Journal of Experimental Botany, Vol. 51, No. 346, pp. 961-964,
May 2000
© 2000 Oxford University Press
A new method for on-line measurement of diurnal change in potato tuber growth under controlled environments
Biotron Institute, Kyushu University 12, Fukuoka, 812-8581, Japan
Received 27 September 1999; Accepted 21 January 2000
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResults and discussionReferences |
|---|
An on-line laser micrometer system was applied to measurement of diurnal change in potato (Solanum tuberosum L.) tuber growth. Diameters of the potato tuber were scanned by moving a laser micrometer along the longitudinal axis of the tuber at constant speed, and tuber volume was evaluated as an aggreg ate of thin discs. A single potato tuber, without competitive sink tubers in the plant, was grown in controlled air at 20 °C and 80% RH, and tuber volume was measured at 30 min intervals. During the growth experiment, the potato tuber increased in size without any inhibitory effect of periodical laser beam irradiation. Greatest expansion generally occurred during the early night, and transient contraction of the tuber occurred at the beginning of the light period.
Key words: Potato, laser micrometer, tuber growth, on-line measurement, controlled environments.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResults and discussionReferences |
|---|
Measurement of diurnal changes in fruit expansion have been made in several crops (Elfving and Kaufmann, 1972
; Higgs and Jones, 1984; Tromp, 1984; Johnson et al., 1992; Kitano et al., 1996), where rapid responses to changes in environmental conditions have been shown. However, similar measurements are difficult to make in root and tuber crops, because their storage organs grow below ground. In potato (Solanum tuberosum L.) studies, diurnal changes in tuber weight were measured by using an electric weighing system (Krauss and Marschner, 1972), and diurnal changes in tuber circumference were measured by using a linear variable differential transformer (Stark and Halderson, 1987). However, these two methods have never been used for further studies relating to environmental effects on potato tuber growth. Because the biomass production of tubers can be independent of root growth, it is desirable that the environments of the tuber and the root be controlled independently for exact analysis of environmental effects on tuber growth. To this end, it is therefore necessary to develop new methods for measuring potato tuber growth, where the environments of the tuber and the root are controlled independently.
A hydroponic system was developed for the analysis of environmental effects on tuberous root growth in sweet potato (Ipomoea batatas Lam.), where the environments of shoot, tuberous root and fibrous roots were independently controlled (Eguchi et al., 1996). An on-line system for volume measurement of the tuberous root was developed by applying a laser micrometer (LM) to scan the contours of the tuberous root (Eguchi et al., 1997a). Diurnal change in tuberous root expansion was successfully calculated (Eguchi et al., 1997b). The method was applied to the analyses of relationships between tuberous root growth and the shoot environment (Eguchi et al., 1998a), as well as humidity around the tuberous root (Eguchi et al., 1998b). The potato tuber has the same function as the tuberous root of sweet potato: both of those organs increase in volume whilst accumulating a large mount of starch. Therefore, the LM method for sweet potato is likely to be useful in measuring diurnal changes in tuber growth in potato plants.
The objective of this study was to modify the LM method to the evaluation of diurnal changes in potato tuber growth under controlled environments.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResults and discussionReferences |
|---|
Laser micrometer system and tuber volume evaluation
Figure 1a
shows a schematic diagram of an on-line LM system for tuber volume measurement. The system consisted of an LM (3Z4L-4403V, Omron Corp., resolution: 0.05 µm), a slider unit (slider: SPH20B10–2PD; motor driver: DFU1514; and programmable controller: LPC100M, Oriental Motor Corp.). Tuber-scanning and processing of the sensor signal were operated on-line by using a personal computer (PC-9801DA, NEC). The LM mounted on the slider was automatically moved along the longitudinal axis of a tuber at a constant speed of 10 mm s-1, and diameters of the tuber were scanned. The scanning range of the LM system covered 30 mm (sensing range of the slider) x200 mm (moving range of the LM on the slider). As shown in Fig. 1b, tuber volume (V) was evaluated by an integral method summing up volumes of thin discs as
 | (00A) |
6 mm).
|
Seven detached tubers were used to examine the performance of the LM system. Each LM measurement was compared with the actual volume that was measured by immersing the tuber in a partially water-filled measuring cylinder. Accuracy of the LM system on repeated measurements was also evaluated by measuring the volume of an imitation tuber made of oil clay that shows no volume change with time.
Plant material
A piece of seed potato (cv. Mayqueen) was potted in 3.5 l plastic pot containing mixture of sand and gravel (2 : 1, v : v). The potato was grown in a phytotron at 20 °C and 70% RH. After about 2 months, plants with several tubers were obtained. The rooting medium was carefully washed off the root, and only one tuber was kept on the plant. Prior to measurement, the potato tuber was soaked in a 1% solution of CaCl2 in order to avoid Ca deficiency which results in necrosis of the potato tuber when grown in air (Tibbitts et al., 1994).
>Growth measurement
Figure 2 shows a schematic diagram of the hydroponic system for on-line measurement of potato tuber growth under controlled environments. Each plant with its single tuber was transplanted into the hydroponic system. The tuber was placed in the scanning range of the LM system. The shoot environment was controlled at an air temperature of 20 °C, relative humidity of 70%, light intensity of 300 µmol m-2 s-1 and a photoperiod of 12 h lpar;07.00–19.00 h). The tuber environment was controlled by an air conditioning unit at an air temperature of 20 °C and a relative humidity of 80% RH. The fibrous root environment was controlled by a water bath system at a nutrient solution temperature of 20 °C. Tuber volume was measured using the LM system at 30 min intervals.
|
|
Results and discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResults and discussionReferences |
|---|
System performance
The performance of the LM system in measuring tuber growth is presented in Table 1
. The standard error of volume measurement was relatively large (±0.8 cm3), because the vertical section of the tuber is a distorted circular shape. However, the LM system shows extremely high accuracy on repeated measurement of the tuber volume (±0.002 cm3). This means that the LM system can evaluate slight changes in volume of the growing tuber. Furthermore, the drift induced by temperature changes in the LM system was found to be negligibly low (less than ±0.01 µm °C-1). Thus, the LM system is a useful tool for measuring tuber expansion.
|
>Tuber growth
Figure 3 shows changes in tuber shape over 5 d as measured by the LM system. The whole of the tuber increased in width and the maximum diameter at 5 d was 128% of the initial value. Changes in tuber length could also be evaluated using the LM system.
|
Figure 4
shows the typical time-course of volume change in the tuber. The tuber decreased in volume during the first part of the light period, whereas volume recovered to the initial value at midnight of the following dark period. Thereafter, the tuber volume kept increasing until the beginning of the next light period. Generally, 2 or 3 d are necessary for acclimation of the plant to new growth conditions, and active growth occurred during subsequent days. Thus, active tuber growth continued without any inhibitory effect of periodical laser beam irradiation on the growth pattern.
|
Figure 5
shows the typical pattern of diurnal changes in tuber growth. At the beginning of the light period, the growth rate dropped to a negative value, but soon rose to a positive value, peaking at the beginning of the dark period.
|
Temporal contraction of the potato tuber was usually observed at the beginning of the light period (Figs 4
, 5). Such transient changes in growth of storage organs have been found in sweet potato: the tuberous root, a storage organ of sweet potato, shows a temporal contraction in response to a rapid increase in evaporative demand around the leaves (Eguchi et al., 1998a, b). The transient change of potato tuber growth at the beginning of the light period was possibly the result of the temporal disturbance of the whole-plant water balance caused by a rapid increase in leaf transpiration in response to illumination and stomatal opening. In conclusion, the LM system is an effective tool for measuring volume change in potato tubers. This study also demonstrated that tuber growth can show rapid responses to changes in environmental conditions. The hydroponic system reported here could be used in further studies of environmental effects on potato tuber growth, with independent control of shoot, tuber and root environments.
|
Notes |
|---|
1 Fax: +81 92 642 3069. E-mail:egut{at}agr.kyushu-u.ac.jp
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResults and discussionReferences |
|---|
Eguchi T, Kitano M, Eguchi H.1996. New system of hydroponics for growth analysis of sweet potato tuber. Biotronics 25, 85–88.
Eguchi T, Kitano M, Eguchi H.1997a. On-line system for volume measurement in sweet potato tuber. Biotronics 26, 103–106.
Eguchi T, Kitano M, Eguchi H.1997b. Measurement of diurnal change in tuber growth of sweet potato plants. Biotronics 26, 67–72.
Eguchi T, Kitano M, Eguchi H.1998a. Water relations and dynamics of tuber growth rate in sweet potato plants (Ipomoea batatas Lam.). Environment Control in Biology 36, 91–95.
Eguchi T, Kitano M, Eguchi H.1998b. Growth of sweet potato tuber as affected by ambient humidity. Biotronics 27, 93–96.
Elfving DC, Kaufmann MR.1972. Diurnal and seasonal effects of environment on plant water relations and fruit diameter of citrus. Journal of the American Society for Horticultural Science 97, 566–570.
Higgs KH, Jones HG.1984. A microcomputer-based system for continuous measurement and recording fruit diameter in relation to environmental factors. Journal of Experimental Botany 35, 1646–1655.
Johnson RW, Dixon MA, Lee DR.1992. Water relations of the tomato during fruit growth. Plant, Cell and Environment 15, 947–953.
Kitano M, Hamakoga M, Yokomakura F, Eguchi H.1996. Interactive dynamics of fruit and stem growth in tomato plants as affected by root water condition. I. Expansion and contraction of fruit and stem. Biotronics 25, 67–75.
Krauss A, Marschner H.1973. Influence of the day/night alternation on tuber weight and Ca translocation within the stolon of potato plants. Journal of Plant Nutrition and Soil Science (Germany) 136, 116–123.
Stark JC, Halderson JL.1987. Measurement of diurnal changes in potato tuber growth. American Potato Journal 64, 245–248.
Tibbitts TW, Cao W, Wheeler RM.1994. NASA Contractor Report 177646: growth of potatoes for CELSS. Washington: National Aeronautics and Space Administration.
Tromp J.1984. Diurnal fruit shrinkage in apple as affected by leaf water potential and vapour pressure deficit of the air. Scientia Horticulturae 22, 81–87.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||