Solute Accumulation in Plant Cells V. An Aspect of Nutrition and Development

Abstract

The need to re-evaluate concepts of salt and solute accumulation in the light of evidence derived from cells at all stages of their growth and development is recognized. The problem is seen in terms of the nutrition of flowering plants, the growing cells of which are essentially heterotrophic, and the solutes of which are progressively acquired and redistributed during ontogeny. This is traced from the zygote in the embryo sac to an established plant body with its evident ‘source-sink’ relationships and physiological ‘division of labour’ between organs. The evidence accrued from aseptic cultures which were manipulated to reveal the range of solutes in cells which simulated the normal course of development in situ as they multiplied, vacuolated, enlarged, and eventually matured. The regulatory control exercised by cells in these developmental stages over the total osmotic value and the relative composition of their solutes (organic and inorganic) is both described and interpreted. The reversible changes that may occur (within a regulated osmotic value) in the solutes of established cells as they replace sugars by salts of organic acids, by organic nitrogen compounds, or by alkali halides are both described and related to events that occur in the developed plant body. Particular significance is attached to the consequences of the normal need of land plants to acquire nitrogen from nitrate and of the intervention of reduced nitrogen under circumstances in which the need for non-metabolizable ions (e.g. alkali halides) is, thereby, drastically curtailed. Cells in multiplication require energy to create new structure and do not emphasize the accumulation of solutes in bulk; however, when they enlarge, energy is obligated to the storage of solutes (organic and inorganic) to support their cytoplasm which is being ‘spread out thin’. These events involve more than the properties of membranes, or their relations to individual ions or molecules, for they require an understanding of cells as compartmented, metabolic, and osmotic machines, and of their variously obligated energy relationships. Moreover, the subject now needs to be seen as an aspect of the over-all nutrition of cells, organs, and organisms as they grow and develop.