Gradual Exposure to Salinity Improves Tolerance to Salt Stress in Rapeseed (Brassica napus L.)

Abstract

Soil salinity is considered one of the most severe abiotic stresses in plants; plant acclimation to salinity could be a tool to improve salt tolerance even in a sensitive genotype. In this work we investigated the physiological mechanisms underneath the response to gradual and prolonged exposure to sodium chloride in cultivars of Brassica napus L. Fifteen days old seedlings of the cultivars Dynastie (salt tolerant) and SY Saveo (salt sensitive) were progressively exposed to increasing soil salinity conditions for 60 days. Salt exposed plants of both cultivars showed reductions of biomass, size and number of leaves. However, after 60 days the relative reduction in biomass was lower in sensitive cultivar as compared to tolerant ones. An increase of chlorophylls content was detected in both cultivars; the values of the quantum efficiency of PSII photochemistry (ΦPSII) and those of the electron transport rate (ETR) indicated that the photochemical activity was only partially reduced by NaCl treatments in both cultivars. Ascorbate peroxidase (APX) activity was higher in treated samples with respect to the controls, indicating its activation following salt exposure, and confirming its involvement in salt stress response. A gradual exposure to salt could elicit different salt stress responses, thus preserving plant vitality and conferring a certain degree of tolerance, even though the genotype was salt sensitive at the seed germination stage. An improvement of salt tolerance in B. napus could be obtained by acclimation to saline conditions. are considered the ions mainly responsible for the salinization, reaching concentration that can inhibit or decrease the development of plants [1][2][3][4]. Leaves accumulate most of the excess of Na + and Cl − absorbed at the roots level, and this accumulation causes an early senescence, associated with more or less marked chlorosis and/or necrosis phenomena, depending on the accumulation rate of these ions and the capacity to compartmentalize them. The effect of salinity on leaves can be either direct, due to the closure of the stomata and the consequent reduction in the rate of assimilation of CO 2 [5], or secondary; due to oxidative stress, which can seriously affect leaf photosynthetic machinery. Besides this, the intracellular accumulation of Na + changes the ratio of K + /Na + and may lead to an osmotic imbalance and the production of Reactive Oxygen Species (ROS), which seems to affect the function of some enzymes, and the amounts of photosynthetic pigments [6]. Oxidative stress, caused by ROS overproduction, is the main cause of loss in productivity of the cultivated species [7].The salt tolerance mechanism is a multigenic trait involving different biochemical pathways: i.e., control of ion uptake by roots and transport into leaves, synthesis of compatible solutes, change in photosynthetic pathway, induction of antioxidant enzymes as well as the synthesis of hormones. The stress response depends to a different extent on both genotypes and developmental stages of the plants; ...

Enhancement of Brassica napus Tolerance to High Saline Conditions by Seed Priming

“…In the literature, NaCl is the most common priming agent [ 16 , 17 , 18 ], able to increase seed germination rate in salt-stressed plants. PAs have been also tested; in plant, PA activity is involved in several growth stages and development, as well as in the responses to biotic and abiotic stresses [ 5 , 19 ]. An essential role has been attributed to SPD for the survival of Arabidopsis embryos, whilst SPM plays a role in stress responses [ 20 ].…”

“…Several tools, such as acclimation [ 5 ] and seed priming [ 6 ], and the use of plant growth-promoting bacteria (PGPB) [ 3 , 7 , 8 ] can be utilized to improve plant salt stress tolerance and represent promising strategies. Seed priming is a pre-sowing treatment, consisting of the soaking of the seeds in a priming agent, acting as an elicitor, for a specific period, followed by drying the seeds to avoid radicle emergence.…”

“…The aim of this work was to seek the possibility to improve salinity tolerance in rapeseed cultivars exposed to high salinity, by evaluating the effectiveness of chemical seed priming as a tool to ameliorate plant survival and fitness. Based on previous results [ 5 ] and preliminary tests, three rapeseed cultivars with different levels of tolerance/sensitivity to salt have been selected, i.e., SY Saveo (sensitive), Edimax CI (intermediate tolerant) and Dynastie (tolerant). Four different priming agents were applied to the seeds 2.5 mM spermine (SPM), 5 mM spermidine (SPD), 40 mM NaCl and 2.5 mM Ca (NO 3 ) 2 in order to determine the most effective ones.…”

Trichoderma parareesei Favors the Tolerance of Rapeseed (Brassica napus L.) to Salinity and Drought Due to a Chorismate Mutase

“…In this sense, little is known about the transcriptomic changes that occur in rapeseed in response to abiotic stress-particularly salinity and drought [38]. In spite of this, it has been observed how salinity stress provokes an inhibition of seed germination and seedling establishment in rapeseed [39], as well as a reduction in biomass, size, and number of leaves, but not in photochemical activity [40]. Moreover, the way in which drought stress significantly inhibited germination and seedling growth led to oxidative stress from excessive H 2 O 2 generation and reduced the chlorophyll content [41], resulting in growth inhibition, oil content reduction, and yield loss during the reproductive stage [42].…”

Evaluation of Multiple Responses Associated with Arsenic Tolerance and Accumulation in Pteris vittata L. Plants Exposed to High As Concentrations under Hydroponics

“…In this context, analysis of chlorophyll fluorescence represents a useful tool for evaluating plant tolerance to pollutants, since it provides an estimation of the photosynthetic activity in a non-destructive way [29]. Moreover, the use of chlorophyll fluorescence imaging allows the evaluation of the heterogeneity in photosynthetic functions throughout a leaf by image analysis of the quantum efficiency of photosystem II (PSII) in plants subjected to several stresses, including heavy metals [30][31][32][33], salinity stress [34], pharmaceuticals [35,36], and emerging contaminants [37].…”