Study On Physiological And Biochemical Responses Of Two Kinds Of Begonia Semperflorens In Leaf Color Under High Temperature Stress

Begonia semperflorens, perennial herb, belongs to Begonia genus of begoniaceae family. Itoriginates from Brazil and prefers warm humid climate condition, but can not endure hightemperature. The optimum growth temperature for Begonia semperflorens is25℃. In recent years,Begonia semperflorens are widely applied as year-round ground cover and parterre flowers. However,many Begonia semperflorens can not resist high temperature. And thus it very important to select theheat tolerant cultivars.In the present work, high semi-lethal temperature of red leaves cultivars ‘Bada Boom’,‘Cocktail’,‘Vision’ and green leaves cultivars ‘Super Olympia’,‘Party’,‘Lotto’ of Begonia semperflorens weredetermined by conductivity method combined with Logistic equation. Then2cultivars with differentheat tolerances (heat-resistant cultivars ‘Bada Boom’ with red leaves and heat-sensitive cultivar‘Lotto’ with green leaves) was selected to study the effects of38℃heat stress onBegoniasemperflorens plants. The results were as follows:1. High semi-lethal temperature of Six cultivars of Begonia semperflorens orders arrangeed fromhigh to low as follows:‘Bada Boom’>‘Cocktail’>‘Vision’>‘Super Olympia’>‘Party’>‘Lotto’. It ispreliminarily concluded that high semi-lethal temperature of red leaves cultivars are higher than greenleaves cultivars, suggesting that red leaves cultivars more resistant to heat stress than green cultivars.This result was consistent with heat injury index and relative conductivity rate performance whenplant exposed to high temperature.2. By studying the differences in pigment content, photosynthetic characteristics and chlorophyllfluorescence parameters of leaves of red leaves cultivars ‘Bada Boom’ and green leaves cultivars‘Lotto’ under high temperature, heat resistance of the two cultivars had been compared. With theextension of heat stress time,‘Bada Boom’ compared with ‘Lotto’, the proportion of chlorophyll a/bincreases, phenylalanin ammonia-lyase (PAL) activity subjects to a lesser degree of inhibition,dihydroflavonol reductase (DFR) has a high activity and chalcone isomerase (CHI) activity is morestable, anthocyanins content also significantly higher than green leaves cultivars ‘Lotto’; maximalphotochemical efficiency of PSⅡphotochemistry (Fv/Fm), efficiency of energy capture by open PSⅡreaction centres (Fv’/Fm’), effective photochemical quantum yield of PSⅡ (Y(Ⅱ)) and electrontransport rate (ETR) subject to a lesser inhibition degree by the high temperature stress, it Has a higher heat dissipation capacity (NPQ) and quantum yield of light-induced non-photochemicalfluorescence quenching (Y(NPQ)), which can dissipate excess light energy to alleviate photic injury, butalso photochemical reaction capacity of PSⅡin light adaptation status is less inhibition caused byhigh temperature stress; Reduction of net photosynthetic rate (A) of two cultivars is firstly caused bystomatal factors and then caused by non-stomatal factors, but ‘Bada Boom’ has a higher netphotosynthetic rate (A), the stomatal conductance (Gs), and transpiration rate (E) than ‘Lotto’, it isless inhibition caused by high temperature stress. All in all, red leaves cultivars ‘Bada Boom’ has ahigher heat resistance than green leaves cultivars ‘Lotto’.3. Antioxidant enzyme activities and antioxidant capacity of leaves of red leaves cultivars ‘BadaBoom’ and green leaves cultivars ‘Lotto’ under high temperature were studied. With the extension ofheat stress time,‘Bada Boom’ compared with ‘Lotto’, Superoxide dismutase (SOD) activity subjectsto a lesser extent inhibited by high temperature, it has a higher ascorbate peroxidase (APX) activity,also a higher and more stable catalase (CAT) activity, it can remain a certain free radical scavengingability in late stage of stress; In late stage of heat stress,‘Bada Boom’ compared with ‘Lotto’, hashigher DPPH scavenging activity and FRAP values, namely has a higher active oxygen radicalscavenging capacity and antioxidant capacity to alleviate the oxidative damage caused by hightemperature stress. For the two different leaves color cultivars, differences in their antioxidantcapacity may be due to the combined effect results of anthocyanin and antioxidant enzyme system,but whether anthocyanins play a major role in antioxidant capacity is needed to further study.