Effects Of Low Temperature And Short Day On Callose Deposition And Gene Expression In The Phloem Of Poplar

Woody plants in the north temperate zone experience a repetitive cold-to-warm transition during their whole life thus have evolved a mechanism that cambium activity ceases during rigorous winter and reactivate it in the next comfortable spring. This nature of cambium arises the hot topic in the field of plant physiology, plant development and forestry. Callose is a polysaccharide in the form of β-1,3-glucan with some β-1,6-branches and it exists in the cell walls or cell wall-associated structures of a variety of higher plants. Callose can be synthesized and degraded in a timely manner during plant development. In vascular plants, callose can deposit specifically in the phloem. However, the way by which the environmental factors control callose deposition in phloem is still poorly understood. Phloem callose deposition in poplar of seasonal changes were described systematically in this paper. Morphology, bioinformatics and molecular biology methods were applied to look into the way how the environmental factors play roles. The results contribute to building the foundation and further revealing the mechanism that during the annual cycle of poplar, as far as how the environmental factors regulate callose deposition in the phloem. The results showed as below:1. We found that phloem-deposited callose had the seasonal change in the annual cycle of poplar. Numerous callose was abundantly deposited in active phase while greatly diminish in the dormancy phase. Therefore, the deposition of callose in the sieve elements during the dormancy-active cycle may have been influenced by environmental factors such as photoperiod and temperature.2. The role of photoperiod /temperature in the development of sieve pores was examined and how they regulate phloem-deposited callose was observed. The results revealed that one-week cold treatment(4 ℃) repressed the callose deposition in phloem completely, but 8-week short-day treatment failed to repress the phloem callosedeposition significantly. We also tested that wounding-induced callose deposition is obvious in plant tissues.3. The structure of phloem sieve elements in Populus trichocarpa was observed by scanning electronic microscope. The results showed that the areas of sieve pores in the treated plants were reduced significantly compared with its control.4. We analyzed the relative expression level of callose synthase and β-1, 3-glucanase by q RT-PCR to further study how the environmental factors control the phloem callose synthase genes. two homologous phloem-specific callose genes Pt Cals7-1 and Pt Cals7-2 were cloned. In addition, callose-deposition level in Populus trichocarpa were observed by q RT-PCR during dormancy-active cycle as well as low tempreture treatment, meanwhile we checked the expression level of known callose hydrolase genes in the process. The results showed that Pt Cals7-2 reduced in dormancy plants significantly, while one callose hydrolase gene Pt GH17-44 or Pt GH17-101 was obviously upregulated in dormancy plants or low tempreture treatment respectively.