Kikuo Wasano

Infection of Rice Plants with the Sheath Blight Fungus Causes an Activation of Pentose Phosphate and Glycolytic Pathways

The response of key regulatory enzymes of the pentose phosphate and glycolytic pathways in disease development was assessed in genetically-related rice plants resistant and susceptible to the sheath blight fungus, Rhizoctonia solani. The plants were grown and maintained under greenhouse conditions and inoculated at 50% flowering. Uninoculated healthy plants served as controls. The activities of pentose phosphate pathway enzymes (glucose-6 phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) increased more than two-fold in both the resistant and susceptible plants. Activities of ATP- and pyrophosphate-dependent phosphofructokinase and phosphoenolpyruvate phosphatase increased in infected plants while activity of phosphoenolpyruvate carboxylase in infected plants was lower than in the healthy plants. Furthermore, for enzymes with increased activity, the levels were higher in the resistant line than in the susceptible line. The enhancement of the enzyme activities correlated well with the post infection period. These data suggest that altered carbohydrate metabolism in sheath blight infections may play an important role in modulating the rice plants response to infection. The isolation of an infection-induced gene encoding a basic enzyme of pentose phosphate and glycolytic pathways could be used to develop plants with more resistance towards sheath blight disease.

Diurnal changes in photosynthesis in sugarcane leaves: II. Enzyme activities and metabolite levels relating to sucrose and starch metabolism.

Summary Diurnal changes in carbohydrate contents, assimilate export, enzyme activities and metabolite levels associated with sucrose and starch 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 change 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.

Diurnal Changes in Photosynthesis in Sugarcane Leaves : I. Carbon dioxide exchange rate, photosynthetic enzyme activities and metabolite levels relating to the C4 pathway and the Calvin cycle

Abstract 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), NADP-malic enzyme (NADP-ME), pyruvate, P1 dikinase (PPDK), 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 changes 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.

Multivariate statistical analysis of yield-determining factors

This study is aimed at developing a multivariate statistical method to identify yield-determining factors and to evaluate their relative magnitude. Principal component analysis was used to summarize the rice growing environment in a “hydromorphic” field into a number of factors which may affect the yield performance. Four major factors were recognized; i) Soil moisture factor, ii) Soil texture factor, iii) Fertilizer factor, and iv) Insect damage factor. Using the scores of the indicated factors as independent variables, stepwise regression analysis was performed to derive a yield prediction function. The coefficient of determination (R2) reached 0.924 and the magnitude of the factor effect on yield followed the order of Soil moisture≫Insect damage>Fertilizer. Soil texture was not significant as a yield-determining factor. Although the current report is only a case study, the method developed should be useful for predicting yield potentials of plant varieties adapting to different soil environments.

Invertase activities in sheath-blight infected rice selection lines and fungus culture filtrates.

Infection of rice plants with Rhizoctonia solani, the sheath blight fungus, at the flowering stage resulted in an increase in acid invertase activity. Activity of the invertase(s) with optimum pH at 3.5 and 4.5 was higher in the susceptible plants compared to resistant plants. Healthy control plants had no change in invertase activity. An invertase of fungal origin produced in sheath blight fungus culture filtrates had an optimum acidic pH of 3.5. The increase in invertase activity observed in the later stages of infection in the susceptible plants compared to the resistant plants demonstrated a relation to fungal growth. These results suggested that the fungus produced an invertase for the hydrolysis of sucrose that resulted in alterations of source-sink relationships in the colonized cells. Thus, the increased invertase activity in the susceptible plants regulated the ratio of hexose to sucrose. This observation is further supported by the lack of a significant invertase increase in the resistant plants.

Chromatographic properties of pyruvate:fructose-6-phosphate1-phosphotransferase (PFP) from leaves of a CAM plant, pineapple (Ananascomosus),Chromatographic properties of pyruvate:fructose-6-phosphate1-phosphotransferase (PFP) from leaves of a CAM pl

PFP has been recognized as a regulating enzyme of the alternative glycolysis in the plants and PEP synthesis in some CAM plants. In this study, chromatographic traits of PFP of pineapple leaves were examined. Pineapple plants were grown in the greenhouse and the experimental plants were moved to the growth-chamber at 10 days before each experiment. Conditions in the growth-chamber were as follows: daylength was 12 hrs from 8:00 to 20:00; PAR on the leaves ca.330µmol/m2/s; air humidity 60%; air temperature of day and night 30°C and 20°C. Extraction was done at 17:00 as day form and at 24:00 as night form, respectively. PFP of pineapple leaves showed different isoelectric points in day and night, such as two points of pH 4.88 and 5.34 of day form and one point of pH 4.80 of night form. Day form PFP also was eluted as two individual peaks on DEAE-cellulose chromatogram (Protein-Pak, DEAE 8HR, 5x100mm, Waters) with non-liner gradient of KCl, and the protein in each peak showed different elution time on molecular sieve chromatogram (Protein-Pak 300, 8x300mm, Waters), such as 14.23 and 12.51 min. As described above, it was suggested that PFP protein of pineapple leaves existed as different molecular aggregation state in day and night.

Temperature and pH responses of phosphofructokinase from three CAM plants, Ananas comosus, Kalanchoë pinnata, and K. daigremontiana

CAM-type photosynthesis uses the glycolylic pathway in both directions to produce phosphoenolpyruvate (PEP) as the substrate of dark CO2 fixation and to convert the C3-residues of malate decarboxylation to sugars in the neoglycolitic direction.