Grafting Increases Chilling Tolerance In Sweet Pepper Seedlings

The root characteristics of'Chifengtexuan'own-root seedlings (control, CK),'Weishi'and'Buyeding'rootstock seedlings (WO, BO), and graft seedlings which'Chifengtexuan'scion grafted onto'Weishi'and'Buyeding'rootstocks (WG, BG), and graft on mechanism of chilling tolorance in sweet pepper were investigated. The results were as follows.1. The total length, weight, volume, tips, surface area, and activity of roots in rootstock seedlings and graft seedlings were significant higher than those of roots in own-root seedlings. Low temperature stress decreased the above indexes of all seedlings, but the decreasing amplitude of WO and WG showed the least and CK the largest. Returned to normal condition, the root length, weight, volume, tips, total surface area, et al. of sweet peppers mostly failed to the primary level in 5 days except to the root activity.2. Low temperature led to decrease in photosynthetic rate (Pn), stomatal conductance (Gs), and carboxylation efficiency (CE) over 50% in 3 days. Then, the Pn and Gs was tending towards stability, but CE decreased continually.The intercellular CO2 concentration (Ci) declined at first, whereas enhanced at latter four days during stress period. Low temperature and weak light intensity decreased maximal photochemical efficiency of PSⅡin darkness (Fv/Fm), actual photochemical efficiency of PSⅡduring illumination (ФPSⅡ), and electron transport rate (ETR), but increased initial fluorescence (Fo). These implied that low temperature stress caused a damage of photosynthetic apparatus, but the damage recovered in 3 days. Compered with the control, Grafting increased Pn, Gs, CE,ФPSⅡ, and Fv/Fm with various degrees, but decreased Fo after both low temperature stress and recovery. So we conclude that grafting leads to increase in photosynthetic function, and alleviate in the effect of low temperature and light intensity on photosynthesis of sweet pepper seedlings.3. Richer kinds of fatty acid were detected in leaves than in roots of own-root and graft sweet pepper seedlings. Low temperature increased the relative content of unsaturated fatty acids in sweet pepper seedlings. The relative content of unsaturated fatty acids in graft seedlings was higher than that of in own-root seedlings on the eve of stress, after stress, and recovery stage.4. Low temperature decreased IAA and GA3 contents in leaves and GA3 content in roots of sweet pepper seedlings, but increased ABA content. Graft seedlings showed higher contents of IAA, GA3 and ABA in leaves and GA3 and ABA in roots, lower ratio of GA3 and ABA, compared with own-root seedlings. These data suggest that lower ratio of GA3/ABA is one of the important internal causes of the increase in chilling tolerance in graft seedlings of sweet pepper.5. The APX and GR activity increased at first day, whereas decreased at latter six days during stress period, and hadn't recovery in 3 d under normal condition. Compared with the own- root seedlings, graft seedlings showed higher activity of APX and GR in all treating stages. The APX and GR activity of WG was significant higher than that of BG. These data suggeste that graft alleviate the chilling damage in sweet pepper seedlings by holding higher antioxidation enzymes activity, and improving the eliminating capacity to reactive oxygen species.6. Water potential and osmotic potential of sweet pepper seedlings decreased gradually in the first, but increased 5 d latter. The soluble sugar and proline contents increased as stress time increased. The potential and osmotic potential of sweet pepper seedlings increased continually in recovey days, but hadn't came to the primary levels in 3 d. The soluble sugar and proline contents decreased at first, while increased afterwards, and were significant higher than those on the eve of stress. Graft seedlings showed higher water potential, osmotic potential, soluble sugar and proline contents compared with own-root seedlings, and those of in WG were higher than in BG. Increase in content of osmoregulation substances is one of the important internal causes of the increase in chilling tolerance in graft seedlings of sweet pepper.