Patterns of molecular genetic variation in Plantago major and P. intermedia in relation to ozone resistance

Patterns of molecular genetic variation were examined in seed collections of Plantago major and Plantago intermedia , used previously to investigate the variations in ozone (O₃) resistance of these species across Europe. Total genomic DNA was amplified with random primers (random amplied polymorphic DNA (RAPD) and inter- single sequence repeats (SSR)) to produce 73 genetic markers. In addition, allozyme and chloroplast variations were surveyed. Genetic markers were examined for association with O₃ resistance in 18 British populations of P. major as well as 27 continental European populations of P. major and P. intermedia . Two populations that exhibited increased resistance to O₃ following several years' exposure to high O₃ concentrations in the field showed decreased genetic variation over time. In addition, their genetic composition showed no drastic change, which suggests that the change in resistance to O₃ was probably the result of selection on genotypes already present in local populations (selection in situ ). It appears that selection for O₃ resistance may occur in independent populations, and also may involve a number of genetically determined traits. Consequently the finding that plants with similar degrees of O₃ resistance are not closely related was not unexpected. However, the finding of an association of several genetic markers with O₃ resistance merits further investigation.     

Modelling of the responses to nitrogen availability of two Plantago species grown at a range of exponential nutrient addition rates

Abstract. Plantago major ssp. major and P. lanceolata were grown in solution culture with exponential nutrient addition rates. Compared with P. lanceolata, P. major major showed a higher shoot weight ratio (SWR, fraction of plant dry weight in the shoot) and a higher net assimilation rate (NAR, expressed on a leaf dry weight basis) at equal plant (PNC) and shoot (SNC) nitrogen concentration, respectively. No difference was observed in shoot nitrogen ratio (SNR, fraction of plant nitrogen in the shoot) against PNC between the two species. The effect of these differences in matter partitioning and NAR on plant growth was examined by using a growth model. The model assumed (1) that the SWR and SNR are a linear function of PNC and (2) that the NAR is a rectangular hyperbolic function of SNC. Curvilinear relationships were observed between relative growth rate (RGR) and PNC. P. major major had a higher RGR at equal PNC and, thus, a higher nitrogen productivity (NP) than P. lanceolata. Steady-stale exponential growth was simulated for different nitrogen availability in the environment. P. major major had a higher RGR over the whole range of nitrogen availability but the difference attenuated with decreasing availability of nitrogen. The simulation also showed P. lanccolata having higher plasticity in the shoot/root ratio, which resulted from its higher variability in PNC.     

Effects of vesicular-arbuscular mycorrhizal infection and phosphate on Plantago major ssp. pleiosperma in relation to internal cytokinin concentrations

Relations between cytokinin concentrations and effects of P and vesicular-arbuscular mycorrhizal (VAM) infection were investigated in Plantago major L. ssp. pleiosperma Pilger. Both mycorrhizal infection by Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe and P addition increased the shoot to root ratio, specific leaf area (SLA), and P concentrations of shoot and roots, and decreased the percentage of dry matter in the shoot during the experiment. In general, P concentration in the shoot and roots of each treatment correlated positively with the shoot to root ratio and specific leaf area, and negatively with the percentage of dry matter in the shoot. Cytokinin concentrations in the tissue of shoots and roots were determined using an enzyme-linked immunosorbent assay. Concentrations of zeatin and zeatin-ribosides in the free base and nucleotide fractions had increased more after P addition than in the case of mycorrhizal infection in both shoot and roots, whereas the P concentrations had increased less. It is suggested that zeatin and zeatin-ribosides are not the primary growth-substances involved in mediating VAM effects.     

Effects of vesicular-arbuscular mycorrhizal infection and phosphate on Plantago major ssp. pleiosperma in relation to the internal phosphate concentration

Two experiments were carried out to study physiological effects of vesicular-arbuseular mycorrhizal infection on Plantago major L., ssp. pleiosperma (Pilger). In the first experiment, infection by the Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe increased growth, shoot to root ratio, P concentrations in both shoot and roots and total uptake of P per plant. The percentages of dry matter in both shoot and roots were lower in mycorrhizal plants.
In the second experiment different P treatments were applied to both mycorrhizal and non-mycorrhizal P. major plants to separate any effects of mycorrhizal infection from increased uptake of P. In addition to the effects found in the first experiment, mycorrhizal, P, and mycorrhizal x P interaction effects were found on root respiration rate and the concentration of soluble sugars in the roots. No clear effects on total dry weight, N and starch concentrations in shoot and roots and sugar concentraion in the shoot were found. Irrespective of the mycorrhizal treatment, increased P concentration in the shoot correlated with an increased shoot to root ratio and root respiration rate, and a decreased percentage dry matter and sugar concentration in the roots. However, the root respiration rate and the P concentration in the roots of mycorrhizal plants were enhanced more than expected from the increased P concentrations in the shoots of these plants.     

Kinetics of nitrate uptake by different species from nutrient-rich and nutrient-poor habitats as affected by the nutrient supply

The species Urtica dioica L., Plantago major ssp. major L., Plantago lanceolata L., Hypochaeris radicata L. ssp. radicata and Hypochaeris radicata ssp. ericetorum Van Soest were grown under high and low nutrient conditions (1/4 Hoagland and 2% of 1/4 Hoagland further called the 100% and 2% treatment, containing 3.75 mM NO^-₃ and 0.075 mM NO^-₃, respectively). After a certain period half of the plants were transferred from low to high or high to low nutrients, yielding the 100%/2% and the 2%/100% treatments. The kinetics of nitrate uptake in the range of system I of the five species grown under the different nutrient conditions were measured during a three week experimental period. The nitrate uptake of all the species showed the characteristic features of Michaelis-Menten kinetics. Under low nutrient conditions the apparent V_max of U. dioica expressed per g dry root was lower than under high nutrient conditions. For H. radicata ssp. radicata and for H. radicata ssp. ericetorum the reverse was found. The V_max values of P. major ssp. major were almost the same for the two treatments. The apparent V_max in young plants of P. lanceolata was higher in the 100% treatment than in 2%; whereas the reverse was found in mature plants. The results are explained in relation to the relative growth rate, the shoot to root ratio and the natural environment of the species. The apparent K_m values were not influenced by the different treatments. Differences in K_m between the species, if any, were very small. It is suggested that the V_max is a more important parameter for the distribution of plant species in the field than the K_m. The rate of nitrogen accumulation was calculated from growth data and the contents of nitrate and reduced nitrogen. It is concluded that the V_max of system I for nitrate uptake in most cases was sufficient to explain the observed growth rates.     

Patterns of leaf asymmetry changes in Plantago major L. (ssp. major) natural populations exposed to different environmental conditions

In the present study, developmental stability of leaf traits was examined in three natural populations of Plantago major L. (ssp. major), representing two polluted environments (Karaburma and Zemun) and an unpolluted area (Crni Lug). Developmental stability was assessed as fluctuating asymmetry (FA). The magnitude of FA is believed to reflect differences in the ability of individuals to buffer their development in natural populations. We hypothesized that there are differences within characters and among characters in response to environmental conditions. Significant patterns of asymmetry correlations and asymmetry changes were detected both within characters and between characters. The manova results revealed a significant effect of individual and a significant individual × environment interaction on actual asymmetry (logL_i ? logR_i) and on the amount of asymmetry |(logL_i ? logR_i)| for leaf width and vein distances within a leaf. Over time, statistically significant and positive correlations of the FA values were detected for each trait separately per sample (population). For both leaf traits, there were differences for (logL_i ? logR_i) and |(logL_i ? logR_i)| asymmetry values among individuals within samples in response to yearly variations. Statistically significant and negative correlations for (logL_i ? logR_i) versus |(logL_i ? logR_i)| asymmetries were detected for both leaf traits. In summary, our results highlight the importance of differences in the ability of individuals to buffer their development under different environmental conditions and point to the concept that developmental stability is character specific.     

Relation between relative growth rate, endogenous gibberellins, and the response to applied gibberellic acid for Plantago major

Relationships between relative growth rate (RGR), endogenous gibberellin (GA) concentration and the response to application of gibberellic acid (GA₃) were studied for two inbred lines of Plantago major L., which differed in RGR. A4, the fast-growing inbred line, had a higher free GA concentration than the slow-growing W9, as analyzed by enzyme immunoassay. GA₃ application increased total plant weight and RGR₃ particularly for the slow-growing line. Chlorophyll a content and photosynthetic activity per unit leaf area were decreased, while transpiration rate was unaffected by GA₃ application. The increase in RGR by GA₃ application was associated with an increased leaf weight ratio; specific leaf area and percentage of dry matter in the leaves were only temporarily affected. Root respiration rate per unit dry weight was unaffected.
The correlation between low RGR, low GA concentration and high responsiveness to applied GA₃ supports the contention that gibberellins are involved in the regulation of RGR. However, the transient influence of GA₃ application on some growth components suggests the involvement of other regulatory factors in addition to GA.     

Effects of light and nutrient availability on leaf mechanical properties of Plantago major: a conceptual approach

BACKGROUND AND AIMS: Leaf mechanical properties, which are important to protect leaves against physical stresses, are thought to change with light and nutrient availabilities. This study aims to understand phenotypic changes of leaf mechanical properties with respect to dry mass allocation and anatomy. METHODS: Leaf lamina strength (maximum force per unit area to fracture), toughness (work to fracture) and stiffness (resistance against deformation) were measured by punch-and-die tests, and anatomical and physiological traits were determined in Plantago major plants grown at different light and nutrient availabilities. A conceptual approach was developed by which punch strength and related carbon costs can be quantitatively related to the underlying anatomical and morphological traits: leaf thickness, dry-mass allocation to cell walls and cell-wall-specific strength. KEY RESULTS: Leaf lamina strength, toughness and stiffness (all expressed on a punch area basis) increased with light availability. By contrast, nutrient availability did not change strength or toughness, but stiffness was higher in low-nutrient plants. Punch strength (maximum force per unit punch area, F(max)/area) was analysed as the product of leaf mass per area (LMA) and F(max)/leaf mass (= punch strength/LMA, indicating mass-use efficiency for strength). The greater strength of sun leaves was mainly explained by their higher LMA. Shade leaves, by contrast, had a higher F(max)/leaf mass. This greater efficiency in shade leaves was caused by a greater fraction of leaf mass in cell walls and by a greater specific strength of cell walls. These differences are probably because epidermis cells constitute a relatively large fraction of the leaf cross-section in shaded leaves. Although a larger percentage of intercellular spaces were found in shade leaves, this in itself did not reduce 'material' strength (punch strength/thickness); it might, however, be important for increasing distance between upper and lower epidermis per unit mass and thus maintaining flexural stiffness at minimal costs. CONCLUSIONS: The consequences of a reduced LMA for punch strength in shaded leaves was partially compensated for by a mechanically more efficient design, which, it is suggested, contributes importantly to resisting mechanical stress under carbon-limited conditions.     

The effects of mineral nutrition and benzyladenine on the plasmalemma ATPase activity from roots of wheat and Plantago major ssp. pleiosperma

There is an increasing awareness of the possibilities of mineral nutrition as regulator of growth substance action and vice versa. The present paper focuses on the effects of mineral nutrition and benzyladenine at the level of the plasma membrane. Seedlings of wheat ( Triticum aestivum L. cv. Drabant) and juvenile plants of Plantago major L. ssp. pleiosperma (Pilger) were grown hydroponically at different mineral levels with or without benzyladenine. Purified plasmalemma preparations from roots of wheat and P. major ssp. pleiosperma were obtained by the two phase partitioning method, using 6.5% (w/w) of each of Dextran T-500 and polyethylene glycol 3350. The Mg²⁺ and (Mg²⁺+ K⁺) dependent ATPase activities of the root plasmalemma in both species and the (Mg²⁺+ Cl⁻) one in P. major ssp. pleiosperma increased with increasing mineral levels, but the ionic strength did not influence the substrate specificity, the sensitivity to inhibitors or the pH optima.
The addition of 10⁻⁸ M benzyladenine to a nutrient solution increased the ATPase activities. The pH optima and the sensitivity to several inhibitors were not affected by benzyladenine, but the substrate specificity for ATP decreased, except for the K⁺ stimulation. In conclusion, benzyladenine mimics the effects of a higher mineral level than actually applied. Data from this and previous experiments indicate that benzyladenine exerts its effects by increasing the endogenous cytokinin concentrations and by modulating membrane components.