Hydropriming changes temperature thresholds for seed germination of tree species from the Caatinga, a Brazilian tropical dry forest

Abstract

This study evaluates the effects of hydration and dehydration cycles (HD cycles) on seed germination of four Caatinga tree species (Anadenanthera colubrina var. cebil, Enterolobium contortisiliquum, Pityrocarpa moniliformis and Pterogyne nitens) subjected to different temperatures and determine the thermal upper and lower limits of germination. For this, seeds were subjected to 0, 1, 2 and 3 HD cycles and set to germinate at temperatures of 5, 10, 15, 25, 35, 40 and 45 °C. Germinability and t50 were calculated and the differences of these parameters were compared by two-way ANOVA. In addition, germination rate (GR = 1/t50), as well as ceiling (Tc), optimum (To) and base (Tb) temperatures were calculated to estimate the limits below or above which the seeds fail to germinate. We observed that the more HD cycles, the better the seed responds, especially at extreme temperatures. Seeds of all studied species showed To between 25 and 35 °C, Tb < 10 °C, and Tc > 40 °C. The slope of regression curves for germination rate showed that submitting seeds to HD cycles expands its thermal tolerance range, revealing that this seed pre-treatment can be efficient for species as it increases their tolerance to thermal stress.

Interpopulational seed hydration memory does not affect seed germination of Xiquexique gounellei (F.A.C.Weber ex K.Schum) Lavor & Calvente subsp. gounellei (Cactaceae) under water deficit

“…In this sense, plants have developed adaptive strategies to guarantee seed germination and seedling establishment in the field, aiming at the maintenance of their populations (Meiado et al, 2012). Due to the environmental conditions imposed on dispersed seeds, which allow them to naturally undergo discontinuous hydration and change their germination responses, an acquisition of tolerance to water deficit is expected in response to HD cycles (Lima & Meiado, 2018a; 2018b; Nascimento et al, 2021).…”

“…HD cycles have positive effects on germination parameters, such as increased germinability and decreased germination time (Alvarado-López et al, 2014; Nascimento et al, 2021). Thus, some species may show improvements during germination after discontinuous hydration, as observed in seeds from different populations of Pilosocereus catingicola (Gürke) Byles & G.D. Rowley subsp.…”

“…Under laboratory conditions, HD cycles are simulated using the hydropriming technique, which consists of promoting hydration until the middle of the first phase of the imbibition process, with dehydration taking place in a forced-air dry oven at a temperature of 30°C, until the seeds return to their initial weight (Lima et al, 2018a). As a result of this process, seeds that undergo HD cycles show greater germinability, shorter germination time, higher germination speed, greater synchrony, and acquisition of tolerance to water deficit and high temperatures (Lima & Meiado, 2018a; 2018b; Nascimento et al, 2021).…”

Changes in seed hydration memory expression through different seasons in a Seasonally Dry Tropical Forest

“…The physiological changes that occur during hydration in the imbibition process are conserved during dehydration periods and, as a HD cycles product, seed hydration memory is expressed and confers ecological implications for the species (Dubrovisky, 1996). Seed hydration memory is related to differential proteins expression (López-Urrutia et al 2013) and provides advantages such as, for example, germination percentage increased, average germination time reduction and tolerance acquisition to abiotic stresses, such as water de cit and salinity (Lima and Meiado 2017;Lima et al 2018;Nascimento et al 2021). This greater tolerance interferes in species population dynamics that inhabit ecosystems with water limitations in certain seasons (Nascimento et al 2021).…”

“…Seed hydration memory is related to differential proteins expression (López-Urrutia et al 2013) and provides advantages such as, for example, germination percentage increased, average germination time reduction and tolerance acquisition to abiotic stresses, such as water de cit and salinity (Lima and Meiado 2017;Lima et al 2018;Nascimento et al 2021). This greater tolerance interferes in species population dynamics that inhabit ecosystems with water limitations in certain seasons (Nascimento et al 2021).…”