Salinity effect on germination, seedling growth and cotyledon membrane complexes of a Portuguese salt marsh wild beet ecotype

Abstract

Sugar beet (Beta vulgaris L.) high yields have been achieved through irrigation and this crop is described as coping with mild salinity (40–120 mM NaCl). However, during seed germination, sugar beet is salinity sensitive and soil salinity should not exceed 3 dS/m. Wild beets, ancestors of sugar beet, are naturally able to germinate and grow in saline environments. Salinity tolerance during germination and early seedling development of three Portuguese wild beet ecotypes [Comporta (CMP), Oeiras (OEI), Vaiamonte (VMT)] and one sugar beet cultivar (Isella) was evaluated. Concerning germination, VMT outperformed all the other beets, with 98% (± 2%) of glomerules germinating in 200 mM NaCl after 14 days of scarification. However, in 500 mM NaCl, only CMP was able to initiate and maintain radicle emergence, though in a very small extension (< 3%). On the basis of the relative salinity tolerance index, CMP is the less affected by salinity, despite reduced seedling growth and biomass. Since cotyledons length and membrane proteins abundance were negatively affected by salinity, the hypothesis was raised that membranes functionality, including the photochemical multiprotein complexes, was compromised. To test this hypothesis, a blue-native two-dimensional electrophoresis was applied to CMP seedlings. In the cotyledonary leaves, complexes LC1 and LC4 and several components of LC2, LC5, LC6 complexes were negatively affected by salinity. The components of the complexes of photosystem I and ATP synthase were less abundant what points out to a lower cotyledon capacity for ATP synthesis and ferredoxin reduction. Lower availability of ATP and reduced ferredoxin imply reduced photosynthetic assimilation and, therefore, lower carbon availability for growth.