GROWTH-SUBSTANCES AND DORMANCY IN CERATOPHYLLUM-DEMERSUM

Ceratophyllum demersum L. occurs in winter in the dormant form, in summer in the vegetative form. Factors that affect growth and dormancy in Ceratophyllum were studied. After several weeks of severe winter conditions the plants changed from dormant to quiescent state. Under natural conditions Ceratophyllum plants remain quiescent for several months, due to unfavourable growth conditions. Experimentally the dormant could also be broken by high and low temperature treatments (shocks), and most effectively by addition of GA, An attempt to induce dormancy in full grown plants by the addition of ABA under extreme summer or winter conditions proved unsuccessful. The IAA and ABA contents in the plants were measured during the year. In winter the concentration of ABA was high and that of IAA low, whereas in summer the IAA concentration increased and that of ABA was variable. IAA only slightly antagonized the inhibition of growth by ABA. Both the growth regulators were readily taken up from the culture medium, as was confirmed by a study with the radioactive labelled compounds. The uptake rate of IAA was significantly higher than that of ABA. being 762 μg and 3.26, μg per plant in 24 h, respectively. GA, was found to have a strong antagonistic effect on the ABA induced growth inhibition. The total GA activity in dormant and quiescent plants was similar, in full grown plants it was much lower. In the dormant state a large part of GA was in a bound form, whereas during quiescence relatively more GA occurred in a free state in the plants. Copyright © 1979, Wiley Blackwell. All rights reserved