Brassica napus L. (oilseed rape) was grown from seeds on a reconstituted soil contaminated with cadmium (100 mg Cd kg-1 dry soil), resulting in a marked chlorosis of the leaves which was investigated using a combination of biochemical, biophysical and physiological methods. Spectroscopic and chromatographic analyses of the photosynthetic pigments indicated that chlorosis was not due to a direct interaction of Cd with the chlorophyll biosynthesis pathway. In addition, mineral deficiency and oxidative stress were apparently not involved in the pigment loss. Leaf chlorosis was attributable to a marked decrease in the chloroplast density caused by a reduction in the number of chloroplasts per cell and a change in cell size, suggesting that Cd interfered with chloroplast replication and cell division. Relatively little Cd was found in the chloroplasts and the properties of the photosynthetic apparatus (electron transport, protein composition, chlorophyll antenna size, chloroplast ultrastructure) were not affected appreciably in plants grown on Cd-polluted soil. Depth profiling of photosynthetic pigments by phase-resolved photoacoustic spectroscopy revealed that the Cd-induced decrease in pigment content was very pronounced at the leaf surface (stomatal guard cells) compared to the leaf interior (mesophyll). This observation was consistent with light transmission and fluorescence microscopy analyses, which revealed that stomata density in the epidermis was noticeably reduced in Cd-exposed leaves. Concomitantly, the stomatal conductance estimated from gas-exchange measurements was strongly reduced with Cd. When plants were grown in a high-CO2 atmosphere (4,000 microliters CO2 l-1), the inhibitory effect of Cd on growth was not cancelled, suggesting that the reduced availability of CO2 at the chloroplast level associated with the low stomatal conductance was not the main component of Cd toxicity in oilseed rape.

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The chromatographic analysis of the free carbohydrate content of leaves and stems of pepper showed 19 major fractions which were gathered in 8 structural classes. A number of correlations were found between the respective carbohydrate levels of two varieties of pepper, one susceptible and the other resistant to downy mildew, and also between those of healthy and inoculated tissues. Some cases of departures from the established correlations were observed and discussed with respect to their hypothetical involvement in the character of resistance and susceptibility to the infection. The concentrations of free carbohydrates of the dideoxyhexose group are increased in inoculated leaves of both susceptible and resistant varieties and those of the rhamnose group are depressed in inoculated leaves of the sole susceptible variety. Sucrose strongly increases in inoculated stems but decreases in the inoculated leaves of the sole resistant variety; concomitantly glucose and fructose also increase in inoculated stems, whereas they decrease in inoculated leaves of both susceptible and resistant strains. The results suggest a number of hypotheses concerning the molecular mechanisms of the host resistance to infection in relation to the cellular pathways of sugar translocation.

A new cytochemical assay of acid phosphatase activity employing Triton WR-1339, a non-ionic detergent, has been used to demonstrate the probable origin of the phytolysosome system and of the organization of the Golgi complex in the root meristem, Cucurbita pepo. The results were controlled biochemically by differential and linear density gradient ultracentrifugation of extracts from normal and Triton-treated roots. The various fractions were characterized by electron microscopy or by assay of marker enzymes.