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.
============================================================================== 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 ----------------------------------------------------------------------------- Total 1 4 9 20 31 47 41 17 8 4 4 ==============================================================================
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.