Levels of (+/-) Abscisic Acid and Xanthoxin in Spinach under Different Environmental Conditions.

The levels of the growth inhibitors(+)-abscisic acid and xanthoxin were determined in the long day plant spinach (Spinacia oleracea L. cv. Savoy Hybrid 612) grown under different environmental conditions. When plants were transferred from light to darkness, the (+)-abscisic acid level always decreased, whereas the xanthoxin content did not change. The (+)-abscisic acid content was higher in plants grown under low than under high relative humidity.Xanthoxin levels were not affected by photoperiod, whereas the (+)-abscisic acid content increased 2 to 3 times upon transferring plants from short day to long day. Shoot tips with young leaves and mature leaves of the same plants analyzed separately did not differ in their inhibitor content when expressed per unit dry weight. No increase in xanthoxin level was observed in wilting plants. In general, the xanthoxin levels of spinach were much less affected by changes in the environment than were those of (+)-abscisic acid. In conclusion, there is no correlation between xanthoxin and (+)-abscisic acid levels in spinach on the one hand, and growth and flowering responses on the other.