Physiological Ontogeny in the Tobacco Plant

Annu. Rev. Plant. Physiol.

1955

208

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.

mentioning

confidence: 50%

Redistribution of Mineral Elements During Development

Annu. Rev. Plant. Physiol.

1955

208

“…This was clearly recognized in ontogenetic studies of wheat and Sudan grass by Ballard and Petrie (1936) and Petrie (1937), of oats by Williams (1936Williams ( , 1938Williams ( , 1948, of tobacco by Petrie, Watson, and Ward (1939), Watson and Petrie (1940), and Petrie and Arthur (1943), of flax by Tiver (1942), and of linseed by Tiver and Williams (1943). More recently, studies on similar lines have been made for barley and rye by Williams and Shapter (1955) and for the tomato plant by Gates (1955aGates ( , 1955bGates ( , 1957.…”

Section: Introductionmentioning

confidence: 83%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Aust. Jnl. Of Bio. Sci.

1960

SummarySeedling growth of wheat in a constant environment is studied over a period of 21 days. Dry weights of leaves, leaf sheaths, stem, and roots are given for 11 occasions. The pattern of dry weight change is also presented in terms of the changing ratios of plant parts.Growth rates of leaf primordia are determined in terms of volume change based on the technique of serial reconstruction.For an ll-day shoot apex, a detailed account is given of cell-size distribution along the leaf primordia and within the apex itself. It is estimated that, prior to the onset of cell enlargement, the mean cell-generation times for the young leaf primordia range from 12 hr to 3 days.An integrated picture of the early growth of the primary shoot is attempted, mainly in terms of the concept of relative growth rate. The rates for leaves and roots are particularly high while seed reserves are available. There is a progressive change in dominance from leaf growth to stem growth. Early growth of each leaf primordium is exponential, but the exponent decreases with leaf number in a rather discontinuous manner. Following the exponential phase, the rates rise to maxima and then fall asymptotically to zero.It is suggested that intra-plant competition for energy substrates may play an important role in determining the pattern of development of the primary shoot of wheat.

“…o Each organ thus has a certain capacity to accumulate nutrients such as phosphorus, and in its senescent phase it constitutes a potential source of these nutrients for younger plant parts. That the demand of younger organs for nitrogen must be regar<ied as the main factor causing loss of nitrogen from mature leaves has been suggested for barley by Walkley (1940), and for tobacco by Watson and Petrie (1940), and it is probable that export of phosphorus is initiated in the same way. At the same time, the demand of each organ for phosphorus is usually met in part, if not entirely, by absorption from the external medium; this rate of intake by the roots, however, is restricted to the extent that phosphorus is more readily available within the plant itself.…”

Section: (I) the Internal Or Growth Factormentioning

confidence: 99%

The Effects of Phosphorus Supply on The Rates of Intake of Phosphorus and Nitrogen and Upon Certain Aspects of Phosphorus Metabolism in Gramineous Plants

Aust. Jnl. Of Bio. Sci.

1948

194

117

SummaryFor experiments previously described, new data are presented relating to the intake of phosphorus by gramineous plants, its distribution within the plant, and its partition in the leaves between alcohol-soluble, nucleic-acid, and "residual" phosphorus.Major determinants of the rate of intake of phosphorus by the plant are: ( a) the demand set up by the growth and normal functioning of various plant parts, and (b) the concentration of the nutrient in the medium.It is considered that the indirect effect of phosphorus treatment on growth, and hence on demand, is more important than the direct effects of external concentration of phosphorus on the rates of intake of that nutrient.Even when growth is not limited by the supply of phosphorus, the rate of intake is limited by the maximal capacity of successive plant parts for accumulation.For the oat experiment, rates of intake of phosphorus and nitrogen are expressed per unit weight of root system. With nitrogen, the supply of which was the same for all treatments, large initial effects of phosphorus treatment on the rates of intake are accounted for in terms of differences in the ratios of roots to shoots.Phosphorus-deficient oat plants derived only 30 per cent. of their inflorescence phosphorus from other plant parts; those with an excessive supply derived no less than 93 per cent. of their inflorescence phosphorus from these sources.The percentage phosphorus contents of the stems, leaves, and roots fell ultimately to lower values with a moderate supply of phosphorus than they did with the deficient supply. A more efficient re-utilization of phosphorus in the plants receiving the greater supply is favoured as an interpretation of this "dilution" effect.From an examination of the data for protein-nitrogen and nucleic-acid phosphorus in the leaves of young plants, it is concluded that the effects of phosphorus treatment on protein-nitrogen content at this stage are due primarily to variation in nucleoprotein content.With phosphorus deficiency, oat seedlings soon exhausted their seed reserves of phosphorus, and this was followed by a drastic change in the partitioning of leaf phosphorus, such that absolute nucleic-acid phosphorus was reduced to one-fifth of the value obtaining eleven days earlier, alcohol-soluble phosphorus decreased slightly, and the water-soluble fractions represented by "residual" phosphorus increased by 30 per cent. Total phosphorus was virtually unchanged in amount. During this same period of eleven days, the whole of the phosphorus intake from the medium was retained by the roots, and there was a stimulation of root growth relative to leaf growth. These facts suggest that the high root weight ratios found with phosphorus deficiency may be due to the fixation in organic forms of a greater proportion of the absorbed phosphorus, so that relatively little is available for shoot growth. The literature relating to the partitioning of phosphorus within plant tissues is discussed and, where comparisons are relevant, this is in substantial agreemen...