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Highly dynamic distributed applications often require flexible coordination among several autonomous components. Space-based middleware provides a suitable, data-driven coordination paradigm for such scenarios, where distributed peers exchange data and commands in a scalable and decoupled way using shared tuple spaces. In its basic form, such a middleware supports access to a data storage and (blocking) queries on the stored tuples. However, in many cases the injection of additional server-side logic would ease the development of complex applications, as the semantics of the tuple space can be adapted to domain-specific requirements.This paper introduces reactive programming features for XVSM, a space-based middleware that enhances the tuple space concept with powerful coordination mechanisms. We present a comprehensive extension mechanism that supports the execution of application logic in reaction to composite and time-based events. As an example for the feasibility of the approach, we provide a bootstrapped solution for a leasing mechanism that manages the lifetime of data in the space.