Application of 6-benzylaminopurine (BAP) into cultivation medium of potato and tobacco plantlets caused changes in their growth, morphology and photosynthetic parameters in dependence on the plant species and the concentration ušed. The stimulating effect of BAP added to the cultivation medium was found only at very low BAP concentrations (up to 0.01 g m'^ in tobacco and 0.1 g m'^ in potato plantlets). BAP induced only a very slight tendency to increasing chlorophyll (Chl) a+b content and the ratios Chl alb, ChLcarotenoids and net photosynthetic rate/dark respiration rate {P^íIRd) in both plant species. Also the increase of the photochemical efficiency of photosystem 2 as indicated by the ratio of variable to maximal fluorescence (FyT^) and was not statistically significant and was found only in potato plantlets. The stomatal transpiration rate {E^ in tobacco plantlets increased with increasing BAP concentrations up to 0.1 g m'^. However, this was a rather negative effect as it increased a danger of plantlet wilting. In both plant species the BAP concentration of 1.0 g m-^ inhibited growth of plantlet roots; their shoots had altered morphology, their P^, light respiration rate {R\), E^, P^IRy, ratio, Chl contents and parameters of in vivo fluorescence (Fy/Fn,, qp, Rfd) decreased and CO2 compensation concentration increased. This negative effect of BAP was more pronounced in tobacco than in potato plantlets. The above mentioned changes in photosynthetic parameters in plantlets treated with BAP corresponded to the changes in photosynthetic parameters in transgenic plants of the same species with T-DNA carrying gene 4 and resulting from increased level of endogenous cytokinins. However, the application of BAP lead to a decrease in endogenous cytokinins level and thus the effects described are probably due to the action of BAP itself
Gas exchange and leaf water potential were investigated with regard to water stress in potted 6-month old plants of Copaifera langsdorffii. Leaf water potential (Ψ = -2.0 MPa) in stressed plants was near the osmotic potential (π = -2.2 MPa) at 0900 h during 22 d with water stress. Transpiration rates (if were in linear relation to stomatal conductance (gs) during stress, while water potential and net photosynthetic rate (PN) at 0900 h were in a curvilinear relation. More pronounced decrease of P N occurred only at gs between 0.01 to 0.08 mol nr2 s-1. Increase in water use efficiency (WUE) coincided with morning Ψ diminution from -2.0 MPa to -2.2 MPa. This 10 % decrease in Ψ corresponded to a 60 % decrease in gs (from 0.15 to 0.06 mol m*2 s*1). When pre-dawn Ψ (-3.4 MPa) was close to the Ψ measured at 0900 h (-3.5 MPa), both the and gs were around zero. Therefore, Ψ at 0900 h, π and values of gas exchange were closely related during the days of stress. Values of Ψ for zero and for stomatal closure (-3.5 MPa) were in the same range for sclerophyllous plants.
The influence of air humidity on leaf-air gas exchange and leaf water potential (4^) was investigated during daily courses in control and water stressed potted young plants of Copaifera langsdorffii. When leaf-air water vapour concentration difference (AW) increased during the day, stomatal conductance (g^) and net photosynthetic rate (P]vj) decreased under both soil moistures. Moderate AW induced lower values of g^ and Pn unwatered than control plants, High AW in atmosphere produced strong depression in g^ (from 0.22 to 0,01 mol m'^ s’’) and (from 6.5 to 0.7 pmol m'2 s'*) in control plants around midday, with recuperation of T'. Expected conductance tese) was calculated as fimction of AW, which was useful for discriminating soil to atmosphere water stress. In špite of momentary T or soil water stress, P^, g^, and water use efficiency decreased when AW increased during day course.
Influence of soil drought (40 d) on gas exchange of 10 cultivars of spring cereals (wheat, barley, triticaie and oats) grown in growth chamber was studied. When soil water content was decreased from 60 to 35 % of Ml water capacity, a new steady levels of net photosynthetic rate, transpiration rate and stomatal conductance (about twice, 3-4 and 2-3 fold lower, respectively) were observed after 3 d for both studied oat cultivars and after 5 d for others. These levels were maintained almost the same till the end of the experiment. Calculated water use efficiency (WUE) of water stressed plants increased 3-4 fold, the highest being for barley while the lowest for Oats. At die beginning of the night dark respiration of well watered plants was a little higher than that of water stressed plants but at the end of ihe night was the Sáme independently of water treatment, aithough 20-30 % lower than at the begitming of the night.
Carbon dioxide, a natural acidic gas, may be ušed for in vivo titration of the buffers in the compartments of cells that contain carbonic anhydíase in intact leaves. A gas systém for the measurement of the CO2 capacity (total inorganic carbon content) of leaves under different extemal CO2 concentrations has been developed. The systém consists of a leaf chamber and of two open (flow-through) channels, one for pre- loading the leaf with CO2 and the other for measurement of the desolubilized CO2. CO2 concentration in the loading channel may be adjusted from 0.03 to 20 %, while CO2 free air is flowing in the burst (desolubilization) channel. The leaf chamber (4.3 X 4.3 X 0.3 cm^) is switched either into the loading channel or into the burst channel. After loading the leaf with high CO2 in the dark the .chamber is switched into the burst channel and the desolubilized CO2 is measured. Preliminary measurements show that the CO2 capacity of a sunflower leaf decreases when the CO2 concentration is increased from 0.03 to 15 %, because of saturation of buffers. The systém can be ušed for direct, non-destructive measurements of pH and buffer capacity in leaf chloroplasts in order to investigate the influence of pH on photosynthesis, the operation of proton pumps and other pH-stabilising mechanisms.