EFFECT OF ENVIRONMENTAL-FACTORS ON WHOLE-PLANT ASSIMILATE PARTITIONING AND ASSOCIATED GENE-EXPRESSION

Partitioning of assimilated carbon among sink organs is a critical fac tor that controls the rate and pattern of plant growth. Time-course me asurements 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 sin ks. Comparison of growth rates among sinks under defined conditions ca n point out key factors that regulate partitioning of recently assimil ated carbon among sinks. Internal control of carbon partitioning by de velopmental programmes regulates the timing and site of carbon distrib ution among developing parts, thereby establishing the adaptive traits of a species, cultivar or transgenic construct. Regulation of partiti oning in response to environmental factors establishes or restores all ometric growth among plant parts and functional balance between the su pply and use of carbon. Environmental stress often restricts resource availability while successful acclimation sets in motion processes tha t restore the supply. A key mechanism contributing to regulation of ca rbon partitioning is an expression of genes that control activity of t he enzymes which initiate sucrose metabolism at specific sites and sta ges of ontogeny.