Abstract
Plant survival under abiotic stress conditions requires morphological and physiological adaptations. Adverse soil conditions directly affect root development, although the underlying mechanisms remain largely to be discovered. Plant hormones regulate normal root growth and mediate root morphological responses to abiotic stress. Hormone synthesis, signal transduction, perception and cross-talk create a complex network in which metal stress can interfere, resulting in root growth alterations. We focus on Arabidopsis thaliana, for which gene networks in root development have been intensively studied, and supply essential terminology of anatomy and growth of roots. Knowledge of gene networks, mechanisms and interactions related to the role of plant hormones is reviewed. Most knowledge has been generated for auxin, the best-studied hormone with a pronounced primary role in root development. Furthermore, cytokinins, gibberellins, abscisic acid, ethylene, jasmonic acid, strigolactones, brassinosteroids and salicylic acid are discussed. Interactions between hormones that are of potential importance for root growth are described. This creates a framework that can be used for investigating the impact of abiotic stress factors on molecular mechanisms related to plant hormones, with the limited knowledge of the effects of the metals cadmium, copper and zinc on plant hormones and root development included as case example.
Highlights
Plant survival under abiotic stress conditions requires morphological and physiological adaptations
The root tip contains the root apical meristem (RAM), a region that consist of a set undifferentiated and dividing cells surrounding the quiescent centre (QC), a group of non-mitotically active cells
Auxin plays a prominent role in all aspects of lateral root formation, this is why interfering with auxin biosynthesis, transport, or response often leads to alterations in the lateral root formation [45]
Summary
Roots of Arabidopsis thaliana have a very simple cellular organization that can be described in a radial and an apical-basal polarity (Figure 1). Cell division occurs in the meristematic zone, especially the apical meristem. The root tip contains the root apical meristem (RAM), a region that consist of a set undifferentiated and dividing cells surrounding the quiescent centre (QC), a group of non-mitotically active cells. Once the lateral root has emerged, its meristem is activated, and further growth results in a similar radial and an apical-basal polarity as described above [2,8]. Auxin is involved in virtually all aspects of plant growth and development including embryogenesis, organogenesis, tissue patterning, tropic responses to light and gravity, maintenance of apical dominance, vascular formation, shoot organ formation, and lateral and adventitious root formation [11,12,13,14,15,16]
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