Covalent Crosslinking of Phytochrome and its Binding Site: a Comparative Study with Different Plant Tissues under in vivo and in vitro Conditions

Abstract

Chemical crosslinking of phytochrome to its binding site(s) was effected using red light irradiated intact tissues (maize coleoptiles and primary leaves, zucchini hypocotyl hooks, barley and oat shoots) or cell-free homogenates derived from them. The following crosslinking reagents were tried: bi-imidoesters (dimethyl adipimidate, dimethyl suberimidate, and dithiobispropionimidate) or glutaraldehyde. Three patterns of responsiveness were observed. Maize coleoptile is responsive to bi-imidoesters and glutaraldehyde under in vivo and in vitro conditions. Zucchini hook is responsive to glutaraldehyde but not to biimidoesters, under in vivo and in vitro conditions. The consistency in the pattern of result obtained under in vivo and in vitro conditions for maize coleoptile and zucchini hook suggests a difference between phytochrome and binding site interaction in these two organs. In general, intact tissues of the cereal leaves are not responsive to bi-imidoesters or glutaraldehyde. On the other hand, substantial enhancement of phytochrome pelletability was observed when cell-free homogenates derived from red light irradiated cereal leaves were treated with crosslinking reagents in vitro . The lack of response of intact cereal leaves to these reagents might be due to cellular impermeability.