Effect of nitrates supplied with the transpiration flow on assimilate translocation

The Role of C to N Balance in the Regulation of Photosynthetic Function

“…As we have shown previously (Batasheva et al, 2007), increased 14 C content in the lower part of plants fed with water is not connected with label accumulation due to synthesis of any high-molecular weight substances in this period. In 30 min after 14 CO 2 assimilation relative content of 14 C-sucrose in source leaves increased both in control and in nitrate fed plants (Table 6).…”

“…The common explanation of reduction in sucrose synthesis after nitrogen nutrition of plants is the following: at enhanced inflow of nitrogen into the plant photosynthetic products and energy are diverted from sucrose synthesis to the formation of nitrogen-containing compounds (Champigny & Foyer, 1992). However, this explanation does not accord with different actions of oxidized and reduced nitrogen on sucrose production (Batasheva et al, 2007). Undoubtedly, the reduction of nitrates requires more energy spending, but the electron transport in chloroplast is known to have significant plasticity and different types of mitochondrial electron transport are probably take part in the maintenance of necessary ATP/NAD(P)H ratio in the cell (Noctor & Foyer, 1998;2000).…”

“…Another reason of decreased sucrose synthesis under nitrate nutrition may be a feedback regulation of photosynthesis resulted from slowdown of sucrose transport from leaves. Injection of nitrate solution into a flax shoot resulted in pronounced response of photosynthetic rate, photosynthetic carbon metabolism and assimilate transport measured in 3 h after 14 CO 2 assimilation (Batasheva et al, 2007). That is why we decided to study those changes in more detail.…”

“…In shoots fed with nitrates, 14 C content outside the donor part in 2.5 h also increased but in lesser degree than in control, and the overall 14 C relative content in the lower shoot part became smaller whereas in the upper part -greater compared to control. In our previous experiments it was found that feeding urea solution (0.15% (w/v)) containing the same amount of nitrogen as potassium nitrate solution (0.5% (w/v)), led to almost the same distribution of 14 C through the shoot as feeding water (Batasheva et al, 2007). NH 4 NO 3 solution feeding led to lesser inhibition of assimilate export and slightly changed the pattern of 14 C partitioning along the shoot compared to those under KNO 3 solution feeding (Batasheva et al, 2007).…”

“…In our previous experiments it was found that feeding urea solution (0.15% (w/v)) containing the same amount of nitrogen as potassium nitrate solution (0.5% (w/v)), led to almost the same distribution of 14 C through the shoot as feeding water (Batasheva et al, 2007). NH 4 NO 3 solution feeding led to lesser inhibition of assimilate export and slightly changed the pattern of 14 C partitioning along the shoot compared to those under KNO 3 solution feeding (Batasheva et al, 2007). In flax, most 14 C-sucrose after being loaded into the phloem terminals in source leaves moves downwards within stem phloem vessels, and 14 C content in the plant lower parts gradually raises (Chikov & Bakirova, 2004).…”