Revising the role of ABA as regulator of flowering and seed development

The time of flowering or heading is regulated by environmental cues, mostly by light and temperature. Abscisic acid (ABA), considered the main phytohormone that regulates plant response to abiotic stress, also plays an important role in flowering. ABA can both stimulate and inhibit flowering. In Arabidopsis, ABA accelerates flowering time during drought escape. On the other side, ABA can also repress flowering transition to ensure the time of flowering at the right moment for plant. In cereals, ABA also plays dual role in regulating heading time. Furthermore, some components of the ABA pathway can simultaneously act as positive and negative regulators of heading. ABA is also involved in another important aspect of the plant reproductive stage: seed/grain development. ABA plays positive role in the synthesis of storage proteins and lipids during seed-filling. In contrast, ABA negatively regulates seed size. In this review, we present recent knowledge regarding the complex role of ABA in the regulation of the reproductive stage in Arabidopsis and in the most important crop plants.