A diffusible signal from germinating Orobanche ramosa elicits early defense responses in suspension-cultured Arabidopsis thaliana

In plant/parasitic plant interaction, little is known about the host plant response before the establishment of the parasite within the host. In the present work, we focused on host responses to parasitic plant, O. ramosa in the early stage of infection. We used a co-culture system of A. thaliana suspension cells and O. ramosa germinated-seeds to avoid parasite attachment. We showed that O. ramosa induced H₂O₂ generation and camalexin synthesis by A. thaliana followed by a drastic increase in cell death. We further demonstrated that a heat sensitive diffusible signal is responsible for this cell death. These data indicate that recognition of O. ramosa occurs before the attachment of the parasite and initiates plant defence responses.Key words: Orobanche ramosa, Arabidopsis thaliana, cell death, hydrogen peroxide, secondary metabolism     

A role for brassinosteroids in the amelioration of aluminium stress through antioxidant system in mung bean (Vigna radiata L. Wilczek)

Brassinosteroids (BRs) elicit diverse physiological responses and ameliorate various biotic and abiotic stresses. With an aim to further explore and elaborate their role in plants subjected to abiotic stress, more specifically the heavy metal stress, the seedlings of mung bean were grown in a plant growth chamber under controlled conditions, on a sandy substratum. The seedlings were subjected to aluminium (0.0, 1.0 or 10.0 mM) stress, at 1-week-old stage and were sprayed with 0 or 10^?8 M of 24-epibrassinolide (EBL) or 28-homobrassinolide (HBL) at 14-day stage. The analysis of the plants at the completion of 3 weeks of growth revealed that the presence of aluminium in the nutrient medium caused a sharp reduction in growth (length, fresh and dry mass of root and shoot), the activity of carbonic anhydrase (E.C. 4.2.1.1), relative water content, water use efficiency, chlorophyll content and the rate of photosynthesis. However, the activity of antioxidative enzymes [catalase (E.C. 1.11.1.6), peroxidase (E.C. 1.11.1.7) and superoxide dismutase (E.C. 1.15.1.1)] in leaves and the content of proline, both in leaves and roots increased in the aluminium-stressed plants. The spray of EBL or HBL, in absence of aluminium strongly favoured the above parameters and also improved them, in the plants grown under aluminium stress. Moreover, it is also noteworthy that EBL and HBL caused a further stimulation of antioxidative enzymes and proline content, which were already enhanced by aluminium stress. This led us to the conclusion that the elevated level of proline in association with antioxidant system, at least in part, was responsible for the amelioration of Al stress in mung bean seedlings.     

A simple apparatus for measuring hardness of agar and Gelrite plates

A simple apparatus for measuring hardness of Gelrite and agar plates, that can be easily fabricated, is described. It gives reproducible results comparable with those obtained with expensive commercial equipment. It has been successfully used to improve enumeration ofThiobacillus ferrooxidans andT. thiooxidans on solid media plates.     

Evidence for the existence of regulatory sites for Ca2+ on the Na+/Ca2+ carrier of cardiac mitochondria.

The Na+-induced efflux of Ca2+ catalysed by the Na+/Ca2+ carrier of cardiac mitochondria is strongly inhibited by extramitochondrial Ca2+. The nature of this inhibition was investigated as follows. (a) The apparent association of external Na+ and the Ca2+ analogue Sr2+ with substrate-binding sites (i.e. those sites involved in cation translocation) is promoted markedly by K+. The inhibition of Na+/Ca2+ exchange by external Ca2+ is affected little by K+. (b) There is a competitive relationship between the binding of external Na+ and external Ca2+ to substrate-binding sites, whereas at low concentrations (less than 4 microM) extramitochondrial Ca2+ is a partial non-competitive inhibitor with respect to external Na+. (c) This inhibiton by external Ca2+ is characterized by a maximal decrease of about 70% in the Vmax of Na+/Ca2+ exchange and by cooperative binding of external Ca2+ to sites that are half saturated by 0.7-0.8 microM free Ca2+. The binding of Ca2+ and Sr2+ to substrate-binding sites shows no co-operativity. These criteria suggest that the Na+/Ca2+ carrier may contain regulatory sites that render the carrier sensitive to changes in extramitochondrial [Ca2+] within the physiological range.     

Purification and determination of the structure of capsular polysaccharide of Vibrio vulnificus M06-24.

Virulence of Vibrio vulnificus has been strongly associated with encapsulation and an opaque colony morphology. Capsular polysaccharide was purified from a whole-cell, phosphate-buffered saline-extracted preparation of the opaque, virulent phase of V. vulnificus M06-24 (M06-24/O) by dialysis, centrifugation, enzymatic digestion, and phenol-chloroform extraction. Nuclear magnetic resonance spectroscopic analysis of the purified polysaccharide showed that the polymer was composed of a repeating structure with four sugar residues per repeating subunit: three residues of 2-acetamido-2,6-dideoxyhexopyranose in the alpha-gluco configuration (QuiNAc) and an additional residue of 2-acetamido hexouronate in the alpha-galactopyranose configuration (GalNAcA). The complete carbohydrate structure of the polysaccharide was determined by heteronuclear nuclear magnetic resonance spectroscopy and by high-performance anion-exchange chromatography. The 1H and 13C nuclear magnetic resonance spectra were completely assigned, and vicinal coupling relationships were used to establish the stereochemistry of each sugar residue, its anomeric configuration, and the positions of the glycosidic linkages. The complete structure is: [----3) QuipNAc alpha-(1----3)-GalpNAcA alpha-(1----3)-QuipNAc alpha-(1----]n QuipNAc alpha-(1----4)-increases The polysaccharide was produced by a translucent phase variant of M06-24 (M06-24/T) but not by a translucent, acapsular transposon mutant (CVD752). Antibodies to the polysaccharide were demonstrable in serum from rabbits inoculated with M06-24/O.     

Hydroxyurea,Leucopheresis, and Splenectomy in Chronic Myeloid Leukaemia at the Problastic Phase

Forty-three patients with chronic myeloid leukaemia have been treated with hydroxyurea in order to be subjected to leucopheresis for white cell transfusions. Hydroxyurea decreases leucocytosis when it is administered and the blood granulocyte number increases soon after the drug is stopped. The survival of the patients is not different from the survival of the patients treated with conventional chemotherapy (busulphan, mitobronitol) and it is superior to the survival of patients treated with external radiotherapy or with ³²P. Half of the patients were subjected to splenectomy during first remission for a phase II trial. They were not randomized, but the distribution according to age was similar in the two groups. A slight difference appears in favour of splenectomy so far as survival is concerned, but there were three post-operative deaths out of 18 patients. We conclude that a phase II trial on the value of splenectomy is indicated ethically, but that the patients should be operated on and nursed in a microbiologically controlled environment.     

Ca2+-dependent inhibition by trifluoperazine of the Na+-Ca2+ carrier in mitoplasts derived from heart mitochondria

The interaction of trifluoperazine and extramitochondrial Ca2+ with the heart mitochondrial Na+-Ca2+ carrier has been investigated. External Ca2+ inhibits the carrier equally in mitochondria and mitoplasts in which the outer membrane is lysed. Sensitivity to Ca2+ is not removed by washing mitoplasts under varied conditions. Trifluoperazine is a potent inhibitor of the carrier in mitoplasts but not in mitochondria. Trifluoperazine inhibition in mitoplasts depends markedly on the presence of extramitochondrial Ca2+ (2 microM).     

Evidence for the presence of a reversible Ca2+-dependent pore activated by oxidative stress in heart mitochondria.

Rat heart mitochondria became permeabilized to sucrose when incubated with 100 nmol of Ca2+/mg of protein in the presence of Pi. Ca2+ chelation with EGTA restored impermeability to sucrose, which became entrapped in the matrix space. t-Butylhydroperoxide markedly promoted permeabilization in the presence of Ca2+ but not in its absence, and Ca2+-plus-t-butylhydroperoxide-induced permeabilization was reversed by EGTA. The data suggest that Ca2+ and oxidative stress synergistically promote the reversible opening of an inner membrane pore.     

Ultrastructural study of cardiotoxicity and skin alterations in the golden hamster after treatment with 8 different anthracyclines]

Golden hamsters were submitted to i.p. administration during 4 weeks of 8 anthracyclines, adriamycin (ADM), detorubicin (DTR), daunorubicin (DNR), 4'-epi-adriamycin (eADM), adriamycin hydrochloride (ADMh), rubidazon (RBZ), aclacinomycin (ACM) and AD32, at doses equivalent to 3/4 of those which are optimally oncostatic on murine L1210 leukemia. The comparative study of the mortality, the electron microscopic (EM) alterations of the myocardium, and the light microscopic (EM) alterations of the myocardium, and the light microscopic (LM) lesions of the skin, show that ACM and AD32 are the least toxic drugs. EM detected almost no early lesions of myocardium in ACM treated animals, but, after 4 week's treatment, severe cardiac alterations appeared which, like those after AD32 treatment, are non lethal and reversible. Similarly. LM revealed no histologic changes in the skin following ACM and AD32 administrations, but pathologic alterations, atrophy and alopecia, were observed in animals receiving all other drugs.