Previously, it was believed that once a developing plant made the decision to break seed dormancy and germinate, it would continue to blossom, unchecked. This new research proposes a second checkpoint, so that, for example in the case of the weed Arabidopsis , the plant has an opportunity to hold-off on growth in case it is accidentally triggered to germinate by a cold summer's night. Arabidopsis , a well-studied weed in the mustard family, is a model system for the study of plant development because of a number of factors, including its small size and rapid generation time. The protein ABI5 may protect Arabidopsis plants from drought by arresting growth. Moreover, they provide evidence that ABA activates a recently isolated Arabidopsis protein called ABI5 and demonstrate that this protein is essential to the newborn plant's ability to protect itself against drought during this developmental delay.
ABA plays a role in both germination in young plants and stress responses in adult plants.
Its levels rise during germination, and it has been shown to have an inhibitory effect on growth. ABA's ability to delay both germination and early growth was discovered when Lopez-Molina and Mongrand realized that seeds would in fact germinate after a certain period of time when grown in the presence of the hormone. Because previous studies demonstrated that mutant Arabidopsis plants lacking the ABI5 protein grew without interruption after germination, the researchers wondered how this protein was linked to ABA's ability to maintain arrested germinated embryos. To study more precisely the role of ABI5, they genetically-engineered strains of Arabidopsis to produce an excess of the protein and then observed the plants' behavior. Newborn plants overproducing ABI5 were found to exhibit a second growth checkpoint only when ABA was present.