In bean (Phaseolus vulgaris L.) seedlings well supplied with water, rates of transpiration (E) and CO2 assimilation (PN) of the primary leaves were measured under blue (BR) or red (RR) irradiance of 150 µmol(photon) m-2 s-1. The leaf conductance to H2O vapour transfer (gH2O), as well as the intercellular concentrations of H2O vapour (ei) and of CO2 (Ci) were calculated. Under BR, gH2O was significantly greater, but PN was lower, and E similar as compared with corresponding values found under RR. The increase of stomata aperture under BR was evident although Ci was higher and ei was lower than under RR. Results agree with the suggestion that BR directly activates guard cell metabolism and in well watered plants determines mainly the stomata aperture. and S. Maleszewski, E. Niemyjska, B. Kozłowska-Szerenos.
Primary leaves of bean (Phaseolus vulgaris L.) seedlings cultivated for 14 days in a growth chamber on complete (control) and phosphate deficient (-P) Knop liquid medium were used for measurements. The -P leaves were smaller and showed an increased specific leaf area (SLA). Their inorganic phosphate (Pi) concentration was considerably lowered. They did not show any significant changes in chlorophyll (Chl) (a + b) concentration and in their net CO2 assimilation rate when it was estimated under the conditions close to those of the seedlings growth. Light response curves of photosynthetic net O2 evolution (P NO2) of the leaves for the irradiation range up to 500 μmol(photon) m-2 s-1 were determined, using the leaf-disc Clark oxygen electrode. The measurements were taken under high CO2 concentration of about 1 % and O2 concentrations of 21 % or lowered to about 3 % at the beginning of measurement. The results obtained at 21 % O2 and the irradiations close to or higher than those used during the seedlings growth revealed the phosphorus stress suppressive effect on the leaf net O2 evolution, however, no such effect was observed at lower irradiations. Other estimated parameters of P NO2 such as: apparent quantum requirement (QRA) and light compensation point (LCP) for the control and -P leaves were similar. However, with a high irradiation and lowered O2 concentration the rate of P NO2 for the -P leaves was markedly higher than that for the control, in relation to both the leaf area and leaf fresh mass. This difference also disappeared at low irradiations, but the estimated reduced QRA values indicate, under those conditions, the increased yield of photosynthetic light reaction, especially in the -P leaves. The presented results confirm the suggestion that during the initial phase of insufficient phosphate feeding the acclimations in the light phase of photosynthesis, both structural and functional appear. They correspond, probably, to the increased energy costs of carbon assimilation under phosphorus stress, e.g. connected with raised difficulties in phosphate uptake and turnover and enhanced photorespiration. Under the experimental conditions especially advantageous for the dark phase of photosynthesis (saturating CO2 and PAR, low O2 concentration), those acclimations may be manifested as an enhancement of photosynthetic net O2 evolution. and B. Kozłowska-Szerenos, A. Jarosz, S. Maleszewski.
Stomatal responses of attached bean (Phaseolus vulgaris L.) leaves to changing spectral composition ("white" - WL., blue - BL, or red - RL radiation), air humidity (100 % or about 4 % RH), and water potential of the root medium (close to 0 or -1.2 MPa) were determined by air flow porometer. Opening of stomata always increased under BL and decreased under RL. In response to decline in air humidity, leaf conductance showed transient increase before it reached lowered steady state. BL enhanced and RL diminished this response. and S. Maleszewski ... [et al.].