Systemic stress effect on the sugar metabolism under photoperiodic constraint.

Spinach plants maintained in a short day photoperiod of 8:16 (L:D) remain v egetative. Transition to flowering (induction) may be initiated by extendin g the light phase of the photoperiod (transfer). We have examined the free sugar content during this transition and observed a sudden and considerable increase (in the order of 3 to 10 times the baseline) in the concentration of glucose already 3-5 h after the start of light extension. Various sourc es of stress affect this response. Pricks and cuts, as well as a brief, str ong increase of an atmospheric pollutant such as ozone turned out to be inh ibitors. At the time of the experiments (4 weeks), spinach plants possess t wo symmetrical and fully developed primary leaves. The pricking of one leaf just before the transfer treatment inhibits this particular carbohydrate r esponse, not only in the directly wounded leaf but also in the adjacent unw ounded leaf. The transmission of the stress effect from one leaf to the oth er is undeniable for both glucose and saccharose, it implies the existence of a systemic mechanism concerning photoperiodic-controlled carbohydrate me tabolism in plants.