Comparative seed longevity under genebank storage and artificial ageing: a case study in heteromorphic wheat wild relatives.

Seed longevity is a complex trait that depends on numerous factors. It varies among species and populations, and within different seed morphs produced by the same plant. Little is known about variation in longevity in different seed morphs or the physiological and molecular basis of these differences. We evaluated the longevity and oxidative stress status in heteromorphic seeds aged in two different storage conditions. We compared controlled ageing tests (seed storage at 45°C and 60% relative humidity; a method of accelerated ageing used to estimate longevity in genebank conditions) with storage in a genebank for up to 40 years (-18°C and 8% seed moisture content). We employed as study species two wild wheats characterized by seed heteromorphism: Aegilops tauschii and Triticum monococcum subsp. aegilopoides. We estimated the ROS content and the expression of genes coding for enzymes related to the H2 O2 scavenging pathway. Results confirmed that seed longevity varies between different seed morphs. Different storage environments resulted in different longevity and survival curves. ROS levels, even if with variable patterns, were higher in several aged seed lots. We observed consistency in the expression of two genes (GSR and CAT) related to ROS scavenging in the late phase of pre-germinative metabolism. Differences in seed longevity between morphs were observed for the first time under genebank conditions. Our results suggest also that controlled ageing tests should be used with caution to infer ranks of longevity under cold storage.

Heteromorphic seeds of wheat wild relatives show germination niche differentiation.

Crop wild relatives are fundamental genetic resources for crop improvement. Wheat wild relatives often produce heteromorphic seeds that differ in morphological and physiological traits. Several Aegilops and Triticum species possess, within the same spikelet, a dimorphic seed pair, with one seed being larger than the other. A comprehensive analysis is needed to understand which traits are involved in seed dimorphism and if these aspects of variation in dimorphic pairs are functionally related. To this end, dispersal units of Triticum urartu and five Aegilops species were X-rayed and the different seed morphs weighed. Germination tests were carried out on seeds, both dehulled and left in their dispersal units. Controlled ageing tests were performed to detect differences in seed longevity among seed morphs, and the antioxidant profile was assessed in terms of antioxidant compounds equipment and expression of selected antioxidant genes. We used PCA to group seed morphs sharing similar patterns of germination traits, longevity estimates and antioxidant profile. Different seed morphs differed significantly in terms of mass, final germination, germination timing, longevity estimates and antioxidant profile in most of the tested species. Small seeds germinated slower, had lower germination when left in their dispersal units, a higher antioxidant potential and were longer-lived than large seeds. The antioxidant gene expression varied between morphs, with different patterns across species but not clearly reflecting the phenotypic observations. The results highlight different trait trade-offs in dimorphic seeds of Aegilops and T. urartu, affecting their germination phenology and longevity, thereby resulting in recruitment niche differentiation.

Comparative germination responses to water potential across different populations of Aegilops geniculata and cultivar varieties of Triticum durum and Triticum aestivum.

Crop Wild Relatives are often used to improve crop quality and yields because they contain genetically important traits that can contribute to stress resistance and adaptation. Seed germination of different populations of Aegilops geniculata Roth collected along a latitudinal gradient was studied under different drought stress in order to find populations suitable for improving drought tolerance in wheat. Different accessions of Aegilops neglecta Req. ex Bertol., Triticum aestivum L. and T. durum Desf. were used as comparison. Under full hydration, germination was high in all populations, but increasing drought stress led to reduced and delayed germination. Significant differences in final germination and mean time to germinate were detected among populations. Wheat, durum wheat and the southern population of Ae. geniculata were not significantly affected by drought stress, germinating similarly under all treatments. However, seed germination of the northern populations of Ae. geniculata was significantly reduced under high water stress treatment. Differences between populations of the same species could not be explained by annual rainfall across populations' distributions, but by rainfall during seed development and maturation. Differences in the germination responses to drought found here highlight the importance of source populations as criteria for genotype selection for pre-breeders.

Influence of apolipoprotein H polymorphism on levels of triglycerides.

Human apolipoprotein H (apo H) displays a genetically determined structural polymorphism: three alleles (H*1, H*2 and H*3) on chromosome 17 code for the six phenotypes (three homozygotes and three heterozygotes). The effect of apolipoprotein polymorphism on individual variations in plasma lipoprotein levels has been underscored in recent years. Since apo H is involved in metabolism of triglycerides (Tg), its phenotype could affect Tg levels. This paper reports an investigation of apo H phenotypes in a sample of 217 subjects of the Italian population by means of isoelectrofocussing followed by immunoblotting. The levels of the main lipid parameters were evaluated in relation to phenotype and other influential factors. Analysis of covariance disclosed a significant association between Tg levels (log transformed) and phenotype (F = 8.27, P = 0.004). Comparison of Tg levels between bearers of the two most frequent phenotypes (H2/2 and H3/2) divided by sex and age classes revealed significantly higher levels in male H3/2 heterozygotes (P = 0.0053) and in H3/2 subjects aged less than 50 (P = 0.0095). Our data support the view that there is an association between hypertriglyceridaemia and apo H polymorphism, especially with the H*3 allele.