On the parameters of the conduction of CO_2 and carbon assimilation in tobacco leaves

Changes of the conduction of CO 2 and the enzyme of carbon assimilation in tobacco (Nicotiana tabacum L.) leaves on different positions were studied. The results suggested that the photosynthetic rate, mesophyll conductance (g m ), carbonic anhydrase (CA) activity and ribulose-1,5-bisphosphate carboxylase (RuBPCase) initial activity decreased quickly, while stomatal conductance (g s ) maintained relatively stable at first and then fell sharply, and intercellular CO 2 concentration (c i ) changed from increase to decrease and increased again along with the decline of leaf position. It was concluded that the photosynthetic rate was significantly positively correlated with mesophyll conductance and non stomatal limitation factors were the main causes of the decline of photosynthetic function in tobacco leaves.