Effect of end-of-day irradiations on polyamine accumulation in petal cultures of Araujia sericifera.
We have studied photoperiodic control and the effect of phytochrome photoconversion at the end-of-day (EOD) on polyamine (PA) accumulation in petal explants of Araujia sericifera. Petals from immature flowers were cultured under long (LD) and short (SD) days. Light was provided by Gro-lux fluorescent lamps (90-100 &mgr;mol m-2 s-1). Red (R), far red (FR), red followed by far-red (R-FR) and far-red followed by red (FR-R) light treatments were applied daily at the end of the photoperiod. The free and bound putrescine (Put), spermidine (Spd) and spermine (Spm) fractions in petal explants were determined 40 days after the beginning of the culture. We also aimed to clarify the involvement of PA changes by using two inhibitors of PA biosynthesis: D-l-alpha-difluoromethylarginine (DFMA) and methylglyoxal bis(guanylhydrazone) (MGBG). We found PA accumulation to be under photoperiodic control, and the inhibitory effect of DFMA on this accumulation suggests that arginine decarboxylase (ADC) is the major pathway for Put biosynthesis. Polyamine levels were higher under LD, mainly as a result of the accumulation of free and bound Put. FR-EOD treatment, which dramatically reduced the R : FR ratio after LD, increased the accumulation of PA, mainly as free Put and free and bound Spd. Sequential R-FR and FR-R-EOD treatments strongly increased bound Spd. The concentration of MGBG used increased total PA accumulation, mainly as Put. However, all EOD light treatments dramatically reduced Put accumulation in the presence of MGBG. This may be due to a dual role of FR light in PA accumulation: (1) FR per se stimulates PA production, probably via ADC, and (2) in the presence of MGBG, FR inhibits Put accumulation, probably via ethylene production.
Moysset
Luisa
L
Unitat de Fisiologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain Departament de Genètica Molecular, IBMB, CID (CSIC), Jordi Girona Salgado, 18-26, E-08034 Barcelona, Spain.
Trull
Olga
O
Santos
M. Asunción
MA
Simón
Esther
E
Torné
Josep M
JM