Abstract
Salt stress responses were studied in three Plantago species (P. crassifolia, P. coronopus and P. major), with different levels of salt stress tolerance, at growth and reproductive stages of the life cycle. Plants were treated with increasing salt concentrations (0, 100, 200 and 400 mM NaCl) under controlled conditions in the greenhouse. Fresh biomass, leaf length and reproductive parameters related to flowering were analysed. To evaluate the reproductive success of salt-stressed plants, seeds produced after two months of treatment were sampled, and the mean number of seeds per plant and mean seed weight per treatment were determined. Seeds were germinated in vitro and seed and seedling quality were assessed by determining germination percentages and rates, length of radicle, hypocotyl, cotyledon leaves, and the angle of cotyledonary leaves. The 'seedling vigour index' was also calculated. Vegetative (fresh weight and leaf length) and reproductive traits (number of inflorescences, scape and spike length, mean number of seeds per spike and mean seed weight) were less affected by salinity in the more stress tolerant species P. crassifolia and P. coronopus than in P. major. Rate and velocity of germination of seeds produced by plants grown under saline treatments were similar in all species; however seedling development was less successful in P. major, as shown by length of the radicle, hypocotyl and cotyledonary leaves. The relative sensitivity to salt of the investigated Plantago species correlated with their distribution in nature: P. major, never present in saline environments, was much more affected by salt than its halophytic counterparts, while P. crassifolia, which grows in saline habitats, exhibited the most efficient responses to salt stress, especially at the early seedling development stage.
Highlights
Soil salinity is an environmental factor that significantly affects the distribution of plants in their natural ecosystems and it is one of the major threats for agriculture
Seeds of P. crassifolia and P. coronopus were harvested in a salt marsh located in the Natural Park of La Albufera (Province of Valencia, Spain), and seeds of P. major were purchased from the company Spicegarden, EU
Maximal fresh weight (FW) was recorded in the control plants of the most vigorous species, P. major, which drastically decreased about 10-fold in the plants treated with 400 mM NaCl
Summary
Soil salinity is an environmental factor that significantly affects the distribution of plants in their natural ecosystems and it is one of the major threats for agriculture. According to FAO (2008), more than 800 million ha of land worldwide are affected by salinity. The immense majority of terrestrial plant species and all major crops belong to the category of glycophytes, or plants that cannot survive in conditions of (relatively) high soil salinity. Halophytes include species that are able to survive and complete their life cycle in the presence of salt concentrations of at least 200 mM NaCl (Flowers et al, 1986; Flowers and Colmer, 2008). Halophytes represent a small group of plants of only about 600 species that belongs to a few genera and families, which have adapted to saline ecosystems under harsh environmental conditions, avoiding competition with glycophytes (Flowers et al, 1986)
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