M. Bassi

Is Cr(VI) toxicity to Daphnia magna modified by food availability or algal exudates? The hypothesis of a specific chromium/algae/exudates interaction

The long-term effects of Cr(VI) on life history traits of Daphnia magna Straus were studied in relation to different feeding conditions or to the presence of Scenedesmus acutus exudates, which had proved to reduce chromium toxicity to the alga. In high feeding conditions the concentration of 14 microg Cr(VI)/L had negative effects on survival, growth and fecundity. In low feeding conditions the effects on growth were not evident, but daphnids changed the reproductive strategy normally adopted in case of food shortage and showed a daily rate of newborn production higher than control; however, newborn were of a smaller size and less resistant to starvation. The most relevant effect of Cr was a shortening of the daphnid life span, which was independent of the feeding conditions and occurred also when growth and daily rate of neonate production were not affected. The algal exudates resulted ineffective in reducing Cr toxicity to daphnids, but caused a strong decrease in daphnid fecundity. Further experiments on S. acutus demonstrated that the detoxifying effect observed in the algae might involve a specific Cr/algae/exudates interaction, which occurs only when the algae are previously subjected to a short-time stress by chromium.

Early phases in in vitro culture of tomato cotyledons: Starch accumulation and protein pattern in relation to the hormonal treatment

SummaryTomato cotyledon explants, cultured in vitro in the presence of sucrose, were subjected to different hormonal treatments to establish whether the induction of different organogenic programmes could be correlated with differences in starch accumulation and protein electrophoretic pattern. The cytohistological changes in explants over the first 15 days of culture were studied by light and electron microscopy. It was found that starch accumulation occurs under all conditions, though varying in duration and amount. Over the first 2 days of culture the protein electrophoretic pattern changes in a similar way under all conditions, while after 7 days changes take place which are probably related to the different developmental programmes induced by the treatments.

Auxin structure and activity on tomato morphogenesis in vitro and pea stem elongation

In order to understand better the relationship between auxin structure and activity on morphogenesis and cell elongation, six different auxins were tested on the regeneration of tomato (Lycopersicon esculentum Miller var. Alice) from cotyledons and on pea (Pisum sativum L. var. Alaska) stem elongation. The auxins were: indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), 1, 2-benzisoxazole-3-acetic acid (BOA), 1,2-benzisothiazole-3-acetic acid (BIA), 1-naphthalenacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D). All these compounds obey the minimum requirement rules for auxin activity and all were effective on cell elongation. At the dose of 10 μM and in the absence of cytokinin, they all, except 2,4-D, induced roots, while in the presence of cytokinin they induced shoots, roots, hairy root-like filaments (HRLF) or callus depending on their concentration. The morphogenetic pattern did not change by varying cytokinin concentration. We conclude that auxin structure plays a minor role in morphogenesis or cell elongation, because it is only responsible for variations in the level of auxin activity.

Origin and function of tomato bushy stunt virus-induced inclusion bodies. II: Quantitative electron microscope autoradiography and immunogold cytochemistry

The possible role of two types of inclusion bodies induced by tomato bushy stunt virus in Gomphrena globosa cells was investigated by electron microscope autoradiography after administration of tritiated uridine and by immunogold labeling on ultrathin sections. Our observations indicate that both multivesicular bodies (MVBs) and associated chloroplast invaginations are involved in virus replication. Since MVBs are always present in infected cells, even in those not containing chloroplasts, they appear to be the main site of virus RNA synthesis, while chloroplast invaginations are likely to provide, when present, an additional vesicular site for the same purpose. Neither of these structures contains viral protein. By contrast, the dense granules are not involved in virus RNA synthesis and consist mainly of virus coat protein, whose production is likely to occur in the cytoplasm.

Effects of benzisoxazole and benzisothiazole on tomato plant regeneration in vitro.

The effects of two synthetic auxins, BOA and BIA, on plant regeneration in vitro have been studied on explants of tomato cotyledons. The activity of these substances on cell elongation has also been tested on pea stem segments. It has been found that BOA is particularly effective in inducing the formation of shoots but has a weak activity on cell elongation, while BIA, which is more effective in inducing cell elongation, is less active in morphogenesis. It is concluded that (1) the two activities are not related to each other, (2) the receptors involved in the two processes are probably different, (3) thechemical structure of the auxin may be an important factor in organogenetic processes.

Effect of 1,2-benzisoxazole-3-acetic acid on plant regeneration from protoplasts of Nicotiana tabacum

SummaryBenzisoxazole-3-acetic acid, a new synthetic growth regulator, was administered to protoplast cultures from Nicotiana tabacum and subsequently to the developed microcalluses, to test its activity on plant regeneration from protoplasts in different culture conditions. Such activity, compared to that of naphthalene-acetic acid, proved to be rather low in the stage of cellular division and microcallus formation but particulary high in the stage of shoot induction from microcallus, thus confirming that the activity of this compound is mainly morphogenetic.

Activity of 1,2-benzisoxazole-3-one and indole-2,3-dione on plant regeneration in vitro and on cell elongation

We tested the morphogenetic and cell elongating activity of 1,2-benzisoxazole-3-one, a compound similar to 1,2-benzisoxazole-3-acetic acid but lacking the lateral carbon chain. For comparison, we tested also the activity of indole 2,3-dione, having the same indolic ring as indole 3-acetic acid but no lateral carbon chain. The tests were made on the regeneration of tomato (Lycopersicon esculentum Miller var. Alice) from cotyledons and on pea (Pisum sativum L. var. Alaska) stem elongation. We found that 1,2 benzisoxazole-3-one retains part of the high shoot inducing activity of 1,2-benzisoxazole-3-aceticacid, while indole-2,3-dione is inactive. Both compounds have no effect on root induction or cell elongation. It seems therefore that the activity of 1,2 benzisoxazole-3-acetic acid is partly related to the structure of its ring, and that also in this respect 1,2 benzisoxazole-3-acetic acid differs from other auxinlike compounds.

Does chlorination modify the auxin-like activity of 1,2-benzisoxazole-3-acetic acid?

Abstract The insertion of a chlorine atom in different positions of the aromatic ring did not increase the activity of benzisoxazole acetic acid, a new syntheti

Auxin-like activity of 1,2-benzisoxazole-3-alkanoic acids

Abstract A series of benzisoxazole-alkanoic acids, differing in the length of the side-chain, have been synthesized and their activity tested on pea stem elongation, flax root growth and shoot regeneration from tomato cotyledon explants. All compounds had little or no effect on cell elongation or root growth, but a stimulating effect on shoot induction in vitro, thus showing that their activity, like that of 1,2-benzisoxazole acetic acid, is partly independent of the side-chain and is linked to the structure of the benzisoxazolic ring.