Effects of partial defoliation, changes of irradiance during growth, short-term water stress and growth at enhanced p(CO2) on the photosynthetic capacity of leaves of Phaseolus vulgaris L.

Abstract

The response of CO₂-assimilation rate to the intercellular partial pressure of CO₂ (p(CO₂)) is used to analyse the effects of various growth treatments on the photosynthetic characteristics of P. vulgaris. Partial defoliation caused an increase in CO₂-assimilation rate at all intercellular p(CO₂). A change in the light regime for growth from high to low light levels caused a decrease of CO₂-assimilation rate at all intercellular p(CO₂). Growth in a CO₂-enriched atmosphere resulted in lowered assimilation assimilation rates compared with controls at comparable intercellular p(CO₂). Short-term water stress initially caused only a decline in the CO₂-assimilation rate at high intercellular p(CO₂), but not at low intercellular p(CO₂). Except under severe water stress, changes in the initial slope of the response of CO₂-assimilation rate to intercellular p(CO₂) were in parallel to those of the in-vitro activity of ribulose-1,5-bisphosphate (RuBP) carboxylase. From the results, we infer that partial defoliation, changes in the light regime for growth, and growth in a CO₂-enriched atmosphere cause parallel changes in RuBP-carboxylase (EC 4.1.1.39) activity and the “capacity for RuBP regeneration”, whereas short-term water stress initially causes only a decline in the RuBP-regeneration capacity.