Chemical determinations of nucleic acids in plant material has often been more difficult than in animal tissues because high concentrations of carbohydrates and other substances present in most plant cells interfere with the reactions normally used to measure the nucleic acids.
Methods have been developed which allow for the extraction of nucleic acids from plant tissues (l-3), but the problem still remains of completely removing the substances which interfere with different reactions used to measure the content of the extracted DNA and RNA. Consequently, methods which, for example, work well on root tips of germinating plant embryos, are not reliable when applied to other plant tissues, in which concentrations of the interfering substances are inherently high.
To assess quantitatively the changes in cell constituents in relation to environmental stress, we felt that it would be more desirable to equate such changes to a specific per cell or DNA basis rather than to a fresh or dry weight of the tissues. We were prompted therefore, to develop a reliable and sensitive method for estimating DNA which can be applied to most plant tissues.
The trimeric dihydrate form of glyoxal reacts with adenine to form a fluorescent product which can be used to determine the content of adenine in DNA or RNA (45. In this communication we describe the successful application of this reaction to the estimation of the content of DNA in several plant tissues.
Seeds of Zea mays were soaked overnight in tap water and then allowed to germinate on moistened filter paper in a covered petri dish at 24Β°C for 2 to 3 days. Two millimeter root tips from the primary roots of uniform lengths were harvested and frozen immediately.
When required, 5 to 10 root tips were thawed and triturated in an ethanol:water (2:l) mixture using a Teflon hand homogenizer. Samples of frozen dried pollen (25-50 mg), obtained from both diploid and tetraploid Zea mays were homogenized as described above. Living bark, obtained from the trunk of the black locust tree (Robinia pseudo-acacia L.), was cut into 2 x 2 mm cubes, weighed and homogenized in a Tekmar Tissuemizer (John's Scientific Co .) .
Delipidation, removal of acid soluble nucleotides and subsequent extraction by alkali were performed by a modification of the Schmidt and Thannhauser method (6). To summerize briefly, the plant tissues were 1 Contribution No. 885. 308