Effects of temperature on phyllody expression and cytokinin content in floral organs of rose flowers

Abstract

Formation of leaf-like organs known as phylloids in Rosahybrida cv. Motrea flowers was promoted by exposure of plants toelevated temperatures. At a day/night temperature regime of26 °C/21 °C respectively theproportion of malformed flowers exhibiting phyllody was four times higher thanthat in flowers of plants grown at21 °C/15 °C. The number ofpetals in phyllody-expressing flowers was higher than that in normal flowers.The total content of endogenous cytokinins in young flower buds of plantsexposed to the lower temperature was six times higher than that at the highertemperatures. The effects of the reduced temperature were pronounced on all thegroups of cytokinins examined. However, the proportion of the various cytokiningroups remained similar at both temperature regimes. In contrast to thecytokinins in the flower buds, the content of all cytokinin types in youngleaves increased following exposure to the higher temperature and was reducedbythe lower temperatures. After 11 weeks at the lower temperature, about18% of the flowers remained malformed, whereas at the higher temperatureabout 20% of the flowers still remained normal. All thephyllody-exhibiting flowers were formed on vigorously grown basal shootscharacteristic to Rosa hybrida plants, whereas the normalflowers at the elevated temperatures were formed on lateral shoots which weremost distal to the plant base. However, irrespective of the season, thepresenceof normal and malformed flowers was observed on plants kept growing at standardconditions of 30 °C/17 °C inthegreenhouse. This phenomenon led us to examine the cytokinins in floral organsofnormal and malformed cv. Motrea flowers grown in the greenhouse as well as inflowers of a complete rose mutant known as a 'Green Rose’(Rosa chinensis viridiflora). The highest content ofcytokinins was found in the pistils and stamens of normal 'Motrea’flowers. On the other hand, the content of cytokinins in leaf-like style-tubesin the malformed flowers as well as in partially malformed ovaries at the baseof phylloids was significantly lower. A low content of cytokinins was alsopresent in petals of both normal and phyllody-exhibiting flowers and the lowestcontent has been found in the phylloids of the 'Green Rose’. Apossibility of mutant deviations in metabolism of cytokinins in rose plants isdiscussed.