Regulation of seasonal patterns in seed dormancy

Buried seeds of many wild species pass annually through a pattern of induction and release of dormancy. These reversible changes in dormancy may be repeated for numbers of years when seeds are deprived from light and other germination-stimulating factors, and are a highly useful adaptation to the climatic conditions which prevail at the habitat.This thesis studied the regulation of germination and reversible changes in dormancy in two related species Arabidopsis thaliana (L.) Heynh. and Sisymbrium officinale (L.) Scop. In A.thaliana, mutants that lack the capacity to synthesize GAs and/or are insensitive to GAs were compared with wild type.Germination of both species is dependent on active phytochrome (Pfr). In seeds of S. officinale Pfr action absolutely requires the co-action of nitrate, seeds of A. thaliana only slightly respond to nitrate. It has been suggested that light stimulates GA biosynthesis since the need for light (and nitrate) can be replaced by gibberellins (GAs). Reversal of lightstimulated germination by tetcyclasis, an inhibitor of GA biosynthesis, supported this conclusion. Preliminary GA determinations showed that irradiation gave elevated levels of GA 1 , GA 4 and GA 9 in A.thaliana. GA 4 was the most active GA. Light also increased sensitivity to GAs in both species.Germination data fitted as logistic dose response curves showed that (soil) temperature is the most important factor in the mechanism by which seeds sense the time of the year. It regulates sensitivity to light (and to nitrate). Upon perception of light (and nitrate) some signal-transduction chain is initiated. In this chain GA biosynthesis is stimulated. Moreover, GA sensitivity is enhanced. Temperature can also directly increase GA sensitivity. Germination invariably depends on the level of bio-active GAs and the available GA-response system. When either factor is limiting, germination is prevented. Both factors do not necessarily accompany changes in dormancy and are therefore not primarily regulatory.In S. officinale it was shown that changes in dormancy cannot be explained by changes in respiratory activity. During prolonged incubation levels of 02 uptake and C02 release were not affected by dormancy-breaking and -inducing treatments. Germination clearly required an increased respiratory activity. The contribution of different respiratory pathways changed during prolonged incubation. A role of the alternative pathway in the regulation of dormancy of S. officinale seeds is unlikely.

Bibliographic Details

Main Author:	Derkx, M.P.M.
Other Authors:	Karssen, C.M.
Format:	Doctoral thesis biblioteca
Language:	English
Published:	Derkx
Subjects:	arabidopsis thaliana, brassicaceae, germination, light, meteorological factors, photoperiod, photoperiodism, seed dormancy, seed germination, shade, sisymbrium officinale, wind, fotoperiode, fotoperiodiciteit, kieming, kiemrust, licht, meteorologische factoren, schaduw, zaadkieming,
Online Access:	https://research.wur.nl/en/publications/regulation-of-seasonal-patterns-in-seed-dormancy
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