Comparison on Changes of Several Photosynthetic Parameters in Leaf Developing Process between Two Tobacco Cultivars

Changes of photosynthetic parameters in leaves developing process in two tobacco cultivars(Nicotiana tabacum L.cv.'NC89' 'JYH')were comparatively analyzed.The results suggested that the photosynthetic rate displayed elevated phase,active photosynthesis duration(APD)and sharp fall phase while the chlorophyll content displayed elevated phase,relative steady phase(RSF)and Sharp fall phase during leaf developing process.The decline of ribulose 1,5-bisphosphate carboxylase(RuBPCase)activities was obviously faster than that of photosynthetic electron transport activity during the period of decline in leaf photosynthetic function.SDS-PAGE showed that thylakoid membrane polypeptide components of two tobacco cultivars and large sub-units(LSU)of ribulose 1,5-bisphosphate carboxylase/oxygenase(Rubisco)of 'NC89' remained relative steady during reversible decline(RD).During irreversible decline(IRD)thylakoid membrane polypeptide components,LSU and small subunits(SSU)of Rubisco of two tobacco cultivars,especially photosystem II(PSII)complex and Rubisco SSU were degraded rapidly.There were no significant differences of photosynthetic parameters in 10-40 day leaves between the 'JYH' and the 'NC89'.But the APD was shorter,the unbalance between electron transport and carbon assimilation during the decline of photosynthetic function was more serious,and the decline of photosynthetic function was sooner and faster in 'JYH' leaves.