No abstract

The genetic basis of cold-tolerance was investigated by analyzing the quantitative trait loci (QTL) of an F2:3 population derived from a cross between two lines bred for contrasting cold-tolerance using chlorophyll fluorescence as a selection tool. Chlorophyll fluorescence parameters, CO2 exchange rate, leaf greenness, shoot dry matter and shoot nitrogen content were determined in plants grown under controlled conditions at 25/22 degrees C or 15/13 degrees C (day/night). The analysis revealed the presence of 18 and 19 QTLs (LOD > 3.5) significantly involved in the variation of nine target traits in plants grown at 25/22 degrees C and 15/13 degrees C, respectively. Only four QTLs were clearly identified in both temperatures regimes for the same traits, demonstrating that the genetic control of the performance of the photosynthetic apparatus differed, depending on the temperature regime. A major QTL for the cold-tolerance of photosynthesis was identified on chromosome 6. This QTL alone explained 37.4 of the phenotypic variance in the chronic photoinhibition at low temperature and was significantly involved in the expression of six other traits, including the rate of carbon fixation and shoot dry matter accumulation, indicating that the tolerance to photoinhibition is a key factor in the tolerance of maize to low growth temperature. An additional QTL on chromosomes 2 corresponded to a QTL identified previously in another population, suggesting some common genetic basis of the cold-tolerance of photosynthesis in different maize germplasms.

method has been used extensively to investigate the Key words: Chlorophyll fluorescence, cold tolerance, response of plants to environmental stress, including the photosynthesis, breeding, maize. effects of low temperature on the photosynthetic apparatus of maize both in a controlled environment (Havaux,

No abstract

Leaves of Zea mays L. seedlings which developed at optimal (25 °C) or suboptimal (15 °C) temperature were exposed to high irradiance (1000/imoI m~^ s~') and a severe chilling temperature (5 °C) for up to 24 h to investigate their ahility to withstand photooxidative stress. During this stress, the degradation of the endogenous antioxidants ascorbate, glutathione and a-tocopherol was delayed and less pronounced in 15 °C leaves. Similarly, the decline in chlorophyll a, chlorophyll b, 3-carotene and lutein was slower throughout the stress period. Faster development and a higher level of non-photochemical quenching (NPQ) of chlorophyll fluorescence, related to a stronger de-epoxidation of the larger xanthophyll cycle pool in 15 °C leaves, could act as a defence mechanism to reduce the formation of reactive oxygen species during severe chilling. Furthermore, plants grown at suboptimal temperature exhibited a higher amount of the antioxidants glutathione and a-tocopherol. The higher a-tocopherol content in leaves (double based on leaf area; 4-fold higher based on chlorophyll content) which developed at suboptimal temperature may play an especially important role in the stabilization of the thylakoid membrane and thus prevent lipid peroxidation.