Eiichi Takahashi

Salt-induced damage to rice plants and alleviation effect of silicate

Rice plants were grown hydroponicaIly in the presence of either NaCI, sea water, or polyethylene glycol (PEG: average molecular weights of 7,800–9,000) at an osmotic potential of up to 186 mOsmol/kg, equivalent to 100 mM NaCI or 20% sea water, and the growth and mineral composition of the plants were compared. NaCI was the most detrimental agent, followed by sea water and PEG. Mineral contents, including nitrogen, phosphorus, potassium, and calcium were not significantly affected by the treatments. Removal of silicate from the culture solution brought about a more severe growth reduction in rice plants subjected to 100 mM NaCI stress. In the plants which received silicate, the contents of sodium in the shoots were nearly half of those in the shoots of plants which did not receive silicate.

Chapter 2 Silicon as a beneficial element for crop plants

Silicon (Si) has not been proven to be an essential element for higher plants, but its beneficial effects on growth have been reported in a wide variety of crops, including rice, wheat, barley, and cucumber. Si fertilizer is applied to crops in several countries for increased productivity and sustainable production. Plants take up Si in the form of silicic acid, which is transported to the shoot, and after loss of water, it is polymerized as silica gel on the surface of leaves and stems. Evidence is lacking concerning the physiological role of Si in plant metabolism. Since the beneficial effects of this element are apt to be observed in plants which accumulate Si, the silica gel deposited on the plant surface is thought to contribute to the beneficial effects of Si, which may be small under optimized growth conditions, but become obvious under stress conditions. In this review, the effects of Si under biotic stresses (disease and insect damage) and abiotic stresses including climate stresses (typhoon and cool summer damage), water deficiency stress, and mineral stresses (deficiency of P and excess of P, Na, Mn, N and Al) are discussed.

EFFECT OF SILICON ON THE GROWTH OF RICE PLANT AT DIFFERENT GROWTH STAGES

Rice plants (Oryza sativa L. cv. Akebono) were cultured in Kimura B solution. The effect of silicon on plant growth and the characteristics of the uptake and distribution of silicon at different growth stages were studied from both aspects: the addition and removal of silicon during the vegetative, reproductive and ripening stages. When silicon was removed during the reproductive stage, the dry weights of straw (stem+leaf blade) and grain decreased by 20 and 50% respectively, compared with those of the plants cultured in the solution with silicon throughout the growth period. Conversely, when silicon was added during the reproductive stage, the dry weights of straw and grain increased by 243 and 30%, respectively, over those of the plants cultured in a solution devoid of silicon throughout the growth period. The effect of silicon on the dry weights of straw and grain was small when silicon was either added or removed during the vegetative and ripening stages. The percentage of filled spikelets remarkably ...

EFFECT OF SILICON ON THE GROWTH OF SOLUTION-CULTURED CUCUMBER PLANT

Abstract Cucumber plants were solution-cultured with and without silicon. Both silicon-free and silicon-supplied (100 ppm SiO2) plants grew normally in the earlier growth stage. In the flowering stage, however, the newly developed leaves (8th or 9th leaves) of silicon-free plants showed malformations such as curling, whereas no abnormal symptoms were observed in leaves developing subsequently. In severe cases, the silicon-free plants began to dry up from the lower-leaves upwards. The growth and yield of silicon-free plants were markedly inferior to those of silicon-supplied plants. The pollen fertility of silicon-free plants was lower than that of silicon-supplied plants. Disease symptoms of powdery mildew were observed on al1leaves of silicon-free plants; however, no such symptoms were observed in leaves of silicon-supplied (100 ppm SiO2) plants. The silicon content of leaves and plant growth increased, proportionally to the silicon concentration in the solutions, while disease symptoms of powdery mildew...

Effect of silicon on the growth and phosphorus uptake of rice.

A pot experiment was conducted to measure the effect of silicon on phosphorus uptake and on the growth of rice at different P levels. Rice (Oryza sativa L. cv. Akebono) was cultured in Kimura B nutrient solution without and with silicon (1.66 mM Si) and with three phosphorus levels (0.014 mM P, low; 0.21 mM, medium; and 0.70 mM, high).Shoot dry weight with Si (+Si) in solution increased with increasing P level, while shoot weight without Si (−Si) was maximum at 0.21 mM P, suggesting that +Si raised the optimum P level for rice. +Si increased shoot weight more when P was low or high than when P was medium.The concentration and amount of inorganic P in shoots increased with increasing P level. +Si did not significantly decrease P uptake by rice at 0.014 mM P, however, uptake at 0.21 and 0.70 mM P was 27 and 30 percent less than uptake with −Si, respectively. In −Si with 0.21 and 0.70 mM P, inorganic P in shoots was more than double the concentration in shoots grown in +Si solutions.The Si concentration in shoots decreased slightly with increasing P level, although Si uptake was not significantly affected by P. +Si decreased the uptake of Fe and Mn by an average of 20 and 50 percent, respectively, thus P/Mn and P/Fe ratios increased in the shoot when P was low.From the results above, the beneficial effect of Si on the growth of rice was clearly shown when P was low or high. This effect may have resulted from decreased Mn and Fe uptake, and thus increased P availability within P deficient plants, or from reduced P uptake when P was high.

Association of Aluminium with Nuclei and Inhibition of Cell Division in Onion (Allium cepa) Roots

Summary In order to elucidate the injurious effect of Aluminium (AI) on root elongation, the localization of Al absorbed at the nucleus and the inhibition of cell division by Al was investigated in Allium cepa roots. The localization of Al at the nucleus was confirmed by staining with aluminon and by chemical analysis of nuclei isolated by zonal centrifugation. The inhibition of cell division was observed microscopically by counting the number of cells in metaphase, which is an index of the meristematic cell. This number decreased abruptly within several hours and no cells in metaphase were detected 10 h after treatment with AI.

Changes in the activities of ferredoxin- and NADH-glutamate synthase during seedling development of peas

Ferredoxin-glutamate synthase (EC 1.4.7.1) and NADH-glutamate synthase (EC 1.4.1.14) activities in pea seedlings (Pisum sativum L., cv. Alaska) were measured during germination and the early stages of growth. Both enzymes were detected at all stages in the developing roots and shoots, but their relative activities varied according to the growth stages. In shoots of 5-d-old seedlings, the ratio of the NADH-enzyme to the ferredoxin-enzyme was 72:28. However, the ferredoxin-activity increased rapidly and in shoots of 17-d-old seedlings, the activities were in the ratio of 3:97. Similar trends in these ratio changes were observed in the roots. In both tissues, the NADH-enzyme was shown to be predominant in the immature parts. When chloroplasts prepared from mature pea leaves were incubated with [14C]glutamine and 2-oxoglutarate, the production of [14C]glutamate was found to be light dependent and was inhibited by azaserine (3 mM) and 3-(3,4-dichlorophenyl)-1-1-dimethylurea (20 μM). In contrast, considerable amounts of [14C]glutamate were formed by chloroplasts from young leaves even in the dark. Addition of malate or dihydroxyacetone phosphate to the reaction mixture resulted in a twofold increase of this dark- and azaserine-sensitive [14C]glutamate formation.

Silicon deficiency of tomato plant

Abstract Tomato plants were solution cultured with and without silicon, and Si deficiency symptoms were observed in the first bud flowering stage when the tomato plants had been cultured in a silicon-free solution; however, normal growth was observed in a solution with 100 ppm SiO2. To induce Si deficiency symptoms, it is necessary to culture the plant in a silicon-free solution under favorable conditions for the growth of tomato plant. Select the most suitable cultivar for the environmental conditions. Optimum temperatures with differences for day and night, high light intensity, sufficient aeration, and low planting density are key points in the development of a Si deficiency. Symptoms of Si deficiency may be summarized as follows: 1) The deficiency symptoms appear after the first bud flowering stage. 2) The leaflets of the new leaves showed malformations such as curving to the outside, warping, hardening, and sometimes thickening. 3) The growing poillt at the top was retarded in development, but did no...

Interaction between calcium and silicon in water-cultured rice plants

The interaction between Ca and Si in water-cultured rice plants (Oryza sativa L. cv. Akebono) was investigated in terms of uptake. The effect of Ca levels in the solution on Si chemical forms and on the formation of silica bodies in the leaf blades was also examined using soft X-ray irradiation for detection of silica bodies. Si addition (1.66 mM Si) decreased both Ca content of the shoot and uptake at each Ca level. This might mainly result from a decreased transpiration rate caused by Si. Si uptake was not affected when the Ca levels were increased. The results of Si forms showed that silica sol constituted more than 90% of the total Si in the leaf blades regardless of Si and Ca levels, and soluble silica and/or polysilicic acid seems to gel physically over 8.0 mM Si within the plants. Significant difference in the numbers of silica bodies on the third leaf blade was not found between different Ca levels at the same Si level. The content of Si in the leaf blade seems to be a determining factor for the formation of silica bodies. ei]H. Marschner

The effect of silicic acid on rice in a P-deficient soil

A pot experiment was conducted to analyze the effect of silicon on the growth of rice grown in a P-deficient soil and on P availability in the soil. Silicic acid was used, rather than a silicate salt, to avoid the complication of changes in soil pH.Shoot dry weight on silicic acid treated soil (0.47 mg Si g−1 soil) increased significantly under both nonflooded and flooded conditions. Shoot Si concentration also increased although P concentration did not. Mn concentration decreased with silicic acid, resulting in a higher P/Mn ratio in shoots.An adsorption and desorption experiment showed that silicic acid did not displace P nor decrease the ability of the soil to adsorb P. In contrast, Si desorption increased with increasing P concentration in the solution, and Si adsorption was reduced when P was applied first.These results suggest that silicic acid does not increase P availability in soil. Increased dry weight may be attributed to a higher P/Mn ratio in the shoot, which may improve P utilization in the plant.