P. Medeghini Bonatti

The protective effect of rust infection against ozone, sulphur dioxide and paraquat toxicity symptoms in broad bean

A localized but highly protective effect of rust infection towards injury induced by the air pollutants ozone and sulphur dioxide, either alone or in mixture and the herbicide paraquat was found. The effect was proportional to inoculum density, was non-translocatable, and dependent on temperature. Protection continued even after the infection was no longer active, and was induced by different strains of the fungus in cultivars of both broad bean and pea. Protection was not due to the exclusion of pollutants resulting from stomatal closure. Histopathological investigations indicated that the effect was present in uncolonized tissues adjacent to the site of infection. Ultrastructural studies showed normal cell structure in the green islands surrounding the infection centres, even when nearby regions had collapsed. Peroxidase activity was increased rapidly in the infected tissues both in the colonized and in the adjacent non-colonized cells. Such activity was not detectable at significant levels in non-parasitized tissues. The results are discussed in connection with the possible mechanisms involved.

Differential Sensitivity to Ozone in Two Selected Cell Lines from Grape Leaf

Summary Two cell populations with different phenol-phenotypes were selected from leaf explants of the ozonesensitive Vitis vinifera L. cv. Lambrusco salamino. Experimental exposure of these cell lines to a 2 h fumigation with 300 ppb ozone caused a differential response. Peroxidative injuries, evaluated on the basis of malondialdehyde production and at the ultrastructural level, were induced in phenol-rich (Ph+) but not in phenol-poorer (Ph-) cells. Apoplastic ascorbate-peroxidase (EC 1.11.1.11), to which a prevailing role in apoplastic H202 scavenging has been attributed, was substantially stimulated in Ph- cells during ozone exposure; guaiacol-peroxidase (EC 1.11.1.7) reached maximum values 12 h later. Only guaiacol-peroxidase was rapidly induced in Ph+ cells, whereas ascorbate-peroxidase was inhibited to some extent. Phenol-poor cells thus proved able to promptly activate the biphasic extracellular peroxidase(s) defence system against ozone induced oxidative stress. On the contrary, the phenol-rich cell type appeared to be a very sensitive target of ozone toxicity; this suggests that the sensitivity displayed by the whole leaf of the grape cultivar used as explant source might be conditioned by the constitutive presence of a great number of such cells.

Occurrence of a mixture of ketocarotenoids in chloroplast plastoglobules of young leaflets of a Cycad

Summary An investigation was carried out on chloroplast plastoglobules in young leaflets of “forma fuscoviridis” of Ceratozamia mexicana Brongn., a cycad characterized by a transitory red-brown colour in the first stages of developing leaves. Plastoglobules were isolated by several ultracentrifugations and the contents of the different “rings” were compared on silica gel layers with natural standards obtained in our laboratory from fully ripe fruits of Murraya exotica L. and of Triphasia trifolia (Burm. f.) P. Wilson, (the two very rare semi-s-carotenone and triphasiaxanthin) and from the leaflets of the same “forma fuscoviridis” (the novel ceratoxanthin). The results pointed out that the red-brown coloration is due to the presence of a mixture of eight ketocarotenoids in the plastoglobules densely packed around the prolamellar body of young chloroplasts.