Leaf senescence in a non-yellowing mutant of Festuca pratensis: Photosynthesis and photosynthetic electron transport

The photosynthetic capacity of detached leaves of a non-yellowing mutant of Festuca pratensis Huds. declined during senescence at a similar rate to that in a normal cultivar. Respiratory oxygen uptake in the dark continued at similar rates in both genotypes during several days of senescence. In chloroplasts isolated from leaves at intervals after excision, the rate of photosystem I (PS I)-mediated methyl viologen reduction using reduced N,N,N,N-tetramethyl-p-phenylene diamine as electron donor also declined in both genotypes, possibly due to loss of integrity of the photosynthetic apparatus in the cytochrome f-plastocyanin region. There was a similar fall in PS II electron transport using water as electron donor and measured at the rate of reduction of 2,6-dichlorophenolindophenol. Partial restoration of this activity by the addition of diphenyl carbazide was evidence for lability of the oxygen-evolving complex during senescence. An accentuated difference between mutant and normal material in this case indicated that the mutant retains a greater number of functional PS II centres. Changes in the light-saturation characteristics of the two photosystems have been discussed in relation to the organization of the photosynthetic membranes during senescence.Abbreviations and symbols DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorophenolindophenol - DMSO dimethyl sulphoxide - DPC diphenyl carbazide - MV methyl viologen - PS I, PS II photosystem I, II - TMPD N,N,N,N-tetramethyl-p-phenylene diamine     

Photosynthetic characteristics of detached barley leaves during greening in the presence of SAN 9785

The effects of the pyridazinone compound SAN 9785 on the photosynthetic competence of leaves, on the photochemical activity of isolated thylakoids and on the formation and spectral properties of chlorophyll-protein complexes were studied during a 72-h greening period of detached etiolated leaves of barley (Hordeum vulgare L. cv. Horpácsi kétsoros). It was established that i) the photosynthetic capacity of the leaves decreased considerably (by 80 and 90%, as determined by¹⁴CO₂ fixation and fast fluorescence induction measurements, respectively); ii) the photochemical activity of isolated thylakoids from water to potassium ferricyanide and from dichlorophenol indophenol/ascorbate to methylviologen exhibited only slight reductions when expressed on a chlorophyll basis compared with the control; iii) the slow fluorescence induction curves of the treated leaves demonstrated the presence of a peculiar fluorescence component interrupting the quenching of fluorescence at around 1 min illumination; iv) a shortage of the chlorophyll-protein complex of photosystem I (CPI) occurred with a higher content of the monomer of the light harvesting complex in the thylakoids of treated leaves; and v) the fluorescence spectrum of the CPI band present in treated leaves indicates the destruction of the structural integrity of this complex during isolation from the membrane.Abbreviations Chl chlorophyll - CPI, CPII chlorophyll-protein complexes of the reaction centres of PSI and PSII - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DPIP 2,6-dichlorophenol indophenol - DPIPH₂ chemically reduced form of DPIP - F _o fluorescence of constant yield - F _v fluorescence of variable yield - F _i ,F _m mitial and maximum yield of fluorescence - LHCP³ monomer of the light-harvesting complex - LHCP² and LHCP¹ oligomers of the light-harvesting complex LHCP³ - PSI, PSII photosystems I, II - SAN 9785 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone, also known as BASF 13-338 - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis     

叶龄及树冠不同部位光强对黄花梨光合速率的影响

笔者以黄花梨为试材,研究了叶龄及树冠不同部位光强对其光合速率的影响。结果表明:黄花梨叶片在展叶后约11天即有少量光合产物输出,25天时,单叶净光合速率接近最大值;密植梨树高光合叶幕厚度约125cm左右。     

点叶绵枣叶片培养及器官分化的研究

点叶绵枣叶外植体培养于MS 6-BA 1 PPm IBA 0.5 ppm培养基中,一月后不定芽仅从近轴面的叶表面产生。组织学的观察表明,不定芽起源于表皮细胞。     

Infidelity of leafcutting ants to host plants: resource heterogeneity or defense induction?

Summary Leafcutting ants have strong among- and within-plant preferences, and generally abandon plants long before they are completely defoliated. Two tropical deciduous forest tree species preferred by the leafcutting ant Atta colombica were studied to determine how variation in resource quality affects ant selectivity and partial defoliation of plants. Significant differences in palatability and leaf characteristics of Spondias mombin and Bursera simaruba were found among trees and among leaf types within trees, but not among branches within trees. No short-term responses to experimental defoliation of up to 50% of total canopy were found in either species. Leaf nutrient and poisture content were positively correlated, and phenolic content negatively correlated, with the palatability of Spondias mombin, a species containing hydrolyzable tannins. Leaf moisture and phenolic content were both positively correlated with the palatability of Bursera simaruba, which contains predominantly condensed tannins. The results suggest that variation in leaf quality among and within plants is at least a partial explanation for ant selectivity and partial defoliation of preferred species. There is no evidence that rapidly induced changes in plant chemistry affect ant decisions to abandon these plants. Instead, it appears likely that ants abandon plants once high-quality leaf patches are exhausted. Quantitative variation in leaf nutrients, moisture, and secondary chemicals all appear to contribute to ant preferences for individuals and tissues of highly palatable plants.     

Leaf thionins, a novel class of putative defence factors

Leaf thionins of barley have been identified as a novel class of highly abundant polypeptides with antifungal activity, which are present in walls and vacuoles of barley leaf cells. Similar thionins occur not only in monocotyledonous but also in various dicotyledonous plants. The leaf thionins of barley are encoded by a complex multigene family, which consists of at least 50–100 members per haploid genome. The toxicity of these thionins for plant pathogenic fungi and the fact that their synthesis can also be triggered by pathogens strongly suggest that leaf thionins are involved in the mechanism of plant defence against microbiol infection.     

Insect capture and growth of the insectivorous Drosera rotundifolia L.

Summary Rates of insect capture increased with leaf area in the insectivorous plant Drosera rotundifolia, and growth of new leaves was related to insect capture. However, increased leaf growth was counterbalanced by leaf abscission which was in turn related to insect capture and leaf growth. Leaf loss equaled leaf growth in plants having natural rate of insect capture. A large proportion of the nitrogen gain from prey was stored in the hypocotyl; it was estimated from feeding experiments that about 24% to 30% of the nitrogen stored in the hypocotyl after winter originated from insect capture in the previous season. The effect of insect capture is discussed in relation to the life cycle of Drosera.     

Trade-off among antiherbivore defences in a south american blackberry (Rubus bogotensis)

Summary The idea of trade-offs among antiherbivore defences in plants is examined using data from a South American blackberry (Rubus bogotensis). Two distinct morphs of R. bogotensis, one with glandular trichomes and one without, were compared with respect to leaf toughness, number of prickles and prickle length. The two morphs were sympatric and grew under similar environmental conditions. The morph lacking trichomes had significantly tougher leaves and also tended to have more and longer prickles. Bioassay showed that Ithomiid larvae fed to a lesser extent on tough leaves than on more tender ones. Correlations between antiherbivore defences within each phenotype revealed three significant or almost significant negative relationships. The comparisons support the hypothesis that trade-offs exist among antiherbivore defences.     

Linkage mapping of genes for resistance to leaf,stem and stripe rusts and ω-secalins on the short arm of rye chromosome 1R

Summary The genes controlling resistance to three wheat rusts, viz., leaf rust (Lr26), stem rust (Sr31) and stripe or yellow rust (Yr9), and -secalins (Sec1), located on the short arm of rye chromosome 1R, were mapped with respect to each other and the centromere. Analysis of 214 seeds (or families derived from them) from testcrosses between a 1BL.1RS/1R heterozygote and Chinese Spring ditelocentric 1BL showed no recombination between the genes for resistance to the three rusts, suggesting very tight linkage or perhaps a single complex locus conferring resistance to the three rusts. The rust resistance genes were located 5.4 ± 1.7 cM from the Sec1 locus, which in turn was located 26.1 ± 4.3 cM from the centromere; the gene order being centromere — Sec1 — Lr26/Sr31/Yr9 — telomere. In a second test-cross, using a different 1BL.1RS translocation which had only stem rust resistance (SrR), the above gene order was confirmed despite a very large proportion of aneuploids (45.8%) among the progeny. Furthermore, a map distance of 16.0 ± 4.8 cM was estimated for SrR and the telomeric heterochromatin (C-band) on 1RS. These results suggest that a very small segment of 1RS chromatin is required to maintain resistance to all three wheat rusts. It should be possible but difficult to separate the rust resistance genes from the secalin gene(s), which are thought to contribute to dough stickiness of wheat-rye translocation lines carrying 1RS.