Photosynthetic Characteristics Of Pod Wall And Physiological Response To Drought Stress In Alfalfa

Leaves have been researched all the time as the unique photosynthetic organ.Studying the photosynthetic characteristics of non-leaf organs to increase the overall photosynthetic capacity of crop is meanfulling to further increase crop yield.Nowdays,most of alfalfa seeds in China are procuded in arid region in Gansu and other provinces.Drought is one of factors restricting alfalfa seed production.Thus,investaging and researching the photosynthetic responses of non-leaf orgeas of alfalfa to drought stress probably provide a novel thought to increase seed yield,which is of great theoretical significance to achieve high yield cultivation.In this study,a non-leaf organ in alfalfa,pod wall,was researched on the relative photosynthetic contribution to pod and seed weight per pod,photosynthetic property,the translation of photosynthetic product and the proteomic analysis of proteins involved in the related pathway with photosynthesis and other metabolism.The main results went as follows:(1)All leaves or pods of two cultivars(Zhongmu No.1,Zhongmu No.2)of Medicago sativa L.and one cultivar(Caoyuan No.3)of M.varia Martyn planted in the filed were shaded with aluminum foil on 15th(T1),20th(T2)and 25th July 2015(T3),respectively and the control was no shading.Results showed that shading all leaves or pods could decrease total pod weight(TWP)and seed weight per pod(SWP),compared to the control.The highest relative photosynthetic contribution of pod wall was observed,when the treatment was T1,to TWP with 15%?40%and to SWP with 26%?48%.In addition,pod wall had the higher relative photosynthetic contribution to TWP and SWP in one-coil spiral pods than in two-coil spiral pods.(2)M.satia L.Gannong No.6 and Zhongmu No.2 were planted in pots in the greenhouse under well-watered and water-stressed treatments.Samples of pod wall on 5 days(DAP5),10 days(DAP10),15 days(DAP15)and 20 days after artificial pollination(DAP20)were collected to determine some indices.Results showed with the development of pod wall,the chlorophyll a,chlorophyll b and gross chlorophyll concentration declined and the chlorophyll concentration of pod wall was higher under well-watered treatments than water-stressed treatments.As the pod wall developed,PEPC activity in pod wall firstly increased and then decreased and drought stress could promote PEPC activity.Nevertheless,RuBPC activity decreased with the development of pod wall and was higher under well-watered than under water-stressed treatments.The structure of chloroplast in pod wall turned blurry and the membrance of chloroplast became damaged as the pod wall developed.Many starch grains accumulated in the chloroplast at the late development stage under well-water treatments.Drought stress did not damage the structure of the chloroplast in the pod wall at the eraly development stage but did at the late development stage resulting in the lack of starch in the chloroplast.(3)M.sativa L.Zhongmu No.2 was planted in pots in the greenhouse under well-watered and water-stressed treatments.Pod wall of pods on DAP 10,DAP 15,DAP20 and DAP25 was labeled with 13CO2 isotope.The value of ?13 was determined in the pod wall and seeds 24 h after completing labeling.Results showed that the value of ?13C decreased in pod wall and seeds of pods under well-watered and water-stressed treatments as the development stages went and drought stress decreased the value of ?13C in pod wall and seeds.In addition,61%-79%of ?13C was measured in seeds proportioning in the whole pod(pod wall+seeds).(4)M.sativa L.Zhongmu No.2 was planted in pots in the greenhouse under well-watered and water-stressed treatments.The proteins in pod wall were extracted,identified and analyzed by label-free quantitative proteomics from pods on DAP10,DAP15 and DAP20.Results showed that chlorophyll a-b binding proteins and proteins involved in photosystem ? and photosystem ? in pod wall were down-regulated as the pod wall developed and drought stress led to their down-regulation expression.PEPC in pod wall was up-regulated with the development of pod wall and drought stress induced up-regulation expression of proteins involved in C4 cycle and the reduction phase of the Calvin cycle but resulted in the down-regulation of proteins involved in the regeneration of RuBPC.In addition,proteins participating in carbohydrate,energy and other metabolism were up-regulated in pod wall under drought stress,which contributed to enhance the resistance to drought stress.