Changes in Growth and Metabolism of Excised Pea Roots Associated With Iron Deficiency

Abstract

The effects of iron deficiency on the growth and metabolism of isolated pea roots grown in sterile culture have been analysed. Changes were followed in whole routs sampled at intervals and in successive sections of roots sampled at a critical stage of deficiency. Transfer of deficient roots to complete nutrient after varying periods in the absence of iron showed the growth restriction was reversible for at least 6 days. Results suggest that the complete cessation of cell division after 6 days in iron-deficient culture was due primarily to a disturbance localized in the apical meristematic cells. Changes which occurred in the levels of protein nitrogen, ethanol-soluble nitrogen, amino acids, soluble carbohydrates and respiration are mainly attributed to the cessation of cell division rather than the cause of it. The rate of cell expansion w as unaffected by iron deficiency but the final size of mature cells was reduced. Addition of iron to deficient roots stimulated cell division more rapidly than protein synthesis or respiration rate. Insofar as the serial-seetioning technique used enabled separation to be made of cell di\ ision and cell enlargement, the results suggest that the effect of iron deficiency is confined primarily t(j the former. In addition, the final phase of cell maturation may also be affected but the evidence was inconclusive and these effects may not be determined directly by depletion of the iron supply. Evidence is presented showing that the metabolic changes associated with the transition from cell division through cell expansion to cell maturation depend on the source of root inocula used. Seedling roots showed marked changes in metabolism and meristem size when first isolated due to the depletion of metabolites translocated from the germinated seed, and it was necessary to use inocula taken from cultured excised roots to provide valid data on the changes due to increasing cell age.

Changes in Growth and Metabolism of Excised Pea Roots Associated With Iron Deficiency Ii. Changes in Nucleic Acids

“…It was demonstrated in a previous paper that iron deficiency caused a complete cessation of cell division (Abbott, 1968) which confirmed earlier results of Brown and Possingham (1957) though there were differences in interpretation of the results. Changes in levels of protein, amino acids, soluble carbohydrates and respiration were attributed TO'iinly to the cessation of cell division rather than implicated as the cause of it.…”

“…During the final four days DNA content per cell fell in deficient roots but increased continuously in control roots. (Abbott, 1968) that the effects of iron deficiency are reversible up to at least day 6, and in general, differences observed were approaching a maximum at this time. After six days, therefore, roots were hars^ested and cut into serial sections as described.…”

“…Sutton's Onward were surface sterilized and germinated in sterile conditions as previously described (Abbott, 1968). Before imposing experimental treatments on the excised root tips, they were grown through a preliminary culture passage to reduce the level of metabolites originating from the seed and to increase the uniformity of growth rate.…”

“…The mean growth rate of roots excised from seedlings was higher than of those excised from the primary culture, 12.5 and 11.3 mm per day respectively, reflecting the superiority of the seed as a source of nutrition to the culture medium alone. The basic medium was that described by Naylor and Rappaport (1950) but modified and purified as previously by Abbott (1968). …”