Genetic differentiation in Plantago major: Ca²⁺‐ and Mg²⁺‐stimulated ATPases from roots and their role in phenotypic adaptation

The Mg 2+ ‐ and Ca 2+ ‐stimulated ATPase activities of the microsomal fractions of the roots of four inbred lines of Plantago major L. were followed at two levels of mineral nutrition. In addition the response of a transfer of plants from one condition to the other was studied. Kinetic properties of the ATPases (K m and V max ) were calculated and used to differentiate between genetic differences among the inbred lines and the plasticity within each inbred line. The V max values of the ATPase activity differed significantly between the lines and were directly related to seed number per capsule (low V max → 11 seeds per capsule, high V max → 33 seeds per capsule). In addition, the V max values of the ATPase acitivty may be related to ecological strategy. Plasticity of enzyme activity is expressed in differences in the V max values of the ATPase activity, as a response to nutritional level or changes of the strength of the nutrient solution. Differences in this plasticity in the four selected lines and in rapidity of response to a change in mineral nutrition were directly related to the ecological strategy. These results are discussed in relation to the strategy of the genotypes for survival in the field. The presence of plasticity in line 4 (ssp. pleiospema ) makes this genotype behave like an annual plant, following a ruderal strategy. The absence of plasticity in line 1 (ssp. major ) fits a more competitive strategy.