BACKGROUND AND AIMS: question of whether homeostasis occurs for some nutrients and, if so, what are the consequences for how plants sense their nutrient status. Particularly for nitrate, this controversy has focused on the methods used and the cellular pools which they measure. Cytoplasm and cytosol have been distinguished and it has been suggested that two ranges of nitrate values can be separated depending on whether the method separates the pools found in organelles. SCOPE: The present study defines homeostasis of nutrient ions and discusses how whole organ averaging techniques can hide important cellular differences that can help to explain some of the discrepancies between results reported by various methods. These results are considered in relation to a possible role in signalling nutrient status, and have relevance to other averaging techniques such as the use of 'omics' technologies.