Diurnal Patterns of Transport and Accumulation of Minerals in Fruiting Plants of Lupinus angustifolius L.

Abstract

Fluctuations in mineral elements id xylem (tracheal) sap, fruit phloem sap, leaflets and dmloping fruits were studied in a field population of Lupinus angustifolius L. by three-hourly sampling over a 39 h period. Elements usually reached maximum contents or concentrations at or near noon, minimum levels during the night. Amplitudes of diurnal fluctuations in minerals lay within the range ±4–33 per cent of the mean content of leaflets, and ±17–157 per cent of the mean concentrations in xylem and phloem sap. Most minerals elements fluctuatcd in phase with daily changes in sugar level of phloem sap and dry matter and carbohydrate fluctuations of leaflets, suggesting a coupling of translocation of photosynthate and minerals from the leaflets. Rates of import of minerals by shoots wereestimated from shoot transpiration and mineral concentrations in tracheal sap. Average day time rates of import of most elements were 12–25 times those at night. Translocation of minerals, nitrogen and carbon to fruits also exhibited diurnal periodicity, average rates of import king three to seven times higher in the day than at night. A model of transport based on the carbon and water economy of the fruit suggested that P, K, Fe, Zn, Mn and Cu were imported predominantly by phloem. Estimates of vascular import accounted for 87–104 per cent of the fruit's actual increment of these elements. Na and Ca were gauged to be imported mainly by xylem, Mg almost equally by xylem and phloem. However, large discrepancies existed for these three elements between estimated vascular import and actual intake by the fruit.