Response to Plant Hormones of Senescence-related Genes for Cucumis sativus L. in Cotyledon Development

Abstract

This study was carried out to discover the response of cucumber (Cucumis sativus L.) senescence-associated genes (SAGs) to several plant hormones in detached and developing cotyledon. Accordingly, a collection of cucumber SAGs were examined to characterize their gene expression response through semi-quantitative RT-PCR. Cotyledons were excised at day 14 after seed sowing from plantlets, then incubated in 100 μM each of IAA or zeatin solution for up to 4 days in light and darkness. They were collected at 2-day intervals and used for total RNA extraction and subjected to RT-PCR. Gene expression levels of several cucumber SAGs were significantly changed during the incubation period. More than five cucumber SAGs involving SAG 60 responded to the IAA and zeatin treatment. In the ethylene response study, cotyledons were exposed up to 10 days by ethylene gas. Most of the cucumber SAGs did not show immediate response to ethylene in green cotyledon. The exceptions were PCK, SAG 158, and SAG 288 genes, which responded after 1 day of exposure to green cotyledon, while ICL and SAG 281 revealed strong responses after 10 days of being exposed to yellowing cotyledon. These results suggest that several cucumber SAGs react actively in response to starvation or senescence against exogenously applied stimulus. This induced senescence response is able to understand the SAGs role in lipids and amino acids metabolism partly and function in organ senescence during development.