Redistribution of Mineral Elements During Development

Abstract

In the course of a recent address on the control of growth and reproduc tion in plants, Gregory (13) drew attention to the fact that over 90 per cent Of the nitrogen and phosphorus taken up by the developing cereal plant had been accumulated when the dry weight was only 25 per cent of the final value. This store of accumulated nutrient was the reserve on which all later growth and development depended, and its level determined the final yield. The nitrogen and phosphorus which was set free from the senescent leaves and tillers was reutilized for production of further leaves which, in turn, provided for the development of the inflorescence. Gregory also stressed the significance of the meristems with their potentially unlimited demand for nutrients, and their capacity to initiate "internal starvation" and senes cence. These observations serve very well to introduce the review which is to follow for, in examining the evidence for the redistribution of mineral ele ments during development, the reviewer has attempted to relate this to the wider problems of growth.From the outset it should be emphasized that we are primarily concerned with the demonstration and explanation of net losses of mineral elements from specific plant parts. To be relevant, therefore, papers for review had to cover two or more plant parts at several stages of growth. Relatively few of the many papers on the mineral composition of plants fulfil these require ments.It seems probable that some elements simultaneously enter and leave the same organ in the course of the normal metabolic flux, and may be regarded as being redistributed from organs which are still undergoing net intake. Such phenomena are not considered here, and it is for this reason that little reference is made to recent work with radioactive tracers. A borderline case is provided by Phillis & Mason (34) who found diurnal variations in the mineral content of the leaf of the cotton plant. The six elements studied showed increases by day and no change or decrease by night. Although the existence of dew losses complicated the picture, it does seem likely that phloem export was responsible for some losses even before maximum absolute contents had been attained. This evidence is a reminder that there can be no hard and fast line between redistribution resulting from normal metabolic activity within the organ considered and redistribution which is conditioned by senescent changes and by demands which arise externally to that organ.

Experimental Modification of Plant Senescence.

“…Thus aging leaves show a more rapid utilization of carbohydrates (14,16), more export of inorganic materials (2,15), and are less effective in photosynthesis (3,12). (c) Mlurneek has proposed that the developing embryos induce senescence in the parent plant.…”

Effects of Changes in Boron Nutrition on Growth and Development of Subterranean Clover

“…With some other deficiencies, notably nitrogen and phosphorus, root growth is relatively at an advantage (Williams 1955). The explanation in the case of boron is best sought in the contrasting character of root and shoot meristems.…”

The Physiology of Growth in the Wheat Plant I. Seedling Growth and the Pattern of Growth at the Shoot Apex

“…The extraction of general principles relevant to the physiology of growth from complex sets of data such as the above is not easy, and has been attended by only partial success when attempted by Watson and Petrie (1940) and by Williams (1955). Perhaps the most significant positive contribution has been their emphasis upon competitive demand within the plants for metabolites and nutrients alike.…”