| In this study,we analyzed the morphological characteristics,photosynthetic characteristics,osmoregulatory effects,and physiological and biochemical mechanisms of peanut seedlings in response to low temperature(15 ℃/10 ℃),drought(40%～45%of field water holding capacity)and their compound stress conditions by using better tolerant peanut varieties NH5 and HY22,and sensitive peanut varieties NH16 and HY20 as test materials in indoor pots.We investigated the physiological and biochemical mechanisms of peanut seedlings in response to low temperature,drought and other complex stresses,and aimed to provide theoretical basis and technical support for peanut stress cultivation in northeast China.The main findings are as follows.1.Seedlings of the four varieties showed significant differences in growth and development,with NH5 and HY22 showing higher growth in main stem height,leaf area,fresh weight,and dry weight than NH16 and HY20.Compared with the single stress of low temperature and drought,compound stress more significantly affected the growth and development of peanut seedlings;the root activity of each variety decreased with stress,with the greatest decrease in root activity under compound stress,and the sensitive varieties NH16 and HY20 showed a greater decrease in root activity compared with the tolerant varieties NH5 and HY22.2.As the degree of stress deepened,significant differences in photosynthetic physiology were shown among the four varieties as well as among the varieties in different treatments.The photosynthetic capacity of each variety decreased significantly after suffering from stress,and the effect of drought stress on photosynthetic capacity was greater,followed by compound stress and low temperature stress;with the extension of stress time,the light dissipation capacity of each variety gradually weakened,therefore,the non-photochemical quenching coefficient(NPQ)increased in the early stage of stress and decreased in the late stage of stress;after restoring normal conditions of culture,the photosynthetic capacity of each variety was recovered to some extent The photosynthetic capacity of each species recovered to some extent after restoration to normal conditions,but some indicators still could not recover to the control level in the short term,such as chlorophyll content.3.The accumulation of osmoregulatory substances in plants under stress conditions is also a way to resist adversity.The water content of plants of each species varied significantly when subjected to stress.The relative water content of each variety decreased significantly during stress,with the greatest decrease under drought stress,followed by complex stress;the natural saturation deficit of each variety gradually increased with the extension of stress time,and the peak natural saturation deficit under drought stress was much higher than that under low temperature and complex stress;it showed more severe water loss in sensitive varieties among varieties.The peak accumulation of osmoregulatory substances in the leaves of NH16 and HY20 seedlings was higher in the sensitive varieties,while the change was relatively stable in the tolerant varieties;the change of osmoregulatory substance content was more significant in the varieties under drought stress and compound stress.The content of osmoregulatory substances in the sensitive varieties was still significantly higher than the control level after 3 days of incubation under normal conditions were restored.4.The content of reactive oxygen species in peanut seedlings increased significantly under stress conditions,among which,sensitive varieties NH16 and HY20 accumulated much more reactive oxygen species in seedlings than tolerant varieties NH5 and HY22 with the prolongation of stress time,and the reactive oxygen species showed higher compound stress than drought stress than low temperature stress between treatments,and the reactive oxygen species decreased after resuming normal conditions of incubation.In terms of the activities of antioxidant enzymes SOD,POD and CAT,the more tolerant varieties NH5 and HY22 had stronger antioxidant capacity than the sensitive varieties NH16 and HY20.The activities of SOD enzymes and POD enzymes of each variety increased and then decreased during the stress treatment,and the CAT enzyme activities of the tolerant varieties NH5 and HY22 increased and then decreased,but the CAT enzyme activities of the sensitive varieties continued to decrease during the treatment;the antioxidant enzyme activities of each variety were stronger during the single stress of drought or low temperature and slightly weaker during the compound stress,and after resuming normal conditions of incubation,the tolerant varieties’ The antioxidant enzyme activity of the tolerant varieties decreased to the control level after restoration to normal conditions,and the antioxidant enzyme activity of the sensitive varieties was still significantly higher than that of the control.5.Under control conditions,the cellular,chloroplast and mitochondrial structures of each variety had high structural integrity.Sensitive varieties NH16 and HY20 lost water severely under drought stress,with complete disappearance of the central large vesicles,severe damage to chloroplast membrane structure and stromal lamellae structure,outflow of starch granules,dissolution of mitochondrial membranes and disappearance of ridges,while tolerant varieties NH5 and HY22 performed better than sensitive varieties,maintaining relatively intact membrane structure as well as part of the wellstructured chloroplast stromal lamellae;after restoration of normal conditions of culture,compound After restoration to normal conditions,the lamellae of NH5 treated with compound stress were disorganized,a large number of metabolites appeared in NH16 vesicles,vesicles were still not seen in HY20 and stromal wall separation was observed,and mitochondria were still severely damaged;compared with single stress,compound stress conditions had more severe effects on leaf cells and organelles. |
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