Growth and metabolism of germinating rice (Oryza sativa L.) seeds as influenced by toxic concentrations of lead

Abstract: Nearly 60 years ago, Prat (1934) initiated the research of heavy metal resistance in plants when he was analysing the growth performance of two populations of Silene dioica (Melandrium sylvestre), one from a copper mine and one from a non-mine soil. He was able to demonstrate a heritable copper resistance in the mine population, relative to the non-mine population, which he explained as a result of evolution by natural selection. Nearly 20 years later Bradshaw (1952) and Baumeister (1954) started further research on ecological and physiological differentiation between plants from metal-enriched and noncontaminated habitats. The species chosen for study were predominantly Agrostis capillaris in the Bradshaw group (Jowett 1959; Gregory 1965; McNeilly 1965; Antonovics 1966) and Silene vulgaris in the Baumeister group (Broker 1962; Ernst 1964; Gries 1965; Riither 1966). In the late 1950s Duvigneaud (1958), while studying the vegetation on metalliferous soils in Central Africa, added to the above approaches a phytogeographic one and introduced the study of speciation processes in metallophytes. In the 1950s, the study of evolutionary and physiological aspects of metal resistance was hampered by the absence of convenient techniques for measuring metal concentrations in small plant samples. The techniques available for metal analysis were either timeconsuming, such as phase separation (Ernst 1964), or costly and only applicable for laboratory-raised plant material, i.e. radiolabelling (Turner & Gregory 1967; Peterson 1969). Only after applying atomic absorption spectrophotometry on wet-ashed plant material (Reilly 1967) did time and cost-effective metal analyses become possible.

Abstract: A study was conducted to determine the extent to which seed coats are a barrier to lead and to what degree germination is affected by this heavy metal. The study was carried out on 25 species of plants from 12 families, represented by different varieties and populations. In all, 34 types of seeds were tested. Comparative observations were conducted on the effect of barium nitrate on seed imbibition and germination. Seeds were treated with solutions of the following salts during imbibition: 100, 1000, and 10 000 mg dm−3 Pb2+ from Pb(NO3)2 and 1000 mg dm−3 Ba2+ from Ba(NO3)2. The histochemical rhodizonate method was used to determine the distribution of lead and barium in the seeds. Water uptake and germination dynamics were also studied. It was found that 28% of the studied plant species had seed coats that were permeable to lead ions, 39% were permeable to barium ions. In both cases these species belonged to three families: Papilionaceae, Crucifereae and Graminae. Lead delayed germination and lowered the ability of seeds to germinate in a dose-dependent manner in the species with highly lead-permeable seed coats. In some other species, germination was delayed only a few hours. In all, a significant effect of lead on germination was found in over half of the studied species. It was shown that lead did not act by inhibiting water uptake during imbibition. It was also shown that seed coat permeability varied during imbibition of seeds with coats highly permeable to lead. Seed coats were impermeable to lead in the first period of imbibition when water uptake is intense. In the final stages of imbibition, when water uptake is reduced, seed coats became more permeable to lead. The lead that penetrated into the embryos in the final stage of imbibition delayed germination. This shows that seed coats are selectively permeable to lead ions.

Abstract: Deterioration of membranes caused by lipoxygenase (LOX) activity under 10 µM PbCl2 or 10 µM HgCl2 was partially alleviated by the exogenous application of 100 µM salicylic acid (SA). In two cultivars of rice (Oryza sativa L. cvs. Ratna and IR 36), the presence of SA ameliorated the increased leakage of electrolytes, injury index, and the content of malondialdehyde caused by these heavy metals. Lead decreased H2O2 content whereas Hg increased it in both cultivars. Application of SA increased H2O2 in presence of Pb, while decreased it in presence of Hg. Both Pb and Hg decreased superoxide dismutase activity, while increased peroxidase activity. The activity of catalase was decreased by Hg but increased by Pb and SA reversed their effects. Thus, SA ameliorated the damaging effects of Pb and Hg on membranes.

Abstract: The present work describes the changes that take place in phytohormone contents in germinating chickpea (Cicer arietinum cv. Aziziye-94) seeds in response to heavy metal stress. For this aim, endogenous abscisic acid (ABA), gibberellic acid (GA3), zeatin (Z) and zeatin riboside (ZR) contents were followed for 24, 48 and 72 h in chickpea seeds germinating at the concentrations of 0.1, 1.0 and 5.0 mM Pb or 0.1, 1.0 and 10 mM Zn. The results showed that Pb and Zn significantly delayed and impeded the germination of chickpea seeds. The negative effect of Pb on germination was higher than that of Zn. Further, Pb increased ABA and Z contents while decreased GA3 content in the germinating seeds. The high concentrations of Zn (1.0 and 10 mM) decreased contents of Z, ZR and GA3 while 0.1 mM Zn increased the content of the same hormones. The ABA content was enhanced by Zn in all concentrations used.

Abstract: Since 1922 when Wu proposed the use of the Folin phenol reagent for the measurement of proteins, a number of modified analytical procedures utilizing this reagent have been reported for the determination of proteins in serum, in antigen-antibody precipitates, and in insulin. Although the reagent would seem to be recommended by its great sensitivity and the simplicity of procedure possible with its use, it has not found great favor for general biochemical purposes. In the belief that this reagent, nevertheless, has considerable merit for certain application, but that its peculiarities and limitations need to be understood for its fullest exploitation, it has been studied with regard to effects of variations in pH, time of reaction, and concentration of reactants, permissible levels of reagents commonly used in handling proteins, and interfering substances. Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.

Abstract: The wide use of the auxin, indoleacetic acid, in physiological and biochemical experiments has promoted interest in methods for its colorimetrie estimation. Mitchell and Brunstetteb (1) have proposed both the nitrite and the ferric chloride-sulphuric acid tests for the quantitative estimation of indoleacetic acid (IAA) in aqueous solutions, basing their suggested procedures upon a study of optimal reaction conditions for these two reagents. According to them, the nitrite method is sensitive to 10 /tig. IAA/ml. and develops a red color that is stable after two hours. In several attempts to duplicate their nitrite method using solutions of IAA varying from 20 to 45 /tg./ml., we could not obtain a stable red color with IAA at the two hours proposed, or at any other time. A faint pink develops almost immediately which rapidly fades to orange or yellow, depending on IAA concentrations, within i hour. If the concentration of nitrite is reduced, the red color becomes sufficiently persistent to be read. Indole likewise gives a strong, relatively stable, red color in this test (cf. table II)?a reaction which is sometimes used as a qualitative test for indole (Nitroso-Indole reaction). Tang and Bonner (2) have modified the ferric chloride-sulphuric acid method for IAA, combining the iron and sulphuric acid as a single reagent to yield improved sensitivity. However, the color produced is also unstable, rapidly developing and then fading. We have found, as have these workers, that the fading color can be practically dealt with by adopting a standard time between addition of reagent and reading of absorbancy or transmittance. Both of the methods discussed above possess disadvantages, lacking either specificity, sensitivity, or stability of color complex formed. During a study of the inactivation of IAA in aqueous solutions, it was frequently necessary to assay at one time many samples where the IAA concentrations were low, or where the degree of significance of small differences in concentrations between experimental unite required evaluation. Hence, we considered it desirable 'to re-examine the ferric chloride-sulphuric acid procedure. Several alterations have been made which produce a more stable color, of increased specificity, which changes in density more rapidly with variation in IAA concentration. 1. The procedure of Tang and Bonner can be improved somewhat by reading at 15 minutes after addition of reagent (instead of 30 minutes as they suggest), since the transient color reaches a maximum at the former time. Maximum absorption was found to occur at 530 ???.

Abstract: BRADSHAW reported1 that root growth was inhibited when plants of Agrostis tenuis were grown in soil from the tip of an old Welsh lead mine, while plants originally growing on the tip produced normal roots. This suggested that some plants of A. tenuis were inherently more tolerant of the lead and zinc in the soil than others. On similar waste tips in Scotland, A. tenuis is replaced by Festuca ovina and Deschampsia flexuosa, and a method has been worked out for the measurement of lead tolerance in F. ovina from soils of different lead contents.