Statistical Databases

This review deals with the adaptive mechanisms that plants can implement to cope with the challenge of salt stress. Plants tolerant to NaCl implement a series of adaptations to acclimate to salinity, including morphological, physiological and biochemical changes. These changes include increases in the root/canopy ratio and in the chlorophyll content in addition to changes in the leaf anatomy that ultimately lead to preventing leaf ion toxicity, thus maintaining the water status in order to limit water loss and protect the photosynthesis process. Furthermore, we deal with the effect of salt stress on photosynthesis and chlorophyll fluorescence and some of the mechanisms thought to protect the photosynthetic machinery, including the xanthophyll cycle, photorespiration pathway, and water-water cycle. Finally, we also provide an updated discussion on salt-induced oxidative stress at the subcellular level and its effect on the antioxidant machinery in both salt-tolerant and salt-sensitive plants. The aim is to extend our understanding of how salinity may affect the physiological characteristics of plants.

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Plant Responses to Salt Stress: Adaptive Mechanisms

Phenolic compounds are a large group of phytochemicals widespread in the plant kingdom. Depending on their structure they can be classified into simple phenols, phenolic acids, hydroxycinnamic acid derivatives and flavonoids. Phenolic compounds have received considerable attention for being potentially protective factors against cancer and heart diseases, in part because of their potent antioxidative properties and their ubiquity in a wide range of commonly consumed foods of plant origin. The Brassicaceae family includes a wide range of horticultural crops, some of them with economic significance and extensively used in the diet throughout the world. The phenolic composition of Brassica vegetables has been recently investigated and, nowadays, the profile of different Brassica species is well established. Here, we review the significance of phenolic compounds as a source of beneficial compounds for human health and the influence of environmental conditions and processing mechanisms on the phenolic composition of Brassica vegetables.

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Phenolic compounds in Brassica vegetables.

Some important physiological selection criteria for salt tolerance in plants

Evaluating physiological responses of plants to salinity stress

The role of plant hormones under saline stress is critical in modulating physiological responses that will eventually lead to adaptation to an unfavorable environment. Nevertheless, the functional level of plant hormones, and their relative tissue concentration, may have a different impact on plant growth and stress tolerance at increasing salinity of the root environment. Vigorous plant growth may counteract the negative effects of salinization. In contrast, low gibberellin (GA) levels have been associated with reduced growth in response to salinity. Based on these facts and considering that the physiological basis of the cause-effect relationship between functional growth control and stress adaptation/survival is still a matter of debate, we hypothesized that exogenous applications of the plant hormone GA3 may compensate for the salt-induced growth deficiency and consequently facilitate tomato plant adaptation to a saline environment. GA3 application (0 or 100 mg GA3 l−1) was compared under four salinity levels, obtained by adding equal increments of NaCl:CaCl2 (2:1 molar basis) (EC = 2.5, 6.8, 11.7, 16.7 dS m−1) to the nutrient solution. GA3 treatment reduced stomatal resistance and enhanced plant water use at low salinity. These responses were associated with an increased number of fruit per plant at harvest. However, moderate and high salinity nullified these differences. The fruit carotenoid level was generally lower in GA3-treated plants, indicating either an inhibitory effect of GA3 treatment on carotenoid biosynthesis or a reduced perception of the stress environment by GA3-treated tomato plants.

Contrasting effects of GA3 treatments on tomato plants exposed to increasing salinity.

Nutritional quality of ten leafy vegetables harvested at two light intensities.

Growth, yield and essential oil content of three cultivars of basil grown under different levels of nitrogen in the field

Physiological response of tomato to saline irrigation in long-term salinized soils.

Production of vegetable crops can be limited by saline irrigation water. The variability of crop salt tolerance under different environmental conditions requires species-specific and environment-specific field evaluations of salt tolerance. Data on field performances of vegetable crops grown on soils that have been irrigated with saline water for many years are lacking. In this study we analyzed the long-term effect of irrigation with saline water on soil properties and on responses of field-grown pepper (Capsicum annuum L.) plants in these soils. Yield, gas exchanges, water relations, and solute accumula- tion were measured in plants grown under three different irrigation treatments: a nonsalinized control (ECw = 0.5 dS·m -1 ) and two concentrations of commercial sea salt, corresponding to ECw of 4.4 and 8.5 dS·m -1 , respectively. In addition, a nonwatered drought stress treatment was included. Irrigation water with an EC of 4.4 dS·m -1 resulted in 46% reduction in plant dry weight (leaves plus stem) and 25% reduction in marketable yield. Increasing the electrical conductivity of the irrigation water to 8.5 dS·m -1 caused a 34% reduction in plant dry weight and a 58% reduction in marketable yield. Leaf and root cellular turgor and net CO2 assimilation rates of leaves in salt-stressed plants decreased along with a reduction in leaf area and dry matter accumulation. High concentrations of Na + and Cl - in the irrigation water did not significantly alter the level of K + in leaves and fruit. In contrast, drought stressed plants had higher concentrations of leaf K + compared to well watered control plants. These results indicate that Na + and K + may play similar roles in maintaining cellular turgor under salinity and drought stress, respectively. The regulation of ion loading to the shoots was most likely functionally associated with physiological modifications of the root/shoot ratio that was substantially smaller in salinized vs. drought stressed plants. From an agronomic perspective, irrigation with moderately saline water (4.4 dS·m -1 ) it is recommendable, compared to no irrigation, to obtain an acceptable marketable yield in the specific environment considered.

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Giancarlo Barbieri

Papers

Contrasting effects of GA3 treatments on tomato plants exposed to increasing salinity.

Nutritional quality of ten leafy vegetables harvested at two light intensities.

Growth, yield and essential oil content of three cultivars of basil grown under different levels of nitrogen in the field

Physiological response of tomato to saline irrigation in long-term salinized soils.

Physiological Responses of Pepper to Salinity and Drought