Studies On The Response To Hypoxic Stress Of Flooding In Lathyrus Sativus

The hypoxic or anoxic environment induced by flooding stress is the most detrimental factor to crop growth and production especially in low-lying or rainy agricultural land.Plant cells shift their metabolism towards anaerobic fermentation,and produce a few ATP.Simultaneously,the production of major elemental and organic phytotoxins including ROS in anaerobic fermentation is the primary cause ultimately leading to root tip death.However,there are genetic diversity in plants in response to flooding stress.For example,most legumes are sensitive to flooding,but some legumes are resistant to flooding stress.Grass pea(Lathyrus sativus L.)is a grain legume and highly tolerant to diversity of stresses,however,it is remains unclear whether the grass pea has a tolerance to flooding stress.The present study shows that the grass pea is indeed resistant to flooding stress compared with pea that is sensitive to flooding.The main results are the following:1 The cells of transition zone in root tips were the highest sensitive to hypoxic stress when suffered from flooding stress and easily dead detected by Evans Blue(displaying cell death)staining in paraffin section.2 A high level of ROS including H2O2 and O2·-accumulated in root tips under flooding stress by DAB(displaying H2O2)and NBT(displaying O2·-)staining,which may be the primary cause leading to root cell death.3 Although hypoxic treatment lead to the death of root tip cells in both pea and grass pea,there were apparent differences between them.For the pea,the cell death from both primary and later root tips occurred after 36 h hypoxic treatment,and the degree of cell death increased along with hypoxic treatment.However,in grass pea,the cell death of primary root tips occurred after 96 h hypoxic treatment,and the cell death degree did not increase.Simultaneously,the lateral root of grass pea grew well and numerous adventitious roots were generated from lateral root after 108 h hypoxic treatment.It was found that the death of root tip cells under hypoxic stress was a programmed cell death(PCD)process using DNA ladder detection.4 Apparently,the contents of H2O2 and O2·-was lower in root tips of grass pea than in pea after treatments with hypoxic stress or re-oxygenation.5 The activities of both antioxidant enzymes,superoxide dismutase(SOD)and catalase(CAT),were apparently higher in root tips of grass pea than those in pea after treated with hypoxic and re-oxygenation by isoenzyme analysis of native polyacrylamide gel electrophoresis(PAGE).6 Electrophoretic analysis of P-cyanoalanine synthase(CASase)isoenzymes were conducted using PAGE with 5-15%gradient gels combined with an enzyme activity stain.CASase,belonging to the cysteine synthase(CSase)family,catalyzes toxic metabolite hydrogen cyanide(HCN)and converts to ?-cyanoalanine.The results suggested that the activity of CASase was apparently higher in both the primary and lateral roots of grass pea than that in pea after hypoxic treatment.7 Membrane leakage was determined by measurement of electrolyte leaked from root tips of grass pea and pea after treated with hypoxic and re-oxygenation treatments,and found that the membrane integrity was obviously higher in the root tips of grass pea than that in pea.Based on the above dates,grass pea has highly scavenging ability to the strong phytotoxins(ROS and HCN),and it can generate abundant adventitious roots to protect membrane integrity during longer flooding stress.And the results indicates that grass pea is coincident with flooding tolerant plants according to its performance under hypoxic stress of flooding,and it may be a member of flooding-tolerant plants.