Photosynthesis and transpiration rate of detached leaves of pea (Pisum sativum L. cv. Itowiecki) exposed to solution of Pb(NO3)2 at 1 or 5 mmol.dm -3 concentrations were inhibited. The higher concentration of this toxicant decreased photosynthesis and transpiration rates 2 and 3 times respectively, and increased respiration by about 20 %, as measured after 24 hours of treatment. Similarly to Pb(NO3)2, glyceraldehyde solution, an inhibitor of phosphonbulokinase, at 50 mmol.dm concentration decreased the rates of photosynthesis and transpiration during introduction into pea leaves. The rate of dark respiration, however, remained unchanged during 2 hours of experiment.The potential photochemical efficiency of PS II (Fv/Fm) and the activity of Rubisco (EC 4.1.1.39) at 5 mmol.dm -3 of Pb(NO3)2 were lowered by 10 % and 20 % respectively, after 24 hours. Neither changes in the activity of PEPC (EC 4.1.1.31) or protein and pigment contents were noted in Pbtreated leaves. The photosynthetic activity of protoplasts isolated from leaves treated for 24 or 48 hours with Pb(NO3)2 at 5 mmol.dm -3 concentration was decreased 10 % or 25 %, whereas, the rate of dark respiration was stimulated by about 40 % and 75 %, respectively. The content of abscisic acid, a hormone responsible tbr stomatal closure, in detached pea leaves treated tbr 24 h with 5 mmol.dm 3 of Pb(NO3)2 solution was increased by about 3 times; a longer (48h) treatment led to further increase (by about 7 times) in the amount of this hormone. The results of our experiments provide evidences that CO2 fixation in detached pea leaves, at least up to 24 hours of Pb(NO3)2 treatment, was restricted mainly by stomatal closure. List of abbreviations."A B A = abscisic acid; F m = m a x i m a l fluorescence; Fo = initial fluorescence; Fv = variable fluorescence; F v / F m = photochemical yield o f p h o t o s y s t e m II; G = D L -g l y c e r a l d e h y d e ; F = CO2 c o m p e n s a t i o n point; P E P C = phosphoenolpyruvate carboxylase; Pn = net photosynthesis; R = dark respiration; R u b i s c o = ribulose-l,5-bisphosphate carboxylase -o x y g e n a s e ; t 1/2 = halfrise time f r o m Fo to F m ; T = transpiration

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The role of irradiance on the activity of antioxidant enzymes: superoxide dismutase (SOD) and catalase (CAT) was examined in the leaves of Pisum sativum L. plants grown under low (LL) or high (HL) irradiance (PPFD 50 or 600 μmol m -2 s -1 ) and exposed after detachment to 5 mM Pb (NO 3 ) 2 for 24 h. The activities of both enzymes increased in response to LL compared with HL and no effect of Pb ions was observed. Photosystem (PS) 1 and PS 2 activities were also investigated in chloroplasts isolated from these leaves. LL lowered PS 1 electron transport rate and changes in photochemical activity of PS 1 induced by Pb 2+ were visible only in the chloroplasts isolated from leaves of LL grown plants. PS 2 activity was influenced similarly by Pb ions at both PPFD. This study demonstrates that leaves of HL grown plants were less sensitive to lead toxicity than those from LL grown plants. Changes in electron transport rates were the main factors responsible for the generation of reactive oxygen species in the chloroplasts and as a consequence, in induction of antioxidant enzymes.Additional key words: antioxidative enzymes, chloroplasts, lead, Pisum sativum, photosystem 1 and 2 activities.

Ab stractThe ef fects of oligomycin on pho to syn the sis and res pi ra tion in re la tion to ATP pro duc tion in chloroplasts and mi to chon dria were in ves ti gated in proto plasts iso lated from the de tached pea (Pisum sativum L cv. Iłowiecki.) and bar ley (Hordeum vulgare L. cv. Gunilla) leaves treated 5 mM Pb(NO 3 ) 2 . The oligomycin (OM), an in hib i tor of ox i da tive phosphorylation at 0.1 µM con cen tra tion caused the in hi bi tion of pho to syn the sis rate in the proto plasts from both the con trol and the Pb-treated pea leaves. The res pi ra tion rate and ATP/ADP ra tio in the protoplasts and the ac tiv ity of ATPase in mi to chon dria, were also dimin ished in the con trol proto plasts. These ef fects were not observed in the proto plasts and mi to chon dria iso lated from the Pb-treated leaves. Oligomycin, an in hib i tor of photophosphorylation at 10 µM con cen tra tion de creased ATPase ac tiv ity in chloroplasts from both the con trol and the Pb-treated leaves.Us ing the method of rapid frac tion ation of bar ley proto plasts it was shown that the ATP/ADP ra tio in the mi to chon dria from Pb-treated leaves was largely sup pressed (from 1.8 to 0.4) by OM un der nonphotorespiratory con di tions (high CO 2 ), whereas un der photorespiratory con di tions (low CO 2 ) this ratio was high (5.3) and un der OM de creased less (to 3.1).Our re sults in di cate that oligomycin, in organelle iso lated from Pb-treated leaves, had no in hib i tory ef fect on the mi to chondrial ATPase, whereas it in hib ited chloroplasts ATPase. We sug gest that Pb ions af fected the cat a lytic cy cle and/or conformational changes of ATPase in pea chloroplasts dif fer ently than in mi to chon dria. The dif fer ences in Pb re sponses may reflect fine mech a nisms for the reg u la tion of ATP pro duc tion in the plant cells un der stress con di tions.List of ab bre vi a tions: CFoCF1, chloroplast ATP synthase; Chl, chlo ro phyll; ∆ pH, the dif fer ence between the ex ter nal and in ter nal pH; OM, oligomycin; PSII, photosystem II; pmf, pro ton mo tive force. In tro duc tionElec tron trans port in chloroplasts and mi to chondria in a plant leaf cell is cou pled with ATP syn thesis. In the dark, only the mi to chon drial ox i da tive phosphorylation operates (Groth and Strotmann 2002, Hisabori et al. 2002, Jagendorf 2002, whereas the ATP re quired in the cytosol dur ing a pe riod of pho to syn the sis is ob tained mainly from the chloroplasts via uti liz ing of the triosephos phate-phosphoglycerate shut tle (Flugge and Heldt 1984). Gardeström (1987) showed that the cytosolic ATP/ADP ra tio of bar ley proto plasts was higher in the light at lim it ing CO 2 con cen tra tion rel a tive to sat u rat ing CO 2 or dark ness. Other authors (Stitt et al.1982), no ticed in wheat proto plasts that this ra tio was lower in the light than in the dark 29 ACTA PHYSIOLOGIAE PLANTARUM

Metabolic responses to Pb(NO₃)₂ (Pb) ions of excised leaves of metallicolous (MPs) and nonmetallicolous populations (NMPs) of Armeria maritima, cultivated on normal soil, were examined. Detached leaves were exposure to Pb for 24 h, and metabolic parameters were investigated. Pb decreased the photosynthesis (Pn) rate and photosystem II (PSII) activity, whereas the photochemical efficiency of PSII remained unchanged. In both populations, Pb ions caused increase in O₂ uptake of dark-treated leaves; however, respiration after Pn was not affected. Pb increased superoxide dismutase activity in MP leaves and malondialdehyde content in NMP leaves. Other metabolites after Pb treatment were increased (proline or H₂O₂) or decreased (malate). Ascorbate peroxidase activity and adenosine triphosphate content decreased more in MP than in NMP leaves. Our results indicate that A. maritima is well adapted to heavy metal-contaminated soils, and we discuss potential causes of the stimulation of respiration by Pb ions and possible reasons for the tolerance to oxidative stress of plants growing in a metal-rich habitat.