Chmelnitsky, I., Kennedy-Leigh Center of Horticultural Research, Faculty of Agriculture, Food and Environmental Science, The Hebrew University of Jerusalem, P.O. Box 12, 76100, Rehovot, Israel
Colauzzi, M., Institute for Crop Breeding and Crop Research N. Strampelli, 36045, Lonigo (Vicenza), Italy
Algom, R., Kennedy-Leigh Center of Horticultural Research, Faculty of Agriculture, Food and Environmental Science, The Hebrew University of Jerusalem, P.O. Box 12, 76100, Rehovot, Israel
Zieslin, N., Kennedy-Leigh Center of Horticultural Research, Faculty of Agriculture, Food and Environmental Science, The Hebrew University of Jerusalem, P.O. Box 12, 76100, Rehovot, Israel

Formation of leaf-like organs known as phylloids in Rosa hybrida cv. Motrea flowers was promoted by exposure of plants to elevated temperatures. At a day/night temperature regime of 26°C/21°C respectively the proportion of malformed flowers exhibiting phyllody was four times higher than that in flowers of plants grown at 21°C/15°C. The number of petals in phyllody-expressing flowers was higher than that in normal flowers. The total content of endogenous cytokinins in young flower buds of plants exposed to the lower temperature was six times higher than that at the higher temperatures. The effects of the reduced temperature were pronounced on all the groups of cytokinins examined. However, the proportion of the various cytokinin groups remained similar at both temperature regimes. In contrast to the cytokinins in the flower buds, the content of all cytokinin types in young leaves increased following exposure to the higher temperature and was reduced by the lower temperatures. After 11 weeks at the lower temperature, about 18% of the flowers remained malformed, whereas at the higher temperature about 20% of the flowers still remained normal. All the phyllody-exhibiting flowers were formed on vigorously grown basal shoots characteristic to Rosa hybrida plants, whereas the normal flowers at the elevated temperatures were formed on lateral shoots which were most distal to the plant base. However, irrespective of the season, the presence of normal and malformed flowers was observed on plants kept growing at standard conditions of 30°C/17°C in the greenhouse. This phenomenon led us to examine the cytokinins in floral organs of normal and malformed cv. Motrea flowers grown in the greenhouse as well as in flowers of a complete rose mutant known as a 'Green Rose' (Rosa chinensis viridiflora). The highest content of cytokinins was found in the pistils and stamens of normal 'Motrea' flowers. On the other hand, the content of cytokinins in leaf-like style-tubes in the malformed flowers as well as in partially malformed ovaries at the base of phylloids was significantly lower. A low content of cytokinins was also present in petals of both normal and phyllody-exhibiting flowers and the lowest content has been found in the phylloids of the 'Green Rose'. A possibility of mutant deviations in metabolism of cytokinins in rose plants is discussed.