Plants transition through distinct stages as they develop, the timing of which, significantly impacts large-scale ecological and evolutionary processes. Vegetative phase change (VPC), the developmental transition from juvenile to adult vegetative growth, has been well studied at the molecular level however, little is known about its importance for plant performance and physiological functioning. VPC is regulated by an evolutionary conserved microRNA, miR156, in land plants from mosses to angiosperms. Young plants in the juvenile phase have high expression levels of miR156. As a plant ages, miR156 expression declines, alleviating repression of its target genes and transitioning the plant into the adult phase. Being that this transition has been conserved throughout much of plant evolution, it is likely to have significant consequences for plant performance. In this study variation in photosynthetic and leaf construction characteristics of juvenile and adult leaves of Zea mays were analyzed. Our objectives were to: 1) Identify if photosynthetic efficiency and capacity varies between leaves produced during the juvenile and adult stages of plant development, 2) determine if leaf resources related to photosynthesis were allocated differently between these leaves and 3) determine the metabolic and construction costs of juvenile and adult leaves.
We found significant variation in photosynthetic efficiency and capacity between juvenile and adult leaves. Additionally, juvenile and adult leaves showed differences in resource allocation and costs to the plant. Juvenile leaves showed traits consistent with lower costs and higher efficiencies at low-light levels; however, their overall photosynthetic capacity was significantly lower than their adult counter parts. Our results suggest juvenile and adult leaves display variation in characteristics likely to be best suited for plant performance at their respective developmental stage. This research begins to uncover the role of vegetative phase change in plant physiology and insight into the reasons for its evolutionary conservation.