Potassium and phosphate absorption by excised ordinary and proteoid roots of the Proteaceae

Potassium and phosphate absorption by excised ordinary and proteoid roots of certain species of the Proteaceae was investigated, using 86Rb (as substitute for 42K) and 32P as tracers. The respiratory uncoupler, 2,4-dinitrophenol (DNP), inhibited the uptake of potassium and phosphate. The greater inhibition obtained with proteoid roots possibly suggests that they possess a greater capacity for metabolic absorption than the ordinary roots. Absorption of potassium and phosphate over a concentration range of 0,005 – 50mmol dm−3 KCI and KH2PO4 respectively, was investigated. Lineweaver-Burk kinetic analysis of the data on potassium absorption in the low concentration range (0,005 – 1,0mmol dm−3 KCI) revealed a more effective absorption mechanism in the case of proteoid roots. Kinetic analysis of the data on phosphate absorption in both the low (0,02 – 1,0mmol dm−3 KH2PO4) and high (1,0 – 50mmol dm−3 KH2PO4) concentration ranges points to a more effective absorption mechanism in proteoid roots. Phosphate absorption by proteoid roots showed a distinct peak between pH 4 and 5,5

Physiological Response of Vi tis vinif era L. ( cv. Chenin blanc) Grafted onto Different Rootstocks on a Relatively Saline Soil

Certain physiological parameters, namely leaf water potential, stomatal resistance and rate of photosynthesis of Chenin blanc grafted onto 10 rootstock cultivars on a relatively saline soil under irrigation in a hot region (V), were measured for two growing seasons. Soil electrical resistance, which varied from 632 to 271 ohms in the shallower soil layers (<500mm) and from 414 to 167 ohms deeper in the soil, decreased during the growing seasons. Although diurnal and seasonal patterns of change of the physiological parameters measured did not differ between rootstock cultivars, significant differences in their magnitudes were apparent. The rootstocks US 16-13-23, 13-5 E.V.E. Jerex were more stressed than 101-14 Mgt, 143-B Mgt and 110 Richter and had lower rates of photosynthesis. Photosynthetic rate was predominantly inversely correlated with stomatal closure. The use of 101-14 Mgt and 143-B Mgt is recommended under relatively saline conditions

Aspects of the sodium and potassium nutrition of the fynbos shrub Leucadendron salignum L. (Proteaceae)

The fynbos shrub Leucadendron salignum (Proteaceae) was used to study the effect of sodium and potassium supply in the nutrient medium on its growth and cation content. The plants were not highly sensitive to sodium, and luxury absorption of potassium was found with higher potassium supply, which was probably then used to maintain growth during a six-month period of potassium deficiency and sodium supply. Short-term absorption studies using excised roots showed active potassium and sodium absorption even when both ions were supplied together, especially from the low-concentration range. Potassium absorption was higher than that of sodium, and uptake by proteoid roots greater than that by ordinary roots