PHOTOREGULATION OF GERMINATION IN SEED OF TRANSGENIC LINES OF TOBACCO AND ARABIDOPSIS WHICH EXPRESS AN INTRODUCED CDNA-ENCODING PHYTOCHROME-A OR PHYTOCHROME-B

Photoinduction and photoinhibition of germination in seed from a homozygous tobacco (Nicotiana tabacum L.) line containing an introduced oat phyA cDNA (encoding phytochrome A) is compared with that of isogenic wild-type (WT) tobacco. Under continuous irradiation by a light source with a low red:far-red (R:FR) ratio the transgenic tobacco seed appeared to be less susceptible to photoinhibition of germination compared with WT seed. However, induction of germination following a short pulse by R (666 nm) was not enhanced in the genotype transformed by oat phyA cDNA compared with the WT; neither did germination of the transgenic tobacco seed show an increased sensitivity to saturating pulses of light of longer wavelengths (666-730 nm). In seeds of transgenic Arabidopsis thaliana (L.) Heynh. which contained an introduced phytochrome-B-encoding cDNA, levels of dark germination were enhanced, consistent with mediation of response by phytochrome B-P(fr). The germination behaviour of Arabidopsis genotypes wich contained an introduced cDNA encoding phytochrome A, however, did not significantly differ from that of the WT.