Main conclusions on the effects of promoters and candidate genes
influenced by drought and salt stress has special characteristic. The size of stomatal aperture becomes smaller, so it will reduce transpirational water loss Cheng et al. 2013. Duan 2011
has been reported that HbERF-IXc5 functions like the ERF1. The response of HbERF-IXc5 to the combined treatment of wounding, MeJA and ET was significantly multiplied Duan
2011. Unfortunately, histological analyses were carried only for HbERF-IXc5 gene, so no comparison was possible for the two candidate genes at this level.
The effect of HbERF-IXc4 and HbERF-IXc5 genes in stress response ability of transgenic plants was successfully conducted on several environmental stress treatments. The
ability of plants species to tolerate cold stress was varying; it depends on gene expression to modify their physiology, metabolism, and growth Chinnusamy et al. 2010. In cold stress
response, HbERF-IXc5 performed a better response than HbERF-IXc4 under control HEV2.1 promoter in parameters: FvFm value, P. Index, and SPAD value. The maximum
photochemical efficiency of the photosystem II FvFm indicated particular responses of the genotypes. However, both of genes HbERF-IXc4 and HbERF-IXc5 had good ability to face
senescence than control. It was described with the leaflets number, all transgenic lines showed more leaflets compared to the control. Similar with ERF1 function, HbERF-IXc5
might play a role to enhance the plants ability to cold stress response. ERF1 was directly regulates abiotic stress response genes cold, salinity, and water deficit in Arabidopsis
Cheng et al. 2013; Hao et al. 2002; Sakuma et al. 2002.
With regard to FvFm and SPAD value, both of genes had a same capability in salinity stress tolerance, but HbERF-IXc5 performed a better P. Index than HbERF-IXc4. The
ratio of v m is a direct measure of the “optimal uantum efficiency” of the plant Genty et
al. 1989. P.Index reflects the functionality of both photosystems I and II and gives quantitative information on the current state of plant performance under stress conditions
Strasser et al. 2004. In the other hand, the SPAD value can be used as an indicator of chlorophyll content that measure greenness based on optical responses Kariya et al. 1982.
However, number of leaflets analysis revealed that transgenic plant with construct of HEV2.1::HbERF-IXc5 also showed a better performance to adapt with salinity stress
compared to control by growing a new shoot.
Leaf abscission was reflecting the effect of ethephon treatment. Ethephon or native ethylene was promoted in abscission by induction of hydrolytic enzyme synthesis and
secretion of this enzyme into cell wall Abeles 1969; Abeles and Leather 1971; Horton and Osborne 1967. Analysis of leaflets number and leaves morphology revealed that HbERF-
IXc4 gene had a great ability to face senescence. It might suggest that this gene could raise the ethephon tolerance in Hevea transgenic plants.