Light And Gibberellin Effect On Arabidopsis Photomorphogenesis And Lignin Biosynthesis

In higher plants, there are at least three kinds of light receptors to capture light signal: phytochrome, cryptochromes and phototropin, which receptor absorb different spectrum of light. The light signal transduction and then entered the stage of plant growth and development, such as seed germination, seedling growth and flowering time. The growth process of Arabidopsis seedlings has become a model system for researching photomorphogenic mechanism. Cryptochromes are blue light receptors that regulate various photomophogenic responses in plant, including inhibition of hypocotyl elongation, stimulation of cotyledon expansion, and regulation of flowering time. It is not clear about how cryptochromes mediate blue light regulating photomophogenic responses, such as inhibition of hypocotyl elongation. Many hormones, including IAA, Gibberellin(GA), ethylene and cytokinin also regulate plant growth as well as light. In addition, light also regulates plant growth by changing GA levels.At present, it is not clear about photomophogenic mechanism how blue light regulate plant grow.To determine the effect of GA on photomorphogenesis in Arabidopsis under blue light, overexpression lines 35S::GFP-GA2ox8-1, 35S::GFP-GA2ox8-8 lines in wild type (WT) Col-4 background and an activation-tagging mutant scc7-D (suppressor of cry1cry2) were used in this research. Our results indicated that compared to cry1cry2, scc7-D showed a phenotype of inhibition of hypocotyl elongation, cotyledons opening and remaining larger hook angle under blue light; 35S::GFP-GA2ox8-1, 35S::GFP-GA2ox8-8 overepression lines also have short hypocotyls and opening cotyledons contrast with WT. cry1cry2 and scc7-D displayed insensitive to blue light are the result of lacking of cry1 and cry2. It was demonstrated that cryptochromes mediate GA regulation of de-etiolated seedlings by analysing chlorophyll and anthocyanin content of seedlings. In agreement with this, light-dependent gene expression, such as CHS,RBCS,CAB2, showed misregulating of light-depended gene in Arabidopsis with reduced GAs level in blue light. These results suggest that cryptochrome may regulate GA response to supresss photomorphogenesis, at least at its early stages.Light is an important environmental factor in plant growth. To study the light and GAs effecting on lignin biosynthesis, many Arabidopsis mutants including red/far-red-light receptor mutants (phyA, phyB , PhyAphyB), blue-light receptor mutants (cry1, cry2, cry1cry2) and GA Biosynthesis mutants (scc7-D, 35S::GFP-GA2ox8-1, 35S::GFP-GA2ox8-8) were used in our paper. The method of bromine acetyl was adopted in measuring different lignin contents in light receptor mutants, and the section of the stem were observed by phloroglucinol staining. We investigated the effects on lignin biosynthesis in different light receptor mutants through above methods. The results showed that compared with WT, lignin contents in red/far-red-light receptor mutants were lower, but the blue-light receptor mutants were higher. These results preliminary suggested that red/far-red-light promoted the lignin biosynthesis, whereas blue light inhibited the lignin biosynthesis. By analysis genes in lignin biosynthesis through RT-PCR and Q-PCR, we found that phyA, phyB-mediated far-red light or red light regulate lignin biosynthesis through regulating 4CL3 expression, but for cry1, cry2 regulating lignin biosynthesis,there may be other signaling pathway not by 4CL3 gene. Additionally, short-term GA3 treatment of petioles of mature plant also proved that GA may also effct the lignin biosynthesis.