| High temperature stress (HTS) is one of the major limiting factors that affect the quality ofintensive seedlings in protected facilitates during summer and autumn, it is an effective way forplant to obtain stress resistance that using temperature stress to induce plant to producecross-adaption. First, in order to explore the alleviating effect of cold-shock intensity on tomatoseedlings under HTS, we use artificial climate chamber to stimulate HTS of gradually-changedtemperature in summer facilities and study the effect of different cold-shock intensity on tomatoseedlings (tomato seedlings were subjected to cold-shock treatments every day with5℃,10℃,and15℃for10min,20min, and30min, respectively, in an artificial climate chamber).Second,on the basis of the intensity of screening on cold-shock, the daily of start time of cold-shock wasscreened from from four kinds of time (before the high temperature stress4h, high temperaturestress before2h, when the high temperature stress begin, heat stress after2h); Next, the optimalduration of cold-shock was screened by duration of cold-shock (Tomato seedlings werecold-shock treated at the first true leaf stage and the treatment was lasted for3d,6d,9d,12d,15d,18d,21d, respectively) and duration of cold-shock (Tomato seedlings were cold-shock treatedat different calendar of tomato seedling and the treatment was lasted for21d,18d,15d,12d,9d,6d,3d, respectively); Last, single cold shock is used to verify the impact of the cold shockintensity on tomato seedling growth. The results are as follows:1. Hypocotylar extension and plant height of tomato seedlings were restrained bycold-shock treatment before HTS was met. The alleviating effect of tomato seedlings under HTSby cold-shock varied greatly with different temperatures and durations. The results indicated thatcross adaptive response of tomato seedling can be induced with moderate cold-shock temperatureand duration before HTS was met. The optimum temperature and duration of cold-shock treatmentwas at10℃for10min per day.2. Considering the effects of the start time of cold-shock on growth and physiology oftomato seedlings, the best treatment is that tomato seedlings were subjected to cold-shocktreatments every day with10℃for10min before the high temperature stress4h.3. Tomato seedlings were cold-shock treated at the first or second true leaf stage duration for15days that is an effective way to improve healthy index and plant stress resistance. If tomatoseedlings were cold-shock duration for21days, tomato seedling chilling injury would be induced,and the relative conductivity of tomato seedlings would be risen, producing an adverse effect ontomato seedlings. On the other hand, as compared with the control, tomato seedlings wascold-shock duration for shorter, such3days, the alleviating effect of cold-shock intensity ontomato seedlings under HTS was no significantly difference.4. Physiological and biochemical reactions of tomato seedlings can be affected once with10℃for10min before the high temperature stress4h.5. With the increasing of tomato seedling age, the restrained effects of cold-shock on plantheight of tomato seedlings was weak gradually, but stem diameter and healthy index of tomatoseedlings still higher than contrast. Cell ultrastructure did not display significant changes underHTS, which suggested that tomato seedling was adapted to HTS. The plasma membrane andtonoplast of cold-shock treatment and the chloroplast and mitochondria structure could beobserved clearly, compact and orderly when shocked tomato seedlings with10℃for10minbefore the high temperature stress4h, and lasted for20days. Cold-shock acclimation can promotethe development of flower bud differentiation of tomato seedlings, especially early flower buddifferentiation, whereas, compared with the control, number of fruits and rate of fruits increasedsignificantly after plant. |
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