Effect of environmental factors on whole plant assimilate partitioning and associated gene expression.

Partitioning of assimilated carbon among sink organs is a critical factor that controls the rate and pattern of plant growth. Time-course measurements of plant and organ growth rates are useful for determining how regulation of carbon partitioning controls plant growth. Measuring growth rates over a 24 h period reveals the current pattern of carbon partitioning that can be used to predict growth rates of specific sinks. Comparison of growth rates among sinks under defined conditions can point out key factors that regulate partitioning of recently assimilated carbon among sinks. Internal control of carbon partitioning by developmental programmes regulates the timing and site of carbon distribution among developing parts, thereby establishing the adaptive traits of a species, cultivar or transgenic construct. Regulation of partitioning in response to environmental factors establishes or restores allometric growth among plant parts and functional balance between the supply and use of carbon. Environmental stress often restricts resource availability while successful acclimation sets in motion processes that restore the supply. A key mechanism contributing to regulation of carbon partitioning is an expression of genes that control activity of the enzymes which initiate sucrose metabolism at specific sites and stages of ontogeny.