Dynamics of the contents and distribution of ABA, auxins and aquaporins in developing caryopses of an ABA-deficient barley mutant and its parental cultivar.

Dynamics of abscisic acid (ABA)and indole-3-acetic acid (IAA)contents were followed in developing barley caryopses of the ABA-deficient mutant AZ34 and its parental cultivar Steptoe. Distribution of these hormones and HvPIP2 aquaporins (AQPs)was studied with the help of immunohistochemical methods in the roots and coleorhiza of developing embryos. In Steptoe, maturation of the caryopsis was accompanied by vast accumulation of ABA, while this hormone accumulated more slowly in the caryopsis of AZ34 and its content was lower than in Steptoe. Accumulation of ABA was accompanied by a decline in IAA level in the developing caryopsis, the process being delayed in AZ34 in accordance with the slower accumulation of ABA. ABA accumulated to high levels in the coleorhiza cells of Steptoe, while the effect was absent in AZ34. The high level of ABA was likely to be important for maintaining the barrier function of the coleorhiza, preventing germination of seminal roots and enabling seed dormancy, while the absence of ABA accumulation in coleorhiza of AZ34 may be responsible for the initiation of root germination inside the caryopsis. The abundance of HvPIP2 AQPs in the seminal roots was higher at the beginning of maturation of Steptoe caryopsis and declined afterwards, while the levels of APQs increased later in AZ34 in accordance with the delay in ABA accumulation. These results suggest the importance of ABA accumulation in coleorhiza for preventing precocious growth of seminal roots, and suggest regulation of IAA and aquaporin levels by this hormone during maturation of embryos.