Phloem Exudate ofPerilla crispaand its Effects on Flowering ofP. crispaShoot Explants

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Abstract
The aim was to develop an assay for the flowering stimulus of a photoperiodically-sensitive plant. Phloem exudate solutions were obtained from photoperiodically induced and non-induced leaves of Perilla crispa (Thunb.) Tanaka, following treatment of excised leaves with solutions of EDTA or phytic acid. The amounts of exudate obtained were estimated polarimetrically, and the conditions for obtaining maximum exudate yields were determined. Shoot explants from non-induced P. crispa plants were grown on a nutrient medium. Under short days the explants reached anthesis after c. 35 d. In continuous light a small proportion of the explants showed signs of flowering after 100 d. The effects of test substances and phloem exudate on the flowering of explants grown in continuous light was investigated. (±)-ABA (4.0 μM), sucrose (14.6 mM) and phloem exudate from both induced and non-induced leaves caused some promotion of flowering. In three experiments, phloem exudate from induced leaves enhanced flowering to a greater extent than exudate from non-induced leaves; in other experiments the effects of the two types of exudate were similar. There was no evidence that ABA or sucrose in the phloem exudate caused flowering. Concentrations of phloem exudate above 2.0 g I−1 were phytotoxic to the explants.

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