Chlorophyll (Chl) fluorescence is a subtle reflection of primary reactions of photosynthesis. Intricate relationships between fluorescence kinetics and photosynthesis help our understanding of photosynthetic biophysical processes. Chl fluorescence technique is useful as a non-invasive tool in eco-physiological studies, and has extensively been used in assessing plant responses to environmental stress. The review gives a summary of some Chl fluorescence parameters currently used in studies of stress physiology of selected cereal crops, namely water stress, heat stress, salt stress, and chilling stress.
The impact of drought stress (DS) on eight Eurasian and North African genotypes of wild barley (Hordeum spontaneum) was evaluated by analysis of chlorophyll (Chl) a fluorescence fast induction curves using the JIP-test. Three-week-old, pot-grown plants were exposed to a DS treatment by withholding water for nine days. The genotype-specific impairment of the functionality of the photosynthetic electron transport chain was quantified using the relative decline of the performance indices (PIabs and PItot), two key parameters of the JIP-test. The genotypes showing the highest (HOR10164) and lowest (HOR10710) relative PIs under DS were subjected to additional experiments, including measurements of leaf gas exchange, water status, pigment content, key enzyme activity, and protein abundance. The genotypes showed a specific profile of DS-mediated inhibition of photosynthesis, associated with higher relative leaf water contents in HOR10164 at the end of the treatment. Whereas decreased photosynthetic rate in HOR10164 was mainly caused by stomatal closure, nonstomatal limitations (decreased Rubisco content and activity) were detected in HOR10710. Additional genotype specific features were the upregulation of the NADP-malate dehydrogenase in HOR10164 and a decreased fraction of QA-reducing reaction centers in HOR10710., C. Jedmowski, S. Bayramov, W. Brüggemann., and Obsahuje bibliografii
In order to understand the physiological traits important in conferring salt tolerance in three barley genotypes, this study was performed under field conditions with three water salinity levels (2, 10, and 18 dS m-1). High salinity decreased net photosynthetic rate, transpiration rate, and stomatal conductance, K+ concentration, K+:Na+ ratio, and grain yield, but increased electrolyte leakage and Na+ content. Under 10 and 18 dS m-1 salinity, Khatam (salt-tolerant) had the maximum stomatal conductance, K+, K+:Na+ ratio, and the grain yield, and a minimum Na+ content and electrolyte leakage, whereas Morocco (salt-sensitive) had the lowest net photosynthetic rate, stomatal conductance, K+ content, K+:Na+ ratio, and grain yield, and the highest Na+ content and electrolyte leakage. This study showed that tolerant genotypes of barley may avoid Na+ accumulation in aboveground parts, facilitating a higher photosynthetic rate and higher grain yield., M. Mahlooji, R. Seyed Sharifi, J. Razmjoo, M. R. Sabzalian, M. Sedghi., and Obsahuje bibliografii
The univoltine leaf miner Chromatomyia fuscula Zetterstedt is a Scandinavian cereal pest. We wanted to compare the phenology of C. fuscula in southern Norway with that of its most important natural enemies: 15 parasitoids of the families Eulophidae and Pteromalidae (Hymenoptera: Chalcidoidea). The use of two Malaise traps in an organically-grown spring barley field and its boundary through 6 seasons (1992-1997) also allowed us to compare these two habitats and to observe the effect of harvesting on the parasitoid activity without interference from pesticides. C. fuscula overwinters as an adult and oviposits in May/June. Few specimens of the next generation, emerging in the crop, were caught in the boundary traps, suggesting the fly hibernates elsewhere. In contrast, the F1 generation of the parasitoids was caught in considerable amounts both in the crop and boundary. The abundance of parasitoids was highest in July/August; in the crop it usually started decreasing well before harvesting; in the boundary it peaked two weeks or more after harvesting. The results suggest that many parasitoids (especially females) move from the crop to the boundary (or beyond) before harvesting. In both habitats parasitoid species richness usually increased until harvesting, and thereafter decreased. The pooled parasitoid female proportion was 0.36; in crop and boundary it was 0.30 and 0.66, respectively, and the majority of species had a higher proportion of females in the boundary than in the crop. The phenology of two of the most common parasitoids is presented: The pupal parasitoid Cyrtogaster vulgaris Walker (Pteromalidae) had a high activity in the boundary, also very early (females only) and late (both sexes) in the season. The larval parasitoid Diglyphus begini (Ashmead) (Eulophidae) was less active early and late in the season, and had a much smaller boundary activity than C. vulgaris. Both sexes were present throughout the season. The annual sex ratio of D. begini was density dependent, being highly male biased in the two years with highest catches. In C. vulgaris neither density nor habitat explained the sex ratio. D. begini probably overwinters inside the mine as a preadult, having one generation on C. fuscula in the crop and another one in an alternate host away from the habitats sampled here. C. vulgaris overwinters as fertilized females in the border habitat.
The univoltine leaf miner Chromatomyia fuscula (Zetterstedt) (Diptera: Agromyzidae) is a regular cereal pest in Scandinavia. The fly and its most important parasitoids were studied in a 15.5 ha organically-grown field in southern Norway. Each year (1992-1997), one Malaise trap was placed in the spring barley part (2.5 ha) of the field, and (except for 1994) another along the nearest wooded boundary for the whole season. Because of crop rotation, the traps changed position every year. C. fuscula and 15 parasitoid species previously reared from C. fuscula were sorted from the catches.
Few C. fuscula were trapped in the boundary, suggesting that at least the lower vegetation strata were unimportant for the overwintering fly (C. fuscula overwinters as an adult). The parasitoid complex was remarkably stable over years, and 13-15 of the species were: found each year (habitats combined); 0-6 of the species were not found in both habitats each year. Only 4 species attained fractions higher than 10% of the total annual catches in both habitats during the 6 years: the larval parasitoids Diglyphus begini (Ashmead) and Hemiptarsenus unguicellus (Zetterstedt), and the pupal parasitoids Cyrtogaster vulgaris Walker and Chrysocharis pubicornis (Zetterstedt). In the boundary, C. vulgaris dominated every year (43-83%). In the crop, this species alternated with D. begini (1992, 1994) or H. unguicellus (1997) as the dominant species.
In most years, the catches of both the leaf miner and its parasitoids were larger in the crop than in the boundary, but the species number and composition were fairly similar in the two habitats. The parasitoid diversity (Shannon-Wiener H') tended to be higher in the crop (0.8-2.0) than in the boundary (0.8-1.8). Correspondingly, the evenness (both Shannon-Wiener J' and species rank on In abundance) was higher, and the dominance (Berger-Parker) lower, in the crop than in the boundary. Every year, overwintered C. fuscula invaded the crop, but only in 1993 and 1997 did the trapping reveal a distinct next generation, suggesting a very high pre-adult mortality the other years. In 1993 and 1997, C. vulgaris and D. begini had rather similar abundances in the crop, and the lowest combined fractions (less than 60%) of the years, leading to the highest diversity and the lowest dominance through the 6 years (in both habitats).
Our results indicate that the boundary was part of the parasitoids' foraging/overwintering area, and that the boundary was more important to the parasitoids than to their leaf miner host. Boundaries therefore seem to be important for the control of C. fuscula.
Twelve-day-old barley seedlings were supplied with 23 μM methyl jasmonate (MeJA) or 10 μM paraquat (Pq) via the transpiration stream and kept in the dark for 24 h. Then they were exposed to 100 μmol m-2 s-1 PAR and samples were taken 1, 2, 3, and 6 h after irradiation. Treatment of seedlings with MeJA alone resulted in decreased content of chlorophyll (Chl), and net photosynthetic (PN) and transpiration rates. Pq treatment led to a decrease in Chl content and to a very strong inhibition of PN, the effects were manifested by 1 h of irradiation. Pq treatment did not affect the activity of ribulose-1,5 bisphosphate carboxylase (RuBPC, EC 4.1.1.39) but increased the activity of the photorespiratory enzymes phosphoglycolate phosphatase (PGP, EC 3.1.3.18), glycolate oxidase (GO, EC 1.1.3.1), and catalase (EC 1.11.1.6). Pre-treatment of seedlings with MeJA before exposure to Pq fully blocked the inhibitory effect of Pq on photosynthesis and protected against subsequent Pq-induced oxidative damage. and V. A. Hristova, L. P. Popova.