![]() The PIN gene family has eight members in Arabidopsis and every member seems responsible for different functions in auxin efflux, and the tomato PIN gene family expanded to ten members ( SlPIN1- SlPIN10). PIN proteins play an important role in polar auxin transport (PAT) due to their asymmetric subcellular localizations. The AUXIN1/LIKE-AUX1 (AUX/LAX) gene family encodes auxin influx symporters. Two major classes exhibit auxin-efflux activity: the plant-specific PIN family of efflux carriers and the ATP-binding cassette (ABC) superfamily of transporters, predominantly the B-type (ABCB/multidrug resistance /phosphoglycoprotein ). There are three classes of auxin carriers and transporters at the plasma membrane. Tomato stem cuttings readily form adventitious roots, which makes them an ideal system to study AR formation in detail.Ĭell-to-cell auxin transport is mediated by a network of auxin influx and efflux carriers that are regulated at the transcriptional and post-translational levels. While auxin (indole-3-acetic acid, IAA) has been shown to regulate AR formation during these three phases and almost every developmental step, the detailed cytology and mechanism of AR formation in species other than Arabidopsis thaliana have not been well-described. Finally, during the extension phase, AR primordia grow through the stem’s cell layers and emerge from the epidermis. In the initiation phase the meristematic cells of the primordia divide and differentiate into root cell layers : epidermis, cortex, endodermis, vasculature, meristem and root cap. During the induction phase, the primordium initial cells are established via de-differentiation of pericycle cells or cambium cells (this depends on the species and the age of the stem cutting) followed by cell division. Īdventitious root formation is generally divided into three developmental phases: induction, initiation and extension. Adventitious roots can also form in response to abiotic stresses such as waterlogging or when embryonic roots are dysfunctional. ![]() Adventitious roots (AR) are post-embryonic roots which form at multiple sites in diverse organs including leaves, the root-shoot junction, stems in contact with the soil surface, and at the base of stem cuttings. Depending on when and from which tissue they originate, roots can be defined as embryonic or post-embryonic. ![]() The root has multiple functions during plant growth and development including water and nutrient absorption. ![]() The gene expression of specific auxin transporters increased during specific developmental phases of AR formation. Hormone profile analyses showed that auxin positively regulated AR formation, whereas perturbations to zeatin, salicylic acid, and abscisic acid homeostasis suggested minor roles during tomato stem rooting. Treatment of stem cuttings with auxin, increased the number of AR primordia and the length of AR, while stem cuttings treated with the pre-emergent herbicide/auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) occasionally developed thick, agravitropic AR. Tomato lines expressing the auxin response element DR5pro:YFP showed an increase in auxin distribution during the AR initiation phase, and was mainly concentrated in the meristematic cells of the developing AR. Auxin and ethylene levels increased in the basal stem cutting within 1 h. ![]() Further growth resulted in emergence of mature AR through the epidermis following programmed cell death of epidermal cells. The first disordered clumps of cells assumed a dome shape that later differentiated into functional AR cell layers. Here we show the progression by which AR form from founder cells in the basal pericycle cell layers in tomato stem cuttings. ![]()
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