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Quantal Response of Seed Germination in Seven Genera of Cruciferae to White Light of Varying Photon Flux Density and Photoperiod

R. H. ELLIS, T. D. HONG and E. H. ROBERTS
Annals of Botany
Vol. 63, No. 1 (January 1989), pp. 145-158
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/42758162
Page Count: 14
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Quantal Response of Seed Germination in Seven Genera of Cruciferae to White Light of Varying Photon Flux Density and Photoperiod
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Abstract

The response of the germination of seeds of Barbarea verna (Mill.) Aschers, Brassica chinensis L., Brassica juncea (L.) Czern. & Coss., Brassica oleracea L. var. gongylodes L., Camelina sativa (L.) Crantz, Eruca sativa Mill., Lepidium sativum L., Nasturtium officinale R. Br., and Rorippa palustris (L.) Besser to white fluorescent light of different photon flux densities applied for different daily durations in a diurnal alternating temperature regime of 20 °C/30 °C (16 h/8 h) was quantified by linear relations between probit percentage germination and the logarithm of photon dose, the product of photon flux density and duration. The low energy reaction, in which increasing dose promotes germination, was detected in all the seed populations but in Barbarea verna and Brassica juncea the lowest photon dose applied (10-⁵³ and 10-⁵⁷ mol m-² d-¹ respectively) was sufficient to saturate the response. Comparisons, where possible, between photoperiods demonstrated reciprocity, i. e. germination was proportional to photon dose irrespective of photoperiod, for the low energy reaction in Brassica oleracea (1 min d¹ to 1 h d¹), Camelina sativa (1 min d¹ to 8 h d¹), Eruca sativa (1 min d¹ to 24 h d¹), Lepidium sativum (1 min d¹ to 8 h d¹) and Rorippa palustris (1 min d¹ to 8 h d¹), but not in Brassica chinensis and Nasturtium officinale. The high irradiance reaction, in which increasing dose inhibits germination, was detected in Barbarea verna, Brassica chinensis, Brassica juncea, Brassica oleracea, and Camelina sativa. The minimum dose at which inhibition was detected was 10-⁰³ mol m-² d-¹. These results are discussed in the context of devising optimal light regimes for laboratory tests intended to maximize germination. The response of germination to photon dose was also quantified with 3 × 10⁻⁴ M GA₃ co-applied (Brassica chinensis, Camelina sativa, and Lepidium sativum) and with 2 × 10-² M potassium nitrate coapplied (Brassica chinensis). In the latter case potassium nitrate had no effect in the dark and inhibited germination in the light, but GA₃ promoted germination substantially in all three species. Variation amongst seeds in the minimum photon dose required to stimulate germination was not affected by coapplication of GA₃ in Brassica chinensis and Camelina sativa, whereas seeds of Lepidium sativum showed a narrower distribution of sensitivities to the low energy reaction in the presence of GA₃.

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