Trehalose Treatment Alleviates Drought Damage To Photosynthetic Apparatusin Apple Leaves

Photosynthesis is the foundation of plant growth and yiel.But drought often restricts photosynthesis.Trehalose is an important osmotic regulator of plant to resist to environmental stress.To study the effects of drought stress on photosynthesis in apple leaves aftertrehalose treatment,two parts experiments were carried out on 3-4-year-old potted plant Changfu2 / M26 / Octopus: part of the leaves were placed in different trehalose concentration solution?0,5,10,20,40,80 mM?and then treated with 1800 ?mol m^-2 s^-1 light intensity,30% PEG6000 and 1800 ?mol m^-2 s^-1light intensitywith 30% PEG6000 respectively.In the other part,20 mM trehalose was sprayed on the foliage and pure water as the control.Then plants were subjected to drought stress,and normal irrigationwas taken as control.Gas exchange and chlorophyll fluorescence parameters were measured at 9:30^-10:30 and 13:30^-14:30,and active oxygen,antioxidant enzyme activities and other physiological indicators were also determined.The main resultswere as follows:1.Drought stress significantly reduced the leaf water potential,leaf relative water content,chlorophyll content,net photosynthetic rate?Pn?,and increased reactive oxygen species?O₂ ·-,H₂O₂?and malondialdehyde?MDA?,and also enhanced the activity of antioxidant enzymes?SOD,CAT,APX?.It may show that the structure of thylakoid membrane was destroyed.And the effects were exacerbated in the plants when exposed to both drought and high temperature with strong light stress.2.The experiments in vitro showed that20 mM was the optimum concentration of trehalose for resistance to drought and strong light stresses.And the trehalose content in the leaves was increased after spraying treatment,which indicates the absorption and utilization in trehalose by apple leaves.Compared with the control,exogenous trehalose treatment could increase leaf water potential and the relative water content in apple leaves under the drought stress,which shows that the trehalose could improve the osmotic adjustment ability of apple leaves.3.Trehalose pretreatment effectively enhanced the photosynthetic rate?Pn?,stomatal conductance?g_s?,transpiration rate?E?and increased the maximum photochemical efficiency?F_v/F_m?,photochemical efficiency?F_v'/F_m'?,the coefficient of photochemical quenching?qP?qL?and effective photochemical quantum yield of PSII(?_PSII),which indicates the improvement of the photosynthesis.Under both drought and high temperature with strong light stress conditions,the non-photochemical quenching?NPQ?decreased but quantum yield of non-regulated heat dissipation and fluorescence emission(?_NO)increased in untreated-trehalose plants.However the change of?_NO in trehalose-treated leaves was not obvious.The results may show that trehalose plays an important role in protecting the photosynthetic mechanisms by enhancing heat dissipation.4.After treatment with trehalose,the contents of O₂ ·-,H₂O₂ and MDA in apple leaves decreased,the activities of antioxidant enzymes such as APX,GR,DHAR and MDHAR increased,and the damage degree of thylakoid membrane also decreased.It indicated that trehalose could protect the integrity of the cell membrane structurethrough the removal of reactive oxygen free radicals.Above results showed that trehalose is an important protective agent for apple treestoresist the drought stress.The protective mechanism is to dissipate excess light energy,remove reactive oxygen free radicals,maintain membrane stability and then protect photosynthetic organs from drought and strong light stresses to keep a higher photosynthesis,which could ensure the normal plant growth.