Study on the Characteristics and Principles of Respiration in Cymbidium sinense

1. Ultrastructure of mitochondria in roots and leaves: The cristae structure of root mitochondria is denser than that of leaves; leaf mitochondria are basically distributed near the chloroplasts, which has important biological significance. 2. Pathways of material metabolism and energy metabolism: Determinations of the key enzyme activities of the glycolytic pathway, the tricarboxylic acid cycle and the hexose monophosphate shunt, as well as studies applying various respiratory inhibitors, indicate that the catabolism of carbohydrates mainly proceeds via the EMP pathway-TCA cycle, with HMP being a secondary pathway. The EMP pathway and HMP pathway are more active in roots and leaf buds, and decline in leaves with increasing leaf age. TCA cycle activity in roots and young leaf buds is lower than in mature leaves. Energy metabolism mainly follows the normal respiratory electron transport chain, and cyanide-resistant respiration appears not to exist. 3. Effects of temperature on respiration rate and respiratory quotient: The respiration rates of both leaves and roots increase with rising temperature, with a temperature coefficient Q10 between 2 and 3. The optimum temperature for leaf respiration is around 35°C, and the optimum temperature for root respiration is around 30°C; exceeding 35°C causes damage to the root respiratory system. The respiratory quotient (RQ value) of roots and leaves is relatively low (＜0.8) below 25°C, and approaches 1 as temperature rises. The respiration rate of leaves in CO2-free air is 1 to 1.5 times higher than in ordinary air, and that of roots is 0.7 times higher. 4. Effects of light on severalorchidsroot respiration rates: Light has a clear stimulating effect on the respiration of the "etiolated roots" of certain epiphytic orchids. However, its promotion of the respiration ofCymbidium sinenseterrestrial roots is relatively small. (Ye Qingsheng, Pan Ruichi)