AbstractsBiology & Animal Science

Plants can perceive light signals through three major classes of photoreceptors: phytochromes (red/far-red light), cryptochromes (blue and UV-A light), and phototropins (blue and UV-A light). Genome-wide gene expression analysis revealed that CRYPTOCHROME1 (CRY1) is critical in the response of Arabidopsis to high irradiance. Database analysis also showed that expression of CRY1 was highly correlated to the expression of a number of anti-oxidant genes. Therefore, I hypothesized that CRY1 is involved in cellular communication responsible for the integration of irradiance-dependent responses in tobacco. To understand the role of CRY1 in seed germination and early seedling development in response to light intensity, experiments were conducted using transgenic plants overexpressing CRY1. Germination kinetics were determined by measuring the time of radicle emergence in seeds subjected to light intensities of 6, 60, or 600 mmol m-2 s-1. In wild type plants, the final germination percentage was unaffected by different light intensities, but high light intensity caused a significant delay in germination. Plants overexprssing CRY1 showed reduced germination percentage and a delay in the timing of germination under both low and high light intensities. Surprisingly, the lower germination percentages in the CRY1 overexpressors was reversed by high light intensities in contrast to seeds of wild-type. Under high light conditions, leaves of CRY1 overexpressing plants contained three-fold more total chlorophyll than wild-type plants, which was probably due to both increased synthesis and a reduction of photooxidative degradation. First, well-developed chloroplasts containing chlorophyll were observed in the cortex of roots of CRY1 overexpressing plants. Second, leaves of CRY1 overexpressing plants contained higher phenolics, flavonoids, and lignin content than wild-type plants. LC-MS results showed that leaves of CRY1 overexpressing plants contained two-fold higher level of chlorogenic acids and ten-fold higher level of rutin than wild-type plants. CRY1 overexpressing plants exhibited reduced ultraviolet-B injury. It may be due to the accumulation of secondary metabolites which have antioxidant activities in protecting cellular structures from oxidative damage.CRY1 overexpression resulted in increased stomatal density. Wild-type plants followed a pattern known as the one cell spacing rule: two stomates are separated by at least one epidermal cell for proper stomatal physiology. In plants overpressing CRY1 there was elevated stomatal density and some of the stomates were clustered in violation of the one cell spacing rule, indicating that stomatal patterning was disrupted in CRY1 overexpression plants. I also observed a severe wilting phenotype in CRY1 overexpression plants when transferred to cold or high light conditions. This may be a result of a reduction in water transport (smaller vessel cells) and the increased transpiration.