The development of desiccation-sensitive seeds in Quercus robur L.: Reserve accumulation and plant growth regulators

The fruits of Quercus robur are shed containing seeds at high moisture contents which remain desiccation sensitive and exhibit recalcitrant storage behaviour. Little is known of the control of seed development in these and other recalcitrant seeds. In the present work the changing concentrations of four plant growth regulators during seed reserve accumulation was studied over five years on seeds from the same tree. The pattern of reserve accumulation and changing ABA content in seeds differed between years. Although ABA content in the cotyledons increased in line with increasing dry weight to different contents at shedding, similar concentrations existed in cotyledons in each year. Thus ABA did not appear to be influencing dry weight accumulation. However, unlike orthodox seeds the decline in ABA concentration prior to shedding was limited and consistent with a continuing role for ABA in preventing precocious germination. An earlier peak in ABA concentration was associated with greater desiccation tolerance at shedding across years. The concentrations of zeatin and zeatin riboside in cotyledons were similar in each year and declined during reserve accumulation in a similar fashion to that reported for orthodox seeds. By contrast, IAA concentration increased in both the cotyledons and axes in the latter stages of seed development, opposite to that reported for orthodox seeds. It is possible that the increasing IAA concentration in cotyledons and axes and the stable concentration of zeatin and zeatin riboside throughout the latter stages of development in the axes of Q. robur are linked to the maintenance of active metabolism for the rapid initiation of germination upon shedding observed in seeds of this species.