The decrease in inorganic phosphate (Pi) content of 10-d-old Phaseolusvulgaris L. plants did not affect rates of photosynthesis (PN) andrespiration (RD), leaf growth, and adenylate concentration. Two weeks ofphosphate starvation influenced the ATP content and leaf growth more than PNand RD. The ATP concentration in the leaves of 15- and 18-d-old phosphatedeficient (-P) plants after a light or dark period was at least half of thatin phosphate sufficient (+P, control) plants. Similar differences were foundin fresh and dry matter of leaves. However, PN declined to 50 % ofcontrol in 18-d-old plants only. Though the RD of -P plants (determined asboth CO2 evolution and O2 uptake) did not change, an increased resistance ofrespiration to KCN and higher inhibition by SHAM (salicylhydroxamic acid)suggested a higher engagement of alternative pathway in respiration and alower ATP production. The lower demand for ATP connected with inhibition ofleaf growth may influence the ATP producing processes and ATP concentration.Thus, the ATP concentration in the leaves depends stronger on Pi contentthan on PN and RD.

The content of cytokinins especially zeatin nucleotide decreased inshoots as a result of temperature increase. Simultaneously the cytokininsaccumulated in roots. The changes in cytokinins distribution were followedby a decline of evapotranspiration after its initial temperature-induceduprising.

Photosynthetic induction phenomena of chloroplast-containing stem tissues and leaves of beech twigs were determined by pulse-modulation chlorophyll fluorometry. The fluorescence transients obtained are of the type characteristic for extremely shade-adapted chloroplasts: a rise in fluorescence to a peak almost as high as Fmax, a very short time required to reach the peak FP, and an elevated steady-state level. Photochemical and energy-dependent quenching coefficients indicate a high reduction state of QA throughout the induction period. These features become increasingly pronounced in the order shade leaves, cortex, xylem and medullary chlorenchyma. The findings indicate a well functioning PS II, the limiting steps being electron flux and Calvin cycle. The functional traits correspond well with ultrastructure and pigment composition. In all stem tissues there are well developed chloroplasts of similar ultrastructure, containing mainly large grana stacks with only a few stromal thylakoids and 1–4 starch grains. The chlorophyll content decreases from bark to xylem to pith; chlorophyll a/b ratios are within the range of 1.7 to 1.9 which is characteristic for shadetype chloroplasts. The results provide evidence for a potential photosynthetic activity of stem chlorenchyma of beech twigs, thus allowing the application of chlorophyll fluorometric methods throughout the entire year on a deciduous tree.

Cowpea [Vigna unguiculata (L.) Walp. var. IT 82 D-889] plants were exposed to a double stress whereby salinization (4–6 weeks at 100, 150 or 200 mM NaCl in the substrate) was the predisposing, and low and high temperatures were the additional constraints. Stress responses were assessed by measuring deviations from normal photosynthetic function by in vivo chlorophyll fluorescence. Salinization alone resulted in considerable changes in morphology, ion concentration and osmolality of the cellular sap of leaves, but had remarkably little effect on fluorescence characteristics at 20 °C. Decreasing and increasing temperatures caused marked changes in the fluorescence quenching kinetics and revealed that temperatures of 5–10 °C are suboptimal, and those around 40 °C, supraoptimal. In non-salinized plants, severe temperature stress at 3–6 °C and 45–50 °C was reflected by break-points in the temperature courses of the quenching coefficients at steady state, of Fv/FM, of (Fv)Mdark/(Fv′)Mlight, and of the heat-induced rise of Fo. Mild superimposed temperature stress enhanced the unfavourable effect of saline stress on the kinetics of qN, indicating an increased impairment of the photosynthetic process in response to the combined stress. With severe superimposed temperature stress, however, the salinized plants appeared to be less susceptible than the control plants, since the threshold temperatures for abrupt deviations of Fv/FM and (Fv)Mdark/(Fv′)Mlight, and for injury indicators (chilling symptoms, tissue freezing temperatures, Tc) shifted by 2–3K in the direction of the stressing temperature. We discuss possible mechanisms for these contrasting effects, i.e. the enhancement of disturbances at sub- and superoptimal temperatures but coadaptive adjustments at extreme stress temperatures. The results demonstrate the value of employing superimposed stressors for intensifying stress expression and for providing more information on interactions between environmental factor combinations as they exist in nature.