One way to promote plant productivity lies in nitrogen nutrition various level usage for photosynthesis intensity regulation. The C4 - plants (amaranth, panic grass, etc.), due to their special type of photosynthesis, have arrange of advantages over C3-plants (wheat, celosia, etc.) in taking carbon dioxide and reaching high productivity (Magomedov I.M., 1988). Nevertheless, for C4-plants the searches of ways to promote the productivity are also important. In C4-plants the nitrogen intake photosynthetic efficiency (NIPE) defined as photosynthesis per nitrogen unit is significantly higher, than in C3-plants (Brown R.H., 1978). However, for not all research men stick to such point of view (Koshkin Ye.I. and others, 1955), clearing up the reasons underlying such a phenomenon is rather topical. The purpose of the present work has been the follow-up study with intent to test the hypothesis about the direct dependence of NIPA on the C4-photosynthesis intensity in amaranth leaves, and also the nitrogen status value clarification for the photosynthesis intensity. The study objects were - amaranth (C4-plant) and celosia (C3-plant) of the Amaranthaceae family. We supposed that in young leaves, where the protein synthesis was going on, the photosynthesis rate (PR) should be higher, than in old ones, where the protein synthesis was restricted. The findings testified that the PR of amaranth young and old leaves in nitrogen variant with an eye to 1dm2 of the surface was high. At the irrigation with the nitrogen free solution the PR decrease occurred. The PR with an eye to dry weight with nitrogen supply remained at the same level in both young and old leaves; but with nitrogen lack a significant PR decrease took place, especially in lower leaves. The dry weight of both old and young leaves of amaranth was twice as high, than that of the C3-plant. The photosynthesis intensity per 1 mg of chlorophyll was higher in young amaranth leaves both with and without nitrogen; the excluding of nitrogen from the solution didn´t change the amaranth PR. In old leaves it was lower, than in young ones. The amount of nitrogen in amaranth old leaves was by 20-25 % lower, than in young ones. The same picture was observed at the NIPE calculation. The value of this factor in amaranth, both in young and old leaves with and without nitrogen, was much higher, than in C3-plant. As it was shown in our previous work (Shumilova A.A., Magomedov I.M., 1994), indeed, in amaranth the NIPE is significantly higher, than in C3-plants, that is consistent with the data of a range of authors (Wrown R.H.,1978; Oaks A.,1994). It is known that more than half of the cell´s soluble protein falls to ribulesobiphosphate carboxylase/oxigenase (RBPC/O), especially in C3-plants. Amaranth contains significantly less RBPC/O, therefore the nitrogen demands for basic enzymatic proteins synthesis are considerably decreased as well, and its main part is used to new cellular structures formation. So, in response to nitrogenous fertilizers application in amaranth a more intensive biomass growth, than that in C3-plants, takes place and less nitrates, than in the last ones, is accumulated in leaves. In all probability, it is it that explains a high NIPE level in amaranth. On the ground of the results obtained it is offered to divide mineral nitrogen in plants into "growth" nitrogen, which is higher in C4-plants, and homeostasis "maintenance" one, which is considerably prevalent in C3-plants.
The work is submitted to the International Scientific Conference "Actual problems of science and education", Cuba (Varadero), March, 19-29, 2008, came to the editorial office on 20.02.2008.