Physiological site of ethylene effects on carbon dioxide assimilation in Glycine max L. Merr

Physiological site of ethylene effects on carbon dioxide assimilation in Glycine max L. Merr

1988

A:PS

The physiological site of ethylene action on CO2 assimilation was investigated in soyabean cv. Davis plants using a whole-plant, open exposure system equipped with a remotely operated single-leaf cuvette. Synchrony in response of CO2 assimilation, stomatal conductance to water vapour, and substomatal CO2 partial pressure; response of CO2 assimilation as a function of a range of substomatal CO2 partial pressures; and response of CO2 assimilation as a function of a range of photon flux densities were studied. After exposure to 410 ?ol ethylene/m3 for 2 h, CO2 assimilation and stomatal conductance declined in synchrony, while substomatal CO2 partial pressure remained unchanged until exposure times were _3 h. Because incipient changes in CO2 assimilation occurred without a change in the CO2 partial pressure in the leaf interior, it was concluded that both stomatal physiology and chloroplast CO2 assimilatory capacity were initial sites of ethylene action. After 3.5 h the effect of ethylene on stomatal conductance and CO2 assimilation exhibited saturation kinetics, and the effect was substantially more pronounced for stomatal conductance than for CO2 assimilation. Based on the response of CO2 assimilation to a range of substomatal CO2 partial pressures, ethylene did not affect either the CO2 compensation point or carboxylation efficiency at subsaturating CO2 partial pressures. Above-ambient supplies of CO2 did not alleviate the diminished rates of CO2 assimilation. In partitioning the limitations imposed on CO2 assimilation in control and ethylene-treated plants, the stomatal component acccounted for only 16 and 4%, resp. The response of CO2 assimilation to a range of photon flux densities suggested that ethylene reduced apparent quantum yield by nearly 50%.

v.86(1):85-92, PLANT PHYSIOLOGY

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