Lignocellulosic plants growing in marginal lands are receiving much attention as sustainable source for bioenergy and bioproducts, avoiding competition with cultivation of food and feed species. However, ideal candidates as industrial feedstock need to be able to survive to environmental stressors, without suffering a significant impact on growth and development. In temperate Mediterranean climates, Arundo donax (giant reed) is considered among the most promising crops for production of high value bio-products. In this regard, its capability to tolerate salt stress has been here investigated. Following a preliminary screening, three giant reed ecotypes were selected and further characterized in order to explore cellular signalling networks responsible of salt adaptation. Giant reed plants, propagated from reed cuttings, were carefully selected for their uniformity in order to reduce heterogeneity and grown in hydroponics, under controlled conditions, in a randomized design with 12-18 replicates for treatment. After three weeks, saline stress was imposed for 21 days by a three-step application of 150 mM NaCl (18.8 mS cm-1). Molecular and biochemical responses to salinity were evaluated after 48 h and 21 days of salt treatment. Since salinity tolerance is a physiologically multifaceted trait, we studied the transcriptional profile of several salt responsive genes in Arundo leaf tissues, namely delta 1-pyrroline-5-carboxylate synthase (P5CS), the rate limiting gene in the biosynthesis of the osmolyte proline; Dehydration-responsive element binding 2a, (DREB2A); Salt Overly Sensitive 1 (SOS); NAC and WRKY53 transcription factors; Sodium-proton exchanger (NHX) and High affinity K+ Transporter (HKT) as transporters. Interestingly, a significant induction of PC5S, SOS and DREB2A, along with a two-fold increase in NHX and HKT expression, was detected in the leaves of one ecotype during early response to salt treatment. Parallely, we measured the accumulation of proline, and of the phytohormone abscisic acid (ABA), which functions as a key regulator of plant adaptation mechanisms to salinity and drought. After 48 h of 150 mM NaCl treatment, proline content significantly increased in two ecotypes, while ABA leaf content was not affected compared to untreated samples. A. donax stress response was also evaluated by biometric (shoot and root growth) and physiological (chlorophyll content) measurements after 21 days of stress treatment. The most significantly affected growth parameters of the aerial part of the plants were shoot fresh weight, culm length and leaf number, comparing with unstressed plants, while the fourth leaf width was not affected. As far as root development, salinity stress mainly increased root FW and main root length, although not always significantly. Chlorophyll content seemed not to be negatively affected by salt and even a slight increase was detected in one ecotype. Albeit some differences were detected between ecotypes, taken together our results suggest possible mechanisms underlying salt resilience in A. donax.
MODULATION OF SALT STRESS TOLERANCE IN ARUNDO DONAX
DE STEFANO R;DOCIMO T;DE PALMA M;TUCCI M
2016
Abstract
Lignocellulosic plants growing in marginal lands are receiving much attention as sustainable source for bioenergy and bioproducts, avoiding competition with cultivation of food and feed species. However, ideal candidates as industrial feedstock need to be able to survive to environmental stressors, without suffering a significant impact on growth and development. In temperate Mediterranean climates, Arundo donax (giant reed) is considered among the most promising crops for production of high value bio-products. In this regard, its capability to tolerate salt stress has been here investigated. Following a preliminary screening, three giant reed ecotypes were selected and further characterized in order to explore cellular signalling networks responsible of salt adaptation. Giant reed plants, propagated from reed cuttings, were carefully selected for their uniformity in order to reduce heterogeneity and grown in hydroponics, under controlled conditions, in a randomized design with 12-18 replicates for treatment. After three weeks, saline stress was imposed for 21 days by a three-step application of 150 mM NaCl (18.8 mS cm-1). Molecular and biochemical responses to salinity were evaluated after 48 h and 21 days of salt treatment. Since salinity tolerance is a physiologically multifaceted trait, we studied the transcriptional profile of several salt responsive genes in Arundo leaf tissues, namely delta 1-pyrroline-5-carboxylate synthase (P5CS), the rate limiting gene in the biosynthesis of the osmolyte proline; Dehydration-responsive element binding 2a, (DREB2A); Salt Overly Sensitive 1 (SOS); NAC and WRKY53 transcription factors; Sodium-proton exchanger (NHX) and High affinity K+ Transporter (HKT) as transporters. Interestingly, a significant induction of PC5S, SOS and DREB2A, along with a two-fold increase in NHX and HKT expression, was detected in the leaves of one ecotype during early response to salt treatment. Parallely, we measured the accumulation of proline, and of the phytohormone abscisic acid (ABA), which functions as a key regulator of plant adaptation mechanisms to salinity and drought. After 48 h of 150 mM NaCl treatment, proline content significantly increased in two ecotypes, while ABA leaf content was not affected compared to untreated samples. A. donax stress response was also evaluated by biometric (shoot and root growth) and physiological (chlorophyll content) measurements after 21 days of stress treatment. The most significantly affected growth parameters of the aerial part of the plants were shoot fresh weight, culm length and leaf number, comparing with unstressed plants, while the fourth leaf width was not affected. As far as root development, salinity stress mainly increased root FW and main root length, although not always significantly. Chlorophyll content seemed not to be negatively affected by salt and even a slight increase was detected in one ecotype. Albeit some differences were detected between ecotypes, taken together our results suggest possible mechanisms underlying salt resilience in A. donax.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
