Distribution of linear growth rates in different directions in root apical meristems

Abstract

Growth of apical meristems in plants may be well described by the growth tensor method. Hejnowicz (Envir. Exp. Bot. 1989, 29) determined growth tensors for roots: one with a minimum and the other with a maximum of the relative elemental growth rate in volume and used them for the description of two types of apices: one with an apical cell and merophytes (I), and the other with files of cells converging towards a quiescent centre, CQ (II). In the present paper the same cases are considered from the point of view of a spatial and directional variation of the relative elemental rate of growth in length, RERG1. Maps of the RERG₁ in two planes: axial and tangential, the latter determined by periclinal-longitudinal (PL) and periclinal-tangential (PT) principal growth directions, are shown. In an apical part of apex i where there is maximum volumetric growth, there also occurs a maximum of RERG₁ for all directions. In regions other than this RERG1 decreases although RERG₁ in the PL direction predominates everywhere. In apex II RERG₁ for all directions has a minimum in CQ and becomes increasingly larger with increasing distance from it - the maximum is in the PL direction in the cylindrical part of the apex. In peripheral parts of both apices, in the place of the root/cap junction, RERG, in the anticlinal direction is significantly small.