65Zn labelled seeds of broad beans (Vicia faba L.) germinated and grown in a complete nutrient solution containing the radioisotope were used to investigate the change in the subcellular distribution of this trace element during subsequent development of the labelled seeds. Homogenates of leaves, stems and roots were fractionated into cell‐wall debris, nuclei, chloroplasts, mitochondria, ribosomes and “soluble” fraction. The concentration of the radioisotope in these fractions, expressed as cpm/mg dry weight, was highest in the soluble fraction and in the ribosomes isolated from young tissues. However, as roots and leaves aged, a general decrease in the overall zinc concentration was followed by a similar drop in the concentration of the metal associated with the “soluble” fraction and ribosomes, causing a more or less uniform zinc distribution pattern. On the other hand, there was a general increase in the zinc concentration of the “soluble” and in the particulate fractions of relatively high sedimentation coefficient from older stem samples. Taking also into consideration the dry weight change per unit volume of the tissues under investigation, the relationship between these variations and the metabolism of the plant is discussed.

No abstract

A factorial culture experiment was designed to investigate the influence of light regimes and of some metal chelators on the accumulation of cadmium by Lemna gibba L. The plants were grown in a complete nutrient solution containing Cd2+ concentrations ranging from 0 to 27 μM with or without EDTA, ethylenediamine‐N,N′‐bis‐(o‐hydroxyphenylacetic acid) (EDDHA) or salicylic acid. Each experiment was run for eight days in 18 h:6 h light:dark or continuous light. An increase in the Cd2+ concentration in plants and a simultaneous drop in accumulation efficiency (ratio of Cd2+ concentration in plants to the initial Cd2+ concentration in the nutrient solution) with increasing ambient Cd2+ levels was best represented by regression power curves. At the lowest Cd2+ concentration which caused a significant decrease in the relative growth rate of duckweed, there was a decrease in manganese and zinc and an increase in the iron level in the plants. EDDHA and EDTA protected in some cases against the toxic action of cadmium without preventing its uptake by plants. It was thus observed that 9 μM or higher levels of Cd2+ were toxic to Lemna gibba depending on the chelator and light regime. Duckweed grown in continuous light produced, in general, more dry matter and hence accumulated more cadmium.

No abstract

A study on the distribution of radioactive zinc ((65)Zn) in flowers of Vicia faba L. and Nicotiana tabacum L. showed the highest activity, expressed as cpm/mg dry weight, in pollen Also, using a histochemical method, it was observed that a portion of the naturally occurring zinc present in pollen grains was transferred into their growing tubes during germination. Calculations in based on the specific activity in (65)Zn-labelled pollen grains and in seeds from flowers pollinated with this pollen showed that about 68% of the radioisotope content of the pollen was incorporated into the seeds. The significance of these results and the possible role of zinc in fertilization is discussed.