Endogenous polyamine content and photosynthetic performance under hypo-osmotic conditions reveal Cymodocea nodosa as an obligate halophyte

Abstract

Endogenous polyamine (PA) content in the seagrass Cymodocea nodosa was monitored at different embryo and seedling developmental stages. Total PA concentration, including putrescine (Put), spermidine (Spd) and spermine (Spm), and the Put (Spm + Spd) −1 ratio decreased during embryo development, from the immature fruit to the mature seed stage (with a sharp decline in the free PA fraction), and subsequently increased during germination and seedling development from the cotyledon to seedling stage, indicating an important role during zygotic embryogenesis and seed germination. In particular, total levels of Put and Spm significantly decreased from the fruit to the mature seed, to be restored after germination. Spd levels remained constant during all the developmental stages studied. When seedlings were subjected to hypoosmotic stress (i.e. salinity decrease from 36 to 5 psu), fluorescence levels decreased, reaching a minimum photochemical efficiency (F v /F m) at 5 psu (0.582 ± 0.025, mean ± SE), indicating that seedlings were under high stress. Contrary to expectations, this was followed by a slight decrease in total PA content (showing a significance difference between 5 psu and higher salinities in bound-insoluble PA) and the accumulation of the PA cadaverine (Cad) at 5 psu (indicating cell death), which revealed the inability of this species to face the abiotic stress promoted by long-term salinity decrease. These 2 physiological indicators may suggest that C. nodosa is an obligate halophyte because it requires an environment with relatively high and stable salinity for its survival. Moreover, exogenous application of Spd significantly improved F v /F m values at the lowest salinity treatment (5 psu: 0.670 ± 0.012), which suggests a protective role of Spd in maintaining the photosynthetic apparatus of C. nodosa seedlings under long-term hypo-osmotic stress.

Plant Growth Regulators Application Enhance Tolerance to Salinity and Benefit the Halophyte Plantago coronopus in Saline Agriculture

“…Few studies have ever examined PAs in other halophytes. In crops with high nutritional values such as quinoa ( Chenopodium quinoa ), PAs (especially, an increase in Spd and Spm under saline conditions) may be useful markers of salt-tolerant genotypes [ 55 , 56 ] and may exert a protective effect improving growth on Cymodocea nodosa [ 57 ] and Solanum chilense [ 58 ]. Specifically, exogenous application of Spd in C. nodosa improving chlorophyll fluorescence levels under different saline treatments, maintaining the photosynthetic apparatus functional, under long-term hypo-osmotic stress [ 57 ].…”

“…In crops with high nutritional values such as quinoa ( Chenopodium quinoa ), PAs (especially, an increase in Spd and Spm under saline conditions) may be useful markers of salt-tolerant genotypes [ 55 , 56 ] and may exert a protective effect improving growth on Cymodocea nodosa [ 57 ] and Solanum chilense [ 58 ]. Specifically, exogenous application of Spd in C. nodosa improving chlorophyll fluorescence levels under different saline treatments, maintaining the photosynthetic apparatus functional, under long-term hypo-osmotic stress [ 57 ]. Nevertheless, the positive effect of PAs may vary depending on the type of biotic and abiotic stress, plant species, time of exposure and physiological status of the tissues/organs [ 59 , 60 ], and therefore the effect of pretreatments must be studied in each halophyte.…”

Polyamines in Halophytes

“…In Cymodocea nodosa , a seagrass, PAs are distributed in all plant tissues, but mainly the apical section of the rhizome (Marián et al, 2000). Zarranz Elso et al (2012) showed a decline in PAs during embryo development (free PAs), and an increase during germination, indicating the key role of these growth regulators in the first steps of the zygotic and germination stages. Exogenous Spd helps improve Fv/Fm -values, exerting a protective role in maintaining the photosynthetic apparatus.…”