Influence of different phosphorus concentrations was studied in four rice varieties (Akhanphou, MTU1010, RP BIO 226, and Swarna) differing in their tolerance to low phosphorus. There was an increase in shoot and root dry mass with the increase in phosphorus concentration. At the low phosphorus concentration at both tillering and reproductive stages, Swarna, followed by Akhanphou, recorded maximum biomass for both roots and shoots, while the minimum was observed in RP BIO 226. Reduction in photosynthetic rate, stomatal conductance, transpiration rate, and internal CO2 concentration at low phosphorus concentrations were observed at both tillering and reproductive stages in all the genotypes. In low phosphorus, maximum photosynthetic rate was found in Swarna followed by Akhanphou. Phosphorus deficiency did not alter the maximum efficiency of PSII photochemistry, however, there was a reduction in effective PSII quantum yield, electron transport rate, and coefficient of photochemical quenching, while the coefficient of nonphotochemical quenching was higher in the low phosphorus-treated plants. Prolonged exposure to excessive energy and failure to utilize the energy in carbon-reduction cycle induced the generation of reactive oxygen species, which affected PSII as indicated by the fluorescence traits. The reduction was less severe in case of Swarna and Akhanphou. The activities of superoxide dismutase, peroxidase, and catalase increased in roots under low phosphorus concentration indicating that photoprotective mechanisms have been initiated in rice plants in response to phosphorus deficiency. Comparatively, Swarna and Akhanphou exhibited a higher biomass, higher photosynthetic rate, and better reactive oxygen species-scavenging ability which conferred tolerance under low phosphorus conditions., N. Veronica, D. Subrahmanyam, T. Vishnu Kiran, P. Yugandhar, V. P. Bhadana, V. Padma, G. Jayasree, S. R. Voleti., and Obsahuje bibliografii
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.