Total lateral root length was calculated by subtracting the primary root length from the total root length.
The turnip root is formed by the thickening of the primary root of the seedling together with the base of the young stem immediately above it.
The RAM produces all the tissues of the primary root by a highly defined pattern of cell divisions [ 2].
At indicated times, the plates were scanned by an Epson perfection V200 photo scanner, and the primary root length was measured by the tool DIGIMIZER 3.2.1.0 (http://www.digimizer.com).
The primary root growth inhibition by 200 μM dichromate was alleviated by more than 70% by increasing the sulfate, phosphate or nitrate concentration in the media, which suggests a relation of dichromate with these mineral nutrients.
Low P availability in arabidopsis promotes the development of a highly branched root system to the detriment of the primary root, characterized by the stimulated formation and emergence of lateral roots and root hairs (Bates and Lynch, 1996; Williamson et al., 2001; Linkohr et al., 2002; López-Bucio et al., 2002; Pérez-Torres et al., 2008; Péret et al., 2011).
Recent studies show that PGPR affect Arabidopsis thaliana root growth and development by modulating cell division and differentiation in the primary root and influencing lateral root development.
If we consider the mechanisms of NH4+ toxicity, a recent study examined the causes of the primary root growth suppression by NH4+ nutrition [ 43].
Kinetic studies of expression of the cell cycle marker CycB1, 1:: uidA and the quiescent centre (QC) identity marker QC46 GUS showed that the reduction in cell proliferation in the primary root was preceded by alterations in the QC under low P supply (Sánchez-Calderón et al., 2005).
The pattern of lateral root formation close to the root tip under P deficiency is comparable with that of roots with damaged primary root meristemic activity, including destruction of meristemic activity by cell ablation or physical decapitation of the primary root meristem, eliciting an increase in lateral root number (Torrey, 1950; López-Bucio et al., 2002).
