Sprungmarken

 
Beck, E; Fusseder, A; Kraus, M: The maize root-system in situ - evaluation of structure and capability of utilization of phytate and inorganic soil phosphates, Zeitschrift für Pflanzenernährung. Bodenkunde, 152, 159-167 (1989), doi:10.1002/jpln.19891520205
Abstract:
The dependence of the morphology of the maize (Zea mays L.) seminal root system on physical, chemical and biotic parameters was investigated with pot cultures in quartz sand and in a natural loamy sand soil. Low O2‐supply to the soil resulted in a substantially smaller root biomass despite a relative increase in total root length. Reduced N‐supply also stimulated root length growth, but also enhanced the formation of laterals. The presence of soil microorganisms, in comparison to sterile cultures, resulted in a reduced length of the main roots, and the production of slender laterals with a decreased root hair density. Generally, the structural variability of laterals in response to different growth conditions was much more pronounced than that of the main roots. A major part of the work reported here was dedicated to a detailed study of phosphate (P) acquisition by the maize root system under field conditions. Radioactive labelling of the roots and radioautography of soil cores revealed the in situ distribution pattern of the maize root system. Controlled labelling of the soil with radioactive phosphate allowed the documentation of the development and replenishment of the phosphate depletion zone around roots. Finally, the longevity and phosphate uptake activity of the different parts and tissues of the primary root system of maize was examined by electron microscopy and tracer studies including pulse chase experiments. From these studies the phosphate‐acquiring strategy of the maize root system appears as follows: The capability of P uptake decreases in the order: root hairs, 1st order laterals, 2nd order laterals, main root. The life‐spans of the components of the maize root system increase by the sequence: root hairs, laterals, main root. Inorganic P uptake, therefore, mainly occurs during the first weeks of root development. Dying back of the root occurs in an ordered manner resulting in a relocation of stored P predominantly into the main root cortex. Furthermore, it could be shown that competition for P between roots of the same or of adjacent maize and/or lupin plants virtually does not occur in situ . The utilization of phytate‐P was studied with 14C/32P‐labelled Camyo‐inositol‐hexaphosphate supplied to maize plants grown in sterile quartz sand or in hydroponic cultures. The ratio of P‐ and C‐uptake as well as the incidence of phytate hydrolysis products in the rooting medium indicated the capability of maize roots to acquire P from phytate by enzymatic hydrolysis. This was confirmed by enzyme studies of the root tissues. A specific hydrolyzing enzyme (phytase; molecular weight 51 kD) could be detected in the cell wall of the root, especially in the root tip, which initiates phytate dephosphorylation. Further breakdown is presumably accomplished by monophosphoric phosphohydrolases.

Letzte Änderung 30.06.2020