Sink strength as a determinant of dry matter partitioning in the whole plant.

Dry matter partitioning is the end result of the flow of assimilates from source organs via a transport path to the sink organs. The dry matter partitioning among the sinks of a plant is primarily regulated by the sinks themselves. The effect of source strength on dry matter partitioning is often not a direct one, but indirect via the formation of sink organs. Although the translocation rate of assimilates may depend on the transport path, the transport path is only of minor importance for the regulation of dry matter partitioning at the whole plant level. To understand the regulation of dry matter partitioning by the sinks, a parameter like sink strength is needed that describes a sink's ability to influence assimilate import and is independent of the rest of the plant. The term sink strength can be defined as the competitive ability of an organ to attract assimilates. However, there is much debate and confusion about the term sink strength because this term is often not clearly defined. Sink strength has been proposed to be the product of sink size and sink activity. Although cell number is often considered as a suitable measure of sink size, it appears not always to be an important determinant of sink size. Moreover, sink strength may depend on sink age rather than sink size. A model for dry matter partitioning into generative plant parts, which is based on sink strengths of the organs, is described. The potential growth rate (potential capacity to accumulate assimilates) has been shown to be an important parameter that quantitatively reflects the sink strength of an organ. The potential growth rates of the plant's organs are not static but change dynamically. The potential growth rate of a fruit is a function of both its age and temperature. For several crops it has been shown that the dry matter partitioning into an organ can be quantitatively described as a function of its potential growth rate relative to that of the other plant organs.