Cortical microtubule orientation in Arabidopsis thaliana root meristematic zone depends on cell division and requires severing by katanin

Abstract Background Transverse cortical microtubule orientation, critical for anisotropic cell expansion, is established in the meristematic root zone. Intending to elucidate the possible prerequisites for this establishment and factors that are involved, microtubule organization was studied in roots of Arabidopsis thaliana, wild-type and the p60-katanin mutants fra2, ktn1-2 and lue1. Transverse cortical microtubule orientation in the meristematic root zone has proven to persist under several regimes inhibiting root elongation. This persistence was attributed to the constant moderate elongation of meristematic cells, prior to mitotic division. Therefore, A. thaliana wild-type seedlings were treated with aphidicolin, in order to prevent mitosis and inhibit premitotic cell elongation. Results In roots treated with aphidicolin for 12 h, cell divisions still occurred and microtubules were transverse. After 24 and 48 h of treatment, meristematic cell divisions and the prerequisite elongation ceased, while microtubule orientation became random. In meristematic cells of the p60-katanin mutants, apart from a general transverse microtubule pattern, cortical microtubules with random orientation were observed, also converging at several cortical sites, in contrast to the uniform transverse pattern of wild-type cells. Conclusion Taken together, these observations reveal that transverse cortical microtubule orientation in the meristematic zone of A. thaliana root is cell division-dependent and requires severing by katanin

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The anatomy and histochemistry of the adventitious roots of Urginea maritima (L.) Baker and the plant's adaptive strategies to the Mediterranean climate were investigated. The adventitious roots of U. maritima are bounded by a multiple-layered velamen, responsible for rapid water uptake. Both the epidermis and endodermis of the root are uniseriate. The cortex is 741.3 Ìm thick and is composed of numerous large parenchyma cells with storing character. In the cortex, scattered idioblastic cells containing numerous raphides of calcium oxalate exist. The average length of the calcium oxalate needles is 72 ± 22 Ìm. The presence in the cortex of cells containing in their vacuoles soluble polysaccharides is conspicuous after employing the Schiff's staining technique. Also, numerous cortical cells are filled with lipids and become intensely stained brown to black when treated with sudan black B. Morphometric studies have shown that idioblastic cells occupy 19.83% of the cortex relative volume, cells containing lipids 14.38%, and cells containing polysaccharides 11.27%. The cortex storage cells occupy 34.11% of the total root volume. The average volume of the cortical cells is 73143 Ìm 3 . The vascular cylinder is usually 10-arched. The root xylem consists of vessels in short radial rows. The phloem consists of sieve elements located between the vessel rays. Urginea maritima possessing adventitious roots proves to be efficient in storing water during the long summer drought, less susceptible to climatic stress and well synchronized with the climatic fluctuations. Specialized features of U. maritima adventitious roots are, at least in part, responsible for the species' occurrence and frequent dominance in a wide array of semiarid ecosystems of the Mediterranean region