Fig. 8.

The onset of leaf senescence is associated with the levels of BiP expression in tobacco transgenic lines under a restricted water regime. Tobacco transgenic lines expressing BiP cDNA either in the sense or antisense orientations were exposed to progressive drought by reducing irrigation to a 40% level of the normal water supply for 35 d. I, normally irrigated plants; DS, drought-stressed plants for the indicated period of time in days. (A, B) Induction of the senescence-associated genes didi A9 and NTCP-23 under progressive drought. Total RNA was isolated from irrigated and drought-stressed leaves of wild type, sense and antisense tobacco lines at the indicated period of treatment and gene induction was monitored by quantitative RT-PCR using gene-specific primers. Values represent the mean ±SD of two replicates. (C) Chlorophyll loss induced by drought for 35 d of restricted water regime. C indicates wild-type plants; S, BIP sense; and AN, BiP antisense lines. I denotes continuously irrigated controls and DS, drought-stressed plants after 35 d of 40% of the normal daily water supply. Values represent the mean ±SD of three replicates. (D) Chlorophyll content during progressive drought. The chlorophyll content was measured in leaves of wild type (control), sense and antisense transgenic lines at the indicated period of drought in days.