Conformational Consequences for Compatible Osmolytes on Thermal Denaturation

Compatible osmolytes are a broad class of small organic molecules employed by living systems to combat environmental stress by enhancing the native protein structure. The molecular features that make for a superior biopreservation remain elusive. Through the use of time-resolved and steady-state spectroscopic techniques, in combination with molecular simulation, insight into what makes one molecule a more effective compatible osmolyte can be gained. Disaccharides differing only in their glycosidic bonds can exhibit different degrees of stabilization against thermal denaturation. The degree to which each sugar is preferentially excluded may explain these differences. The present work examines the biopreservation and hydration of trehalose, maltose, and gentiobiose.

Salinity Duration Differently Modulates Physiological Parameters and Metabolites Profile in Roots of Two Contrasting Barley Genotypes

Hordeum maritimum With. is a wild salt tolerant cereal present in the saline depressions of the Eastern Tunisia, where it significantly contributes to the annual biomass production. In a previous study on shoot tissues it was shown that this species withstands with high salinity at the seedling stage restricting the sodium entry into shoot and modulating over time the leaf synthesis of organic osmolytes for osmotic adjustment. However, the tolerance strategy mechanisms of this plant at root level have not yet been investigated. The current research aimed at elucidating the morphological, physiological and biochemical changes occurring at root level in H. maritimum and in the salt sensitive cultivar Hordeum vulgare L. cv. Lamsi during five-weeks extended salinity (200 mM NaCl), salt removal after two weeks of salinity and non-salt control. H. maritimum since the first phases of salinity was able to compartmentalize higher amounts of sodium in the roots compared to the other cultivar, avoiding transferring it to shoot and impairing photosynthetic metabolism. This allowed the roots of wild plants to receive recent photosynthates from leaves, gaining from them energy and carbon skeletons to compartmentalize toxic ions in the vacuoles, synthesize and accumulate organic osmolytes, control ion and water homeostasis and re-establish the ability of root to grow. H. vulgare was also able to accumulate compatible osmolytes but only in the first weeks of salinity, while soon after the roots stopped up taking potassium and growing. In the last week of salinity stress, the wild species further increased the root to shoot ratio to enhance the root retention of toxic ions and consequently delaying the damages both to shoot and root. This delay of few weeks in showing the symptoms of stress may be pivotal for enabling the survival of the wild species when soil salinity is transient and not permanent.

Tolerance in Maize Landraces to Diabrotica speciosa (Coleoptera: Chrysomelidae) Larvae and Its Relationship to Plant Pigments, Compatible Osmolytes, and Vigor

The rootworm Diabrotica speciosa (Germar) is native to South America and causes severe economic losses to several crops due to root feeding and disease spread. In maize (Zea mays L.), losses in production come from larval rootworm attack on plant roots resulting in plant health problems, including stalk lodging. More options for controlling this pest are needed to create well balanced, integrated pest management programs for farmers in this region. Natural sources of tolerance in maize genotypes are important for maize breeding programs, and this study investigated the expression of tolerance in several Brazilian maize landraces to D. speciosa. Plant vigor and compounds associated with plant health, including chlorophylls, carotenoids, glycine betaine, and proline were assessed for each landrace. Five landraces and one maize cultivar were selected based on their levels of antibiosis-resistance to D. speciosa that were determined in a prior screening. The percent reduction in plant growth was used as the measure of tolerance. The landrace Azteca was classified as tolerant to D. speciosa larval feeding, displaying less reduction in plant matter despite having lower plant vigor. This landrace also had higher amounts of chlorophyl and carotenoid pigments, suggesting a positive correlation between tolerance to D. speciosa and higher contents of these photosynthetic pigments. The compatible osmolytes glycine betaine and proline do not seem to be associated with tolerance in maize landraces to D. speciosa larvae. Landrace Azteca seems promising for plant breeding, and repeated field studies are needed to confirm its suitability in maize integrated pest management.

Impact of Drought on Soluble Sugars and Free Proline Content in Selected Arabidopsis Mutants

Water shortage is an increasing problem affecting crop yield. Accumulation of compatible osmolytes is a typical plant response to overcome water stress. Sucrose synthase 1 (SUS1), and glucan, water dikinase 2 (GWD2) and δ1-pyrroline-5-carboxylate synthetase 1 (P5CS1) are members of small protein families whose role in the response of Arabidopsis thaliana plants to mild osmotic stress has been studied in this work. Comparative analysis between wild-type and single loss-of-function T-DNA plants at increasing times following exposure to drought showed no differences in the content of water-insoluble carbohydrate (i.e., transitory starch and cell wall carbohydrates) and in the total amount of amino acids. On the contrary, water-soluble sugars and proline contents were significantly reduced compared to wild-type plants regardless of the metabolic pathway affected by the mutation. The present results contribute to assigning a physiological role to GWD2, the least studied member of the GWD family; strengthening the involvement of SUS1 in the response to osmotic stress; showing a greater contribution of soluble sugars than proline in osmotic adjustment of Arabidopsis in response to drought. Finally, an interaction between proline and soluble sugars emerged, albeit its nature remains speculative and further investigations will be required for complete comprehension.

Individual and concurrent effects of drought and chilling stresses on morpho-physiological characteristics and oxidative metabolism of maize cultivars

Maize belongs to tropical environment and is extremely sensitive to drought and chilling stress, particularly at early developmental stages. The present study investigated the individual and combine effects of drought (15% PEG-Solution) and chilling stress (15°C/12°C) on the morpho-physiological growth, osmolyte accumulation, production and regulations of reactive oxygen species (ROS) and the activities of antioxidants in two maize hybrids i.e., ‘XD889’ and ‘XD319’ and two inbred cultivars i.e., ‘Yu13’ and ‘Yu37’. Individual and combined drought and chilling stresses stimulated the production of O2□, H2O2, OH□ and enhanced malondialdehyde (MDA) contents which led to reduced photosynthetic pigments and morphological growth. Drought, chilling and drought + chilling stress conditions induced the compatible osmolytes, ROS detoxifying proteins and antioxidants to counterbalanced the oxidative damage. It was found that the concurrent occurrence of drought + chilling stress was more lethal for maize seedling growth than the drought and chilling individual stresses. However, the performance of hybrid maize cultivars (XD889 and XD319) was better than the inbred maize cultivars (Yu13 and Yu37). For improving tolerance to individual and concurrent drought and chilling stress in maize, future research focus should be on developing genetically engineer plants that have the ability to generate specific response against sub-optimal temperature and water deficit conditions.

Contribution of Glycine Betaine and Proline to Water Deficit Tolerance in Pepper Plants

Water stress is the main factor responsible for decreased productivity, which affects the growth and development of crops. Plants respond to stress by accumulating compatible solutes, which have a key role in osmotic adjustment, thereby resulting in osmoprotection of the plants. The loss of water can increase the concentration of compatible osmolytes and molecules that regulate the plant metabolism. These solutes can be metabolized as sugars (sucrose, fructose, trehalosa), amino acids (proline), an amphoteric quaternary amine (glycine betaine), and other low-molecular-weight metabolites. However, among all these compatible solutes, proline and glycine betaine occur the most. Proline is an amino acid that can accumulate in low concentrations under optimal conditions; however, stress conditions contribute to its increased content. Few data are available regarding the levels of endogenous glycine betaine on Solanaceae, which is considered a nonaccumulator under water deficit conditions. The objective of this research was to evaluate the role of compatible osmolytes, glycine betaine and proline, in Capsicum sp. plants under different water deficit conditions. In this study, the presence of endogenous levels of proline and glycine betaine in two species of pepper (Capsicum chinense var. Genesis and Rex and Capsicum annuum var. Padron) were found. The concentration levels of proline were 362, 292, and 246 μmol·g−1 DW for Genesis, Rex and Padron respectively, and irrigation conditions (rehydration) of proline levels increased to 381, 395, and 383 μmol·g−1 DW at 21 days. However, glycine betaine levels were 30–70 μmol·g−1 DW. The relative water content, electrolyte leakage, and soil water potential were also analyzed; therefore, the information suggests that proline contributes better to tolerance to water deficit in the genus Capsicum after 14 days of water deficit treatment. It seems that the contribution of glycine betaine is less effective than that of proline; therefore, it does not have an important role in osmotic adjustment.