Figure 5.

Transgenic plants overexpressing ABI5 are hypersensitive to ABA. (A) WT Ws and Ws/35S∷HA-ABI5 transgenic plants were grown for 5 days with 0, 0.5, and 5 μM ABA. Transgenic seeds were arrested in development at 0.5 μM ABA and only started to geminate after 5 days. WT Ws seeds were insensitive to 0.5 μM ABA and were fully germinated in 5 μM ABA after 5 days. (B) Inhibition of root growth by exogenous ABA is exacerbated in Ws/35S∷HA-ABI5 transgenic lines (dotted bars) as compared with WT Ws plants (black bars). Five-day-old seedlings grown in absence of ABA were transferred to 0, 5, and 10 μM ABA plates for 5 days. The root length of ABA-treated seedlings was expressed as a percentage of nontreated controls (n = 15). Bars indicate standard deviations. (C) Ws/35S∷HA-ABI5 (open circles) transgenic plants retained water more efficiently. Young rosette leaves from WT Ws control (crosses) and transgenic plants at the same developmental stage (one month) were excised and weighed at different times indicated (n = 3). abi1 measurements (lozenges) are included as a control for water loss. (D) Seeds from WT Ws, abi5-4 and 3 independent abi5-4 transgenic lines carrying a 35S∷HA-ABI5 transgene were treated with 5 μM ABA as described in Fig. 1. The picture depicts representative seedlings after 5 days. Western blots using anti-ABI5 antibodies were performed on the same plants. Each lane contained 5 μg protein.