Aluminum toxicity in the primary meristem of wheat roots Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kp78gk61f

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  • The progression and consequences of aluminum toxicity were studied microscopically in the root tips of four wheat varieties representing different classes of Al tolerance. The root tips studied were collected from seedlings grown in nutrient solution cultures containing either sublethal or lethal Al treatments which were unique for each variety. The lethal treatment resulted in the destruction of both cytoplasm and nuclei throughout the root primary meristem of each variety. Some damage was sustained by root tips exposed to the sublethal treatment but if an adequate number of viable cells remained throughout the primary meristem, apical root growth could be reinitiated in an Al-free recovery solution. Reinitiation of apical root growth occurred in spite of the death and subsequent loss of the quiescent center following most sublethal Al treatments. The movement of Al into the root tip could be followed during the Al treatment by using dyes that either combined with Al. or fluoresced in ultra violet light when chelated with Al. There was strong evidence that Al penetrated the boundary between the root apex and rootcap and then, during a lethal treatment, ascended into and throughout the meristematic cells of the central cylinder. Al had also penetrated the epidermis and cortex but was prevented from entering the central cylinder by the endodermis which apparently constituted an additional barrier to the movement of Al. Ascension of Al into the central cylinder from the root apex would by-pass the barrier at the endodermis. Microscopic examination of Al injured root tips revealed that the primary effect of Al was the death of cells. Death occurred rapidly, usually within the first 24 to 48 hours of exposure to Al. The mitotic cycle, however, was affected almost at the onset of the Al. treatment. Evidence in this study suggested that the entire mitotic cycle was impeded by Al although the process of mitosis was least affected. The mitotic cycle proceeded again if the Al stress was removed before the cell's cytoplasm was completely displaced by vacuoles. The cause of varietal tolerance to Al could not be attributed to any structural feature observed through a microscopic examination of root tips from the several wheat varieties grown in this study.
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