The relationship between sucrose supply, sucrose-cleaving enzymes and flower abortion in pepper

Abortion of pepper flowers depends on the light intensity perceived by the plant and on the amounts of sucrose taken up by the flower (Aloni B, Karni L, Zaidman Z, Schaffer AA. 1996. Annals of Botany 78: 163-168). We hypothesize that changes in the activity of sucrose-cleaving enzymes within the flower ovary might be responsible for the changes in flower abortion under different light conditions. In the present study we report that the activity of sucrose synthase, but not of cytosolic acid invertase, increases in flowers of pepper plants which were exposed, for 2 d, to increasing photosynthetically active radiation (PAR) in the range of 85-400 mu mol m(-2) s(-1) at midday. Sucrose synthase activity increased in parallel with the increasing concentrations of starch in the flower ovary. Feeding flower explants, prepared from 3-d-predarkened plants, with 100 mM sucrose for 24 h, caused a 23 % increase in reducing sugars and a 25-fold increase in starch concentration, compared with explants fed with buffer. Likewise, feeding explants of pepper flowers with sucrose, glucose, fructose and also mannitol increased the sucrose synthase activity in the ovaries. Concomitantly, sucrose, glucose and fructose, but not mannitol, reduced the abortion of flower explants. It is suggested that sucrose entry into the flower increases the flower sink activity by inhibiting abscission and inducing metabolic changes, thus enhancing flower set. (C) 1997 Annals of Botany Company.