Root Development and Abiotic Stress Adaptation - Abiotic Stress: Plant Responses and Applications in Agriculture - page 136

edge of molecular, genetic and cellular processes that modulate post-embryonic root develop‐
ment in the model plant Arabidopsis thaliana making emphasis in the cell cycle. We will continue
to focus on the modulation of PERDP in response to salinity and water. We will describe the
changes in the RS induced by nutrients such as nitrogen, potassium and iron. The modulation
of RSA by phosphorous will be discussed taking into account molecular, genetic and cellular
responses. Finally, we will discuss how abiotic stress modulates apical root meristem activity.
2. Root system
Raven and Edwards (2001) define: “roots are axial multicelular structures of sporophytes of
vascular plants which usually occurs underground, have strictly apical elongation growth,
and generally have gravitropic responses which range from positive gravitropism to diagra‐
vitropism, combined with negative phototropism”. The apical meristem of one (lower vascular
plants) to many (all seed plants) diving cells produces a root cap acropetally and initials of
stele, cortex and epidermis basipetally. The branching of roots involves the endogenous origin
of new root apical meristems in the pericycle [2]. The most conserved functions of roots present
in extant plants are anchorage to substrate, and uptake of water and mineral nutrients. The
evolution of multicellular organs such as roots was necessary to successful colonization of land
by early plants [1, 4].
2.1. Origin and evolution
Over 470 million years ago, in the mid-Palaeozoic era, took place one event with far-reaching
consequences in the history of the life, the origin and early evolution of embryophytes (land
plants). It appears that margins of drying pools were the place where early embryophytes evolved
from algal ancestors. The earliest land plants probably presented a system of rhizoid-like
filaments that performed the rooting functions (anchorage and uptake water and nutrients)
helped by associated fungi. They grow in superficial soil produced for weathering of rock surface
similarly to bryophytes (mosses). Their appearance started changes on energy and nutrient fluxes
among terrestrial and freshwater ecosystems and consequently for the evolution of animal,
bacteria and fungi groups that lives in those habitats. Roots as the ones we know now are present
only in vascular plants (tracheophyta), they evolved in the sporophyte of at least two different
lineages of tracheophytes, lycophytes (licopods) and euphyllophytes (ferns and seed plants),
during the Early and middle Devonian. Roots of early Euphyllophytes started to penetrate deeper
into substrate increasing the anchorage and funding the inorganic nutrients produced by rock
leaching. In Euphyllophytes a fundamental difference in the anatomy of embryonic roots among
seed plants and free-sporing monilophytes, suggesting that roots evolved independently. At
this time root developed more branched axes and finer structures involved in the nutrient uptake,
root hairs. In Carboniferous (300 millions of years ago) gymnosperms appear and their RS is
highly branched and depth penetration, they break up rocks letting exposed mayor rock area
exposed to weathering. By late Cretaceous (100-65 millions of years) angiosperms are presents
showing similar root system as exant angiosperms [1, 2, 8].