The Role of Sink-Source Relationships between Different Organs in Regulation of Photosynthesis and Productivity

It is known that in agronomy removal of a part of sinks for assimilates (axillary buds, flowers, fruits, etc.) is successfully used for fruitage regulation. When sink-source relationships are disturbed no investigators' attention is usually paid to the root system. Our task was to find out the role of competition for assimilate acquisition between the roots and other sink organs in regulation of photosynthesis. The investigation of ontogenetic changes in assimilate distribution throughout the wheat plant showed that to the end of the phase of caryopsides formation (as the sink strength of the latters' grew) the supply of assimilates to the roots decreased. Making excess of assimilates in the plant (by removal of spike part) eliminated this effect, and leaf photosynthesis as well as growth processes in the roots increased. Appearance of the assimilate excess enhanced the uptake of nitrogen from soil. Apoplastic invertase is an enzyme that is active in acid environment. It was shown that artificial changing of apoplastic pH by introduction of HCl or NH3 vapors in the gaseous medium led to differently directed changes in photosynthesis intensity and accumulation of labeled assimilates in the apoplast. For stable increase of apoplastic fluid pH a solution of catalytic amounts of ammoniates of copper and zinc (10(-6) M) was introduced into the apoplast of a flax shoot. The treatment resulted in stimulation of photosynthesis, enhancement of its carbohydrate orientation and increase of the labeled sucrose to hexoses ratio. Spraying of plants with ammoniate solution significantly enhanced their productivity, with concurrent increase of nitrogen acquisition from soil.