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

No abstract

Tlie effects of oxygen conci-nliafion ami light intensity on tho rates of apparent jihotosynthesis, true ptiotosynthesi.s, ptiotorespiration aud dark respiialiun of delachcd spruce (wigs were determined by means of au infra-red carbon dioxide analyzer (lltCA). A closed circuit system IRCA was filted with either 1 per cenI of oxygen iu nitrogen, air {21 o/o Og) or pure oxygen {tOO »/o O^). Two tight intensities 30 x 10ê rg • cm-• .s^' and !20 >; 10=* erg • cm"^ • s'^ were applied.It has heeu found ttiat Ihe iiitiibitory effect of higti conceutiHtion of oxygen on (he appareni phofosyuthe.sis was mainly a result of a stimulaliou of the rate of COg production in light (pliotorespiration). In the atmosphere of 100 Vo O^, photorespiration accounts tor (16-80 per cent of totat CO^ uptake (true photcsyuthesis). Owing lo a sfiong acceleration nf ph<)tores])iration by high oxygen concentrations, the rate of true photosyntliesis calcutated as the sum of api)arent photosynttiesi.s and photolespiiation was by several time.s less inhibifed by oxygeu than the rate of apparent photosynthesis. The rates of dark res|)iration were essentially unaffected Ijy the oxygen concentrations used in the experiments. An increase in the intensity of tight from 30 x lO^ erg • cur^. s'l to 120 x tO^ erg • cnr^ • s^ enhanced the rate of i)hotorespiration in the iitnu.spheres of 2t and tOO »/o oxygen hut not in 1 «/o Oo. Ttie rate of apparent photosynftiosis, however, was tittle affected by light intensity in au atmosphere of 1 Vo oxygeu.

No abstract