Architectural constraints: Consequences for seed production and carbohydrate translocation in Perilla frutescens Britt. (Lamiaceae)

My research examinines the consequences of plant architecture for an important life history trait, reproductive output, and a physiological trait, carbohydrate translocation, in the photoperiodic annual Perilla frutescens Britt. (Lamiaceae). Both traits can affect fitness and vary with architecture in a population. In Perilla, architecture is determined at flowering, when all branch apices give rise to inflorescences, precluding further vegetative growth. Reproductive output is constrained by the number of branches a plant produces before receiving the photoperiodic cue to flower. Carbohydrate translocation patterns reflect vascular connections that parallel architecture.;I explored the effects of flowering time on architecture and seed production in two experiments. In the first (Chapter 1), plants collected from northern and southern populations of Perilla were grown in reciprocal common gardens at the populations' home latitudes. In the second (Chapter 3), plants were grown under daylength treatments that recreated the photoperiodic conditions of the gardens. In both experiments, southern-grown plants flowered first, having developed fewer branches, and consequently fewer inflorescences, than the northern-grown plants. In the garden experiment, the architectural limitation on inflorescence number also limited total flower production in the southern-grown plants. By contrast, in the greenhouse, southern-grown plants made more flowers per inflorescence than the northern-grown plants, and total seed production did not differ between the two treatments. The southern-treatment plants compensated for an architectural constraint on one trait (inflorescence number) with plasticity in another (flowers per inflorescence).;In two greenhouse experiments I used radiolabeled carbon dioxide to examine the relationship between architecture and patterns of carbohydrate translocation. Architecture, the location of the labeled leaf, and the stage of plant development all affected carbohydrate movement. These results demonstrate that plants are not a homogeneous collection of subunits; rather, the role of each leaf in carbon translocation is a function of its age and location on the plant. Furthermore, greater seed production per branch in the southern-treatment plants was correlated with less movement of assimilate between branches. Thus, in response to architectural constraints, plants showed plasticity in seed production within inflorescences and in resource movement between them.