Root Development and Abiotic Stress Adaptation - Abiotic Stress: Plant Responses and Applications in Agriculture - page 138

meristems, body axes and major tissue layers are established [12-15]. Unlike metazoans, almost
all the body of the mature plant is generated during the PED. The PE begins during germina‐
tion, when the mitotic activity of meristems commences. Primary root meristems occupy one
end of the main body axis and originate the RS [9, 14, 16]. During the post-embrionary root
development traits such a i) primary meristems activity, ii) cell elongation, where both
determine the anatomy, length and trajectory of roots and iii) de novo formation of secondary
meristems and organs increase the branching to explore new soil zones [5, 6].
In Arabidopsis, the root consists of a series of concentric cylinders of different tissues (Figure
1 B), and this pattern is formed by sequential and ordered cell divisions during embryogenesis
[17]. The outer epidermal layer covers all root tissues, and by itself contains the trichoblasts, a
cell lineage that produces root hairs by tip growth, providing the root with additional
anchoring and nutrient uptake surface. Cortex layers give mechanical support and protection
while the endodermis forms an ion barrier. Inwards the endodermis, the pericycle cells
maintain meristematic properties that can give place to root primordia or diverge into vascular
tissues or cambium during secondary root growth. This pattern is established during the
embryogenesis by a series of asymmetric and formative divisions [18, 19].
Figure 1. Arabidopsis root system. Typical tap root system of dicots (A). Transversal section of primary root (B). Longitudi‐
nal section of primary root meristem (C) and primary root tip. Primary root (PR), lateral roots (LR), adventitious roots (AR),
pericycle cell layer (*), QC cells (arrow), root meristem (RM), elongation area (EA) and differentiation area (DA).
3.1. Cellular proliferation, elongation and differentiation
Root growth is produced by the biosynthesis of cell wall combined with cell division. In the
root meristem (RM) (Figure 1C-D), the cell layers apart from the epidermal and root cap ones
are originated around a region that consist of three or four slowly proliferating cells, the