The growth rate modulates time to first bud appearance in Physaria mendocina

Abstract

Physaria mendocina is under domestication because its seeds contain significant amounts of hydroxy fatty acids for several industrial uses, but displays a facultative biennial behavior which may represent a drawback in terms of production. Previous work revealed that the time to flower induction in this species is insensitive to temperature, photoperiod and vernalization, but suggested that this length of time could be determined by radiation, water and nutrients and/or the acquisition of a minimum growth rate. We aimed to determine whether the attainment of a threshold plant growth rate (GRt) triggers the initiation of the flowering phase in P. mendocina. Nutrient, water and radiation availability were manipulated to modify the timing of acquisition of that rate, expecting a concomitant modification of the time to flowering. We also explored the possibility that the stimulus is mediated by an accumulation of active gibberellins (GAs). Linear regressions were fitted between plant dry weight and time, and slopes of the relationships were considered as the growth rates. Radiation, water and nutrients constraints increased the duration of the phase between emergence and, concomitantly, first bud appearance (FBA). However, plants from all treatments reached FBA, after acquiring a growth rate of around 0.01g d−1pl −1 (GRt).When exogenous GAs was applied under limiting radiation, plants reached FBA despite the fact that they never acquired a GRt; conversely, when GAs biosynthesis was inhibited under high irradiances, the plants required more days to reach FBA than controls, despite the fact that they acquired a GRt. The information obtained allow us to conclude that the time to FBA, which is the first visible manifestation of floral induction in this system, is modulated by factors controlling growth mediated by an accumulation of (GAs) and suggest that the acquisition of GRt is the internal feature that triggers floral induction. This knowledge offers a frame within which cropping systems could be designed in order to avoid or not a biennial behavior.