BLUE NUCLEI IN TULIP PETALS

RECENTLY MCWHORTER (1938) reported the interesting phenomenon of pigmented nuclei in the petals of the black tulip. The striking feature was that the nuclei were blue both in the blue and red areas of the petal. There was a question as to whether the coloration of the nucleus was natural or due to injury. A reference kindly sent me by Dr. McWhorter of a paper by Gigante (1938) also mentions the frequent presence of deep bluish grey nuclei of the epidermal and mesophyll cells in the violet and red areas of variegated tulip flowers. Gigante noted that colored nuclei were not seen in the cells of the white and yellow areas of the petal. He concluded that the dark coloration of the nuclei was due to the blue pigment present in them. Pigmented nuclei have also been reported in the pollen tubes of Hemerocallis tubiflora by Beck and Joly (1940), who state that the generative nuclei were reddish brown in color from the time the pollen grains were sown on a culture medium until the well developed tube burst at the tip. They make no statement suggesting that this pigment has a pH visage. The nuclei of the tulip cells are of more immediate interest, since the pigment of many tulip cells changes color with pH. The recorded color in these nuclei may be a means of demonstrating an alkaline reaction for the nucleus. Dr. McWhorter generously put at my disposal bulbs of a number of varieties of the tulip known as "Mendel." McWhorter had shown that tulip petals which "break" dark from tulip virus infection usually contain dark blue pigments in their bases and that the blue nucleus condition also correlates with the presence of this condition. This is particularly true of all Mendels; hence they were selected for this test. The fresh undamaged petals under microscopic observation showed cells with actively streaming protoplasts containing relatively large, spheroid, granular nuclei. The pigment was restricted to the sap within the large cell vacuoles. The protoplasts and nuclei were colorless. A peeled-off strip of the epidermis was mounted in water, also in 0.2 mol. sucrose solution between a slide and coverslip. Pressure was then exerted on the coverslip until some of the cells were damaged. This was evidenced by a breakdown of the tonoplast and escape of the contained sap. The coloration of the nuclei of the crushed cells was not immediate. The preparation was allowed to stand for ten to fifteen minutes and crushed again. The result was now striking. In many of the cells there was a more extensive breakdown of the tonoplast and an escape of the contained sap. In these cells the nuclei began to take up an ever deepening blue color. In the red 1 Received for publication January 22, 1941. areas the extruded sap retained a red color but it was paler than when it was more concentrated in the intact tonoplasts. In some cases enough of the pigment remained or was collected within the cell walls of damaged cells so that the contrasting deep blue color of the nucleus against the red background of the cell contents made a striking picture. In the violet areas the nuclei of the damaged cells also became progressively deep blue in reddish violet sur-