PHYSIOLOGICAL QUALITY AND ANTIOXIDANT ENZYMATIC ACTION IN SUNFLOWER SEEDS EXPOSED TO DETERIORATION1

ABSTRACT This work aimed to evaluate the physiological and biochemical changes resulting from controlled deterioration in different lots of sunflower seeds. Two sunflower seed lots of the cultivar Hélio 253 were subjected to simulated deterioration, using the accelerated aging test methodology (41 °C and 100% RH) for 0, 48, 72, and 96 h. Then, the seeds were subjected to the tests of germination, first germination count, seedling length and dry matter, emergence, accelerated aging, electrical conductivity, and total seedling length. The antioxidant activity was evaluated through the enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POX) at 0, 2, 4, and 6 days after sowing. Deterioration caused a reduction in the germination and vigor of the seeds, mainly in the lot with lower initial vigor and for the longest exposure times (72 and 96 h). For both lots, reductions in SOD activity and increases in POX and APX were observed during seed germination, mainly after 48 h of exposure to aging deterioration. Peroxidase enzymes are activated in deteriorated and non-deteriorated sunflower seeds, mainly after two days of germination.

Cathodic Water Enhances Seedling Emergence and Growth of Controlled Deteriorated Orthodox Seeds

All orthodox seeds eventually deteriorate during storage, a well-known problem in seed banking. Here we used a greenhouse study to test if priming deteriorated seeds with cathodic water can improve the emergence and subsequent seedling growth of three South African tree species, Bolusanthus speciosus, Combretum erythrophyllum and Erythrina caffra. Other priming solutions investigated were calcium magnesium (CaMg) solution and deionized water. In the present study, seeds were subjected to an artificial deterioration by increasing their water content to 14% and keeping them at 40 °C and 100% RH until they had lost 50% of their germination under laboratory conditions. Fresh and deteriorated seeds were primed with cathodic water, CaMg solution and deionized water, with non-primed fresh and deteriorated seeds as controls. Controlled deterioration significantly reduced total emergence and the biomass and photosynthetic parameters of the resulting seedlings. In one species (Bolusanthus speciosus), priming the deteriorated seeds with cathodic water significantly improved emergence parameters. However, in all species cathodic water significantly improved the total biomasses and other growth parameters of the seedlings derived from deteriorated seeds. Priming with CaMg solution and deionized water had little effect on emergence and while improving the growth of seedlings derived from deteriorated seeds, they were less effective than cathodic water. In fresh seeds, priming with all solutions resulted in small improvements in some parameters. Controlled deterioration of fresh seeds reduced the membrane stability index (MSI) in two of the three species and in all species increased the levels of the lipid oxidation products MDA and 4-HNE. Priming deteriorated seeds with cathodic water increased the MSI and reduced the MDA contents in all species and the 4-HNE content in one species. Other priming solutions were generally less effective in ameliorating oxidative stress. Results suggest that the strong antioxidative properties of cathodic water can explain its ability to ameliorate deterioration. In conclusion, the present study shows that priming with cathodic water is an effective way of invigorating deteriorated orthodox seeds and that it may have considerable potential in orthodox seed conservation.

The Histone Chaperone HIRA Is a Positive Regulator of Seed Germination

Histone chaperones regulate the flow and dynamics of histone variants and ensure their assembly into nucleosomal structures, thereby contributing to the repertoire of histone variants in specialized cells or tissues. To date, not much is known on the distribution of histone variants and their modifications in the dry seed embryo. Here, we bring evidence that genes encoding the replacement histone variant H3.3 are expressed in Arabidopsis dry seeds and that embryo chromatin is characterized by a low H3.1/H3.3 ratio. Loss of HISTONE REGULATOR A (HIRA), a histone chaperone responsible for H3.3 deposition, reduces cellular H3 levels and increases chromatin accessibility in dry seeds. These molecular differences are accompanied by increased seed dormancy in hira-1 mutant seeds. The loss of HIRA negatively affects seed germination even in the absence of HISTONE MONOUBIQUITINATION 1 or TRANSCRIPTION ELONGATION FACTOR II S, known to be required for seed dormancy. Finally, hira-1 mutant seeds show lower germination efficiency when aged under controlled deterioration conditions or when facing unfavorable environmental conditions such as high salinity. Altogether, our results reveal a dependency of dry seed chromatin organization on the replication-independent histone deposition pathway and show that HIRA contributes to modulating seed dormancy and vigor.

The Relationship between Seed Vigor and Germination Performance under Various Chloride Salts in Pea

Background: Salinity is a severe abiotic stress resulting in inhibiting germination, seedling growth of crop plants. Germination performance under salinity depends on seed vigor and genotypic factors. This study aimed to determine if there was a relationship between germination and seedling growth of eight pea cultivars subjected to three chloride salts and the results of seed vigor tests. Methods: Pea cultivars Ambassador, Bolero, Electra, Esprit, Puccet, Rainer, Utrillo and Winner were germinated in the medium with three chloride salts of NaCl, MgCl2 and CaCl2 with the electrical conductivity (EC) of 20 dS m-1. Also germination percentage, mean germination time, controlled deterioration (CD) and electrical conductivity (EC) test were evaluated. Result: The seed vigor of pea cultivars was significantly different and salinity led to a significant decline in parameters of the cultivars. The most hazardous salt was MgCl2, while the least harmful was NaCl. Germination percentage was negatively related with MGT and EC values and EC test was strongly correlated with CD test. Utrillo and Winner were the most sensitive cultivars to MgCl2 and CaCl2. Although germination percentage of Rainer under non-saline was the lowest with 76%, it showed better performance under salinity than Utrillo and Winner. Germination percentage and CD gave a negative significant correlation with NaCl, but MGT and EC associated positively with NaCl. It was concluded that seed vigor should be considered as an indicator for the germination performance of pea seeds under NaCl, whereas genotypic factors play a key factor for tolerance to salinity during germination and early development stages.

Controlled deterioration test to evaluate the physiological potential of sweet corn seeds

The evaluation of the physiological potential of sweet corn seeds is essential in a quality control program and the choice of vigor tests using an adequate analysis methodology is essential to obtain reliable results. In this sense, this study aimed to standardize the methodology of the controlled deterioration test through combinations between time and temperature to evaluate the vigor of sweet corn seeds. Six lots of sweet corn seeds were characterized by the degree of moisture and the initial physiological potential through the following tests: germination, first germination count, cold test, electrical conductivity, accelerated aging, length and dry mass of normal seedlings, seedling emergence in sand, and emergence rate index. Subsequently, these lots had their initial water content adjusted to 20% using the wet substrate method. The seeds from the six lots were subjected to the controlled deterioration test under two temperatures for four periods, obtaining a completely randomized design in an 8 × 6 factorial scheme with eight combinations of time/temperature and six lots. Germination and the first germination count were evaluated after the deterioration test. The data were subjected to analysis of variance with a comparison of means by the Tukey test at a 5% significance. The results of the first count and germination tests after deterioration were subjected to a simple linear correlation study together with the initial characterization data. The combinations 8 h – 40 °C and 8 h – 45 °C in the controlled deterioration test were efficient in distinguishing the vigor of seed lots. The shorter exposure period and the first germination count after deterioration are more suitable for evaluating the vigor of sweet corn seeds.

QTL analysis of seed germination traits in tobacco (Nicotiana tabacum L.)

Genetic mapping of seed germination traits has been performed with many plant species. In tobacco, however, investigations are rare. In the present study, a bi-parental mapping population consisting of 118 doubled haploid lines and derived from a cross between ‘Beinhart-1000’ and ‘Hicks’ was investigated. Four germination-related traits, total germination (TG), normal germination (NG), time to reach 50% of total germination (T50), and the area under the curve after 200 h of germination (AUC) were considered by examining seeds either untreated or after a moderate controlled deterioration (CD). Quantitative trait loci were found for all traits distributed on 11 out of the 24 linkage groups. It was demonstrated that, as in many other species, germination-related traits are very complex and under polygenic control.

Ethanol release as an indicator of seed vigour in radish, pepper, watermelon, aubergine, leek and onion seed lots

Ethanol release was tested in relation to seed vigour measured by seedling emergence and controlled deterioration tolerance in radish, pepper, watermelon, aubergine, leek and onion seed lots. Ethanol release, measured with six lots from each species after four and eight hours at 40&deg;C and 30% seed moisture, was highly negatively correlated with controlled deterioration tolerance (45&deg;C, 48 hours, 20% seed moisture) in radish (r = 0.05, P &lt; 0.05), with seedling emergence in watermelon (r = 0.99, P < 0.01) and to both traits in pepper (r = 0.87 to 0.94, P &lt; 0.05), but not with any variable for aubergine and leek. One single case was significant between ethanol release after eight hours and controlled deterioration for onion seeds. Results indicate that there is a relationship between ethanol release and seed vigour, but this appears to be species dependent.

Early counts of radicle emergence, counted manually and by image analysis, can reveal differences in the production of normal seedlings and the vigour of seed lots of cauliflower

The ability of a single early count of radicle emergence (RE) to predict differences in the production of normal seedlings (NG) and seed vigour was examined in four seed lots from each of three varieties of cauliflower (Brassica oleracea var botrytis). Initial seed quality was assessed in germination and controlled deterioration (CD) vigour tests. RE (first appearance of the radicle) was counted manually after 48 hours in the germination test (RE 48h 20/30&deg;C) and every two hours for 144 hours at 20&deg;C using automated image analysis. Seed vigour was assessed in field and glasshouse trials. A large proportion of the variance in NG was explained by the RE count. The same RE counts at 20/30&deg;C and 20&deg;C predicted seed vigour in the field and glasshouse and revealed the same vigour differences as the validated CD test. Differences in vigour (field and glasshouse emergence) observed between varieties were related to the extent of previously sustained seed ageing revealed by the CD test, although genotypic differences in vigour could not be excluded. We propose that single counts of RE taken manually or by image analysis can be used to reveal differences in the NG and vigour of seed lots of cauliflower.

Determination of tobacco (Nicotiana tabacum) seed vigour using controlled deterioration followed by a conductivity test

Seeds of eight lots of four tobacco varieties differing in vigour were studied. The initial germination percentage (GPUT) was 81-100% and the controlled greenhouse emergence percentage (CEP) was 55-91%. All seeds were treated by controlled deterioration (CD) at 20% moisture content and 45°C for 24 hours, then some seeds were subjected to a standard germination test and the rest of the seeds were subjected to a conductivity test. The electrical conductivity (EC) of seed soak water was measured every six hours up to 54 hours. The results showed that relative conductivity after CD (RCCD) was highly significantly correlated with GPCD after 30 to 48 hours soaking (r = -0.9324 to -0.9409, P < 0.001). After 36 and 42 hours, RCCD was significantly correlated (P < 0.01) with CEP (correlation coefficients of -0.9120 and -0.9137, respectively). Therefore, it is suggested that measuring relative conductivity after CD could be used to rank tobacco seed lots for vigour. In addition, the best seed soaking time for EC measurement is 36 to 42 hours, with respect to both efficiency and accuracy.