REGULATION OF PHOTOSYNTHETIC CO2 EXCHANGE IN LEAVES DURING DEVELOPMENT OF WATER-DEFICIT IN THE RADICLE ZONE OF COTTON

Gasometric methods were used to study the effect of water deficit on p arameters of photosynthetic CO2 assimilation on undetached 19- to 20-d ay leaves of cotton plants (Gossypium hirsutum L., cv. 108-F) grown in greenhouse vessels in open air. The effect of water deficit on compon ents determining the rate of photosynthetic CO2 exchange is presumed t o be predominantly indirect and associated with disturbances of the gr owth function and alteration of source-sink relations in the system of the whole plant. Decline of photosynthesis under conditions of water stress (37-40% of field moisture capacity) is shown to be linked to a greater extent with decrease of stomatal conductivity than with the ph otosynthetic capacity of mesophyll cells. Invariability of measured pa rameters characterizing biochemical reactions of photosynthesis-such a s mesophyll conductivity in nitrogen, the RuBP pool, and CO2-saturated photosynthesis-probably is associated with leaf tissue thickening and a certain increase in the effective concentration of photosynthesizin g structures as calculated per unit of leaf area in the test plants.