44. Varietal differences in photosynthetic capacity of rice leaves measured by oxygen polarographic method

Tsukasa Nagamine
National Institue of Agrobiological Resources, Yatabe, Tsukuba Science City, 305 Japan


To look into the genetic control of photosynthetic capacity of rice varieties, we are trying to establish simple, steady, and quick measuring methods. The oxygen polarographic method by which many samples can be examined in a short time, and the data on oxygen exchange rate obtained by using this method are reported in this paper.

Based on the principle in the reports of Jones and Osmond (1973) and Yamashita et al. (1978), we developed a new compact apparatus so as to handle many samples; 12 measuring sets were equiped in the apparatus with automatic recorder. Each set comprised a reaction cell, a light source and an oxygen electrode. The new apparatus using an oxygen polarographic method can measure 12 samples within 40 minutes under the following conditions: 1) Small leaf disks are prepared with a disk punch by removing the mid-rib portion of leaf blades. 2) Leaf disks are kept in distilled water in petri dishes in a growth chamber (temperature: day 28C-night 22C, illumination: 6:00-20:00, light intensity 40 Klux) for 22 hours before measurement. 3) Optimum measuring conditions for obtaining high and constant values of oxygen exchange rate are: pH 7.2 of HEPES bufier solution, 70 Klux of light intensity, and 25C of reaction solution temperature.


Table 1. Variation in oxygen exchange rate in leaves of rice varieties from various regions.

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Region                              Oxygen exchange rate (umolO\2\/dm2.hr)
                     --------------------------------------------------------
                           301  351  401  451  501  551  601  651  701  751
                      300  350  400  450  500  550  600  650  700  750
==============================================================================
Northern China.Japan                       2         2         1
Southern China                        2    4    5    4    1
Indonesia.Philippines            1    2    2    2    8    1    1           1
Burma.Laos.Thailand    1    4    7   12    12   20   9   10    1    2      1
Yunnan                           1    4     5   10  10    3    2    2      2
India.Bangladesh.Nepal                      4    3   5    1    3
Others                                      2    7   3    1
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         Total        1     4    9   20    31   47   41   17   8    4       4
==============================================================================

A total of 186 rice strains from various countries, most of them landraces, were measured with fully expanded leaves on the main stem at 30-40 days after transplanting, with 4 replications. The strains showed a wide range of oxygen exchange rate, the lowest being 300 umol O\2\/dm2. hr, while the highest was 780. Both varieties showing the lowest and highest values were landraces from Laos. The magnitude of oxygen exchange rate among varieties from different countries is summarized in Table 1. The highest/lowest ratio was 2.6 suggesting the presence of a noticeable genetic variation in photosynthetic capacity. A higher ratio was observed when measured by the CO\2\ exchange (Akita 1980). The differences in the ratios may also be attributed to different sampling methods employed. The genetic basis of varietal differences in oxygen exchange rate will be investigated in the future.


References

Akita, S., 1980. Studies on the differences in photosynthesis and photorespiration among crops, I. The differential responsis of photosynthesis, photorespiration and dry matter to oxygen concentration among species. Bull. Nat. Inst. Agr. Sci. D31: 1-58 (in Jap. with Eng. summary).

Jones, H.G. and C.D. Osmond, 1973. Photosynthesis by thin leaf slices in solution, I. Properties of leaf slices and comparison with whole leaves. Austr. J. Biol. Sci. 26: 15-24.

Yamashita, T.,H.Kohda, J. Nanri and G. Tomita, 1978. The simultaneous measurement of O\2-\ evolving and Co\2-\ fixing activities in fresh leaves. J. Fac. Agr., Kyushu Univ. 22: 107-118.