GAS EXCHANGE AND ENZYME ACTIVITY DURING LEAF EXPANSION IN PHASEOLUS VULGARIS L.

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SUMMARY

Net photosynthesis, transpiration, boundary layer plus stomatal resistance to CO2 diffusion, and CO2 compensation point were monitored in the central leaflet of expanding first trifoliate leaves of Phaseolus vulgaris L. Simultaneously, the activities of three enzymes related to net photosynthesis, photorespiration and dark respiration were measured. Net photosynthesis rate and ribulose 1,5-diphosphate carboxylase activity increased with leaflet expansion, reaching peaks just prior to full expansion. Concurrently, boundary layer plus stomatal resistance, CO2 compensation point and malate dehydrogenase activity decreased, reaching lowest values at full leaflet expansion.

Shortly after peak photosynthetic activity was reached all trends reversed, as the physiological activity of the first trifoliate leaf of this determinate type bean plant changed to that characterized by a senescing leaf.

Ancillary