Studies On Heat-adaptation Mechanism And Selection Of Heat-tolerant Clones For Nut Production Of Ginkgo

In this paper, 20 clones of Ginkgo biloba growing in Ginkgo germplasm nursery in Pizhou city and 6 half-sib families 2a seedlings (the F1 of the above-mentioned 20 clones) were materials for study. First, the heat-tolerance of 6 half-sib families was assessed. Based on the result, the mechanism of heat adaptation was explored by comparing heat-sensitive half-sib family and heat-tolerant half-sib family. Further, 20 clones were assessed comprehensively basing on heat tolerance, nut yield, single nut weight, and photosynthetic productivity. The results were as follows:(1) The heat-tolerance of 33# half-sib familiy was poor, while that of 37# half-sib familie was strong, the two half-sib families were ideal contrast materials for exploring the mechanism of heat adaptation of G. biloba.(2) Under heat stress, the ultrastructuress of leaf mesophyll cells of G. biloba injured significantly, which happened more seriously in heat-sensitive half-sib family than heat-tolerant half-sib family. To a certain extent, there was a correlation between the change of ultrastructure and heat-tolerance.(3) Under heat stress, the physiological and biochemical activities of G. biloba changed dramatically. The leaf relative water content decreased with the increase of heat stress, the decrease range of relative water content of heat-sensitive half-sib family was larger than that of heat-tolerant half-sib family. Compared with heat-tolerant half-sib family, the increase amplitude of the production rate of O2-, the content of H2O2 and MDA, and relative electric conductivity were more. There was an obvious difference in SOD activity and ASA content between different heat-tolerance of materials and stress degree, and the increase amplitude of both SOD activity and ASA content of heat-tolerant half-sib family was more than that of heat-sensivity half-sib family. Heat stress caused soluble sugar and proline accumulate in both half-sib families, but more in heat-tolerant half-sib family compared to heat-sensitive half-sib family. The temperature at which normal proteins synthesis was blocked and the temperature at which heat shock proteins synthesis occurred was higher on heat-tolerant half-sib family than on heat-sensitive half-sib family. With the increasing of heat stress, photochemical efficiency deacreased and the reduction range of heat-sensitive family was larger than that of heat-tolerant family. The photosynthetic rate of heat-tolerant half-sib family was less affected by heat stress than heat-sensitive half-sib family, heat-tolerant half-sib family could strengthen transpiration to reduce leaf temperature in order to adapt to high-temperature environments.(4) Electrophoresis patterns of total proteins in the leaves of G. biloba were significantly affected by heat stress; down-regulated proteins and their ratio to the total proteins were higher in the heat-sensitive half-sib family, on the contrary, Up-regulated proteins and their ratio to the total proteins were higher in the heat-tolerant half-sib family. It suggested that the higher heat-tolerance in the heat-tolerant half-sib family may be related with its ability to produce more up-regulated proteins and special expressing proteins under heat stress.(5) Under heat stress, Ca2+ in leaf mesophyll of G. biloba tended to transport from vacuole to cytoplasm. Compared to control, the calcium antimonite deposits of Ca2+ in cytoplasm of heat-sensitive half-sib family were larger and aggregated abnormally as block shape, but the shape of the calcium antimonite deposits of Ca2+ of heat-tolerant half-sib family hardly changed. Under heat stress, different responses of Ca2+ distribution in two half-sib families on heat stress might be closely related to the heat-tolerance of G. biloba.(6) Based on the correlation between the heat-tolerance and semi-lethal temperature of above-mentioned 6 half-sib families of G. biloba, semi-lethal temperature was regarded as an effective parameter to assess heat tolerance of G. biloba. Hence, further assessment on the heat-tolerance of above-mentioned 20 clones was conducted by measuring the semi-lethal temperatures. The results showed that the heat-tolerance order among half-sib families was in agreement with that among clones. Moreover, to select tolerant superior clones, the nut yield clones, single nut weight, and photosynthetic of 20 strain were measured. The results showed that the clones of 27#, 31#, and 57# for nut-production clones had a great potential to grow in south China. Among them, 27# was the best choice for introduction towards south China.