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

Photosynthetic pathway variation among C4 grasses along a precipitation gradient in Argentina

Aim Based on the biochemical and physiological attributes of C4 grasses, and on the close association between decarboxylation pathways and the taxa in which they evolved, the hypotheses tested were: (1) that C4 grasses would become progressively more abundant as precipitation decreased, with grasses of the NADP-me subtype more abundant in wetter sites and those of the NAD-me subtype more common in arid regions; and (2) that the distribution of grass subfamilies would also be correlated with annual precipitation. Location The study was conducted along a precipitation gradient in central Argentina, from the eastern Pampas (>1000 mm year)1 ) to the western deserts and semi-deserts near the Andes (<100 mm year)1 ). Methods Percentage of species and relative cover of C3 and C4 grasses (including C4 subtypes) in local floras from 15 lowland sites of central Argentina were obtained from our own unpublished data and from recently published floristic surveys. Pearson correlation coefficients were obtained between grass distribution parameters and the available climatic data. Results The percentage of C4 grasses increased towards the arid extreme and showed a strong negative correlation with annual rainfall (r = )0.74, P < 0.01). Within the C4 subtypes, the NADP-me species showed a higher proportional representation at the wetter extreme, whereas the representation of NAD-me species increased towards the more arid extreme. The relationship of PEP-ck species with climatic parameters in central Argentina was less evident. The distributions of the Panicoideae and Chloridoideae subfamilies along the precipitation gradient were diametrically opposed, with the Panicoideae positively (r = 0.86, P < 0.001) and the Chloridoideae negatively (r = )0.87, P < 0.001) correlated with annual precipitation. Main conclusions Our data are consistent with the broad observation that C4 grasses tend to dominate in areas where the wet season falls in the warmer summer months. In agreement with previously reported results for Africa, Asia, Australia and North America, we describe here for the first time a significant relationship between annual precipitation and the prevalence of the NADP-me and NAD-me photosynthetic pathways along climatic gradients for the Neotropics. We also report for the first time that correlations between C4 species and annual rainfall are stronger when the relative cover of grass species is considered. The association of grass subfamilies Panicoideae and Chloridoideae with rainfall is as strong as that recorded for the NADP-me and NAD-me variants, respectively, suggesting that characteristics other than decarboxylation type may be responsible for the geographic patterns described in this studyFil: Cabido, Marcelo Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Pons, Stella Maris. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Cantarero, Juan Jose. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria; ArgentinaFil: Lewis, Juan Pablo. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Anton, Ana Maria Ramona. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin