盐胁迫对2种抗性苹果砧木叶片生理及解剖结构的影响

Effects of salt stress on leaf physiology and anatomical structure of two resistant apple rootstocks

【目的】探究盐胁迫对2种抗性不同苹果砧木垂丝海棠‘9-1-6’(Malus halliana Koehne)和山定子(Malus baccata Borkh.)叶片生理特性和解剖结构的影响。【方法】通过盆栽浇灌Hogland营养液的方法,在100 mmol·L^(-1) NaCl短期(3 d)和长期(40 d)胁迫下测定2种苹果砧木叶片生理指标和解剖结构变化情况。【结果】随着胁迫的持续,2种砧木叶片相对叶绿素含量(SPAD)、吲哚乙酸(IAA)、玉米素(ZT)、异戊烯基呤核苷(iPA)含量和IAA/脱落酸(ABA)均显著下降,叶绿素酶(Chlase)活性、脱镁螯合酶(MDCase)活性、脱镁叶绿素a氧化酶(PaO)活性、ABA和茉莉酸(JA)含量均显著上升,胁迫40 d后,2个品种叶片Chlase活性无显著差异,‘9-1-6’叶片的iPA含量显著低于山定子,其余指标‘9-1-6’的变幅均小于山定子;2种砧木叶片、上下表皮、栅栏组织厚度和叶肉组织结构紧密度(CTR)均显著减小,海绵组织厚度和叶肉组织结构疏松度(SR)均显著增加,且‘9-1-6’变幅均小于山定子。【结论】垂丝海棠‘9-1-6’通过保持较高的SPAD、较厚的叶片和完整的双层栅栏组织缓解了植株的光合损伤,通过调节叶绿素代谢酶活性和内源激素(IAA、ZT和ABA)含量的平衡响应盐胁迫。

【Objective】Mauls domestica Borkh.is one of the most important cultivated fruit trees in temperate regions.The Northwest Loess Plateau has sufficient sunlight,large diurnal temperature difference,and suitable altitude.It has been the world’s largest apple eugenic area,but more than 70% of this area is saline-alkali land.In addition,due to the lack of organic fertilizers and excessive application of chemical fertilizers,secondary salinization of the soil is becoming serious,which restricts the further development of apple industry in this region.Therefore,it is of great significance to select and apply rootstocks with strong resistance for high-quality and high yield of fruit trees.Previous studies mostly focused on the comparison of salt tolerance among different varieties,but there were no reports on physiological mechanisms behind their difference in tolerance.Related research of perennial plants including fruit trees focus on photosynthesis,antioxidant system and fruit quality,while studies on chlorophyll metabolism and endogenous hormones are rarely reported.M.halliana Koehne is distributed in Hexi Corridor of Gansu,which has the characteristics of drought tolerance and saline alkali tolerance.M.baccata Borkh.,native to the northeast,is resistant to cold and drought but not tolerant to salt and alkali stresses.In this study,two apple rootstocks with significant difference in resistances,M.halliana‘9-1-6’(selected by this research group)and M.baccata,were used to determine the changes in the activities of key enzymes in chlorophyll metabolism under salt stress.The relationship between endogenous hormones and the anatomical structure of the leaves and the saline environment was analyzed.The study would enrich the physiological and ecological understandings of salt tolerance of apple rootstocks.【Methods】The experiment consisted of two treatments,the control(pH 6.8)and salt stress treatment(pH 7.0).Each treatment had 5 biological replicates each with 4 pot plants.According to previous experiments,100 mmol·L^(-1) NaCl was used for the salt stress treatment.The materials were one-yearold 9-1-6 and M.baccata seedlings.The Hogland nutrient solution was applied for the potted seedlings.After short-term(3 d)and long-term(40 d)exposure to salt stress,relative chlorophyll content(SPAD),key enzymes of chlorophyll metabolism(Chlase,MDcase and PaO),contents of endogenous hormones(IAA,ABA,iPA,ZT,JA)and anatomical structure of the leaves were analyzed and compared.【Results】Compared with control,SPAD of the leaf of M.halliana‘9-1-6’and M.baccata was decreased by 44.56% and 74.00%,the activity of chlase increased by 42.83% and 32.44%,MDcase activity increased by 70.59% and 68.52%,and PaO activity increased by 87.70% and 72.73% by salt stress,respectively.There was no significant difference between the two rootstock leaves in Chlase activity after 40 days of salt stress.However,MDcase and PaO activities in‘9-1-6’leaves were significantly lower than those in M.baccata.In addition,under salt stress,IAA content of the leaves decreased by 7.17% and 20.24%,ZT by 26.98% and 52.65%,iPA by 50.04% and 43.59%,and IAA/ABA by 10.53% and 23.47% in‘9-1-6’and M.baccata,respectively,but ABA increased by 6.28% and 0.96%,JA by 110.88% and 115.03%,respectively.After 40 days of salt stress,the decrease in iPA of‘9-1-6’blades was significantly higher than that of M.baccata,while the declines in IAA,ZT and IAA/ABA were significantly lower in M.baccata.In addition,the content of ABA in leaves of‘9-1-6’was significantly higher than that of M.baccata after salt stress for 40 days,while the content of JA in leaves of‘9-1-6’was significantly lower than that of M.baccata.Under salt stress,leaf thickness,epidermal thickness,palisade tissue thickness and CTR of the two rootstocks were significantly reduced,but the decline rates were different.Compared with CK,leaf thickness,epidermal thickness,palisade tissue thickness and CTR of the leaves of‘9-1-6’decreased by 24.52%,39.71%,28.04%,37.08%,and 16.65%,respectively,while that of M.baccata leaves,decreased by 33.87%,47.85%,31.02%,53.62% and 29.89%,respectively.The decline in‘9-1-6’was significantly smaller than in M.baccata.The thickness and SR of the sponge tissue in the two rootstocks increased significantly.The thickness and SR of the sponge tissue of‘9-1-6’leaves were significantly smaller than those of M.baccata.【Conclusion】Under salt stress,the chlorophyll metabolism enzyme activity,endogenous hormones and leaf anatomical structure of the two rootstocks changed significantly.In the high salt-resistant M.halliana‘9-1-6’photosynthetic damage was alleviated by maintaining high SPAD,thick leaves and intact double-layered palisade tissue,and by regulating of the activities of chlorophyll metabolizing enzymes and balancing endogenous hormones content(IAA,ZT and ABA).