SUMMARYThe tolerance of plants to toxic metals is frequently measured by comparing rates of root growth in culture solutions with and without the addition of the metal, but many variants of the technique are available. Toxicity is often reduced by the presence of other ions, particularly calcium. Control growth rates may be measured beforehand on the same roots or in parallel on a duplicate set. With a single toxic concentration tolerance is defined as the ratio of the two growth rates; with a range of concentrations the slope of the regression of growth on concentration may be used, but there are some complications with stimulation at low concentrations. Probit analysis may be valuable. There is good evidence that tolerance differences are largely of genetical origin.

No abstract

The abundance of transcripts of cab‐7 and cab‐3C, which code for the chlorophyll a/b binding proteins of the light‐harvesting complexes I and II, respectively, and the abundance of transcripts of Rca, which encodes Rubisco activase, were reduced in tomato plants exposed to high CO2 for up to 9d, whereas the abundance of mRNA from psa A–psa B and psb A, which encode the proteins of the core complex of PSI and the D1 protein of PSII, respectively, and the abundance of glycolate oxidase, which is involved in photorespiration, were not affected. However, the abundance of the transcript for the B subunit of ADP‐glucose pyrophosphorylase was increased after 1 d at elevated CO2. The chlorophyll a/b ratio decreased significantly over 9 d of exposure to elevated CO2. The responses of the nuclear genes to high CO2 were enhanced when leaves were detached so as to deprive them of any major sink. The responses of these transcripts to high CO2 were mimicked when sucrose or glucose was supplied to the leaf tissue, whereas acetate or sorbitol had no effect. Carbohydrate analyses of leaves grown in high CO2 or supplied with sucrose revealed that major increases occurred in the amount of glucose and fructose. Based on these and other published data, a molecular model involving the repression or activation of the transcription of nuclear genes coding for chloroplast proteins by photosynthetic end‐products is proposed to account for photosynthetic acclimation to high CO2 in tomato plants and other species.

No abstract

Summary Seedlings of Betula spp. were grown in conjunction with isolates of Amanita muscaria Hooker and Paxillus involutus Fr. under aseptic conditions. Mycorrhizas were established in sterilized peat and vermiculite to which nutrient media had been added. Zinc was supplied at various levels and growth of the host was assessed after eight weeks. The mycorrhizas increased the tolerance to Zn of both tolerant and non‐tolerant Betula. This was coupled with a reduction in the translocation of zinc to the shoots of Betula, but an accumulation of zinc in the mycorrhizas.