Biomechanical proposal as a cause of incomplete seed and pericarp development of the sunflower (Helianthus annuus L.) fruits

HERNÁNDEZ, LUIS; BELLÉS, PM; BIDEGAIN, M.A.; POSTEMSKY P.D.

PHYTON - INTERNATIONAL JOURNAL OF EXPERIMENTAL BOTANY BA ARGENTINA

FUNDACION ROMULO RAGGIO

Lugar: Buenos Aires; Año: 2018 vol. 87 p. 198 - 208

0031-9457

Absence or underdevelopment of sunflower fruitscome usually from failure in fertilization, stresses as well as physiological and morphological defects in the ovary. Tigmomorphogenesis has never been included as a possible cause. We have previouslyshown that a 2-3 day fertilization shift can occur between neighboring florets in the sunflower capitulum. It is proposed here thatthose ovaries with advanced fertilization can generate a signifcantradial and axial compressive stress on ovaries with delayed fertilization. Tis mechanical stimulus could be strong enough to trigger athigmo response that affects further ovary development. In vivo testswere performed, isolating ovaries by removing the adjacent flowersand rubbing them several times using a micromanipulator applying aforce of 1 to 3 N. Total peroxidases in treated and untreated ovaries,isolated and not isolated were measured 24 h after treatments. Ovarydevelopment was studied in control and isolated flowers, both rubbedand not rubbed. Also a mechanical a model was made to simulate themechanical behavior of an ovary surrounded by advanced growingneighboring ovaries. A meshed 3-D model of a young ovary wasconstructed and a computer simulation was performed using fniteelement analysis. Shear stresses generated by the friction of neighboring ovaries in contact with the model, fertilized three days later,were then estimated. After rubbing, isolated ovaries in planta showeda thigmo response that resulted in empty or incompletely developedfruits. Total peroxidase levels (ΔAbs470 min-1.g fresh weight-1) rosefrom 22 in control ovaries to 72 in rubbed ones. Te number ofovaries that did not develop any seed from these incompletely developed fruits rose from 16.2 to 20.0% in the control non-isolatedflowers to 61.1 to 86.7% in the rubbed ovaries, but dropped to 6.7to 7.3% in the non-rubbed but isolated ovaries. From the simulationit was found that the area of contact with the receptacle was prone to show a higher magnitude of stress after deformation induced byshear forces generated by neighboring ovaries. Tigmomorphogenesis can also explain the failures observed at early stages of the sunflower ovary development. Te ovary tissue sensitivity at this stagecould contribute to the rapid response of the mechanically generatedstimulus between neighbouring ovaries