Abstract
Abstract: Hydrotime (θH) models provide information on seed tolerance to low water potential and time to germination under different conditions. Here it was evaluated the capacity of graphic and probit model to describe germination parameters and germination times (t) in a tropical legume (Peltophorum dubium). Germination tests were conducted under reduced water potentials (polyethylene glycol solutions from 0 to -1.2 MPa) at 25 °C. Regression lines were applied to investigate the relationship between germination rates (1/t) and water potential for different germination percentages (fractions 10, 30, 50 and 70%). Those regressions were used in the graphic model to calculate θH (1/slope) and determine the base water potential (Ψb) as the point which the line intercepts the x-axis (G% = 0). In the probit model, germination percentages were transformed to probit units and plotted against Ψb-values to describe germination response under a single regression line. Values for θH varied from 1.8 to 2.0 MPa day in both models, and Ψb showed a normal distribution, as presupposed by the probit model. Predicted germination times (t10 and t50) mostly fell within observed times, thus showing biological relevance of the models to describe the effects of water potential on seed germination.
Highlights
Water uptake is the principal factor starting the germination process, promoting cell respiration, DNA synthesis and growth (Bewley et al, 2013)
Some studies evaluated the role of Ψ on seed germination of Brazilian species (Botelho and Perez, 2001; Fonseca and Perez, 2003; Rego et al, 2007), but rarely explaining whether germination would fit the presupposes of hydrotime models (Cardoso and Pereira, 2008; Oliveira et al, 2019)
This study aimed to investigate the role of water potential in seed germination of Peltophorum dubium, a tropical tree legume typically occurring in South American seasonal forests
Summary
Water uptake is the principal factor starting the germination process, promoting cell respiration, DNA synthesis and growth (Bewley et al, 2013). The decrease of water potential reduces germination capacity (G%), as well as the rate of the germination process (Gummerson, 1986; Bradford, 1995). The germination rate (GR, inverse of germination time, t) seems to linearly decrease with negative Ψ-values, until the point at which seeds stop the germination process due to low water potential (base water potential, or Ψb). Ψb, seeds require an accumulated Ψ (MPa) through time (hydrotime, or θH) to germinate and, hydrotime models were used to describe germination responses to reduced water potentials, mostly in crops Concerning native species, few studies in current literature investigated such threshold models regarding water relations and seed germination of tropical trees (Daws et al, 2008). Most attention regards to the role of temperature, rather than water potential, as described by thermal time models in neotropical species (Cardoso and Pereira, 2009; Pires et al, 2009; Daibes and Cardoso, 2018; Duarte et al, 2018)
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