The Inter‐relations of Catalase, Respiration, After‐ripening, and Germination in Some Dormant Seeds of the Polygonaceae

Abstract

Mature seeds of some species of the Polygonaceae have dormant embryos which must undergo a period of after-ripening before germination can take place. Studies reported in this paper have to do with the dormancy, after-ripening, catalase, respiration, and germination of seeds of several species of this family. Especial attention has been given the relation between the so-called enzyme catalase and the rate of respiration as found in these seeds.As the enveloping coats have a direct relation to the rate of after-ripening and germination in the seeds, a brief morphological description of the seeds will be given.According to Woodcock (1914) the seed of the polygonums at maturity is enclosed in a thick hard coat, consisting of the cutinized epidermal layer and the compressed inner layers of the ovary. The integuments have become closely compressed and their crushed remains form a thin layer surrounding the embryo and endosperm. Just inside the integuments is a thin aleurone layer. The embryo is free from the mealy endosperm and occupies a cavity just beneath the aleurone layer in an angle of the seed. The two inner layers forming the seed coat and aleurone layer cannot be removed without separating the embryo from the endosperm, so experiments have necessarily been limited to entire fruits and to seeds with the fruit coat removed.Fruits of Polygonum scandens, P. pennsylvanicum, P. aviculare, P. acre, P. virginianum, P. lapathifolium, and Rumex crispus were collected in October, 1931, at Manhattan, Kansas. They were then dried, cleaned, and the lighter and immature fruits eliminated by a seed blower.The fruit coats on some seeds of Polygonum scandens were removed by treatment with concentrated H 2S0 4• In this process the fruits were treated with the acid for five minutes, after which they were washed thoroughly and the ovary wall was rubbed off. Due to the structure of the seed, it was found impossible to remove the seed coat mechanically without injury to the embryo.Germination tests previous to low temperature treatment were made upon both fruits and seeds in Petri dishes with moist cotton as a medium. Various temperatures were employed, and observations were made from time to time to detect any signs of germination. AFTER-RIPENING AND GERMINATION OF SEEDSIn the seeds of Polygonum spp. studied in these experiments, the embryos are dormant at maturity. About 6S per cent of the mature seeds of Rumex crispus germinated readily at room temperature, though the remaining 3S per cent were dormant and required varied periods of low temperature treatment in the imbibed condition at 3°e. before germination took place.The fruit coat and probably the seed coat and aleurone layer are instrumental in retarding the after-ripening and preventing the germination of the seeds of the Polygonaceae. Seeds with the fruit coats intact required three times as long for after-ripening as those with the fruit coats removed. Also the rate of respiration in the seeds with the fruit coats removed was considerably higher than in those with the fr...

Field and laboratory germination responses of achenes of Polygonum lapathifolium, P. pensylvanicum, and P. persicaria

“…This innate dormancy ensures that potentially fatal seedling emergence does not occur prior to the onset of winter. The dormancy found in fresh achenes collected in Ontario is comparable with the innate dormancy described for achenes collected and studied elsewhere (Ransom 1935;Justice 1941;Timson 1965;Porter 1966;Hammerton 1967c1, 19676). According to Timson (1965) and Hammerton (1967~1, 1967b, the degree of dormancy differs from population to population and a few strains show no innate dormancy at all.…”

“…2D). Justice (1941) and Ransom (1935) found that air drying caused a 'hard' induced dormancy in 2111 three species.…”

“…Many authors have recommended afterripening at constant low temperatures (0-6°C) in moist or wet conditions for breaking dormancy in Po!\~gonurn species, but none has studied Canadian material (Dorph-Petersen 1924;Ransom 1935;Justice 1941;Yamada 1954;Bayer and Bucholtz 1957;Bayer 1958;Maguire and Overland 1959;Timson 1965;Porter 1966;Hammerton 19670, 19670). The precise conditions and required durations of cold temperatures varied for achenes of different plants and populations (Ransom 1935;Justice 1941;Hammerton 1967a, 19676) and also varied between years for the same population (Justice 1941). The requirement of moisture during cool storage to break dormancy was not critical for our Ontario achenes but was critical for those collected by Justice (1941) in the United States.…”

“…Fruit coat scarification, leaching pretreatments, variations in light and temperature regimes, and provision of different substrate types did not increase pel-centage germination. Attempts to shorten the aftel-ripening period by val-ious treatments (Ransom 1935;Justice 1941;Bayel-1958;Porter 1966;Hammerton 19670) have little relevance to Ontario plants in the field because our environmental conditions do not become suitable for germination until late spring.…”

“…For example, Witts (1960) found that P. pet.siccrricr was more abundant in arable fields than two other species of Polygotzutn because some of its seeds would germinate after herbicide treatments had destroyed the entire seedling populations of the three species. Other studies of the germination requirements of the achenes of one or more of these species have been made in Europe (Hammerton 1967cr,1967bTimson 1965) and in the United States (Ransom 1935;Justice 1941;Dalci 1975). One problem in applying results obtained by other authors to Canadian material is that their plants grew in different environments to ours and this can cause differences in seed germination (Hammerton and Jalloq 1970).…”