Introduction
Seed 'dormancy-breaking chemicals are useful for
attainment of at least two major objectives: (i) they serve
as molecular probes of the mechanisms involved in the
transition from developmental arrest to growth and (ii)
they can increase the efficacy of weed control and crop
establishment. Despite the complementary utility of
these research areas, successful field applications have
been limited due to insufficient potency of available
chemicals, and the mechanisms of chemical action are
poorly understood (Cohn, 1987).
Using red rice (Oryza sativa L.)- an economically
important weed of southern USA, Central and South
American rice production regions- as a model system,
we have attempted to define the chemical features required
for the activity of non-hormonal dormancy-breaking compounds
(Cohn, 1989). This work has also advanced some
elucidation of the involved mechanisms of action. On both
counts, significant success has been achieved, albeit with
rather slow progress towards the ultimate objectives.
In this paper, results from structure-activity studies
are summarized and integrated, where possible, with
studies addressing physiological mechanisms of seed
dormancy. The data demonstrate clearly that uptake of
dormancy-breaking chemicals by seeds is extremely
rapid, and the physiological response by the seeds can
be equally fast. However, structurally related dormancybreaking
chemicals can elicit dramatically different levels
of the same physiological marker. In addition, the
structural integrity of a dormancy-breaking chemical
inside the seed is not static, i.e. applied dormancybreaking