The cadmium treatment of dark-grown leaves and isolated etioplast inner membranes of wheat resulted in a decrease of the amount of the 657 nm emitting (77 K fluorescence) protochlorophyllide (PChlide) form, a simultaneous increase of the 633 nm form and the appearance of a 641.5 nm emitting form. This effect did not occur if excess NADPH was added to the isolated membranes: these samples showed spectral properties identical to those of non-treated (control) samples. Inhibition of the PChlide phototransformation was observed in the cadmium-treated leaves and membranes, the irradiation resulted in the appearance of a smáli amount of chlorophyllide (Chlide) with characteristic emission band at 678 nm. If excess NADPH was added, the inhibition did not occur and flash irradiation resulted in formation of the 694 nm Chlide form similarly as in control plants.
Chlorophyll content, photosynthetíc oxygen evolution and the activities of ATP- sulphurylase (ATP-s) (E.C. 2.7,7.4.), OAS-sulphydrylase (OAS-s) (E.C, 4.2.99.8.), nitráte reductase (NR) (E.C. 1.6.6.1.) and glutamine synthetase (GS) (E.C. 6.3.1.2), were determined in leaves of Zea mays L. Dekalb cv. Sponsor plants grown in the presence of 0, 10, 100, 250 pM Cd in order to evaluate the effect of this metal on sulphate and nitráte assimilation pathway. Cd induced a slight decrease of photosynthetíc oxygen evolution (-21 % of the control at 250 pM), whereas the enzyme activities were differently influenced: OAS-s and GS increased up to 40 and 25 % of the control, respectively, at 250 pM Cd; NR showed a 20 % stimulation at 100 pM Cd, and ATP-s was slightly inhibited. The results stress the importance of experimental conditions adopted on the response of enzyme activities to Cd and suggest that the observed increases of enzyme activities are related to a defence mechanism.
The influence of surplus normál oř deficient nitrogen nutrition on the organization of maize chloroplast pigment apparatus was investigated. The amoímt of light- harvesting pigment-protein complexes (LHC) was the highest in chloroplasts fi^om high-nitrogen plants. Nitrogen deficiency resulted in a strong reduction of LHC, especially of its oligomer form. The fine structure of low temperature chloroplast absorption spectra revealed a relative decrease in the intensity of the 663, 666 and 678 nm components, while that of the components at 672 and 674 nm was increased. The changes in fine structure of the red fluorescence excitation spectra (F720 and F736) reflected similar changes in absorbance spectra. The changes do not allow to draw conclusions about the disturbance in energy transfer efficiency between some chlorophyll forms.
Development of water stress in Trifolium subterraneum L. plants, growing in growth room or in the field during autumn-winter and latě springtime, was studied under ťhe conditions of irrigation replenishing every day the evaporated water (1), withholding watering (WW), and slowly induced drought, replenishing daily with a fraction of water evaporated (SID). The method ušed to induce drought substantially affected the leaf water relations. In WW plants drought developed rapidly and in consequence the leaf water relations dramatically changed afler 10 d of treatment. The treatment maintained a stable moderate water stress (SID) that enabled the development of new acclimated leaves even under high tempertures and low humidity.
The CO2 assimilation rate the transpiration rate (E), the stomatal conductance (gg), C index and the instantaneous water use efficiency of attached leaves háve been estimated in sixteen cultivars of subterranean clover (Trifolium subterraneum L.) fíeld growing plants, both irrigated and subjected to water stress, during latě spring in Mallorca, Spain. Variability among the genotypes with regard to the and other related parameters was highly significant for tiie irrigated plants. Drou^t promoted a marked decrease in both gg and ®ven when the relative water content of leaves was only slightly decreased. For water-stressed plants, genotypic variability in E and C index was also statistically significant. However, variability among the genotypes with regard to gg and was no longer evident under drought. The C index might represent a valuable parameter for evaluation of the genotypic responses of plants to drought.
The effect of elevated CO2 on ovemight malate accumulatíon in the CAM epiphyte Tillandsia ionantha and the CAM terrestrial species Crassula arborescens was compared. Both species showed an increase in nocturnal accumulatíon of malate with increasing CO2 concentrations. This study is the first to show an increase in nighttime malate accumulatíon with increasing levels of CO2 at near-ambient concentrations in a CAM plant. The results indicate that some CAM plants can respond to increasing levels of CO2 in the atmosphere, potentíally leading to an increase in productívity.
Leaf tissue of azalea cultivars was treated with fluoride by floating leaf discs on Solutions or by allowing KF to enter intact leaves via stem segments and petioles. In each čase, the photosynthetic rate was more strongly influenced by KF than the respiration rate or content of chlorophyll were.
Heat temperature is a limiting factor for plant growth, but some plants are able to acclimate showing a marked heat resistance. Pea seedlings {Pisum sativum L.) cv. Pleven 10 (winter cv.) and Auralia (spring cv.) grown in hydroponie cultures were heat acclimated at 40, 45 and 50 °C. Non-acclimated and acclimated plants were subjected to heat stress at 55 °C and in isolated thylakoid membranes fatty acid composition and changes in the main lipid classes (monogalactosyldiacylglycerols, digalactosyldiacylglycerols and phospholipids) were determined. The acelimation to heat lead to some resistance towards heat stress, and was more expressed in the cv. Auralia.
The survival of Encephalitozoon cuniculi Lcvaditi, Nicolau et Schoen, 1923 spores suspended in distilled water and exposed at defined temperatures was investigated. Infectivity of E. cuniculi spores was tested by inoculation of SCID mice. There was no marked loss of infectivity of spores stored at 4°C for two years or frozen at -12°C and -24°C for 1, 8, and 24 h. Although there was a remarkable loss of infectivity, spores remained infective after freezing at -70°C for 1 and 8 h. Heating at 60°C and 70°C for 5 min and 1 min, respectively, rendered the microsporidia non-infective. These findings demonstrate that E. cuniculi spores suspended in water can survive freezing temperatures but lost infectivity in water that reached a temperature of 60°C at 5 min.