Drought-Induced Modifications on the Outer Part of the Root (OPR) and Root Endodermis of Selected Rice Genotypes

Abstract

Rice production is oftentimes confronted by environmental constraints such as drought which affects the water uptake of roots. The internal apoplastic barriers in the roots are believed to regulate/constrain the radial water flow through the gaps in between the cells. Thus, in this study, a screenhouse experiment was conducted using four rice cultivars namely, Jasmine, Arabon, Basmati, and UPLRi-3 (drought-tolerant variety), to determine the effects of 3 weeks of drought stress in the common sites of root apoplastic barriers, such as the outer part of the root (OPR) (composed of epidermis, exodermis, and sclerenchymatous layer) and root endodermis, and to identify from these tissues putative responses that may be relevant to drought-tolerance of rice roots. The exodermis was not affected during drought while the epidermis shrank extremely. The second week of drought imposition resulted in a significant increase in exodermal and endodermal cell sizes. Drought enhanced the lignification in the sclerenchymatous layer and suberization in the endodermis. The drought-tolerant variety UPLRi-3 developed the thickest lignification of sclerenchymatous layer (2.15 μm), followed by Jasmine (1.9 μm), and lastly Arabon and Basmati (1.59 and 1.51 μm, respectively). The varieties UPLRi-3, Arabon, and Jasmine produced high suberin deposition in the endodermis, which were not significantly different from each other (3.76, 3.51, and 3.49 μm, respectively), while Basmati produced the lowest (2.81 μm). The control variety UPLRi-3 demonstrated a highly positive root response which can be associated to its drought-tolerance trait. The results obtained suggest rice root’s dynamic coping mechanisms with the effects of drought to protect itself from rapid dying and prevent internal water loss.