Conclusion
Here we characterize the mechanism behind the p-type response of ABA dynamics exhibited by highly drought tolerant species under long term drought. The use of rapid bench dehydration to assess ABA biosynthesis revealed that ABA biosynthesis on dehydration is inhibited once plants are drought stressed to Ψtlp. Continual conjugation of ABA appears to drive a decline in ABA levels once biosynthesis is inactivated. Future work is needed to assess the occurrence of the p-type behaviour in a wider range of species of seed plants, including in herbaceous species which usually die after a slight decrease in Ψl below Ψtlp.