Changes of root structure in connection with the development of lateral root primordia in wheat and pumpkins

Abstract

The root structure and its changes in connection with development of lateral root primordia were studied in Triticum aestivum and Cucurbita pepo seedlings. Seedlings of these two species differ in respect of the localisation of parent root site where primordia development occurs. In T. aestivum roots, primordia initiation takes place at a considerable distance from root tip opposite phloem poles, while in C. pepo roots, it occurs in meristem opposite xylem poles. The structure of parent root site where primordia initiation occurs determines the tissues and the cells which take part in this process. In T. aestivum roots, primordium initiation is a result of the resumption of cell proliferation in stelar parenchyma, pericycle and endodermis. The resumption of cell divisions is preceded by the resumption of DNA synthesis in some cells of these tissues. In C. pepo roots, the local reduction of the mitotic cycle duration occurs in cells of pericycle, endodermis and 4–5 inner cortical layers participating in primordium initiation. The plane of the first cell division is anticlinal in both investigated species. We suggest that the increase of number of anticlinal cell walls in any site of the pericycle (the founder root tissue between central cylinder and cortex) creates conditions for the origin of the growth vector during initiation of lateral root primordia. The sequence of involving cells in different tissues in the primordium initiation, as well as their contribution to formation of primordium and lateral root, were investigated in both species.