Two hybrids of maize (Zea mays L.) differing in resistance to drought, were grown in chernozem soil in a greenhouse and were fertilized with two different forms of nitrogen: Ca(NO3) 2 and (NH4)2SO 4 in concentrations corresponding to 100 kg of N ha z. After emergence of the 4th leaf, plants were exposed to drought. During the drought period, the parameters of plant water status (water potential, osmotic potential, turgor pressure and relative water content) and chlorophyll a + b concentration were monitored every two days. N and K concentration and accumulation over the drought period were also monitored.Next to differences in adaptability of the two hybrids to drought, the results demonstrate different adaptability of NH 4 and NO3-treated plants within each hybrid. NH4-plants of each hybrid maintain higher turgor pressure during the drought by better osmotic adaptation. Especially significant differences appear between chlorophyll (a + b) values of NH 4 and NO3-treated plants and as affected by drought. Chlorophyll concentrations of NH4-plants are higher than those of NO3-plants both in control and droughted plants. NH 4 plants show a characteristic initial chlorophyll increase at the beginning of the drought period while in N O 3 plants chlorophyll constantly decreases throughout the whole drought period. The influence of the nitrogen form on chlorophyll concentration changes during drought does not appear to be affected by regulation of the K concentration. ~2C
The content of endogenous cytokinins has been analysed in leaf and inflorescence extracts of male and female R. acetosella plants, using gas chromatography . Plant parts were extracted at four stages of development : leaves of juvenile plants, leaves of adult plants at the time of flower initiation and in full bloom, and upper internodes of the inflorescence stalks . Cytokinins with characteristics similar to isopentenyl adenine and adenosin, zeatin, zeatin riboside, and a bound form of zeatin, were all found in the extracts . The total amount of cytokinins was higher in female than in male plants during all these stages .
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