Tham khảo tài liệu 'advances in photosynthesis fundamental aspects part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 292 Advances in Photosynthesis - Fundamental Aspects roots. In the second case interaction of nitrates with sugars and NO signal system triggering will occur in roots and the process of new secondary root formation will become activated. This thesis is well illustrated by experiments of L. B. Vysotskaya Vysotskaya 2001 . Removal of the largest part of roots from seven-days old wheat seedlings suppressed shoot growth and activated biomass growth of remaining roots in as soon as 2 h. In the remaining roots auxins and cytokinins were accumulated while in the growing part of the shoot a rapid decline of auxin content compared to intact plants was found. This suggests that excessive sugar flow to the reduced root system creates prerequisites for interaction of the changed nitrate to sugar ratio and NO signal system triggering alike an analogue of apical dominance alleviation and synthesis of cytokinines that activate new root formation. Initially the prerequisites are most probably the immediate fueling of the nitrate uptake process by better sugar supply of roots. Additional nitrates in their turn will trigger NO signal system. The proposed concept on the role of NO signaling in the regulation of plant metabolism is supported by split-root experiments where plant roots were exposed to culture mediums of different concentrations Trapeznikov et al. 1999 . By placing one part of roots of an individual potato plant into a medium of high concentration and the other part into low-salt one the authors have found that in the concentrated medium a massive formation of small absorbing roots occurred while in the low-salt one numerous tubers appeared Fig. 11 . LS HS Fig. 11. Root system of an individual potato plant at local nutrition. HS - high-salt culture medium LS - low-salt culture medium Trapeznikov et al. 1999 6. Conclusion Nitrate has been shown to act as a signal molecule inducing expression of genes primarily related with nitrogen metabolism and organic acid synthesis.
