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Wild wheat (Triticum aestivum L.) relatives could represent a valuable source of genetic variation for improvement of abiotic stress tolerance in cultivated wheat. A better knowledge of the adaptive strategies developed by these species is needed. A collection of 157 Aegilops geniculata accessions originating from different ecogeographical regions was studied during two successive years for several traits related to water status, chlorophyll content, and plant thermal regulation under Mediterranean field conditions. Close association was found between the studied traits and the origin of accessions. Two adaptive strategies were distinguished. Accessions originating from harsh environments had low biomass, low grain production and high water-use efficiency (low C isotope discrimination). They were early, with small, thick leaves exhibiting low chlorophyll content, high surface temperature and low epidermal transpiration. We suggest that in these accessions, decreased leaf chlorophyll content could limit the energy load from strong sunlight. In accessions originating from regions with a mild Mediterranean climate, thermal regulation of the leaf may rather depend on transpiration, as suggested by high C isotope discrimination values. These accessions also were characterized by high chlorophyll content, leaf area, and biomass production. Associations between the physiological traits observed could help to better understand the relationship between abiotic stress tolerance and yield in cultivated wheats. Results obtained confirmed the potential value of Aegilops geniculata for improvement of high temperature and drought stress tolerance in wheat and could contribute to the choice of traits to be introgressed and the accessions to be used in wide hybridization programs., THE GENUS Aegilops is closely related to Triticum (Kerby and Kuspira, 1988). Interest has developed in recent years in exploiting Aegilops spp. as important genetic resources for wheat improvement (Comeau [...]

Cytochrome c6, the product of the petJ gene, is a photosynthetic electron carrier in cyanobacteria, which transfers electrons to photosystem I and which is synthesised under conditions of copper deficiency to functionally replace plastocyanin. The photosystem I photochemical activity (energy storage, photoinduced P700 redox changes) was examined in a petJ-null mutant of Synechocystis PCC 6803. Surprisingly, photosystem I activity in the petJ-null mutant grown in the absence of copper was not much affected. However, in a medium with a low inorganic carbon concentration and with NH4+ ion as nitrogen source, the mutant displayed growth inhibition. Analysis showed that, especially in the latter, the isiAB operon, encoding flavodoxin and CP43′, an additional chlorophyll a antenna, was strongly expressed in the mutant. These proteins are involved in photosystem I function and organisation and are proposed to assist in prevention of overoxidation of photosystem I at its lumenal side and overreduction at its stromal side. [Copyright &y& Elsevier]

Small discs punched out from leaves of tobacco (Nicotiana tabacum L.) were exposed for 3 rain in the dark to a high temperature of around 48°C. This caused a progressive inhibition of the gas-exchange (oxygen evolution) type photoacoustic signal, resulting' finally in phase inversion (i.e. leading to negative values), which indicates that oxygen uptake replaces the normal oxygen evolution. This effect was also observed in various other plant species. Oxygen uptake was rapidly reversed (within ca. 4-5 min) to a certain low value of oxygen evolution (about 20% of the control) by continuous illumination with relatively strong white light (minimum 55 W m-2). However, a few minutes in darkness following this heat treatment induced reappearence of the uptake signal. This photoacoustically detected oxygen uptake after heat shock may be interpreted as reflecting stimulated oxygen photoreduction (Mehler reaction) caused by (light dependent) inactivation of the Calvin cycle by heat, suggesting that oxygen may act as a major photosynthetic electron acceptor under stress conditions. Leaves suffering from such heat shock effects were completely restored to normal behaviour after a 24-h incubation at room temperature (25°C). Analysis of the modulation frequency and wavelength dependence of the photoacoustic signals showed that heat shock-induced oxygen uptake is a very complex phenomenon, composed of at least two components differing in kinetics and sensitivity to DCMU. [ABSTRACT FROM AUTHOR]

Chilling temperatures drastically inhibited the photochemical quenching of chlorophyll fluorescence (q[SUBQ]) measured in intact leaves photosynthesizing under steady state conditions. This effect appeared, however, to be characteristic of chilling- susceptible plant species and was not observed in plants which are known to be chilling-tolerant, indicating that the measurement of q[SUBQ] can serve in practice to estimate rapidly the relative chilling tolerance of crop plants A large number (28) of sweet sorghum (Sorghum bicolor) and sudan grass (Sorghum sudanense) genotypes were screened for chilling tolerance using this rapid q[SUBQ] n method. Although sweet sorghum and sudan grass obviously behaved as chilling sensitive plants, a considerable variation tot chilling susceptibility was observed among the different genotypes tested, Some sweet sorghum vane ties. such as Dale' and 'Keller', and most of the sudan grass varieties appeared to possess a certain degree of resistance towards low temperature stress, indicating the existence of useful germplasms in Sorghum for improving stress tolerance. [ABSTRACT FROM AUTHOR]

Abstract Background Vitamin B6 is a collective term for a group of six interconvertible compounds: pyridoxine, pyridoxal, pyridoxamine and their phosphorylated derivatives. Vitamin B6 plays essential roles as a cofactor in a range of biochemical reactions. In addition, vitamin B6 is able to quench reactive oxygen species in vitro, and exogenously applied vitamin B6 protects plant cells against cell death induced by singlet oxygen (1O2). These results raise the important question as to whether plants employ vitamin B6 as an antioxidant to protect themselves against reactive oxygen species. Results The pdx1.3 mutation affects the vitamin B6 biosynthesis enzyme, pyridoxal synthase (PDX1), and leads to a reduction of the vitamin B6 concentration in Arabidopsis thaliana leaves. Although leaves of the pdx1.3 Arabidopsis mutant contained less chlorophyll than wild-type leaves, we found that vitamin B6 deficiency did not significantly impact photosynthetic performance or shoot and root growth. Chlorophyll loss was associated with an increase in the chlorophyll a/b ratio and a selective decrease in the abundance of several PSII antenna proteins (Lhcb1/2, Lhcb6). These changes were strongly dependent on light intensity, with high light amplifying the difference between pdx1.3 and the wild type. When leaf discs were exposed to exogenous 1O2, lipid peroxidation in pdx1.3 was increased relative to the wild type; this effect was not observed with superoxide or hydrogen peroxide. When leaf discs or whole plants were exposed to excess light energy, 1O2-mediated lipid peroxidation was enhanced in leaves of the pdx1.3 mutant relative to the wild type. High light also caused an increased level of 1O2 in vitamin B6-deficient leaves. Combining the pdx1.3 mutation with mutations affecting the level of 'classical' quenchers of 1O2 (zeaxanthin, tocopherols) resulted in a highly photosensitive phenotype. Conclusion This study demonstrates that vitamin B6 has a function in the in vivo antioxidant defense of plants. Thus, the antioxidant activity of vitamin B6 inferred from in vitro studies is confirmed in planta. Together with the finding that chloroplasts contain vitamin B6 compounds, the data show that vitamin B6 functions as a photoprotector that limits 1O2 accumulation in high light and prevents 1O2-mediated oxidative damage.