In five species of teleost from the Swan-Avon river system (Mugil cephalus, Aldrichetta forsteri, Amniataba caudavittatus, Acanthopagrus butcheri and Nematalosa vlaminghi), the concentration of nine different heavy metals in muscle tissue either declined or remained relatively constant with increasing body weight. The data for the biologically important iron, zinc, copper and manganese were almost invariably represented better by a logarithmic rather than a linear regression. The concentration of these four metals generally ceased to change markedly with body size at weights above approximately 50 g. The mean concentrations of all nine heavy metals in those individuals heavier than 50 g were very low in every species and are probably close to the minimum levels found in these fish in unpolluted environments. The concentrations of heavy metals were greater in fish which ingested bottom material than in those which fed on organisms such as polychaetes. molluscs and crustaceans, and on various forms of plant.
Black gram (Vigna mungo (L.) Hepper) cv. Regur was grown to maturity in three potted soils [Badgingarra (Sl), Lancelin (S2) and Quailing (S3)] with (+B) or without (-B) added H3BO3. The subsequent germination and vigour of seeds from treated plants was tested by germinating them for 7 days with 2000 8M CaSO4 and 98M H3BO3and, for S2 and S3 only, by staining with tetrazolium. No symptoms of B deficiency were observed in plants on any soil:leaf B concentrations at early vegetative and flowering stages were above values regarded as critical for this species (7-8 mg kg-1). On S1, B depressed pod and seed dry matter (DM), weight per seed and % hard seed (14 v. 58); it enhanced % non-viable imbibed seed (18 v. 5) and abnormal seedlings (37 v. 2). On S2, -B had no effect on reproductive yield or % hard seed but increased the % abnormal seedlings (32 v. 0) and depressed the tetrazolium rating for seed vigour, and weight per seed. No effects of B were observed on seeds from plants grown on S3 soil. When considered over all replicates of all treatments, a B concentration of 6 mg kg-1 DM seed was critical for viability of imbibed seed and production of normal seedlings. The results suggest that the subsequent germination and morphology of seeds and seedlings are more sensitive to low B supply during seed production than are growth of the plant and the amount of seed produced. It is thus likely that black gram crops low in B but with no symptoms of B deficiency may produce seed with low % germination and a high % abnormality in their seedlings.
Effects of zinc supply on the distribution of zinc and dry weight among plant parts were examined during the first 55 days of vegetative development of Seaton Park subterranean clover grown in a zinc-deficient soil in a glasshouse. Symptoms of zinc deficiency first appeared in young trifoliate leaves. Zinc deficiency decreased the expansion of blades and petioles, delayed the development of leaves and lateral branches, depressed dry weights of roots and shoots, and increased the proportion of plant dry weight in roots and leaf blades. In each treatment and at each harvest, zinc concentrations varied widely amongst plant parts and with their physiological age. Plant parts also differed widely in the response of their dry matter and zinc concentrations to both zinc treatment and harvest time. It is suggested that these complex relationships explain why plant samples consisting of composite plant parts are not suitable for diagnosis of zinc deficiency. In the present experiment, zinc concentration in whole shoots was unsatisfactory for diagnosing zinc deficiency since concentrations were higher in young, zinc-deficient plants than in older, zinc-adequate plants. In young leaf blades of the same physiological age, zinc concentrations showed reasonably constant relationships with plant growth throughout the entire experiment. However, they varied two- to three-fold in leaves of different ages from the same plants. The results show the importance for diagnosis of zinc deficiency of selecting as a sample a single organ of defined physiological age. The youngest open leaf blade is recommended for diagnosis of zinc deficiency in subterranean clover.
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