Ryoichi Yamamoto

Growth promotion and an increase in cell wall extensibility by silicon in rice and some other Poaceae seedlings.

Abstract The effect of silicon on organ growth and its mechanisms of action were studied in rice (Oryza sativa L. cv. Koshihikari), oat (Avena sativa L. cv. Victory), and wheat (Triticum aestivum L. cv. Daichino-Minori) seedlings grown in the dark. Applying silicon in the form of silicic acid to these seedlings via culture solution resulted in growth promotion of third (rice) or second (oat and wheat) leaves. The optimal concentration of silicon was 5–10 mM. No growth promotion was observed in early organs, such as coleoptiles or first leaves. In silicon-treated rice third leaves, the epidermal cell length increased, especially in the basal regions, without any effect on the number of cells, showing that silicon promoted cell elongation but not cell division. Silicon also increased the cell wall extensibility significantly in the basal regions of rice third leaves. These results indicate that silicon stimulates growth of rice and some other Poaceae leaves by increasing cell wall extensibility.

Nondestructive Measurement of Kiwifruit Ripeness Using a Laser Doppler Vibrometer

A laser Doppler vibrometer was applied to evaluate the viscoelastic properties of kiwifruit [ Actinidia deliciosa (A. Chev.) Liang et Ferguson, cv Hayward] at various stages of ripeness. A stiffness coefficient (S) was defined as f 2 n=2 m 2/3 , where f n=2 was the frequency of the second resonance peak and m was the fruit mass. A loss coefficient ( η ) was defined as (f 2 - f 1 )/f n = 2 , where frequencies f 1 and f 2 were determined at 3 dB below the second resonance peak (f 2 > f 1 ). Fruit firmness of the samples that had been used for the laser Doppler measurement was determined by measuring the force required to insert a conical probe 5 mm into the cut surface of a fruit slice. There was a highly significant relationship between the stiffness coefficient and the firmness of the kiwifruit core (r 2 = 0.967). The loss coefficient correlated well with soluble solids content. The loss and stiffness coefficients changed during ripening at 20 ° C; the stiffness coefficient decreased, while the loss coefficient increased. There was a characteristic inverse relation between the loss and stiffness coefficients. When the stiffness coefficient decreased to 1 × 10 7 in the early stages of ripening, the loss coefficient increased only from 0.1 to 0.2. When the stiffness coefficient decreased further from 1 × 10 7 to 0.1 × 10 7 in the late stages of ripening, the loss coefficient increased drastically from 0.2 to 0.8. The results indicate that early stages of fruit softening are reflected by the stiffness coefficient, and late stages are reflected by the loss coefficient. Therefore, the two coefficients clearly distinguish between ripe and unripe kiwifruit.

Evaluation of fruit tissue texture and internal disorders by laser Doppler detection

Ripening-dependent changes in fruit texture and the development of physiological disorders affecting texture were sensed remotely by laser Doppler detection based on changes in surface vibrations. Intact fruit of kiwifruit (Actinidia deliciosa (A. Chev.) Liang et Ferguson, `Hayward), peach (Prunus persica Batsch., `Akatsuki), and Japanese pear (Pyrus pyrifolia Nakai, `Cyouju), at different maturity stages, were placed on a vibration generator stage and the sample was subjected to sine wave excitation through a frequency series from 5 to 2000 Hz. Vibration transmitted through the fruit to the upper surface was measured by a laser Doppler vibrometer. Phase shift caused by the transmission through the fruit was determined based on the comparison of the difference between input and output vibration signal. To reconcile changes in the phase shift with other methods used for texture analysis, a probe with a load sensor was inserted into the sliced fruit and displacement force was measured. The correlation coefficient (r) between displacement force and phase shift at either 1200 or 1600 Hz was 0.81 to 0.92 (P<0.01). The laser Doppler technique was also capable of detecting citrus fruit (Citrus tamurana Hort. ex Tanaka) afflicted with internal defects. These data suggest that laser Doppler detection of fruit vibration signals has the potential for use as a versatile remote sensing tool for evaluation of fruit tissue firmness and maturation. It also offers a possible means of evaluating otherwise concealed internal defects that render fruit unacceptable.

Measurement of viscoelastic properties of root cell walls affected by low pH in lateral roots of Pisum sativum L.

Mechanical extensibility of the cell wall limits the elongation growth of roots. Low pH, ranging from pH 3–4.5, induces rapid elongation of excised roots, a phenomenon known as acid growth. The creep-extension analysis was carried out to measure and elucidate the viscoelastic properties of root cell walls in the acidic environment in vitro. The viscoelastic properties were determined at the elongation zone of the lateral roots of pea (Pisum sativumL. cv. Alaska) and described by the physical parameters of three elastic (E0, E1, E2) and three viscosity (η0, η1, η2) parameters using a Kelvin–Voigt–Burgers model. The present method could measure the viscoelasticity of 1-mm long root zones from 2 to 9 mm behind the tip. Among the parameters, E0 and η0 were the most significant parameters to represent the whole extensibility of the roots. The parameter η0 markedly declined in response to the environmental low pH (acid growth), whereas other parameters were not much affected by low pH. Relationship between the change in these physical parameters and the change in cell wall extensibility under low pH was discussed in order to elucidate the rheological processes taking place in the elongating cell walls.

Comparison of a non-destructive acoustic method with an intrusive method for firmness measurement of kiwifruit

Abstract A non-destructive acoustic measurement and an intrusive method for determining tissue firmness were compared to assess the textural properties of kiwifruit (Actinidia deliciosa (A. Chev.) Liang et Ferguson, cv `Hayward). Kiwifruit were treated with ethylene to initiate development and thereby provide a range of tissue textures. Individual fruit were subjected to pulsed sound, generated by a function synthesizer. The elapsed time for sound transmission through fruit tissues, which was measured by a storage oscilloscope (non-destructive method), increased as a function of the duration of ethylene treatment. Transverse slices of comparable kiwifruit tissue (2 cm in thickness) were placed on a stage and a conical probe attached to a load sensor was inserted to a depth of 5 mm. Tissue firmness was related to the maximum force required to achieve the constant strain (intrusive method). The results obtained by acoustic measurements were in good agreement with those achieved by the more conventional intrusive method, demonstrating that sound can be applied for the evaluation of firmness of intact kiwifruit.

ANALYSIS OF THE VIBRATION MODE OF APPLE TISSUE USING ELECTRONIC SPECKLE PATTERN INTERFEROMETRY

Apples placed on a vibrating table were subjected to sine–wave vibrations at specific frequencies, and the response nwas observed by electronic speckle pattern interferometry (ESPI). The speckle pattern was analyzed to determine the nvibration modes. The lowest resonant frequency was a longitudinal vibration and the second lowest a 0S2 mode. Third and nfourth lowest resonant frequencies were estimated as a 0S3 and a 0S4 mode, respectively. The fact that the response to the second nlowest resonant frequency is the 0S2 mode confirms that the elastic modulus of an apple can be calculated by the equation nproposed by Yamamoto and Haginuma (1984). The influence of the surface contact between the vibrating table and the apple nwas examined. When the apple was bonded to the table with glue, the lowest resonant frequency greatly increased by 80%, nbut the second, third and fourth were little influenced. The second lowest resonant frequency of an apple can be accurately ndetermined by placing the apple directly on the table without bonding and it affords a practical measurement of fruit firmness.

Physical measurement of firmness of banana fruit pulp: determination of optimum conditions for measurement

Abstract Stress-relaxation curves were obtained by plunging a conical probe into the pulp of green and yellow banana fruits [ Musa (AAA group, Cavendish subgroup) ‘Giant Cavendish’]. Three stress-relaxation parameters, minimum stress-relaxation time ( T 0 ), relaxation rate ( R ), and maximum stress-relaxation time ( T m ), were calculated from the stress-relaxation curve. Plunging depth and plunging speed varied the parameters. When parameters were fixed, with a plunging speed of 0.5 mm/s and the plunging depth of 0.6 mm, the yellow bananas showed significantly lower T 0 and T m than green bananas. The lower, T 0 and T m can predict the degradation of polymers responsible for the pulp texture. Measurements of stress-relaxation parameters in different parts of banana pulp revealed that the physical properties were not uniform within the same fruit.

Stress relaxation property of the cell wall and auxin-induced cell elongation

AbstractA stress-relaxation method has been developed to measure the mechanical property of the plant cell wall, as a physically defined terms. In the method, the stress relaxation property of the cell wall is simulated with a Maxwell viscoelastic model whose character is represented by four parameters; the minimum relaxation time, To, the relaxation rate, b, the maximum relaxation time, Tm and the residual stress, c. Thus, the mechanical property of the cell wall is represented by the four parameters. Physical and physiological meanings of the parameters are discussed. Auxin effects on the parameters were also studied.The cell elongation is simply thought to be extension of the cell wall under a force. The extension of the cell wall can be simulated by the mechanical property of the cell wall. However, the calculated extension was found to be incomparable to the real cell growth, indicating that there has to be other factors limiting the rate of cell growth. Major factors governing cell growth are discussed to be the cell wall mechanical property, the osmotic potential and water movement in the apoplast. A possibility to predict cell expansion with the three factors was discussed and a novel equation representing cell growth was obtained:n

Effects of sodium chloride on the fatty acids composition in Boekelovia hooglandii (Ochromonadales, Chrysophyceae)

1/R = 1/R_w + 1/R_p