Phenotypic plasticity of capitulum morphogenesis in Microseris pygmaea (Asteraceae: Lactuceae)
1994
Battjes, J. | Bachmann, K.
Inbred populations of the annual Chilean species Microseris pygmaea show phenotypic plasticity in the number of florets per capitulum. In order to find out how this plastic variation may arise during development, two inbred lines (A92 and C96) were grown under short day conditions. Groups of plants from each strain were transferred to long day conditions at about 2 week intervals. In this way we introduced variation for plant size (number of leaves per plant) at onset of flowering. The number of florets per mature capitulum increased linearly with plant size. After transfer to long day conditions, plants were harvested daily for light microscopic measurements of meristem whole mounts. Only the first capitulum of each plant was analysed. All florets were formed after 12 d in strain C96 and after 14 d in strain A92. In order to detect the effect of plant size on morphogenesis, we performed a multiple regression analysis of developmental parameters on time and number of leaves. Width and height of the capitulum receptacle increased daily with a growth rate depending on the starting size. Differences in meristem size were detected already in vegetative plants of different sizes. In contrast, there was no influence of plant size on floret primordium size. We combined the multiple regression models in one simple model for prediction of floret numbers from numbers of leaves per plant at onset of flowering. Predictions of this model agree with observed relationships in both inbred lines.
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