Echinochloa crus-galli seed physiological dormancy and germination responses to hypoxic floodwaters

Hypoxic floodwaters can seriously damage seedlings. Seed dormancy could be an effective trait to avoid lethal underwater germination. This research aimed to discover novel adaptive dormancy responses to hypoxic floodwaters in seeds of Echinochloa crus-galli, a noxious weed from rice fields and lowland croplands. Echinochloa crus-galli dormant seeds were subjected to a series of sequential treatments. Seeds were: (i) submerged under hypoxic floodwater (simulated with hypoxic flasks) at different temperatures for 15 or 30 days, and germination tested under drained conditions while exposing seeds to dormancy-breaking signals (alternating temperatures, nitrate (KNO3), light); or (ii) exposed to dormancy-breaking signals during hypoxic submergence, and germination monitored during incubation and after transfer to drained conditions. Echinochloa crus-galli seed primary dormancy was attenuated under hypoxic submergence but to a lesser extent than under drained conditions. Hypoxic floodwater did not reinforced dormancy but hindered secondary dormancy induction in warm temperatures. Seeds did not germinate under hypoxic submergence even when subjected to dormancy-breaking signals; however, these signals broke dormancy in seeds submerged under normoxic water. Seeds submerged in hypoxic water could sense light through phytochrome signals and germinated when normoxic conditions were regained. Hypoxic floodwaters interfere with E. crus-galli seed seasonal dormancy changes. Dormancy-breaking signals are overridden during hypoxic floods, drastically decreasing underwater germination. In addition, results indicate that a fraction of E. crus-galli seeds perceive dormancy-breaking signals under hypoxic water and germinate immediately after aerobic conditions are regained, a hazardous yet less competitive environment for establishment.Fil: Peralta Ogorek, Lucas León. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos; ArgentinaFil: Striker, Gustavo Gabriel. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. University of Western Australia; AustraliaFil: Mollard, Federico Pedro Otto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos; Argentin

Shade Avoidance

The presence of neighboring vegetation modifies the light environment experienced by plants, generating signals that are perceived by phytochromes and cryptochromes. These signals cause large changes in plant body form and function, including enhanced growth of the hypocotyl and petioles, a more erect position of the leaves and early flowering in Arabidopsis thaliana. Collectively, these so-called shade-avoidance responses tend to reduce the degree of current or future shade by neighbors. Shade light signals increase the abundance of PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5 proteins, promote the synthesis and redirection of auxin, favor the degradation of DELLA proteins and increase the expression of auxin, gibberellins and brassinosteroid-promoted genes, among other events downstream the photoreceptors. Selectively disrupting these events by genetic or pharmacological approaches affects shade-avoidance responses with an intensity that depends on the developmental context and the environment. Shade-avoidance responses provide a model to investigate the signaling networks used by plants to take advantage of the cues provided by the environment to adjust to the challenges imposed by the environment itself