bisphosphate carboxylase / oxygenase (Rubisco) and chloroplast fructose-1, 6-bisphosphatase (FBPase) all exhibited distinct diurnal changes. The levels of C4 metabolites, malate, phosphoenolpyruvate (PEP) and pyruvate, showed large diurnal fluctuations, but the oxaloacetate levels were extremely low and exhibited no significant changes in the day-night cycle. Diurnal changes in CER and gs paralleled the chages in radiation of sunlight. The results in this study suggest that at midday when CER is in steady-state and saturated by full sunlight, CER is limited by PPDK activity; under lower radiation of sunlight, I.e., before CER is saturated in the morning and during the period when CER is decreasing in the afternoon, CER is possibly limited by PEPcase activity or gs.
Diurnal changes in carbohydrate contents, assimilate export, enzyme activities and metabolite levels associated with sucrose and sarch synthesis in field-grown sugarcane (Saccharum sp. cv. NiF4) leaves were investigated during a natural 24 h day-night cycle. Eighty percent of the carbon fixed in sugarcane leaves at midday was exported immediately. Of the total carbon fixed during the day, 82% was exported in the daytime and 17% was accumulated as leaf starch which was exported at night. The activities of sucrose phosphate synthase (SPS), cytosolic fructose-1, 6-bisphosphatase (FBPase), UDP-glucose pyrophosphorylase (UDPG-PPase) and ADP-glucose pyrophosphorylase (ADPG-PPase), and the levels of triose phosphates (triose-P) and fructose-1, 6-bisphosphate (FBP) showed distinct diurnal fluctuations during the day-night cycle. The levels of hexose phosphates fluctuated at smaller magnitudes compared with those in triose-P and FBP. The diurnal chage in triose-P level was highly related to the changes in carbon exchange rate and sucrose content, while the sucrose content was closely related to the changes in activities of SPS, cytosolic FBPase and UDPG-PPase in leaves of sugarcane. The present results suggest that the availability of triose-P is a key factor in determining the rate of sucrose synthesis in sugarcane leaves.
We previously observed that gravistimulation changes the localization of acetylcholinesterase (AChE) and IAA-inositol synthase in maize shoots. In the present study, we analyzed the localization patterns of these enzymes in a lazy strain of rice, which lacks gravitropic responses. AChE was detected by color development due to enzymic reaction in the coleoptile of dark-grown rice plants under a light microscope. IAA-inositol synthase was detected immunochemically using an anti-IAA-inositol synthase polyclonal antibody. Gravistimulation was given by moving 5-d-old rice seedlings from a vertical to a horizontal position. AChE and IAA-inositol synthase in both normal and lazy rice strains were both distributed asymmetrically in the vascular bundles in the lower half of the horizontally oriented coleoptile at the 90th min. At the 4th h, they were distributed asymmetrically in normal rice, but symmetrically in the lazy rice. The immunoreaction of IAA-inositol synthase in the lazy rice was weak compared to that of the normal rice. Neostigmine bromide inhibited AChE activity and asymmetric distribution of IAA-inositol synthase in both normal and lazy rice strains. The results showed that AChE responded to gravistimulus, and consequently controlled the distibution of IAA-inositol synthase in both normal and lazy rice strains.
The characteristics of adenosinetriphosphatase (ATPase) and inorganic pyrophosphatase (PPase) in the tonoplasts isolated from leaf mesophyll homogenates of Ananas comosus (pineapple), a hexose-utilizing species with high PPi-PFK activities, and Kalanchoe pinnata and K. daigremontiane, starch-utilizing species with high ATP-PFK activities, were investigated. The ATPase and nitrate-sensitive ATPase (ΔNO3--ATPase) activities were higher than the PPase activity of pineapple, but the reverse was the case in the two Kalanchoe species. The optimum pH for ΔNO3--ATPase in pineappe, K. daigremontiana and K. pinnata was 7.0∼8.25, 7.5∼8.25 and 7.5∼8.25, respectively, and that for PPase was 6.5∼7.5 in all species. The Km of ΔNO3--ATPase for Na2-ATP for pineapple, K. daigremontiana and K. pinnata was 0.47, 0.48 and 0.43 mM, respectively, and Vmax was 52.6, 27.0 and 40.0 μmol Pi mg-1 protein h-1, respectively. The optimum MgSO4 and Na4PP1 concentrations for the PPase activity of the three CAM species were approximately 2 mM and 0.16 mM, respectively. The optimum temperature for the ΔNO3--ATPase in pineapple, K. daigremontiana and K. pinnata was 35∼43, 35∼43 and 37°C, respectively, and that for PPase was 46∼49°C. In addition, at a high temperature, the decrement of tonoplast ΔNO3--ATPase and PPase activities in pineapple was less than that in the two Kalanchoe species. Thus, pineapple obviously maintained high tonoplast ΔNO3--ATPase and PPase activities at high temperatures.
A significant difference in the seed germinability was observed between the two rice cultivars, 'Nipponbare' and 'Suweon 287', under anoxia (i.e., during germination in submerged soil at 18°C), althouth little difference was seen under aerobic (in air) or hypoxic (in water) conditions. The number of α-amylase isoforms synthesized in germinating seeds was inversely proportional to the O2 concentrations at the early gemination stage. The formation of isoform B was promoted by oxygen supply, while isoform H was undetectable if the seeds were unable to germinate. The activity of isoform H was highly correlated with the coleoptile length in the submerged soil at 18°C, indicating that isoform H is a critical factor for seed germination under anoxia. The expression of the rice α-amylase RAmy1A gene was repressed when the seeds germinated under hypoxia or anoxia. The interations between oxygen stress, gibberelin, and carbon metabolites on the expression of α-amylase in rice are discussed.
The temperature coefficient (Q10) of dark respiration in rice gradually decreased in continuous darkness, fluctuating as the circadian rhythmic variation in dark respiration. The solar radiation (MJ m-2) on the day of measurement and the nitrogen concentration in the culture solution hardly affected the Q10 value. However, the plants exposed to high-intensity light (260W m<-2>) for two weeks showed a higher Q10 of dark respiration than those exposed to low-intensity light (70W m-2). The seasonal variation in Q10 value was not observed. The average Q10 value during the growth stage measured at 15 to 25°C, 20 to 30°C, and 25 to 35°C was 2.14, 1.76, and 1.56, respectively. High crop yield in the regions where the day / night temperature difference is large may be partly explained by the high Q10 at low night temperature. Thus, the Q<10> may be an important physiological factor determining high crop yield.
Allelochemicals were isolated from the germinating maize (Zea mays L.) seeds in order to know the allelopathic constituents in the plants at the early developmental stage. Three allelochemicals were found in the acetone extract obtained from the mesocotyls and coleoptiles of the 5-day-old seedlings. By spectral analysis, they were identified as 5-chloro-6-methoxy-2-benzoxazolinone (Cl-MBOA) which is a naturally occurring new benzoxazolinone, 6-methoxy-2-benzoxazolinone (MBOA) and 2, 4-dihydroxy-1, 4-benzoxazin-3-one (DIBOA). At concentrations greater than 0.03mM for Cl-MBOA and DIBOA and 0.1 mM for MBOA, respectively, were inhibited the growth of the roots of cress (Lepidium sativum L.) seedlings. Activity of a new benzoxazolinone, Cl-MBOA, was greater than that of its analogue, MBOA. These results suggest that germinating maize seeds have at least three allelochemicals which may affect the growth or germination of other plant species.
To characterize the allelopathic activity of a new benzoxazolinone, 5-chloro-6-methoxy-2-benzoxazolinone (Cl-MBOA), seeds or seedling of monocotyledonous and dicotyledonous plants were exposed to Cl-MBOA for two or three days in a Petri dish, and effects of Cl-MBOA on the sees germination and the plant growth were determined and compared to those of its analogues, 6-methoxy-2-benzoxazolinone (MBOA) and benzoxazolinone (BOA). Cl-MBOA, MBOA and BOA dose-dependently inhibited the seed germination and growth of roots and shoots og cockscomb (Amaranthus caudatus L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), crabgrass (Digitaria sanguinalis L.), timothy (Phleum pratense L.) and ryegrass (Lolium multiflorum Lam.). A newbenzoxazolinone, Cl-MBOA was the most active in all bioassays followed in order by MBOA and BOA. The results that the attachment of Cl at C-5 position on MBOA leads to an increase in the activity.
The effect of porous hydrated calcium silicate (PS) application on the resistance of rice plants (Oryza sativa L.) to rice blast (Pyricularia olyzae) was evaluated. Experiments were conducted in Andisol at the experimental farm of Tohoku University from 1993 to 1995. The blast infection in the PS plot was much less than that in the control plot. On the other hand, slag (commercial slag silicate fertilizer) used in our experiment had no effect on blast infectioln. The number of silicified bulliform cells, the main invasion site for rice blast, was increased 320-980% by PS application, but only 80% by commercial slag. These results imply that PS application is effective in preventing fungal infection through silicification of bulliform cells. The number of silicified bulliform and trichome cells increased exponentially with increasing content of the silicon in the leaf blade, whereas the number of silicified short cells, which are smaller than bulliform cells and tichomes, had no relation to the silicon content in the rice leaf blade. We may conclude that the application of porous hydrated calcium silicate for rice plants is effective in incrasing rice blast resistance because PS incrase the number of silicified bulliform cells.
The growth of crown and lateral roots emerged from the excised phytomers of pearl millet (Pennisetum typhoideum Rich.), barnyard millet (Echinochloa frumentacea Link.) and maize (Zea mays L.) was studied under normal and low osmotic potential conditions. The plants were grown in two solutions with osmotic potentials of -0.02 and -0.54 MPa for 6 days. The ralative growth rate of the roots in total length (RGRL), was not affected by osmotic stress in pearl and barnyard millets, but that in stressed maize was reduced to 64% of the control. Similarly, the raltive growth rate of the roots in dry weight (RGRw), was not affected by osmotic stress in pearl and barnyard millets, but significantly reduced in maize. Osmotic stress increased the specific root length of the lateral roots in pearl and barnyard millets, but did not affect that of maize. The photosynthetic rate (Pr) in the two millets was decreased to ca. 60% of the control by the stress, and that in maize was reduced to 21%. Under the stress, Pr in the three species was limited mainly by low stomately conductance, but no clear relationship was found between Pr and osmotic adjustment of the leaf. The relative water content of the leaf was lower in maize than in the two millets. The resistance to water flow through the phytomer (R) was significantly increased by osmotic stress in maize, but not significantly in the two millets. The mean root length ((RL)^^-) was decreased by the stress in maize, but not in the two millets. The maintenance of RGRL in the two millets was associated with sustanied R, (RL)^^- and also with the maintenance of Pr and allocation of assimilates to roots.
The variation in the seed coat colour of adzuki beans among varieties, harvest years and growing locations, using a two-dimentsional colour mapping technique was investigated. It was found that the differences of the seed coat colour among varieties contributed to the variation of chroma (C*) values, while the differences of the seed coat colour among harvest years were associated with lightness (L*) values. The L* values for the seed coat colour increased when the temperature during the maturing period of adzuki beans was low, and decreased when the temperature was high. The difference in the seed coat colour among the samples from different growing locations was much larger in the L* values than the C* values for samples of the same variety. The seed coat colous of adzuki beans harvested in Hokkaido and China had significantly different C* values, and were easily discriminated by the colour mapping method. This study showed that the two-dimensional colour mapping was useful for evaluating the seed coat colour of adzuki beans, which varies among samples of different varieties, harvest years and growing locations.
For the detailed analysis of a canopy structure, e.g., solar radiation envrionment, it is necessary to obtain spatial data related to the leaf position in a canopy. We approximated a leaflet shape into an ellipsoid because, if it is possible, necessary data for determining the spatial position of each leaflet can be obtained by using the manipulator technique, which is used to measure a certain point in space accurately. The coincidence of a soybean leaflet area, which was measured using an area meter, and an ellipsoid area, which was obtained by approximating the maximum width and maximum length of a leaflet to the short axis and long axis of an ellipsoid, respectively, was ascertained in five cultivars of the soybean plant. Then, for a soybean population, the spatial factors of each leaflet were measured with a manipulator, i.e., the spatial position of each leaflet was determined at four points (in three-dimensional spaces) two for the maximum width and two for the maximum length of a leaflet. These data were used for the computer simulation of the canopy structure including the leaf area density in each layer with inclination angles of leaflets and the sunlit area.