Maja Kovač

Peroxidases and photosynthetic pigments in susceptible potato infected with potato virus YNTN

Abstract The aim of this work was to investigate the activity of soluble, ionically- and covalently-bound peroxidases (EC 1.11.1.7), the protein content, and the photosynthetic pigment metabolism in the potato (Solanum tuberosum L.) cv. Igor, at the time of local lesion development resulting from infection with potato virus YNTN. In comparison to intact plants, mock inoculation with the sap of healthy plants induced changes in peroxidase activity and metabolism of photosynthetic pigments which could, in most cases, be distinguished from the changes induced by virus infection. An inverse correlation was observed between chlorophyll content and the activity of soluble and ionically-bound peroxidases. This activity increased while that of covalently-bound peroxidase decreased, even in green leaves of infected plants which were visibly unchanged, as well as in green leaves with local lesions. Lower chlorophyll content, and higher carotenoid to chlorophyll ratio than those in intact and mock-inoculated controls – signs of senescence – were observed in leaves with local lesions and in yellow leaves of infected plants. Differences in measured parameters in intact, mock-inoculated, and infected plants showed that processes induced by virus infection differ from those induced by mock inoculation, and that viral induced senescence is clearly not the same as natural senescence.

The effect of jasmonic acid on the photosynthetic pigments of potato plants grown in vitro

Abstract We analysed the effect of 1 μM jasmonic acid (JA) on the leaf photosynthetic pigments of the potatoes cv. Sante and cv. Ulster grown in vitro. In treated and untreated plants of both cultivars the chlorophylls represented 79–85% of the total pigments and the four major carotenoids were lutein (45–48% of the total carotenoids), β-carotene (21–25%), all-trans-violaxanthan (12–19%), and 9-cis-neoxanthin (14–15%). Antheraxanthin and two unidentified carotenoids X and X1 were minor components, representing less than 1% of the total carotenoids. JA enhances stem elongation, leaf expansion and development of root systems. In leaves of the potato cv. Sante treated with JA where the morphological changes were more pronounced than in cv. Ulster, the photosynthetic pigments on a dry weight basis showed a reduction from 70 to 50%. In contrast to cv. Sante, no significant reduction of the total photosynthetic pigments was found in the leaves of the treated potato cv. Ulster. Antheraxanthin was the only photosynthetic pigment which increased in the leaves of JA treated plants. It seems that this phenomenon is JA induced as it was detected in both cultivars.

The effect of aluminium on the cytokinins in the mycelia of Lactarius piperatus

Abstract The effect of aluminium on the endogenous cytokinins in the mycelium of Lactarius piperatus , whose growth is stimulated by this ion, was investigated. Based on co-elution with standards by HPLC, retention by anti-cytokinin antibody columns, and by the Amaranthus bioassay, five cytokinins were detected: zeatin, dihydrozeatin, zeatin riboside, dihydrozeatin riboside and isopentenyladenine. No significant change in total cytokinin activity was found in the mycelia treated with 0.1 and 1 mM aluminium. Treatment with 10 mM aluminium resulted in an increase in cytokinins largely due to zeatin and isopentenyladenine. At the same time the relative amounts of dihydrozeatin and zeatin riboside decreased. Isopentenyladenine seemed to be the most affected by aluminium stress as its increase was observed even at lower concentrations of aluminium treatment. The results are compared with previous investigations of aluminium effects on mycorrhizal fungi.

The effect of aluminum on cytokinins in the mycelia of Amanita muscaria

High performance liquid chromatography analysis of immunoaffinity-purified extracts of mycelia of Amanita muscaria, and the Amaranthus bioassay of the eluted fractions, revealed the following seven cytokinins: zeatin, zeatin riboside, zeatin N-9-glucoside, dihydrozeatin, dihydrozeatin riboside, isopentenyl adenine, and isopentenyl adenosine. The decreased growth of aluminum-treated mycelia correlated with a 35% decrease in the total amount of the cytokinins. Among individual cytokinins, zeatin was the most affected, exhibiting a reduction of about 90%. The results are compared with previous investigations of aluminum effects on cytokinins in the mycelia of Lactarius piperatus, whose growth is stimulated by aluminum.

Morphology of potato (Solanum tuberosum L. cv. Sante) stem node cultures in relation to the level of endogenous cytokinins

Stem node culture of the potato (Solanum tuberosum) cv. Sante was used to examine the phenotypical alterations due to different levels of endogenous cytokinins. The altered phenotype, which dramatically deviates from the control phenotype, was induced after treatment of plantlets with 1 μm jasmonic acid. Plantlets grown on the medium supplemented with jasmonic acid were taller, with well developed root systems, expanded leaves, thickened stems, and they showed hyperhydric symptoms. Their cytokinin content was about half that of the control plantlets. Morphologic characteristics corresponding to transgenic plants that overproduce cytokinins, including release of axillary buds and inhibited rooting, correlated with the high cytokinin levels in control plants.