Abstract:

Some important physiological characters of Liriodendron reciprocal hybrids and parents under water stress were studied.The results were as follows:The decrease rate of relative water content, chlorophyll content as well as protein content and increase rate of RNase activity in leaf blades under water stress were L.chinense (Hemsl.) Sarg.> L.tulipifera Linn.>plus crossing F₁>minus crossing F₁.L.chinense was severely damaged by short water stress. Direct evidences from ³H-Gly labeling under water stress proved both that RNase genes of parents and hybrids were expressed in translation level as well as RNase were synthesized de novo and that intensity of RNase gene expression was L.chinense>L.tulipifera>plus crossing F₁>minus crossing F₁. Indirect evidences from protein synthetic inhabitor under water stress indicated that RNase activity increase of parents might be involved in cytoplasmic mRNA translation and RNase release, activation and/or synthesis of chloroplast and/or mitochondria, but RNase activity increase of hybrids might originate mainly from cytoplasmic mRNA translation, not from chloroplast and/or mitochondria. The above-mentioned experimental evidences fully proved both that reciprocal hybrids displayed notable super-parent heterosis of resistance to water stress and that minus crossing F₁ possessed stronger powerful heterosis of resistance to water stress than plus crossing F₁. The researches revealed molecular mechanism of powerful positive heterotic formation of growth, adaptability and resistance on the basis of the resistance to water stress and showed geneticists and breeders of forest-tree who are engaged in fixation and utilization of heterosis of the hybrid tulip tree must lay special stress on clones of minus crossing F₁.

Key words: Water stress, Liriodendron, Hybrid tulip tree, Physiological character, Heterosis