Archs Sei. _ _l_a_sc_._3_-'--_P_P_·_3_3_7_-3_4_6__, ___ D_é_ce_m_b_re_19_9_8 __ ---l Communication présentée à la séance du 11 décembre 1997 SYSTEMIC STRESS EFFECT ON THE SUGAR METABOLISM UNDER PHOTOPERIODIC CONSTRAINT BY Robert DEGLI AGOSTI* & Hubert GREPPIN ABSTRACT Systemic stress effect on the sugar metabolism under photoperiodic constraint. - Spinach plants maintained in a short day photoperiod of 8:16 (L:D) remain vegetative. Transition to flowering (induction) may be initiated by extending 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 arder of 3 to 10 times the baseline) in the concentration of glucose already 3-5 h after the start of light extension. Varions sources of stress affect this response. Pricks and cuts, as weil as a brief, strong increase of an atmospheric pollutant such as ozone turned out to be inhibitors. At the time of the experiments (4 weeks), spinach plants possess two symmetrical and fully developed primary leaves. The pricking of one leaf just before the transfer treatment inhibits this particular carbohydrate response, not only in the directly wounded leaf but also in the adjacent unwounded leaf. The transmission of the stress effect from one leaf to the other is undeniable for both glucose and saccharose, it implies the existence of a systemic mechanism concerning photoperiodic-controlled carbohydrate metabolism in plants. Key-words: glucose, photoperiodism, Spinacia olereacea, stress, sugars, systemic, wounding. Abbreviations: ATP, Adenosine triphosphate; F.W., Fresh weight; NADPH, Nicotinamide adenine dinucleotide phosphate (reduced form); NADP+, Nicotinamide adenine dinucleotide phosphate (oxidised form); SD, Short day; T, Transfer; Tris, Tris (hydroxymethyl) -aminomethane. INTRODUCTION The interaction between plants and sunlight are essential for life on Earth. Indeed, thanks to the photosynthetic process, energy in the form of light is captured in order to be fixed in the form of organic molecules which constitute the basis of the construction of al! living beings, as weil as in their structure and as a source of energy. We usually symbolise this process by the equation: Light (energy) · ----------7 C 6 H 1 z0 6 (sugars) + 6 0 2 *Laboratoire de Biochimie et Physiologie végétales, LABPV/CUEH, Université de Genève, Place de l'Université 3, CH-1211 Genève 4, Suisse. E-mail: Robert.DegliAgosti@bota.unige.ch