Usin‘gZhangqiu Dacong’scallion as control,changes of malondialdehyd(eMDA)content, electrolyte leakage,chlorophyll fluorescence parameters and antioxidant enzyme activities were studied in leaves of heat-tolerant scallion,‘Chunwei’,‘Jiye Wanchou’And‘Changyue’,at 25–50℃.The results showed that the extent of decrease in the maximum photochemical efficiency of photosystemⅡand of the increase in electrolyte leakage in leaves of the heat-tolerant scallion was less than that in leaves of the ‘Zhangqiu Dacong’scallion at high temperature,indicating that the thermostability of photosystemⅡand cell membrane was higher in the heat-tolerant scallion than that in the‘Zhangqiu Dacong’scallion.At high temperature,the activities of superoxide dismutase(SOD),catalase(CAT)and ascorbate peroxidase (APX)increased in leaves of the heat-tolerant scallion and‘Zhangqiu Dacong’scallion,but the increase extent was greater in the summer scallion,which suggests that heat-tolerant scallion had a higher antioxidant capacity than the‘Zhangqiu Dacong’scallion did.Having higher antioxidant ability is one of the reasons for higher heat tolerance in the leaves of heat-tolerant scallion.

For the purpose of detecting QTLs associated with photosynthetic related traits, a set of 168 doubled haploid (DH) lines derived from the cross between Huapei 3 and Yumai 57 was tested with 324 SSR markers covering the whole genome of wheat (Triticum aestivum L.). The net photosynthetic rate, gas changes, chlorophyll content, and chlorophyll fluorescence in leaves were investigated in both DH population and the parents at seedling stage. QTL analysis was carried out using QTLNetwork version 2.0 based on the mixed linear model. A total of 17 additive QTLs and 20 pairs of epistatic QTLs were detected for the photosynthetic related traits. All additive QTLs and 16 pairs of epistatic QTLs had interactions with environments. In agreement with the high correlations of phenotypes, several traits shared common QTL regions, and showed tight linkages of these QTLs or pleiotropisms. In the interval between Xwmc215 and Xgdw63 on chromosome 5D, three major additive QTLs for chlorophyll a, chlorophyll b, and carotinoid contents explained the phenotypic variations by 18.23%, 10.40%, and 27.25%, respectively, whose positive alleles were all originated from Huapei 3. These QTLs are favorable for marker-assisted selection. In addition, this region was near the QTLs for net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and the ratio of Ci to gas conductance (Cr). The QTL for Ci on chromosome 5B was a minor locus but explained relatively great phenotypic variation in the interactions between QTLs and environments.

Quantitative trait loci (QTLs) for chlorophyll content were studied using a doubled haploid (DH) population with 168 progeny lines, derived from a cross between two elite Chinese wheat cultivars Huapei 3 × Yumai 57. Chlorophyll content was evaluated at the maximum tillering stage (MS), the heading stage (HS), and the grain filling stage (GS), at three different environments in 2005 and 2006 cropping seasons. QTL analyses were performed using a mixed linear model approach. A total of 17 additive QTLs and nine pairs of epistatic QTLs were detected. Ten of 17 additive QTLs for chlorophyll content were persistently expressed at more than two growth stages, which suggest developmentally regulated loci controlling genetics for chlorophyll content in different growth stages in wheat. One novel major QTL for chlorophyll content was closely linked with the PCR marker Xwmc215 and was persistently expressed at three growth stages.

In order to offer stable and consistent growth environment,the phytotron was used to study the gene assignment for photosynthetic characters of DH winter wheat seedlings.The results showed that this method could alleviate the environmental deviation and make the measured results more stable and accurate.