EFFECT OF NONRANDOM LEAF ORIENTATION ON REPRODUCTION IN LACTUCA SERRIOLA L.

The cauline leaves of an annual, Lactuca serriola L., are naturally oriented vertically with the lamina perpendicular to the east and west. Previous physiological data indicated that this nonrandom leaf orientation should reduce water loss without substantially reducing photosynthesis and could thus influence plant growth and reproduction (Werk and Ehleringer, 1984, 1985). The effect of leaf orientation on flower and seed production was tested experimentally using potted L. serriola grown outdoors. Leaves of half the plants were forced to remain approximately horizontal while the other plants were allowed to orient naturally. The plants with horizontal leaves lost water more rapidly than the plants with naturally oriented leaves. Above-ground weight, below-ground weight, seed weight, and the number of seeds per flower were not significantly affected by leaf orientation. Flower production was a linear function of plant size for both treatments with plants with natural leaf orientation having a significantly greater slope. These results indicate that the nonrandom leaf orientation observed in L. serriola is a morphological character which can enhance reproduction.     

Performance of two Picea abies (L.) Karst. stands at different stages of decline

Summary The water relations of Picea abies in a healthy stand with green trees only and a declining stand with trees showing different stages of needle yellowing were investigated in northern Bavaria. The present study is based on observations of trees differing in their nutritional status but apparently green on both sites in order to identify changes in the response pattern which might be caused by atmospheric concentrations of air pollutants and could lead to the phenomenon of decline. Transpiration was measured as water flow through the hydroactive xylem using an equilibrium mass-flow measurement system. Total tree transpiration was monitored diurnally, from July 1985 until October 1985 at both sites. The relationship between transpiration and meteorological measurements indicated that transpiration was a linear function of the vapor pressure deficit. No differences in transpiration of green trees were observed between the two sites. Canopy transpiration was 57%–68% of total throughfall and 41%–54% of total rainfall. Due to this positive water balance, soil water potential at 10 and 20 cm depths remained close to-0.02 MPa (max.-0.09 MPa) for most of the summer. Soil water potential was correlated with the difference between the weekly precipitation and transpiration. No differences in the water relations of apparently healthy trees in the two P. abies stands were observed. It is concluded that differences between green trees at the two sites in terms of nutrient relations or growth rate cannot be explained by changes in whole-tree transpiration or soil water status.     

Performance of two Picea abies (L.) Karst. stands at different stages of decline

Summary The annual replacement of tillers of Agropyron desertorum (Fisch. ex Link) Schult., a grazing-tolerant, Eurasian tussock grass, was examined in the field following cattle grazing. Heavy grazing before internode (culm) elongation seldom affected tiller replacement. Heavy grazing during or after internode elongation, which elevates apical meristems, increased overwinter mortality of fall-produced tillers and reduced the number and heights of these replacement tillers. Unexpectedly, tussocks grazed twice within the spring growing season tended to have lower overwinter tiller mortality, greater tiller replacement, and larger replacement tillers than tussocks grazed only once in late spring. These responses of twice-grazed tussocks, however, were still less than those of ungrazed tussocks or tussocks grazed moderately in early spring. The presence of ungrazed tillers on partially grazed tussoks did not increase the replacement of associated grazed tillers relative to tillers on uniformly grazed plants. This result indicates that resource sharing among tillers, if present, is short-lived or ecologically unimportant in this species. Although A. desertorum is considered grazing-tolerant, tiller replacement on heavily grazed tussocks, particularly those grazed during or after internode elongation when apical meristems were removed, was usually inadequate for tussock maintenance. These observations at the tiller (ramet) level of organization in individual tussocks (genet) may explain the often noted reduction in stand (population) longevity with consistent heavy grazing.     

Relationships between foliage and conducting xylem in Picea abies (L.) Karst.

Summary The relationship of leaf biomass and leaf area to the conductive area of stems and branches was investigated in Picea abies. A total of 30 trees were harvested to determine if these relationships were different in different crown zones and in trees growing with and without competition for light. Two methods were compared. In the first, data were accumulated from crown zones situated at the top of trees to the bottom; in the second, data were used from individual crown zones. The results indicated that the latter method is much more sensitive in detecting differences in the relationship of leaf biomass or leaf area to conductive area. The analysis also indicated that ratios such as leaf area/sapwood area are frequently size-dependent. This size-dependency can in some cases result in the differences being abscured, but more often leads to the false impression that the relationship between the variables changes. The relationship between leaf biomass and leaf area and conductive area of stems or branches was different in different crown zones and under different growth conditions. The slopes of these regressions appear to increase with decreasing transpirational demand and decrease with increasing hydraulic conductivity. The intercepts are probably related to the amount of identified sapwood actually involved in water conductance.     

Gaining target access for deoxyribozymes

Antisense oligonucleotides and ribozymes have been used widely to regulate gene expression by targeting mRNAs in a sequence-specific manner. Long RNAs, however, are highly structured molecules. Thus, up to 90% of putative cleavage sites have been shown to be inaccessible to classical RNA based ribozymes or DNAzymes. Here, we report the use of modified nucleotides to overcome barriers raised by internal structures of the target RNA. In our attempt to cleave a broad range of picornavirus RNAs, we generated a DNAzyme against a highly conserved sequence in the 5' untranslated region (5' UTR). While this DNAzyme was highly efficient against the 5' UTR of the human rhinovirus 14, it failed to cleave the identical target sequence within the RNA of the related coxsackievirus A21 (CAV-21). After introduction of 2'-O-methyl RNA or locked nucleic acid (LNA) monomers into the substrate recognition arms, the DNAzyme degraded the previously inaccessible virus RNA at a high catalytic rate even to completion, indicating that nucleotides with high target affinity were able to compete successfully with internal structures. We then adopted this strategy to two DNAzymes that we had found to be inactive in our earlier experiments. The modified DNAzymes proved to be highly effective against their respective target structures. Our approach may be useful for other ribozyme strategies struggling with accessibility problems, especially when being restricted to unique target sites.     

Formation of false stems in Cymopterus longiopes: an uplifting example of growth form change

Summary The leaves of Cymopterus longipes form prostrate rosettes early in the spring. As the weather warms, these leaves are elevated on a pseudoscape (false stem) which develops below the rosette through the elongation of the caudex (in the region between root and shoot). The effect of this growth form change on the water relations and photosynthesis in C. longipes was investigated. Pseudoscape height was not linked to phenology or plant size. Leaf conductance, leaf temperature, and leaf water potential were notably similar between plants with different pseudoscape height growing in different microsites. Experimental manipulation of the microclimate around plants growing naturally allowed us to demonstrate that increased temperature led to an increase in the rate of pseudoscape elongation. By changing the distance above the ground surface of the rosettes of some plants we determined that leaf temperature, leaf to air vapour concentration deficits, leaf conductances, and leaf water potentials were all influenced by pseudoscape height. Leaf conductance in C. longipes had a strong negative relationship with W. Since the temperature response of net photosynthesis was extremely flat it was concluded that pseudoscape elongation may be an important morphological means of increasing water use efficiency.     

Artenschwund trotz Naturschutz

Species loss despite nature conservation: need for action and research About 40 per cent of all plant and animal species occurring in Germany (insects, mammals, fish, birds, amphibians and reptiles) are endangered or threatened with extinction; 3–4 per cent are already considered lost. A comparison with other European countries shows that the risk situation in Germany is also very serious from an international point of view. In order to better anchor nature conservation in modern society as a prerequisite for globally sustainable development, it is necessary (1) to rethink and change the actions of each individual through education, communication and discussion; (2) to refocus policy and existing funding instruments; (3) to strengthen biodiversity and nature conservation concerns in and through universities and colleges, and (4) to invest in nature conservation in order to preserve nature as the basis of human life (ecosystem services) and on account of its intrinsic value. Conservation must be economically viable. This should not only be the case for farmers, but also for any land use that meets the requirements of nature conservation. Any conservation effort should be rewarded. To ensure that the actually set and clearly defined objectives of the EU nature conservation directives can be achieved, the Federal Working Group on Nature Conservation, Landscape Conservation and Recreation (LANA) predicts that at least 1.4 billion euros additionally will be needed annually. This would correspond to about 17 euros per inhabitant and year. This comparatively small amount would more than double the budget available in Germany for the protection of biodiversity.     

Assessment of potential impacts associated with gene flow from transgenic hybrids to Mexican maize landraces

Genetically modified (GM) maize has been grown and safely consumed on a global scale since its commercialization in 1996. However, questions have been raised about the potential impact that GM maize could have on native maize landraces in Mexico, which is the center of origin and diversity of maize. This research was conducted to evaluate potential changes to maize landraces in an unlikely event of transgene introgression. For this study, two GM traits that confer insect protection and herbicide tolerance in maize (MON 89034 and MON 88017), designated as VT3Pro, were introgressed into two Mexican landraces, Tuxpeño and Tabloncillo. Field trials were conducted across four environments to assess phenotypic characteristics, plant response to stressors, and kernel composition of landraces with and without VT3Pro traits. Furthermore, materials from four backcrossing generations were analyzed for segregation of these GM traits. Generally, no significant differences were observed between landraces with and without VT3Pro traits for the evaluated characteristics and the segregation analysis showed that GM traits, when introgressed into landraces, followed Mendelian principles. These results support the conclusion that, if inadvertently introgressed into landraces, VT3Pro traits are not expected to alter phenotypic or kernel characteristics, plant response to stressors (except for targeted insect protection and herbicide tolerance traits) and would segregate like any endogenous gene. These results should be taken into consideration when discussing benefits and risks associated with commercial production of GM maize hybrids in the centers of origin and diversity of maize.