Research On Leaf Morphology And Physiological Responses Of Perennial Ryegrass Under Cold Stress

Perennial ryegvass(Lolium perenne L.) is a cool-season turfgrass species which is widely used in China. However, perennial ryegrass is vulnerable to cold and windy condition in winter, which resulting in dehydration and death.’Uno’(freezing-tolerant cultivar) and’Linn’(freezing-sensitive cultivar) were used as plant materials in this experiment. Leaf morphology of these two cultivars was observed and relative water loss rate of detached leaves was measured. Under cold stress-2℃ and-10℃, plant materials are placed in windy environment and some physiological indexes were measured. This study was conducted to explore the relationship between leaf morphology and physiological responses in different cultivars of perennial ryegrass under cold stress. The results showed that:1.The morphological differences between two cultivars under natural condition showed that, the stomatal number, long cells and short cells number of ’Uno’ was significantly higher than’Linn’ (P<0.05). Stomatal length, stomatal size, leaf epidermal cell,epidermal hair size, motor cell size and the degree of water wettability of leaf surface was significantly lower than’Linn’(P<0.05). After losing water for 12 hours, leaf relative water loss in freezing-tolerant cultivar’Uno’was 35.55% and it was 52.13% in freezing-sensitive cultivar’Linn’, the difference between them was significant(P<0.05).2.Different physiological changes between two cultivars showed that, under-2℃ cold stress conditions, electrolyte leakage of freezing-tolerant cultivar ’Uno’ was 14.3% which was significantly lower than’Linn’23%(P<0.05). Relative water content of ’Uno’ and ’Linn’ was 75.29% and 76.74% respectively and showed no significant difference between each other. The accumulation of proline in’Uno’was significantly higher than ’Linn’ but they showed no significant difference in the content of soluble sugar. In terms of osmotic pressure, freezing-sensitive cultivar was significantly lower(-1.244MPa) (P<0.05) than freezing-sensitive cultivar(-1.219 MPa), but stronger osmotic adjustment ability. Under-10℃ cold stress condition, perennial ryegrass showed more damage. Electrolyte leakage of perennial ryegrass of two different cultivar ’Uno’ and ’Linn’ were 51.78 and 62.51% separately,’Linn’ was significant higher than’Uno’(P<0.05); the amount of proline and soluble sugar accumulation under cold stress in’Uno’was 854.29μg·g-1 and 34.10 mg·g-1, which was significantly higher than that in ’Linn’ (P<0.05). Freezing-tolerant cultivar ’Uno’ had more stronger osmotic adjustment ability, the osmotic pressure was-1.65MPa and it was significantly higher than that in ’Linn’ -1.59 MPa.3.Under windy-cold stress, freezing-tolerant cultivar’Uno’can still be alive after 4 days of treatment in-10℃, but ’Linn’ cannot be alive under the same situation.In conclusion, there is a close correlation between morphology along with physiological responses under cold stress in freezing-tolerant cultivar. Larger quantity of stoma, smaller stomatal size, smaller leaf epidermal cell, larger quantity of long cells, short cells and epidermal hair number might contribute to cell membrane integrity, accumulation of osmotic substances, osmotic adjustment and the enhancement of cold hardiness.