Photosynthetic Performance And Response To Water Stress In Wheat Varieties With Different Ecotype

This study was conducted in Agricultural University of Hebei, Baoding during 1999-2001. The photosynthetic performance, physiological mechanism and the response to water stress during late growing period of wheat varieties from different ecological regions, of which JingdongS from Beijing Acdemy of agricuture and forestry, Henong859 from Agricuturial University of Hebei, and Yangmail58 from Nanjing Agricuturial University as materials were studied. The main results were as follows:1. Net photosynthetic rate (PJ, chlorophyll content (Chi), stomatal conductance (gj and mesophyll conductance (g^) of flag leaves reached maximum values for all tested varieties at leaf full expansion, then gradully declined with senescence process. All the dynamics of the parameters above showed different patterns for different varieties. Spring variety had the highest chlorophyll content and stomatal conductance, while the semi-winter variety showed the highest photosynthetic rate and the highest mesophyll conductance, winter variety had the middle values among all the parameters related.The relative steady phase of chlorophyll content (RSP), photosynthetic active durition (PAD) and leaf source capacity (LSC) of varieties with different ecotype were different. And also, LSC were positively correlated to RSP and PAD significantly. Among the three varieties, semi-winter variety had the highest photosynthetic rate, higher chlorophyll content, longer RPS and PAD, but smallest LSC. Winter variety had the lowest chlorophyll content, shortest RSP and PAD, but there were not remarkable difference between semi-winter and .winter varieties for photosynthetic rates and photosynthetic areas. While spring variety showed that the photosynthetic areas and the PAD were biggest, but the net photosynthetic rate was lowest, the LSC between the winter variety and semi-winter variety.2. When exposed to water stress, the Pn, Chi, g,, ,, RSP, PAD and LSC of flag leaves for the three varieties with different ecotypes were significantly lower than those with necessary irrigation. The declining values of different photosynthetic physiologicalparameters were also different for different varieties. The response of spring variety (Yangmail58) to water stress showed that the seriously inhibited parameter was gm, and the RSP and PAD followed, then were the photosynthetic area and g,, and the inhibitation of chlorophyll content and pthotosynthetic rate by water stress were the least. Semi-winter variety (Henong859) showed that gm was inhibited most severely, and followed by RSP and PAD, photosynthetic rate, chlorophyll content, gs was also the least inhibited parameter. While the winter variety showed that RSP and PAD were the biggest inhibition, followed by LA, gm, gs, and Pn, chlorophyll content was least inhibited. The results showed that wheat varieties with different ecotype were differently affected by water stress for their carbon assimilation characters.3 The Hill reaction activity, unicycle photosynthetic phosphorylation activity and ATPase activity of flag leaves showed commonly dynamics patterns among the three varieties with different ecotype, that is semi-winter variety (henong859) had the highest activity on above physiological parameters, the second was winter variety (jingdongS), spring variety had the lowest activity. And also Hill reaction activity, unicycle photosynthetic phosphorylation activity and ATPase activity of flag leaves were positively correlated with photosynthetic rate. But when exposed to water stress, ATPase activity showed differently compared with Hill reaction activity and unicycle photosynthetic phosporylation activity. That is , the Hill reaction activity and unicycle photosynthetic phosporylation activity declined under water stress, but the ATPase activity declined at first and then increased rapidly. This was probably due to the denaturation of membrane protein which inhibited the photosynthetic phosphorylation activity leading to the increase of ATPase activity.The Hill reaction activity, unicycl...