Varietal differences in physiological and biochemical responses to changes in the ionic environment

Summary

Experimental assessment of differences between cultivars of crop species or ecotypes of wild species from different localities in their capacities for ion absorption and transport is made difficult by the problem of obtaining seed material of comparable ionic content. When young seedlings are used this problem is particularly acute if the seeds of the different cultivars have not been raised under identical soil conditions. Propagation of material from ecotypes under controlled conditions is one approach to the solution of this problem. Six maize cultivars have been selected for similarity of phosphate content and the capacity for phosphate absorption from 5 μM KH₂PO₄ has been shown to vary by threefold whereas the proportion of the accumulated phosphate that reaches the shoot differs by much less. This level of phosphate supply approached that likely to induce deficiency and when the concentration is reduced to 1 μM differences in transport capacity of up to fourfold were observed when the rate of arrival at the tip of the first leaf was continuously monitored. The rapidity with which the transport is shut off by adding 1 mM D(+) mannose to the root environment also varies significantly indicating that sizeable differences in either the accumulation of mannose or the activity of phosphomannoisomerase exist in these cultivars.

Ecotypes of Armeria maritima collected from three sites, inland serpentine, inland mine dumps and coastal salt marsh were maintained as stock plants on the same peat mixture. Samples taken from these stocks were raised on a standard culture solution to provide genetically different material grown under constant conditions. The capacities for ion uptake were shown to differ very considerably and these differences were accentuated when the plants were grown in a range of concentrations of MgSO₄, NaCl and MnSO₄. The absorption of phosphate and its incorporation into nucleic acids were increased temporarily in the presence of 50 mM MgSO₄ but the pattern of these changes was different in the three ecotypes. The absorption of Na, Cl, and Rb was measured after treatment with a range of concentrations of NaCl and the effect of treatment with MnSO₄ on subsequent absorption of Mn and SO₄ was also measured. The coastal plants were significantly more efficient in their absorption of these ions when treated at the lower levels of NaCl (0.5 and 10.0 mM). The short term absorption rates were not reflected in the overall accumulation of sodium over periods of 10 weeks and the coastal plants appeared to reduce the root content of sodium by transfer to the shoot and by increased active pumping to the exterior.