Deposition rates in growing tissue: Implications for physiology, molecular biology, and response to environmental variation

Background Net rates of biosynthesis and mineral deposition are needed to understand the physiology and molecular biology of growth and plant responses to environmental variation. Many popular models ignore cell expansion and displacement. In contrast, the continuity equation, used with empirical data on growth velocity and concentration, allows computation of biosynthesis and deposition rates in growing tissue. Scope This article describes data and methods needed to calculate deposition rates and reviews some insights into environmental physiology and molecular biology. Conclusions Growth zones actively and strongly deposit mineral elements, even though local concentrations may not be changing in time. Deposition rate profiles give important insight into the mechanism of plant responses to drought and salinity, and they clarify many aspects of nitrogen metabolism in roots and leaves. This approach is also essential to understand molecular regulation of growth. A pioneering study determined transcript densities and calculated rates of change in gene expression; this study revealed how Actin 11 is highly regulated by a balance of transcription and decay during growth of roots. New technologies ( in planta cytometry, coupled with powerful computational routines and real-time confocal microscopy) will allow determination of deposition rates in growing organs and advancement in understanding of gene regulation.