Seed Coat Permeability And Location Of Semipermeable Layer In Seeds Of Several Grass Species

Semipermeability may be defined as the ability of seed coverings to allow water uptake and gas exchange while solute diffusion is restricted or prevented. The researches on microstructure of testa in seed have been paid rare attention due to the undeveloped technology before. As a result, the structure of seed coat and its function are not fully understood. In this research, the modern techniques of transmission electron microscope, energy dispersive X-ray analysis, and lanthanum tracer, were used to study the difference of testa permeability, the location of semipermeable layer of seed coat among species, and the relation of semipermeability with seed dormancy of grass species. Total seven forage grass species were studied, including Sorghum sudanense, Elymus sibiricus, E. nutans, Festuca arundinacea, Lolium perenne, Leymus chinensis and Avena sativa. The main findings obtained are as follow:1 The differencees presented in seed testa permeability, and the testa permeability influenced on electrical conductivity (EC) to test seeds vigor. All species readily imbibed water both intact and pierced seed coat. Seed coat uptaking TTC varied by species. The correlations between intact seed vigor for S. sudanense, E. sibiricus, E. nutans, L.chinensis and L. perenne and EC were not relevant (P>0.05). However, significant positive correlation presented between vigor and EC value in seeds of F.arundinacea and A. elatius (P<0.05). Whlie the vigor of all seeds and EC correlations were relevant after piercing (P<0.05). The results suggested that semipermeability of seed coat restricted to use EC method to test grass seed vigor.2 The basic structures, under light microscope observation were different between species at seed coat and endosperm nearby. The epidermis and aleurone layer was loose and non palisade tissues formed in A. sativa. However, for other species, the epidermis and aleurone layer was compact with specialized palisade tissues formed.3 The first study was made internationally on the location of the semipermeable layer in seeds of E. nutans, L. chinensis, L. perenne and A. sativa. The results showed that semipermeable layer was presented in the testa, but the specific location was different among species. The semipermeable layer was found in all test species except for A. sativa. For E. nutans and L. chinensis species, the semipermeable layer was located at the inside of the testa, next to the palisade tissue; for L. perenne, it was located at the surface of the testa cells.4 Using 3 seed lots study on seed dormancy found that L. chinensis has coat-imposed dormancy:palea, lemma, testa and endosperm which were components of exogenous dormancy. The results showed that palea, lemma, preicarp/testa and endorsperm all significantly influence on seed dormancy. The average reduction of 3 dormant seed lots were 5%,19%,23% and 34%, respectively. First discovered that testa controlled a significant role on seed dormancy in the international.5 Using single treatments about soaking in distilled water or 30%NaOH for different times, and combined tratments for dormancy breaking. The most effective method to break L. chinensis dormancy was that seeds which were soaked in 30%NaOH for 60min after pre-soaking in water for 1d, then treated with 300μg·g-1 GA3.