Desiccation Tolerance Of Seedlings Research Articles

Wide variation in post-emergence desiccation tolerance of seedlings of fynbos proteoid shrubs

Fynbos Proteaceae that are killed by fire and bear their seeds in serotinous cones (proteoids), are entirely dependent on seedling recruitment for persistence. Hence, the regeneration phase represents a vulnerable stage of the plant life cycle. In laboratory-based experiments we investigated the effect of desiccation on the survival of newly emerged seedlings of 23 proteoid species (Leucadendron and Protea) occurring in a wide variety of fynbos habitats. We tested the hypothesis that species of drier habitats would be more tolerant of desiccation than those from more moist areas. Results showed that with no desiccation treatment, or with desiccation prior to radicle emergence, all species germinated to high levels. However, with desiccation treatments imposed after radicle emergence, there were significant declines in seedling emergence after subsequent re-wetting. Furthermore, other than three species that grow in waterlogged habitats, germination responses could not be reliably modeled as a function of soil moisture variables. An important finding was that the species had highly individualistic responses to desiccation. In conclusion, early seedling emergence represents a species-specific stage that is highly sensitive to a decrease in soil moisture. Since species are killed by fire (non-sprouting), vulnerability to increasing aridity associated with anthropomorphic climate change would increase the odds of local and global extinction.

The role of desiccation tolerance in determining tree species distributions along the Malay–Thai Peninsula

1 Patterns of water availability are frequently implicated in local and regional tree species distributions. A major floristic and climatic transition from aseasonal to seasonal evergreen tropical forest is the Kangar–Pattani Line (KPL) in the Indo-Sundaic region of Southeast Asia. We hypothesize that differences in species’ drought tolerance will correspond with their distribution with respect to the KPL. Using a common garden study, we assess the role of differences in physiological drought tolerance traits to geographic distributions for 24 tropical tree species in relation to rainfall seasonality. 2 Inherent differences in desiccation tolerance of seedlings were quantified as water potentials and relative water contents (RWCs) below which the plant could no longer support living tissue, and plant water relation parameters were measured using pressure–volume analysis. The relationships among these traits were examined using bivariate trait relationships and a principal components analysis (PCA). The physiological traits contributing most to lethal water potential and RWC were assessed using multiple regression analysis. 3 Distribution-related differences in all desiccation tolerance and pressure–volume traits were detected both with and without phylogenetic correction. Widespread species that occurred in seasonally dry forests were able to maintain living tissue at more negative water potentials and lower RWCs than were species restricted to aseasonal forests. Likewise, widespread species demonstrated more negative water potentials at turgor loss, more negative saturated osmotic potential, lower symplastic water fraction and higher bulk modulus of elasticity values. Turgor loss point (TLP) and bulk modulus of elasticity were the best predictors of lethal water potential while symplastic water fraction and bulk modulus of elasticity were included as predictors of lethal RWC. 4 Inherent differences in physiological traits contributing to drought tolerance are associated with differences in tropical tree species distributions in relation to rainfall seasonality. These results, combined with lack of support for hypothesized historical factors, strongly implicate climate as a determinant of tree species distributions around the KPL.

Genetic basis of barley caryopsis dormancy and seedling desiccation tolerance at the germination stage

The genomic regions controlling caryopsis dormancy and seedling desiccation tolerance were identified using 152 F4 lines derived from a cross between Mona, a Swedish cultivar, and an Israeli xeric wild barley Hordeum spontaneum genotype collected at Wadi Qilt, Israel. Dormancy, the inability of a viable seed to germinate, and desiccation tolerance, the ability of the desiccated seedlings to revive after rehydration, were characterized by fitting the germination and revival data with growth curves, using three parameters: minimum, maximum, and slope of germination or revival rate derived by the least square method. The genetic map was constructed with 85 genetic markers (SSRs, AFLPs, STSs, and Dhn genes) using the MULTIPOINT: -mapping algorithm. Quantitative trait loci (QTLs) mapping was conducted with the MULTIQTL: package. Ten genomic regions were detected that affected the target traits, seven of which affected both dormancy and desiccation tolerance traits. Both the wild barley genotype and the Swedish cultivar contributed the favorite alleles for caryopsis dormancy, whereas seedling desiccation tolerance was attributed to alleles descending from the cultivar. The results indicate that some barley dormancy genes are lost during domestication and that dormancy QTLs are associated with abiotic stress tolerance.

Seedling desiccation tolerance of Leymus racemosus (Poaceae) (wild rye), a perennial sand-dune grass inhabiting the Junggar Basin of Xinjiang, China

Leymus Racemosus, The Mammoth Wild Rye, Is A Rhizomatous Perennial Grass, Mainly Distributed In The Moving Or Semi-Stabilized Sand Dunes In Deserts Of The Junggar Basin In Xinjiang, China. The Revival Ability Of The Young Seedling After Periods Of Desiccation Can Be Influenced By Several Factors: (1) The Stage Of Seedling Development – The Later The Stage At Dehydration, The Longer The Root Length And The Lower Is The Percentage Of Seedlings That Survive; (2) The Length Of The Period Of Desiccation – The Longer The Period That The Seedlings Are Under Desiccation, The Lower Is The Percentage Of Seedlings That Survive; (3) Endosperm Size – The Smaller The Proportion Of Endosperm That Remains In The Caryopses, The Lower Is The Percentage Of Seedlings That Revive, Determined By (A) The Stage Of Seedling Development, And (B) The Proportion Of The Endosperm That Is Removed By Cutting; And (4) Caryopsis Size – The Larger The Polymorphic Caryopses, The Higher Is The Percentage Of Young Seedlings That Revive From Periods Of Desiccation. The Physiological And Ecological Implications Of L. Racemosus Seedling Desiccation Tolerance Are That Under Extreme Desert And Unpredictable Environmental Conditions, The Chances Of Seedling Establishment Are Increased.

Can a Genetic Correlation with Seed Mass Constrain Adaptive Evolution of Seedling Desiccation Tolerance in Wild Barley?

Very young seedlings of wild barley Hordeum spontaneum have the ability to survive extended periods of severe drought. This desiccation tolerance is considered an adaptation to the rain‐limited and unpredictable habitats that the species occupies. Genetic variation has been observed for this trait, but the limited evidence to date does not consistently show that genotypes from more xeric populations have better desiccation tolerance. As large seed endosperm volume may buffer the desiccating seedling from drought stress, we explored the hypothesis that tolerance to temporary but severe drought is affected by seed mass. We crossed a big‐seeded with a small‐seeded H. spontaneum genotype and measured seed mass and seedling survival rates after 6‐ddesiccation in 140 F4 progeny families. A positive correlation was observed between family mean scores of the two traits. At the genetic level, this indicated that at least some genes underlying variation in the two traits overlapped (or show close chromosomal linkage), which is inevitable if seed mass causally affects desiccation tolerance. Quantitative Trait Loci (QTL) analysis, which can identify chromosome regions responsible for trait variation by exploring associations between trait expression and genetic markers dispersed over the genome, did not confirm this hypothesis of shared genetic control. Despite the lack of QTL evidence, the observed genetic association between seed mass and desiccation tolerance indicates that the two traits are not fully independent, implying that selection targeting one trait will cause a correlated response in the other. We discuss this finding in the context of adaptive differentiation of H. spontaneum populations, which is thought to involve selection of increasingly smaller seeds along a gradient of decreasing predictability and amount of annual precipitation.

Differential patterns of germination and desiccation tolerance of mesic and xeric wild barley (Hordeum spontaneum) in Israel

Differential patterns of germination were identified in mesic (Maalot) versus xeric (Wadi Qilt) ecotypes of wild barley, Hordeum spontaneum C. Koch, in the following traits: afterripening (dormancy), seedling desiccation tolerance, and the effect of glumellae and ethanol on afterripening and seedling growth. The following results were indicated: (i) Dispersal unit afterripening average (75%) was identical, but its coefficient of variation was larger in the xeric than in the mesic ecotype (29.9% and 9.9%, respectively). (ii) Survival ratio of seedlings after 1-month dehydration was higher in the xeric ecotypes indicating that seedling desiccation tolerance was higher in the xeric ecotype. (iii) Inhibition of germination and seedling growth by glumellae were higher in the mesic ecotypes. Ethanol sterilization of naked caryopsis promoted root growth of mesic seedlings but not xeric seedlings. Seedlings originating from xeric ecotypes had longer roots than mesic seedlings. It appears that, in the germination stage, natural selection adapted wild barley to a xeric environment by increasing the diversity of afterripening, enhancing desiccation tolerance, and improving root length growth.

Laboratory screening of the juvenile responses of grassland species to warm temperature pulses and water deficits to predict invasiveness

Summary Two laboratory screening experiments tested the juvenile‐phase responses of 14 C3 and 12 C4 grassland species to pulses of warm temperature and water deficits. The first experiment determined germination response in relation to duration of warm temperature exposure (30/20 °C day/night). The second experiment determined the desiccation tolerance of seedlings immediately following germination. The C4 species were more dependent on warm temperatures for germination than the C3 species. However, there was considerable variation within C3 and C4 types. In particular, Panicum dichotomiflorum was identified as the C4 species least dependent on warm temperatures, exhibiting > 50% of maximum germination in continuous cold (7 °C). The C3 species were generally more desiccation‐tolerant than the C4 species, but there were several exceptions. Trifolium repens (C3) was ranked as the least desiccation‐tolerant whereas Setaria geniculata (C4) was the eighth most tolerant species. Large‐seeded species were more desiccation‐tolerant than small‐seeded species. We suggest that poor desiccation tolerance contributes to the observed restriction of C4 grass invasion into productive grasslands of the wetter regions of New Zealand. On the basis of juvenile‐phase attributes, we ranked the C3 species as more invasive of these grasslands than the C4 species, and annuals as more invasive than perennials. Having invasive juvenile‐phase attributes is an advantageous adaptation for species that rely solely on regeneration from seed.

Amounts of winter or summer rain triggering germination and ‘the point of no return’ of seedling desiccation tolerance, of some Hordeum spontaneum local ecotypes in Israel.

In this study we observed an important interrelationship between the ability of Hordeum spontaneum C. Koch (Poaceae) seeds to germinate after a small rainfall in winter and the dehydration tolerance of young seedlings after one, two or three weeks in dry conditions. In winter, local ecotypes of H. spontaneum started to germinate after only 10 mm of ‘rain’, when temperatures were mild, daily evaporation rates were low, and soil water content was 5.8%. In summer, however, germination was not triggered until at least 50 mm of ‘rain’ was received, at higher temperatures, evaporation rates and soil water content. The ‘point of no return’ is the earliest stage of germination or after germination at which dehydration will cause the death of the seedling and it depends on the duration in a dry environment, root length before desiccation and on the ecotype. Seedlings were stored in dry conditions for one, two or three weks and then rewetted. A higher percentage of seedlings which had developed roots of 5–20 mm long before desiccation, developed adventitious roots than that of seedlings with roots 1–4 or 40–50 mm long before desiccation. The strategy of regulating germination according to different amounts of rainfall, depending on the season, and seedling drought tolerance, are important survival adaptations in arid and semi-arid regions. These adaptations may enable the young seedlings to overcome drought periods between rainfalls.