Links between germination, DNA replication and p-tubulin accumulation were studied with cabbage (Brassica oleracea L) seeds, by using flow cytometric analysis of nuclear DNA content and immunodetection of p-tubulin levels The seeds were incubated in water or 0 1-500 ITIM hydroxyurea solutions Radicle tips isolated from dry cabbage seeds revealed most 2C (G o or G 1 stage) and some 4C (G 2 stage) signals of nuclear DNA contents and a constitutive level of (3-tubuhn The onset of DNA replication in the radicle tip was observed between 12 and 24 h of imbibition in water and was preceded by an increase of (3-tubuhn levels Incubation of the seeds in 1 mM hydroxyurea retarded DNA replication, whereas an arrest of DNA replication occurred upon incubation in 10 mM hydroxyurea or higher concentrations The arrest of DNA replication and cell division did not block radicle protrusion and allowed some extension of the radicle This demonstrated that DNA replication is not a prerequisite for radicle protrusion and initial extension However, further seedling development, including root growth and root hair development, was dependent on DNA replication Accumulation of (3-tubulin was not affected by hydroxyurea Thus, it can be deduced that both DNA replication and p-tubuhn accumulation are two parallel and independent cell cycle events during seed germination

The effects of Asahi SL (sodium ortho and para-nitro phenolate, sodium 5 nitro guaiacolate) sprays on China aster plant height, seed yield and some metabolic events were investigated. The plants were sprayed with Asahi SL, in concentration of 0, 0.1, 0.2 or 0.4 %, three times before or during flowering, and six times before and during this stage. It was found that Asahi SL applied three times during flowering brought about an increase in the seed yield, germination and metabolic activity and did not modify vegetative growth of plants. The chemical used earlier, before flowering, had detrimental effect on seed yield and quality, although it stimulated vegetative growth. The positive effect of Asahi SL was more prominent in weather conditions unfavourable for seed production.

No abstract

The aim of this study was to develop the method for increasing resistance of sunflower seedlings 'Wielkopolski' to chilling. Seeds were conditioned at 25°C for 2 days in water to 15, 20 and 25 % moisture content or in salicylic or jasmonic acid in concentration of 10 -2 ; 10 -3 and 10 -4 M or brassinolide in concentration of 10 -6 ; 10 -8 and 10 -10 -15 % moisture content. After 2 days of incubation the conditioned seeds were heat shocked at 45°C for 0, 30, 60, 120 and 240 min and 5 mm seedlings were exposed to chilling at 0°C for 21 days. The effectiveness of the methods was assessed by evaluation of roots growth in Phytotoxkit Microbiotest, changes in the activity of dehydrogenases, the integrity of the cytoplasmic membrane and formation of polysomes after seedling were returned to 25°C for 72 h. Seeds were conditioned at 25°C for 2 days in water to 15 % moisture content and then heat shocked at 45°C for 2 h decreased chilling injury of seedlings expressed by subsequent growth of the roots, electrolyte leakage, dehydrogenases activity and polysomes formation. Application of heat shock of 45°C for 2 h during seed conditioning additionally provided seedling protection against subsequent chilling conditions. Brasinolide, salicylic acid or jasmonic acid applied during seeds conditioning exhibited further beneficial effect on seedling resistance to chilling. The most pronounced effect was obtained due to seed conditioning to 15 % moisture content in solutions of brassinolide in concentration of 10 -8 M. After 2 days of imbibition treated in this way seeds were exposed to heat shock at 45°C for 2 h. The role of physiological events in improvement of sunflower chilling tolerance are discussed.

The objective of this study was to analyze the mechanism of some physiological processes accompanying acquisition of sunflower (Helianthus annuus L.) chilling resistance due to seeds hydropriming in the presence of salicylic acid, jasmonic acid, 24-epibrassinolide followed exposition of seeds to short-term heat shock treatment. The seeds were hydroprimed at 25°C in limited amounts of water or solution of salicylic or jasmonic acid at 10 -2 , 10and 10 -4 M concentration, 24-epibrassinolide at 10 -6 , 10 -8 and 10 -10 M concentration. The seeds were incubated for 2 days, subjected to short-term heat shock (45°C, 2 h) and chilled for 21 days at 0°C. Sunflower chilling susceptibility and physiological responses were evaluated according to the inhibition of radicle growth, the inhibition of the number of lateral roots formation, the activity of catalase and changes in soluble carbohydrates in seedlings developing for 72 h at 25°C. Hydropriming and short-term heat shock application explicitly reduced inhibition of roots as well as lateral roots development by allowing the germinating seeds to recover from the growthinhibiting effects of chilling. Seeds hydropriming in solutions containing salicylic acid, jasmonic acid and 24-epibrassinolide followed heat shock treatment additionally promoted the activity of catalase and sugars metabolism, which stimulated seedlings development and alleviated the decrease of F v /F m caused by chilling conditions. These beneficial effects contributed to increased resistance of sunflower seedlings to chilling stress. The present study demonstrated that the most profitable effect on reducing negative effect of chilling may be achieved by short-term heat shock applied during hydropriming in water supplemented with 24-epiBL (10 -8 and 10 -10 M) or salicylic acid (10 -3 and 10 -4 M).