Problems in the methods of estimation of growth and maintenance respiration

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Abstract
According to Thornley, J.H.M. (Nature, 227, 304-305, 1970) and McCree, K.J. (Crop Sci., 14, 509-514, 1974), respiratory substances are used only for maintenance respiration when plants are exposed to the dark conditions for a long period of time (more than 2 d). The maintenance respiration is also affected by the nitrogen status in plant, because protein turnover is one of the major energy consumption sources under maintenance process. Therefore, to determine whether respiratory substances are used only for maintenance, 14C- [U] -sucrose or a mixture of 14C- [U] -amino acids was introduced to rice and soybean plants from the tip of leaf. Plants were grown under natural light conditions and under dark conditions for 4 d with 2 nitrogen levels (0.2 and 0.02 g N L-1 soil). After the introduction of the 14C-compounds, the 14CO2 respiratory rate was monitored during 24 h, then the 14C distribution to organic acids, free amino acids, proteins, sugars, and polysaccharides was analyzed. Following results were obtained. Based on the above results, it is suggested that since the 14C-distribution ratio into each chemical component did not change regardless of light treatment, nitrogen treatment, or leaf age, It was impossible to separate respiration into two components, such as growth and maintenance respiration. The results also indicated that current photosynthates and storage substances were not used only for growth and maintenance, respectively.