Biotechnology and Plant Membranes: Future Implications
Matthew B. Wheeler, Stephen K. Farrand, and Jack M. Widholm
Diagram of the structure of biological membranes, showing the lipid bilayer and membrane-associated proteins.
Source: Adapted from Biochemistry and Function of Vacuolar Adenosine-Triphosphate in Fungi and Plants, B. P. Marin, ed. (1985).
Membranes define the outer boundary of plant cells and the structure of their internal organelles. In this role, membranes regulate the flow of materials between cells and their environment as well as their internal compartments. These materials can include mineral nutrients acquired from the soil and metabolites important for crop growth and development. At the whole-plant level, transport across membranes can serve to define allocation patterns for the products of photosynthesis and metabolism, which can determine the quantity and quality of crop yield.
Membranes are composed primarily of lipids and proteins. The bilayer lipid arrangement defines the plane of the membrane to which proteins are associated (see figure). The lipid portion of the membrane can represent a substantial barrier to material flow, but the proteins associated with the membrane impart the means for selective transport and accumulation of solutes. This function is defined by the structure of the transport protein, which is, in turn, a reflection of its primary amino acid sequence encoded by its respective gene.
With current advances in molecular biology, this approach would appear to represent a powerful tool for modification of membrane transport processes, with the ultimate goal being the development of improved crop cultivars. But there is a paucity of basic knowledge about how membrane transport systems operate and are regulated. Therefore, before biotechnology of membrane processes can become a reality, much work is needed to define the function and structure of membrane transport proteins at the molecular level.
At the University of Illinois Agricultural Experiment Station, work is being conducted to understand the biochemistry of the transport system involved in nitrate uptake by maize roots. This mineral nutrient represents a major limiting factor for determining maize growth and yield as demonstrated by the increase in yield for maize grown in Illinois with the advent of nitrogen fertilizer application. Our work focuses on not only understanding which properties of this transport system determine its function and regulation but also on elucidating the factors that limit its efficiency. The ultimate goal is to provide important information about this transport system, so that its activity can be modified through gene manipulation to produce crop plants with greater efficiency for nitrate acquisition and allocation. Potentially, then, novel maize cultivars could be developed that require less nitrogen fertilizer for a given yield and hence realize higher productivity.
Donald P. Briskin, associate professor of plant physiology, Department of Agronomy
