Mediation of phytochrome in the inductive action of low temperature on dark germination of lettuce seed at supra-optimal temperature

The induction of dark germination in light-requiring lettuce (Lactuca sativa) seed at supraoptimal temperatures by cold treatment (in darkness) was partly reversed by a brief far-red irradiation made at time of transfer, and even more so when the irradiation was made at the beginning of the cold pretreatment. When the inhibitory far-red irradiation was followed by additional cold treatment, the promotion was greatly restored. The promotive effects of brief irradiations with red light were further enhanced by a following cold period, before transfer to the supraoptimal temperature. These results are interpreted as indicating that the active (far-red absorbing) form of phytochrome is pre-existing in the dry seed, and interacts with a co-factor which is built-up during imbibition. The rate of build-up of this co-factor, as well as of the dark inactivation of active phytochrome increase with temperature. The products of the interaction pass through a photo-labile thermo-stable phase, before becoming photo-stable as well.     

In vivo phototransformation of phytochrome in relation to its binding to a particulate fraction of maize coleoptiles

When the phytochrome molecule of maize coleoptiles absorbs sufficientenergy it binds to its putative binding site in a particulatefraction irrespective of whether or not it is in the P_fr form.The extent of binding depends on the light dosage. Red lightis more efficient than far red light but both are effectivein causing phytochrome to bind. Using phytochrome binding tosubcellular particles as the prototype of a primary physiologicalresponse it is concluded that P_fr may not necessarily be theonly physiologically active form of phytochrome. (Received May 31, 1976; )     

Lectin activity of the nucleocytoplasmic EUL protein from Arabidopsis thaliana

The Euonymus lectin (EUL) domain was recognized as the structural motif for a novel class of putative carbohydrate binding proteins. Confocal microscopy demonstrated that the lectin from Euonymus europaeus (EEA) as well as the EUL protein from Arabidopsis thaliana (ArathEULS3) are located in the nucleocytoplasmic compartment of the plant cell. ArathEULS3 as well as its EUL domain were successfully expressed in Pichia pastoris and purified. The EUL domain from Arabidopsis interacts with glycan structures containing Lewis Y, Lewis X and lactosamine, indicating that it can be considered a true lectin domain. Despite the high sequence identity between the EUL domains in EEA and ArathEULS3, both domains recognize different carbohydrate structures.