Heat Tolerance Study Under High Temperature Stress Of Beta Vulgaris L

This experiment mainly explored the changes of photosynthetic characteristics of Betavulgaris L. under different heat treatments. It is composed of three modules: Firstly, wesearched for the critical tolerant temperature of Beta vulgaris L. under high temperature stress.Secondly, the recovery of photosynthesis after high temperature stress under light and darkconditions of Beta vulgaris L. was conducted. Finally, Beta vulgaris L. was pretrented withsality before high temperature treatment to test the cross-resistance of high temperature andsalinity in Beta vulgaris L. The results are as follows:1. The critical temperature of high temperature stress in Beta vulgaris L.With the increase of processing temperature, the net photosynthetic rate (Pn) of Betavulgaris L. decreased and began to be negative at51℃. The stomatal conductanceincreased astreatment temperature rose. At temperatures below42℃, the decrease of Pn ofBeta vulgaris L.was chiefly caused by stomatal limitation factors. Non-stomatal limitation factors such as thedamage to photosynthetic apparatus or mesophylls played a fundamental role whentemperatures were higher than45℃.With the rising of treatment temperature, ΦPSII gradually reduced and started to show Kphase at42℃inBeta vulgaris L. Meanwhile, ΦPo and ΦEo also decreased, while ΦDoincreased significantly, suggesting that Beta vulgaris L. alleviated the influence of hightemperature on the growth and development by increasing heat dissipation. High temperaturetreatments reduced RC/CSm、ABS/CSm and TRo/CSm. However, ETo/RC increased. DIo/RCalso increased under high temperature.Above all,42℃was the critical temperature forBeta vulgaris L. to heat stress.2. The recovery of Beta vulgaris L. after high temperature treatmentsAfter high temperature treatments, the recovery of photosynthetic oxygen evolution was consistent with Pn in Beta vulgaris L., which returned to normal after8hours when treated at39℃. The same results were observed after48hours at42℃. But it showed no recovery whentreated at48℃.The initial fluorescence Fo didn’t increase at39℃until the temperatures got higher than42℃. It returned to normal within48hours under light when treated at42℃, but no visiblerecovery in the dark was observed. When treated at45℃, however, it also recovered to somedegree under light, but didn’t recover in the dark.Beta vulgaris L. could restore to the level before processing after treatment at39℃in thelight, suggesting the damage to PSII was minimal. After treatment at42℃, PSII recovered inthe light to some extent, but this didn’t happen in the dark, implying that42℃damagedphotosystem in Beta vularis L., but the damage was reversible and the repair waslight-dependent.3. The cross-resistance to salt stress and high temperature in Beta vulgaris L.At normal temperature of25℃, salt treatment reduced the RC/CSm in Beta vulgaris L..However, the RC/Csm of Beta vulgaris L. under salt treatment was significantly higher than thecontrol group at42℃and even at45℃. The ΦEo、PIABS、Pn、ΦPo of Beta vulgaris L. showedthe same trend with RC/CSm under salt and high temperature treatment, but ΦDo changedoppositely. This indicated that pre-salt treatment alleviated the damage to Beta vulgaris L.under high temperature treatment. Pre-salt treatment contributed to reduce heat dissipation andincreased the energy consumption by electron transport, however, the reduction of RC/CSm andPIABSwas inhibited. Overall, moderate salt treatment enhanced the heat resistance of Betavulgaris L.. And there was considerable cross-resistance between salt and high temperaturetreatment in Beta vulgaris L..