Spatial distribution of leaf form and the self-thinning exponent are affected by the sensitivity of the response to abscisic acid in anArabidopsis thaliana population

The spatial distribution of leaves is related to the exponent of the self-thinning relationship in plant populations. In this study, we evaluated the fractal dimension of rosette leaves of wild-type (WT)Arabidopsis thaliana and of an abscisic acid (ABA) -insensitive mutant (abi2-1) to test a model of the spatial distribution of leaf form in anArabidopsis population based on subdivision of a cube surrounding the leaf into uniform boxes and to investigate ABA’s affect on this model of the leaf. The values of the self-thinning exponent were -1.31 and -1.45 for WT andabi2-1. The mean dimensions of the box used to model the spatial distribution of leaf form, estimated using our model, were 2.08 and 2.03, respectively. By assuming that the box dimension equals the fractal dimension within the populations, the predicted self-thinning exponent equaled -1.40 for WT and -1.49 forabi2-1. When exogenous ABA was applied to both genotypes, the self-thinning exponent became -1.26 and -1.43 for WT andabi2-1, and the exponents predicted using the dimensions of the box were -1.37 and -1.46, respectively. The empirically predicted exponent equaled that predicted using the dimensions of the box (95% confidence interval). Empirical prediction of the spatial pattern using the two genotypes with and without ABA showed that ABA influenced the spatial form of the rosette leaves. Therefore, sensitivity to ABA can affect self-thinning through genetically determined changes in leaf form and its spatial distribution.