Why Tetrazolium Chloride Does Not Enter Intact Seeds (of most species) During Imbibition?

Transcription

1 Why Tetrazolium Chloride Does Not Enter Intact Seeds (of most species) During Imbibition? 30 th ISTA Conference, June 14, 2013 Antalya, Turkey Dr. Alan Taylor and Sarah Pollicove Cornell University, NYSAES Geneva, New York, USA

2 A Translation of Lakon s 1942 Paper on Tetrazolium Seed Testing, M. Witty, 2012, Seed Technol. 34: Development of a topographic method TZ eliminated the use of selenium salts Significant milestone in the history of botany Keen insights in the loss of viability From my (Lakon s) investigation into declining germination of seeds, it was clear that in highly organized cereal embryos, necrosis begins at the top of the main root system.

3 Tetrazolium is Globally the Most Routinely Used Viability Stain However, seeds of most species must first be cut, punctured or in some manner the seed covering layers lacerated prior to staining. Why are these steps necessary?

4 Early Investigations Crop % Germination % Intact Seeds Stained with TZ Cabbage Leek Onion Tomato 96 8 Pepper 78 7

5 Seed Coat Permeability Seed coats and other seed covering layers are non-living tissues. Seed coat permeability can be assessed by: 1) if compounds diffuse from the the soak water to the embryo 2) if compounds leak from nonviable seeds into the environment

6 Amino Acid Leakage from Viable (control) and Heat-Killed (dead) Cabbage Cabbage (Brassica) seeds have permeable seed coats to amino acids leaking from dead seeds.

7 Amino Acid Leakage from Viable (control) and Heat-Killed (dead) Tomato Tomato seeds do not have permeable seed coats that leak amino acids from dead seeds.

8 Effect of Seed Viability on Amino Acid Leakage of Onion Seeds Onion (Allium) seeds do not have permeable seed coats that leak amino acids from dead seeds.

9 Effect of Seed Viability and Seed Coat Integrity on Amino Acid Leakage of Onion DEAD Puncturing nonviable onion seeds resulted in amino acid leakage. Thus the barrier to leakage resides in the seed coat.

10 Semi-Permeable Nature of Seed Coats Semipermeability is defined as the ability of seed coverings to allow water uptake and gas exchange, while solute diffusion is restricted or prevented. (Taylor et al, 1995)

11 Seed Coat Permeability to Rhodamine B, a Colored and Fluorescent Tracer Phaseolus vulgaris Cucumis sativus

12 Light and Electron Micrographs of Onion Seeds showing Semipermeable Layer Semipermeable layer (SPL) is colored white by Lanthanum tracer SPL composed of cutin

13 Electron Micrographs of Tomato Semipermeable layer (SPL) is colored white layer of by Lanthanum tracer. SPL is composed of suberin

14 Electron Micrographs of Pepper Semipermeable layer (SPL) is the colored white by Lanthanum tracer. SPL is composed by suberin

15 Seed Coat Permeability - Study Methods apply dry TZ chemical to intact seeds sow treated seeds in moist sand allow seeds to imbibe at 20 C remove seeds from sand prior to radicle emergence remove seed coats and observe embryos under white light with magnification qualitative assessment of embryo staining

16 Species Investigated Fabaceae G. max Soybean P. vulgaris Snap Bean Brassicaceae B. oleracea Cabbage Lilliaceae A. cepa Onion Solanaceae S. lycopersicon Tomato C. annuum Pepper Poaceae P. virgatum Switchgrass Cucurbitaceae C. sativus Cucumber Asteraceae L. sativa Lettuce Euphorbiaceae R. communis Castor

17 References Taylor, A. G., S. S. Lee, M. B. Beresniewicz and D. H. Paine Amino acid leakage from aged vegetable seeds. Seed Sci. & Technol. 23: Beresniewicz, M. B., A. G. Taylor, M. C. Goffinet and B. T. Terhune Characterization and location of a semipermeable layer in seed coats of leek, onion, tomato and pepper. Seed Sci. & Technol. 23: Beresniewicz, M. B., A. G. Taylor, M. C. Goffinet and W. D. Koeller Chemical nature of a semipermeable layer in seed coats of leek, onion, tomato and pepper. Seed Sci. & Technol. 23:

18 References Salanenka, Y. A and A. G. Taylor Uptake of model compounds by soybean, switchgrass and castor seeds applied as seed treatments. Symposium Proceedings No. 83. Seed Production and Treatment in a Changing Environment. British Crop Protection Council, Alton, Hampshire, UK. p Salanenka, Y. A. and A. G. Taylor Seed coat permeability: Uptake and post-germination transport of applied tracer compounds. HortSciences, 46: Taylor, A. G. and Y. A. Salanenka Seed treatments: phytotoxicity amelioration and tracer uptake. Seed Science Research 22, S86-S90.