photosynthesis and photorespiration

1. Structure: dissecting the structure of the leaves of Cymbidium sinensis, the leaves are covered with thick angular layer and waxy, the stomata are distributed on the back of the leaves, the stomatal density is 100,130 mm-2, the stomatal cover is covered with a round or oval stomatal cover, and there is a circular opening in the center of the stomatal cover. These characteristics are related to the reduction of transpiration rate. The cross-sectional structure is similar to that of general C3 plants. Mesophyll cells have no differentiation between spongy tissue and palisade tissue, and there are no chloroplasts in vascular bundle sheath cells. There are piles of thick-walled and woody subepidermal fiber bundles between the upper and lower epidermis, which play a supporting role. Leaf chloroplast grana is more developed, there are more osmiophilic granules, no starch granules.

2. The quantum yield of photosynthesis: the quantum yield of functional leaves is about 0.082 (quantum requirement 12). The light compensation point of photosynthesis is only 5uEm-2s-1, and the light saturation point is about 200uEm-2s-1. Within the range of 100uEm-2s-1 light intensity, the increase of O _ 2 release rate of photosynthesis is linear. The quantum yield of three-year-old leaves is only about 0.005, and the leaves have shown senescence. The result of light saturation point has application value in orchid cultivation. The light intensity of light saturation point is 10: 15% of that at noon in summer.

3. The activities of several enzymes related to photosynthesis and photosynthetic pathway, glycolic acid metabolism and chlorophyll a / b ratio in leaves, the leaves of Magnolia had higher activity of 1.5-ribose bisphosphate carboxylase (RuBPC), but the activities of phosphoenolpyruvate carboxylase (PEPCasc) and acetone phosphate dikinase (PPDK) were very low, and the activity of glycolate oxidase was also higher. The content of glycolic acid in leaves treated with a-HPMS under light increased significantly, and the determination of chlorophyll content showed that the ratio of chlorophyll a to b was basically stable at about 2.7. These results show that Cymbidium is a plant of C3 photosynthetic pathway.

4. The effects of photosynthetic rate and temperature on leaves of Cymbidium chinense: the photosynthetic rate of leaves of Cymbidium is very low, the photosynthetic rate of functional leaves is generally about 2.6umolco2m-2s-1 (2.2~3.0umolco2m-2s-1), while that of general plants is between 5.0~50umolco2m-2s-1. The optimum temperature for photosynthesis of annual functional leaves is about 25 ℃. The photosynthetic rate of three-year-old leaves decreased with the increase of temperature. Their law of change has its own characteristics.

5. The effect of temperature on CO2 compensation point and CO2 release rate in CO2-free air: the compensation point of * CO2 in leaves of Magnolia is between 105 and 220ppm (usually 35~90ppm in C3 plants). In CO2-free air, leaves had a higher CO2 release rate under light, and increased with the increase of temperature. (Ye Qingsheng, Pan Ruichi)