Abstract
The adaptation mechanism of Melilotus officinalis was studied to understand this species’ mechanisms. Seedlings of Melilotus officinalis were treated with different NaHCO3 levels, with the control plants being grown without NaHCO3. Anatomical structure of three organs and ultrastruture of two organelles widespread were observed by making paraffin and ultrathin sections. The results showed that NaHCO3 treatments significantly affected vascular system of Melilotus officinalis. Vascular tissue throughout the roots, stems and leaflets underwent changes. Particularly, the diameter of xylem vessels declined significantly, which greatly limited the transportation and transverse diffusion of water; the cross section of stems was changed from near quadrangle to irregular shape, which increased the surface area of the stems and furthered the ability of photosynthesis; epidermis cell walls cutinization occurred and the diameter of xylem vessel decreased greatly, which reduced water loss through stomata and non-stomata cells. In spite of these dramatic morphological changes, organelles in cells, both chloroplast in stems and leaflets and mitochondria in roots, had minor changes. Particularly, thylakoid in chloroplast and cristae in mitochondria still had intact membrane system and sharp-edged laminated structure. Vascular tissue, the cross section of stems, cell walls of epidermis and mesophyll cell all underwent changes in Melilotus officinalis under NaHCO3 stress. While organelles in cells had minor changes. Maybe structural integrity of organelle was protected by active morphological change of tissues and cells in Melilotus officinalis.
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