The seed constitutes the main vector of plant propagation and it is a critical development stage with many specificities. Seed longevity is a major challenge for the conservation of plant biodiversity and for crop success. Seeds possess a wide range of systems (protection, detoxification, repair) allowing them to survive in the dry state and to preserve a high germination ability. Therefore, the seed system provides an appropriate model to study longevity and aging.

Iconography : Seed longevity: Survival and maintenance of high germination ability of dry seeds

Yellow seed is a desirable characteristic for the breeding of oilseed Brassica crops, but the manifestation of seed coat color is very intricate due to the involvement of various pigments, the main components of which are flavonols, proanthocyanidin (condensed tannin), and maybe some other phenolic relatives, like lignin and melanin. The focus of this review is to examine the genetics mechanism regarding the biosynthesis and regulation of these pigments in the seed coat of oilseed Brassica. This knowledge came largely from recent researches on the molecular mechanism of TRANSPARENT TESTA (tt) and similar mutations in the ancestry model plant of Brassica, Arabidopsis. Some key enzymes in the flavonoid (flavonols and proanthocyanidin) biosynthetic pathway have been characterized in tt mutants. Some orthologs to these TRANSPARENT TESTA genes have also been cloned in Brassica species. However, it is suggested that some alterative metabolism pathways, including lignin and melanin, might also be involved in seed color manifestation. Polyphenol oxidases, such as laccase, tyrosinase, or even peroxidase, participate in the oxidation step in proanthocyanidin, lignin, and melanin biosynthesis. Moreover, some researches also suggested that melanic pigment in black-seeded Brassica was several fold higher than in yellow-seeded Brassica. Although more experiments are required to evaluate the importance of lignin and melanin in seed coat browning, the current results suggest that the flavonols and proanthocyanidin are not the only roles affecting seed color.

Molecular mechanism of manipulating seed coat coloration in oilseed Brassica species

In this study, the correlations among these characters were investigated in 18 rapeseed (Brassica napus L.) accessions with different seed coat color. The results indicated that seed water uptake and flooding tolerance were significantly correlated with seed color and melanin pigment content of testa. The red or black-seeded accessions had higher melanin content in testa, showed slower water uptake and lower leakage and higher flooding tolerance. The majority of yellow-seeded rapeseed accessions which had low melanin pigments content in testa showed a rapid water uptake and higher leakage than the red or black-seeded, which led to imbibition damage and lower flooding tolerance. The results suggest that the yellow-seeded cultivars experienced poor field emergence and more serious pre-harvest sprouting in raining weather than the dark-seeded cultivars. Some yellow-seeded accessions showed a slow imbibition behavior and relative high flooding tolerance, indicated these accessions can be used as a genetic resource to improve the flooding tolerance and reduce imbibition damage for the yellow-seeded B. napus L.

Imbibition behavior and flooding tolerance of rapeseed seed ( Brassica napus L.) with different testa color

Mavi K., 2010. The relationship between seed coat color and seed quality in watermelon Crimson sweet. Hort. Sci. (Prague), 37: 62–69. This work was carried out to determine the relationship between seed coat color and seed quality in Crimson sweet watermelon. Seed lots (1, 2, 3, and 4) were prepared taking into consideration seed coat colors in fresh seeds with naked eye. The color parameters of these prepared seed lots were determined using Minolta colorimeter. To determine quality differences between the seed lots, standard germination test, seed weight, water uptake ratio, mean germination time, emergence percentage, mean emergence time, seedling fresh weight, seedling dry weight and electrical conductivity values were determined. The seed weight (57.22 mg), germination percentage (86.5%), emergence percentage (77.5% total and 76.5% normal), seedling fresh weight (978.7 mg), and dry weight (64.7 mg) of the brown seed lot (Lot 1) were markedly higher than lots having lighter seed coat (2, 3, and 4). On the other hand the mean emergence time (7.7 days) and electrical conductivity value (128.8 μS/cm g in 24 h) of the brown seed lot (Lot 1) were lower than lots having lighter seed coat (2, 3, and 4). The obtained data indicated that seed quality differences can be determined according to the seed coat color of Crimson sweet seeds. It was found that seed lot 1 had higher seed vigor and viability than seed lots 2, 3, and 4. Color parameters b*, C*, L*, and H°, determined by Minolta colorimeter, showed significant correlation with seeds quality parameters.

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The relationship between seed coat color and seed quality in watermelon Crimson sweet.

The success of seed germination and the establishment of a normal seedling are key determinants of plant species propagation. At present, only few studies have focused on the genetic control of the seed germination by proteomic approach in Brassica napus. In the present study, the protein expression pattern of seed germination was investigated using differential fluorescence two-dimensional gel electrophoresis (2-D DIGE) in B. napus. One hundred thirteen differentially expressed proteins (DEPs), which were mainly involved in storage proteins (23.4%), energy metabolism (18.9%), protein metabolism (16.2%), defense/disease (12.6%), seed maturation (11.7%), carbohydrate metabolism (4.5%), lipid metabolism (4.5%), amino acids metabolism (3.6%), cell growth/division (3.6%), and some unclear proteins (2.7%) were observed by proteomic analysis. Seventeen genes corresponding to 11 DEPs were identified within or near the associated linkage disequilibrium regions related to seed germination and vigor quantitative traits reported in B. napus in previous studies. The expression pattern of proteins showed the heterotrophic metabolism could be activated in the process of seed germination and the onset of defense system might start during seed germination. These findings will help us more in-depth understanding of the mobilization of seed storage reserves and regulation mechanisms of germination process in B. napus.

Proteomic Dissection of Seed Germination and Seedling Establishment in Brassica napus.

Yellow-seeded rapeseed (Brassica napus L.) is a new kind of breeding resources with yellow color, increased oil and protein content and less unwanted crude fiber content due to the thinner and transparent testa compared with traditional black or brown-seeded rapeseed. To analyze the longevity of the yellow-seeded rapeseed during storage, the physiological differences between the yellow and black-seeded near-isogenic lines were studied by artificial ageing method. The testa rate, anthocyanin content and melanin content of yellow-seeded rapeseeds decreased by 20.1, 25.2, and 80.4% respectively than black-seeded rapeseed. During artificial ageing, the yellow-seeded rapeseed showed significantly different effect of ageing compared with the black-seeded, as demonstrated by faster deterioration with lower germination percentage, seed vigour index, reducing sugar and soluble protein contents than the black-seeded, as well as a drastic increase in electrical conductivity, malnodialdehyde (MDA) content and a rapid decrease in activities of antioxidant enzymes catalase (CAT)and superoxide dismutase (SOD). The results suggested that the transparent testa of the yellow-seeded rapeseed lost some abilities to protect the embryo against adverse environmental conditions and thus led to a poor storability.

Physiological Differences Between Yellow-Seeded and Black-Seeded Rapeseeds （Brassica napus L.）with Different Testa Characteristics During Artificial Ageing

LIJia-na

Papers

Physiological Differences Between Yellow-Seeded and Black-Seeded Rapeseeds （Brassica napus L.）with Different Testa Characteristics During Artificial Ageing