Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy

Integrated Transcriptomic and Metabolomics Analysis of the Root Responses of Orchardgrass to Submergence Stress

Submergence stress can severely affect plant growth. Orchardgrass (Dactylis glomerata L.) is an important forage grass, and the molecular mechanisms of orchardgrass to submergence stress are not well understood. The roots of the flood-tolerant cultivar "Dian Bei" were harvested at 0 h, 8 h and 24 h of submergence stress. The combined transcriptomic and metabolomic analyses showed that β-alanine metabolism, flavonoid biosynthesis, and biosynthesis of amino acid pathways were significantly enriched at 8 h and 24 h of submergence stress and were more pronounced at 24 h. Most of the flavonoid biosynthesis-related genes were down-regulated for the synthesis of metabolites such as naringenin, apigenin, naringin, neohesperidin, naringenin chalcone, and liquiritigenin in response to submergence stress. Metabolites such as phenylalanine, tyrosine, and tryptophan were up-regulated under stress. The predominant response of flavonoid and amino acids biosynthesis to submergence stress suggests an important role of these pathways in the submergence tolerance of orchardgrass.

Metabolomic Study of Dactylis glomerata Growing on Aeolian Archipelago (Italy)

The Aeolian Islands (Italy) are a volcanic archipelago in the Tyrrhenian Sea comprising seven main islands, among which are two active volcanoes. The peculiar geological features and the wide variety of environments and soils have an important impact on native plants, and in particular, the Aeolian populations of Dactylis glomerata (a perennial cool-season bunchgrass) exhibit remarkable phenotypic variability. Considering that environmental drivers also strongly affect the production of plant metabolites, this work aimed at comparing the metabolomic profiles of D. glomerata (leaves) harvested at different altitudes on four islands of the Aeolian archipelago, namely: Lipari, Vulcano, Stromboli and Panarea. Samples were analyzed by ¹H NMR profiling, and data were treated by PCA. Samples collected on Stromboli were very different from each other and from the samples collected in the other islands. Through an Orthogonal Partial Least Squares (OPLS) model, using altitude as the y variable, it emerged that the concentration of proline, glycine betaine, sucrose, glucose and chlorogenic acid of D. glomerata growing on Stromboli decreased at increasing altitude. Conversely, increasing altitude was associated with an increment in valine, asparagine, fumaric acid and phenylalanine.

Allelopathic interaction between two common meadow plants: Dactylis glomerata L. and Trifolium pratense L

Under natural conditions, plants compete for environmental resources, including by the release of allelopathic compounds with a various spectrum of activity. Therefore, the effect of aqueous extracts of cock’s-foot Dactylis glomerata L. on germination and early growth phases and electrolyte leakages of a red clover Trifolium pratense L. was investigated. The 5, 10, and 15% of the aqueous extracts of cock’s-foot separately from shoots and inflorescences were used in two type of treatments tested in parallel. In first treatment the red clover seeds were watered directly with the aqueous extracts by eight days of experiment time, in second the seeds were pretreated with extracts for 24, 48 and 72 h and next they were watered with distilled water during experiment time. The results showed that the germination capacity of red clover seeds decreased with increasing concentrations of cock’s-foot aqueous extracts. Regardless of the duration of seed treatment with the extracts, the highest inhibition of germination was found when the 15% cock’s-foot shoot extracts was used. For red clover seedlings pretreated with extracts for 72 h, the highest and statistically significant differences in the growth were observed. With the increasing of concentration of cock’s-foot extracts significant inhibition of the underground and aboveground organs growth were observed. The increase of fresh and dry masses of red clover seedlings varied depending on the duration of contact with the extracts and their concentrations. The electrolyte leakage, as compared to the control, increased with the concentration of extracts, regardless of types and duration of extracts. The obtained results clearly confirm that leaving biomass of cock’s-foot on the field can lead to the release of phytotoxins that may inhibit germination and growth of red clover.

Are winter and summer dormancy symmetrical seasonal adaptive strategies? The case of temperate herbaceous perennials

BACKGROUND

Dormancy in higher plants is an adaptive response enabling plant survival during the harshest seasons and has been more explored in woody species than in herbaceous species. Nevertheless, winter and summer shoot meristem dormancy are adaptive strategies that could play a major role in enhancing seasonal stress tolerance and resilience of widespread herbaceous plant communities.

SCOPE

This review outlines the symmetrical aspects of winter and summer dormancy in order to better understand plant adaptation to severe stress, and highlight research priorities in a changing climate. Seasonal dormancy is a good model to explore the growth-stress survival trade-off and unravel the relationships between growth potential and stress hardiness. Although photoperiod and temperature are known to play a crucial, though reversed, role in the induction and release of both types of dormancy, the thresholds and combined effects of these environmental factors remain to be identified. The biochemical compounds involved in induction or release in winter dormancy (abscisic acid, ethylene, sugars, cytokinins and gibberellins) could be a priority research focus for summer dormancy. To address these research priorities, herbaceous species, being more tractable than woody species, are excellent model plants for which both summer and winter dormancy have been clearly identified.

CONCLUSIONS

Summer and winter dormancy, although responding to inverse conditions, share many characteristics. This analogous nature can facilitate research as well as lead to insight into plant adaptations to extreme conditions and the evolution of phenological patterns of species and communities under climate change. The development of phenotypes showing reduced winter and/or enhanced summer dormancy may be expected and could improve adaptation to less predictable environmental stresses correlated with future climates. To this end, it is suggested to explore the inter- and intraspecific genotypic variability of dormancy and its plasticity according to environmental conditions to contribute to predicting and mitigating global warming.

Effect of HbDHN1 and HbDHN2 Genes on Abiotic Stress Responses in Arabidopsis

Dehydrin is a type of late embryogenesis abundant (LEA) protein. The dehydrin genes, HbDHN1 and HbDHN2, in Hevea brasiliensis were previously found to be induced at the wounding site of epicormic shoots, with local tissue dehydration identified as the key signal for laticifer differentiation. However, the exact role of the HbDHNs remains unknown. In this study, HbDHN1 and HbDHN2 expression was examined under multiple abiotic stresses; namely, cold, salt, drought, wounding, abscisic acid (ABA), ethylene (ET), and jasmonic acid (JA) treatment. Although, both HbDHNs were defined as SK2-type dehydrin, they showed different cellular localizations. Overexpression of the HbDHNs in Arabidopsis thaliana further revealed a significant increase in tolerance to salt, drought and osmotic stresses. Increased accumulation of proline and a reduction in electrolyte leakage were also observed under salt and drought stress, and a higher water content was indicated under osmotic stress. The transgenic plants also showed higher activity levels of ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase, and accumulated less hydrogen peroxide (H₂O₂) and superoxide ([Formula: see text]). Given that reactive oxygen species (ROS) are thought to be a key signal for laticifer differentiation, these findings suggest that HbDHNs act as ROS scavengers, directly or indirectly affecting laticifer differentiation. Both HbDHNs therefore influence physiological processes, improving plant tolerance to multiple abiotic stresses.

Any trait or trait-related allele can confer drought tolerance: just design the right drought scenario

Most traits associated with drought tolerance have a dual effect, positive in very severe scenarios and negative in milder scenarios, or the opposite trend. Their effects also depend on other climatic conditions such as evaporative demand or light, and on management practices. This is the case for processes associated with cell protection and with avoidance, but also for the maintenance of growth or photosynthesis, high water use efficiency, large root systems or reduced abortion rate under water deficit. Therefore, spectacular results obtained in one drought scenario may have a limited interest for improving food security in other geographical areas with water scarcity. The most relevant questions on drought tolerance are probably, 'Does a given allele confer a positive effect on yield in an appreciable proportion of years/scenarios in a given area or target population of environment (TPE)?'; 'In a given site or TPE, what is the trade-off between risk avoidance and maintained performance?'; and 'Will a given allele or trait have an increasingly positive effect with climate change?' Considerable progress has already occurred in drought tolerance. Nevertheless, explicitly associating traits for tolerance to drought scenarios may have profound consequences on the genetic strategies, with a necessary involvement of modelling.

Differential accumulation of dehydrins in response to water stress for hybrid and common bermudagrass genotypes differing in drought tolerance

Expression of dehydrin proteins may be induced or enhanced by environmental stresses that lead to cell dehydration. The objective of the this study was to investigate genetic variation in dehydrin protein accumulation in response to drought stress of whole-plants or dehydration of detached leaves and to identify dehydrins differentially expressed in bermudagrass (Cynodon spp.) genotypes differing in drought tolerance. Plants of four hybrid bermudagrass (Cynodondactylon L. xCynodontransvaalensis L.) ('Tifway', 'Tifdwarf', 'Tifeagle', 'Kan1') and four common bermudagrass (Cynodon dactylon) ('C299', 'Sportbermuda', 'H10', and 'H19') genotypes were subjected to 14d of drought stress and detached leaves of two genotypes were exposed to dehydration in growth chambers. Turf quality and leaf relative water content (RWC) decreased while electrolyte leakage (EL) increased during whole-plant drought stress for all genotypes, with more pronounced changes in each parameter for 'C299' and 'Tifeagle' than those for other genotypes ('Tifway', 'Kan 1', 'Sportbermuda', 'H10', and H19'), suggesting that the former two genotypes were more sensitive to drought stress than the other genotypes. During dehydration of detached leaves, relative water loss rate (RWL) was significantly lower in drought-tolerant 'Tifway' than in drought-sensitive 'C299'. Immunoblotting analysis indicated that no dehydrin polypeptides were detected in all genotypes under well-watered conditions. A 24-kDa polypeptide was detected in 'C299' at 6 d of drought, but not in the other genotypes. The dehydrin polypeptides of about 14-74kDa accumulated at 10d of drought stress and in a range of RWL for detached leaves, and two dehydrins (31 and 40kDa) exhibited differential accumulation in the drought-sensitive 'C299' and tolerant 'Tifway', as demonstrated by the whole-plant drought responses. The 31-kDa dehydrin polypeptide was present only in 'Tifway' and 'H19' at 10d of drought stress, and accumulated with the increasing RWL in detached leaves of 'Tifway'. The expression level of 40-kDa dehydrin polypeptides was greater in 'Tifway'' than in 'C299' at the same level of water deficit (from 10% to 65% RWL). These results indicated that the accumulation of 31- and 40-kDa dehydrins may contribute to drought or dehydration tolerance in warm-season bermudagrass.

Water deficit and induction of summer dormancy in perennial Mediterranean grasses

BACKGROUND AND AIMS

Summer dormancy is a trait conferring superior drought survival in Mediterranean perennial grasses. As the respective roles of environmental factors and water deficit on induction of summer dormancy are unclear, the effect of intense drought were tested under contrasting day lengths in a range of forage and native grasses.

METHODS

Plants of Poa bulbosa, Dactylis glomerata 'Kasbah' and Lolium arundinaceum 'Flecha' were grown in pots (a) from winter to summer in a glasshouse and subjected to either an early or a late-spring drought period followed by a summer water deficit and (b) in controlled conditions, with long days (LD, 16 h) or short days (SD, 9 h) and either full irrigation or water deficit followed by rehydration. Leaf elongation, senescence of aerial tissues and dehydration of basal tissues were measured to assess dormancy. Endogenous abscisic acid (ABA) in basal tissues was determined by monoclonal immunoassay analysis.

KEY RESULTS

Even under irrigation, cessation of leaf elongation, senescence of lamina and relative dehydration of basal tissues were triggered only by a day length longer than 13 h 30 min (late spring and LD) in plants of Poa bulbosa and Dactylis glomerata 'Kasbah' which exhibit complete dormancy. Plants of Lolium arundinaceum 'Flecha' maintained leaf growth under irrigation irrespective of the day length since its dormancy is incomplete. ABA concentrations were not higher during late-spring drought than early, and could not be associated with spring dormancy induction. In summer, ABA concentration in bulbs of the desiccation-tolerant Poa were greater than in basal tissues of other species.

CONCLUSIONS

The results of both experiments tend to invalidate the hypothesis that water deficit has a role in early summer-dormancy induction in the range of tested grasses. However, a late-spring drought tends to increase plant senescence and ABA accumulation in basal tissues of forage grasses which could enhance summer drought survival.

Measurement of summer dormancy in temperate perennial pasture grasses

The search to improve drought survival in temperate perennial grasses has led to a renewed interest in summer dormancy and how to quantify it. This endogenously controlled trait, found in some temperate perennial grasses, is associated with drought that normally occurs in summer. While cessation of leaf growth and senescence of herbage occurs in all grasses in response to drought, it is under summer irrigation that these same responses are observed only in summer-dormant germplasm and hence the trait can be identified in germplasm. Across the spectrum from completely summer-dormant to non-dormant, there is a range of expression. Our objective here is to highlight differences in characteristics of indices which measure summer dormancy and to identify aspects for incorporation into a superior index for use in measuring this trait. The experimental program comprised three field trials that compared 6 cultivars and a fourth that assessed a larger group of 12 cultivars of the same three species, cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), and phalaris (Phalaris aquatica L.). Seasonal herbage yield and foliage senescence were measured under three summer watering regimes: complete drought, mid-summer storm, and full irrigation at Mauguio, France. Different indices were calculated to compare against the approach which evaluates senescence under drought. The key outcomes are as follows. (1) The assessment of summer dormancy needs to be viewed as the plant response to a period of non-limiting water supply over summer. It makes little difference whether this is produced by full summer irrigation or a mid-summer simulated storm after a drought. Assessment of this trait under conditions of unbroken drought is discouraged because it can result in false scores. (2) The determination of summer dormancy intensity under full summer irrigation is most appropriate for the intensive study of the dynamics of dormancy expression over the entire summer. A simulated mid-summer storm within a drought gives an instantaneous view of dormancy intensity at a specific observation date and may be well adapted to the requirements of plant breeding. These methods are complementary. (3) Summer dormancy intensity can be assessed either by measuring herbage production or by a visual assessment of the level of herbage senescence. (4) An index of summer dormancy based on comparing irrigated summer herbage yield of any cultivar with that of a high, summer-yielding, non-dormant control cultivar was able to provide a reliable score of dormancy intensity. This index functions across a range of cultivars and species of perennial grasses. Further refinement of the index is needed to identify ‘standard’ high and low summer-dormant populations.

Summer dormancy in perennial temperate grasses

BACKGROUND AND AIMS

Dormancy has been extensively studied in plants which experience severe winter conditions but much less so in perennial herbaceous plants that must survive summer drought. This paper reviews the current knowledge on summer dormancy in both native and cultivated perennial temperate grasses originating from the Mediterranean Basin, and presents a unified terminology to describe this trait.

SCOPE

Under severe drought, it is difficult to separate the responses by which plants avoid and tolerate dehydration from those associated with the expression of summer dormancy. Consequently, this type of endogenous (endo-) dormancy can be tested only in plants that are not subjected to moisture deficit. Summer dormancy can be defined by four criteria, one of which is considered optional: (1) reduction or cessation of leaf production and expansion; (2) senescence of mature foliage; (3) dehydration of surviving organs; and (4, optional) formation of resting organs. The proposed terminology recognizes two levels of summer dormancy: (a) complete dormancy, when cessation of growth is associated with full senescence of foliage and induced dehydration of leaf bases; and (b) incomplete dormancy, when leaf growth is partially inhibited and is associated with moderate levels of foliage senescence. Summer dormancy is expressed under increasing photoperiod and temperature. It is under hormonal control and usually associated with flowering and a reduction in metabolic activity in meristematic tissues. Dehydration tolerance and dormancy are independent phenomena and differ from the adaptations of resurrection plants.

CONCLUSIONS

Summer dormancy has been correlated with superior survival after severe and repeated summer drought in a large range of perennial grasses. In the face of increasing aridity, this trait could be used in the development of cultivars that are able to meet agronomic and environmental goals. It is therefore important to have a better understanding of the genetic and environmental control of summer dormancy.

Summer dormancy in Dactylis glomerata L.: the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars

A series of trials to increase understanding of the summer dormancy trait in Dactylis glomerata was conducted. Autumn-sown reproductive and younger, spring-sown plants of 2 drought-resistant cultivars, contrasting for summer dormancy, were established and then tested in summer 2002 under long drought, drought + mid-summer storm, or full irrigation. The autumn-sown reproductive plants of cv. Kasbah were summer dormant under all moisture regimes and exhibited the characteristic traits including growth cessation, rapid herbage senescence, and dehydration of surviving organs (–6.7 MPa). Cultivar Kasbah used 8% less soil water over the summer and also began to rehydrate its leaf bases from conserved soil water before the drought broke. The non-dormant cv. Medly grew for 10 days longer under drought and whenever moisture was applied; Medly also responded to the storm with a decline in dehydrin expression in leaf bases, whereas no decline occurred in Kasbah, presumably because it remained dormant and therefore much drier. The irrigated, younger, spring-sown swards of cv. Kasbah had restrained growth and produced only about 25% of the herbage of cv. Medly. Drought reduced activity and growth of young plants of both cultivars, but whereas Medly regrew in response to the storm, cv. Kasbah did not, indicating that dormancy, although only partially expressed after spring sowing, was reinforced by summer drought. A longer drought in 2003 caused a 22% loss of the basal cover in cv. Medly, whereas Kasbah fully maintained its sward and therefore produced a higher post-drought autumn yield. This work confirms summer dormancy as a powerful trait for improving persistence over long, dry summers.

Summer dormancy in Festuca arundinacea Schreb.; the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars

Due to the shortage of information on summer dormancy in tall fescue (Festuca arundinacea, syn. Lolium arundinaceum), we tested the response of 2 cultivars of differing dormancy expression and growth stage to a range of summer moisture conditions, including full irrigation, drought, and a simulated mid-summer storm and analysed whether traits associated with summer dormancy conferred better survival under severe field drought. Autumn-sown reproductive and younger, spring-sown plants of 2 cultivars, claimed to exhibit contrasting summer dormancy, were established and then tested in summer 2002 under either long drought, drought + simulated mid-summer storm, or full irrigation. The autumn-sown reproductive plants of cv. Flecha exhibited traits that can be associated with partial summer dormancy since under summer irrigation they reduced aerial growth significantly and exhibited earlier herbage senescence. Moreover, cv. Flecha used 35% less soil water over the first summer. However, the water status of leaf bases of young vegetative tillers of both cultivars was similar under irrigation and also throughout most of the drought (leaf potential and water content maintained over –4 MPa and at approx. 1 g H2O/g DM, respectively). The summer-active cv. Demeter did not stop leaf elongation even in drought and produced twice as much biomass as Flecha under irrigation. Cultivar Demeter responded to the simulated storm with a decline in dehydrin expression in leaf bases, whereas no decline occurred in Flecha, presumably because it remained partially dormant. The younger, spring-sown swards of both cultivars had similar biomass production under summer irrigation but whereas Demeter regrew in response to the simulated storm, cv. Flecha did not, indicating that dormancy, although only partially expressed, was reinforced by summer drought. In all trials, cv. Flecha out-yielded Demeter in autumn regrowth. In particular, the severe drought in 2003 caused a 25% loss of the basal cover in cv. Demeter, whereas Flecha fully maintained its sward allowing it to produce a higher post-drought autumn yield. This work links summer dormancy with higher persistence over long, dry summers.