Abstract
The effects of 0, 50, 150, 250 and 500 mM NaCl for a short duration on the accumulation of Na, Cl and proline betaine in the roots, stems and leaves of young Poncirus trifoliata seedlings were investigated. The degradation of nuclei in the cells of the apical meristem of the root was observed by fluorescence microscopy after the nuclei were stained with 4'-6-dlamidino-2-phenylindole (DAPI). With increasing concentrations of NaCl, the Na and Cl content in the leaves, stems and roots increased while tree growth was reduced proportionately. The leaves accumulated more Na and Cl than did the roots, resulting in severe injuries, more so in the former than in the latter, with increasing NaCl concentrations. Proline betaine accumulated in the roots at 250 and 500 mM NaCl, but it did not increase in the leaves at any treatment. Salt stress also induced several anatomical changes in the apical meristem from the root tip to 2-3 mm, such as vacuolation in the cortical cells, abscission of root cap cells, and nuclear degradation.
